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Degradation kinetics of anthocyanin, flavonoid, and total phenol in bignay (Antidesma bunius) fruit juice during ohmic heating

Abstract

The effect of ohmic heating on bioactive compounds in bignay (Antidesma bunius) fruit juice during ohmic heating were evaluated. The parameters measured were total phenol, anthocyanin, flavonoid, and antioxidant activity. Ohmic heating was conducted at 70, 90, and 110 °C, and samples were collected at heating times of 0, 15, 30, and 45 minutes. Electrical conductivity of bignay fruit juice increased linearly with temperature with values ranged from 0.012 S/m at 32 °C to 0.039 S/m at 110 °C. Insignificant change in total phenol was observed, while anthocyanin and flavonoid showed significant degradation and the degradation kinetics followed the first-order kinetic model. The degradation rate constants for anthocyanin ranged from 0.0016 to 0.0213 min-1 with activation energy (Ea) of 63.880 kJ/mol and the degradation rate constants for flavonoid were in the range of 0.0107 to 0.0209 min-1 with activation energy of 18.210 kJ/mol. Antioxidant activities (IC50) obtained from DPPH method ranged from 0.106-0.168 mg/mL while those obtained from ABTS method ranged from 0.131-0.161 mg/mL. The results indicate that anthocyanin and total phenol in bignay fruit juice is much more stable during heating compared to flavonoid.

Keywords:
bignay fruit juice; ohmic heating; bioactive compounds; antioxidant activity

1 Introduction

During the past decade, fruit juice has gained remarkable interests in beverage market sector. Processing of fruits into juices has been a commercial way to diversify the usage of the fruits and to fulfill demands beyond harvest season. In addition, fruit juice has been viewed as a more convenient way to obtain comparable health benefits from the fruits to those from direct consumption. As the markets for fruit juice are approaching saturation, however, competitions among industries to attract consumers with their juice products are escalating. This condition requires industries to constantly innovate and introduce new products to the market. One approach that the beverage industry can use to win the competition is by introducing exotic fruit juice to the market.

Exotic fruits from tropical countries such as bignay (Antidesma bunius), Indian black plum or jamun (Syzygium cumini L), red mulberry (Morus rubra L.), and black mulberry (Morus nigra L.) have gained interests from researchers for their potential as sources of bioactive compounds and natural antioxidants. Studies on bignay fruits (Butkhup & Samappito, 2008Butkhup, L., & Samappito, S. (2008). Analysis of anthocyanin, flavonoids, and phenolic acids in tropical bignay berries. International Journal of Fruit Science, 8(1-2), 15-34. http://dx.doi.org/10.1080/15538360802365913.
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) indicate that these fruits are rich in phenolic compounds such as flavonoids and athocyanins which have the potential to provide health benefits as reported by numerous authors (Aiyer et al., 2008Aiyer, H. S., Srinivasan, C., & Gupta, R. C. (2008). Dietary berries and ellagic acid diminish estrogen-mediated mammary tumorigenesis in ACI rats. Nutrition and Cancer, 60(2), 227-234. http://dx.doi.org/10.1080/01635580701624712. PMid:18444155.
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). Bignay fruit is an exotic fruit which is mostly found in Southeast Asian countries such as Thailand and Indonesia. This fruit resembles berries with a purplish-black color and a sweet-sour taste when fully ripe. In addition, due to its chemical contents, this fruit can be used as a raw material for production of antioxidant-rich beverages (Chaikham et al., 2016Chaikham, P., Prangthip, P., & Seesuriyachan, P. (2016). Ultra-sonication effects on quality attributes of maoberry (Antidesma bunius L.) juice. Food Science and Technology Research, 22(5), 647-654. http://dx.doi.org/10.3136/fstr.22.647.
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In production of drinks and beverages, microbial safety of the products is of paramount importance. This is usually achieved through thermal treatments such as pasteurization and sterilization or non-thermal treatments such as pulsed electric field processing and high-pressure processing. One of the negative impacts of heat treatments of foods is the degradation of quality attributes such as nutrient contents, texture, color, and bioactive compounds. To minimize these effects, thermal technologies which can provide rapid and uniform heating such as ohmic and microwave heating technologies and non-thermal technologies have been developed. In the case of ohmic heating, rapid and uniform heating have been shown both experimentally and through mathematical simulations (Cokgezme & Icier, 2019Cokgezme, O. F., & Icier, F. (2019). Effect of voltage gradient on ohmic thawing characteristics of sour cherry juice concentrates for the temperature range of −18 °C to +4 °C. Food Science & Technology International, 25(8), 659-670. http://dx.doi.org/10.1177/1082013219857897. PMid:31238739.
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The use of ohmic technology in heating and processing of various types of solid and liquid foods has been studied extensively (Abedelmaks et al., 2018Abedelmaks, T. G., Mohsen, S. M., Duedahl-Ol, L., Elnikeety, M. M., & Feyissa, A. H. (2018). Effect of ohmic heating parameters on inactivation of enzymes and quality of not-from-concentrate mango juice. Asian Journal of Scientific Research, 11(3), 383-392. http://dx.doi.org/10.3923/ajsr.2018.383.392.
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). Many of these studies were mainly conducted to evaluate the possibility of using ohmic heating in thermal treatments of food products.

In recent years, there are several new applications of ohmic heating that have recently been reported such as application in carrageenan extraction (Hasizah et al., 2018Hasizah, A., Mahendradatta, M., Laga, A., Metusalach, M., Supratomo, Waris, A., & Salengke, S. (2018). A novel ohmic-based technology for seaweed processing. International Food Research Journal, 25(4), 1341-1348.), cocoa and coffee beans fermentations (Supratomo et al., 2019Supratomo, S., Laga, A., Tahir, M., Mochtar, A. A., & Salengke, S. (2019). Design and performance test of ohmic-assisted cocoa fermentation apparatus. Journal of Engineering and Applied Sciences, 14(8), 1515-1523.; Salengke et al., 2019Salengke, S., Hasizah, A., Reta, & Mochtar, A. A. (2019). Technology innovation for production of specialty coffee. IOP Conference Series: Earth and Environmental Science, 355, 012105. http://dx.doi.org/10.1088/1755-1315/355/1/012105.
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), cheese production (Rocha et al., 2020aRocha, R. S., Silva, R., Guimarães, J. T., Balhtazar, C. F., Pimentel, T. C., Cucinelli, R. P. C. No., Tavares, M. I. B., Esmerino, E. A., Freitas, M. Q., Cappato, L. P., Calvacanti, R. N., Rodrigues, F. N., Raices, R. S. L., Silva, M. C., & Cruz, A. G. (2020a). Possibilities for using ohmic heating in Minas Frescal cheese production. Food Research International, 131, 109027. http://dx.doi.org/10.1016/j.foodres.2020.109027. PMid:32247497.
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), whey beverages production (Ferreira et al., 2019aFerreira, M. V. S., Cappato, L. P., Silva, R., Rocha, R. S., Cucinelli, R. P. C. No., Tavares, M. I. B., Esmerino, E. A., Freitas, M. Q., Bissagio, R. C., Ranadheera, S., Raices, R. S. L., Silva, M. C., & Cruz, A. G. (2019a). Processing raspberry-flavored whey drink using ohmic heating: physical, thermal and microstructural considerations. Food Research International, 123, 20-26. http://dx.doi.org/10.1016/j.foodres.2019.04.045. PMid:31284969.
http://dx.doi.org/10.1016/j.foodres.2019...
, b Ferreira, M. V. S., Cappato, L. P., Silva, R., Rocha, R. S., Guimarães, J. T., Balthazar, C. F., Esmerino, E. A., Freitas, M. Q., Rodrigues, F. N., Granato, D., Cucinelli, R. P. C. No., Tavares, M. I. B., Silva, P. H. F., Raices, R. S. L., Silva, M. C., & Cruz, A. G. (2019b). Ohmic heating for processing of whey-raspberry flavored beverage. Food Chemistry, 297, 125018. http://dx.doi.org/10.1016/j.foodchem.2019.125018. PMid:31253265.
http://dx.doi.org/10.1016/j.foodchem.201...
; Coimbra et al., 2020Coimbra, L. O., Vidal, V. A. S., Silva, R., Rocha, R. S., Guimarães, J. T., Balthazar, C. F., Pimentel, T. C., Silva, M. C., Granato, D., Freitas, M. Q., Pollonio, M. A. R., Esmerino, E. A., & Cruz, A. G. (2020). Are ohmic heating-treated whey dairy beverages an innovation? Insights of the Q methodology. LWT, 134, 110052. http://dx.doi.org/10.1016/j.lwt.2020.110052.
http://dx.doi.org/10.1016/j.lwt.2020.110...
), dairy dessert and milk product production (Kuriya et al., 2020Kuriya, S. P., Silva, R., Rocha, R. S., Guimarães, J. T., Balthazar, C. F., Pires, R. P. S., Tavares, E. R. Fo., Pimentel, T. C., Freitas, M. Q., Cappato, L. P., Raices, R. S. L., Cruz, A. G., Silva, M. C., & Esmerino, E. A. (2020). Impact assessment of different electric fields on the quality parameters of blueberry flavored dairy desserts processed by Ohmic Heating. Food Research International, 134, 109235. http://dx.doi.org/10.1016/j.foodres.2020.109235. PMid:32517929.
http://dx.doi.org/10.1016/j.foodres.2020...
; Silva et al., 2020Silva, R., Rocha, R. S., Guimarães, J. T., Balthazar, C. F., Scudino, H., Ramos, G. L. P. A., Pimentel, T. C., Silva, M. C., Silva, P. H. F., Duarte, M. C. K. H., Freitas, M. Q., Cruz, A. G., & Esmerino, E. A. (2020). Dulce de leche submitted to ohmic heating treatment: consumer sensory profifile using preferred attribute elicitation (PAE) and temporal check-all-that-apply (TCATA). Food Research International, 134, 109217. http://dx.doi.org/10.1016/j.foodres.2020.109217. PMid:32517897.
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), and paraprobiotics production (Barros et al., 2021Barros, C. P., Pires, R. P. S., Guimarães, J. T., Abud, Y. K. D., Almada, C. N., Pimentel, T. C., Sant’Anna, C., De-Melo, L. D. B., Duarte, M. C. K. H., Silva, M. C., Sant’Ana, A. S., Freitas, M. Q., & Cruz, A. G. (2021). Ohmic heating as a method of obtaining paraprobiotics: Impacts on cell structure and viability by flow cytometry. Food Research International, 140, 110061. http://dx.doi.org/10.1016/j.foodres.2020.110061.
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). These studies indicate that ohmic heating can provide faster extraction and fermentation process (Hasizah et al., 2018Hasizah, A., Mahendradatta, M., Laga, A., Metusalach, M., Supratomo, Waris, A., & Salengke, S. (2018). A novel ohmic-based technology for seaweed processing. International Food Research Journal, 25(4), 1341-1348.; Supratomo et al., 2019Supratomo, S., Laga, A., Tahir, M., Mochtar, A. A., & Salengke, S. (2019). Design and performance test of ohmic-assisted cocoa fermentation apparatus. Journal of Engineering and Applied Sciences, 14(8), 1515-1523.), better and consistent coffee bean quality (Salengke et al., 2019Salengke, S., Hasizah, A., Reta, & Mochtar, A. A. (2019). Technology innovation for production of specialty coffee. IOP Conference Series: Earth and Environmental Science, 355, 012105. http://dx.doi.org/10.1088/1755-1315/355/1/012105.
http://dx.doi.org/10.1088/1755-1315/355/...
), better sensory attributes and consumer acceptance (Coimbra et al., 2020Coimbra, L. O., Vidal, V. A. S., Silva, R., Rocha, R. S., Guimarães, J. T., Balthazar, C. F., Pimentel, T. C., Silva, M. C., Granato, D., Freitas, M. Q., Pollonio, M. A. R., Esmerino, E. A., & Cruz, A. G. (2020). Are ohmic heating-treated whey dairy beverages an innovation? Insights of the Q methodology. LWT, 134, 110052. http://dx.doi.org/10.1016/j.lwt.2020.110052.
http://dx.doi.org/10.1016/j.lwt.2020.110...
; Rocha et al., 2020aRocha, R. S., Silva, R., Guimarães, J. T., Balhtazar, C. F., Pimentel, T. C., Cucinelli, R. P. C. No., Tavares, M. I. B., Esmerino, E. A., Freitas, M. Q., Cappato, L. P., Calvacanti, R. N., Rodrigues, F. N., Raices, R. S. L., Silva, M. C., & Cruz, A. G. (2020a). Possibilities for using ohmic heating in Minas Frescal cheese production. Food Research International, 131, 109027. http://dx.doi.org/10.1016/j.foodres.2020.109027. PMid:32247497.
http://dx.doi.org/10.1016/j.foodres.2020...
; Silva et al., 2020Silva, R., Rocha, R. S., Guimarães, J. T., Balthazar, C. F., Scudino, H., Ramos, G. L. P. A., Pimentel, T. C., Silva, M. C., Silva, P. H. F., Duarte, M. C. K. H., Freitas, M. Q., Cruz, A. G., & Esmerino, E. A. (2020). Dulce de leche submitted to ohmic heating treatment: consumer sensory profifile using preferred attribute elicitation (PAE) and temporal check-all-that-apply (TCATA). Food Research International, 134, 109217. http://dx.doi.org/10.1016/j.foodres.2020.109217. PMid:32517897.
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), and improved health benefits (Rocha et al., 2020aRocha, R. S., Silva, R., Guimarães, J. T., Balhtazar, C. F., Pimentel, T. C., Cucinelli, R. P. C. No., Tavares, M. I. B., Esmerino, E. A., Freitas, M. Q., Cappato, L. P., Calvacanti, R. N., Rodrigues, F. N., Raices, R. S. L., Silva, M. C., & Cruz, A. G. (2020a). Possibilities for using ohmic heating in Minas Frescal cheese production. Food Research International, 131, 109027. http://dx.doi.org/10.1016/j.foodres.2020.109027. PMid:32247497.
http://dx.doi.org/10.1016/j.foodres.2020...
, bRocha, R. S., Silva, R., Guimarães, J. T., Balhtazar, C. F., Silveira, M. R., Martins, A. A., Rojas, V. P., Graça, J. S., Pimentel, T. C., Esmerino, E. A., Sant’Ana, A. S., Granato, D., Freitas, M. Q., Barros, M. E., Silva, M. C., & Cruz, A. G. (2020b). Ohmic heating does not influence the biochemical properties of Minas Frescal cheese but decreases uric acid levels in healthy Wistar rats. Journal of Dairy Science, 103(6), 4929-4934. http://dx.doi.org/10.3168/jds.2019-17712. PMid:32229115.
http://dx.doi.org/10.3168/jds.2019-17712...
; Barros et al., 2021Barros, C. P., Pires, R. P. S., Guimarães, J. T., Abud, Y. K. D., Almada, C. N., Pimentel, T. C., Sant’Anna, C., De-Melo, L. D. B., Duarte, M. C. K. H., Silva, M. C., Sant’Ana, A. S., Freitas, M. Q., & Cruz, A. G. (2021). Ohmic heating as a method of obtaining paraprobiotics: Impacts on cell structure and viability by flow cytometry. Food Research International, 140, 110061. http://dx.doi.org/10.1016/j.foodres.2020.110061.
http://dx.doi.org/10.1016/j.foodres.2020...
). In addition, physical properties of beverage produced via ohmic heating can be tailored by varying ohmic heating parameters such as frequency and filed strength (Ferreira et al., 2019bFerreira, M. V. S., Cappato, L. P., Silva, R., Rocha, R. S., Guimarães, J. T., Balthazar, C. F., Esmerino, E. A., Freitas, M. Q., Rodrigues, F. N., Granato, D., Cucinelli, R. P. C. No., Tavares, M. I. B., Silva, P. H. F., Raices, R. S. L., Silva, M. C., & Cruz, A. G. (2019b). Ohmic heating for processing of whey-raspberry flavored beverage. Food Chemistry, 297, 125018. http://dx.doi.org/10.1016/j.foodchem.2019.125018. PMid:31253265.
http://dx.doi.org/10.1016/j.foodchem.201...
).

Many studies on the effects of ohmic heating on degradation of phenolic compound and anthocyanin in processed foods have been reported (Brochier et al., 2019Brochier, B., Mercali, G. D., & Marczak, L. D. F. (2019). Effect of moderate electric field on peroxidase activity, phenolic compounds and color during ohmic heating of sugarcane juice. Journal of Food Processing and Preservation, 43(12), 1-10. http://dx.doi.org/10.1111/jfpp.14254.
http://dx.doi.org/10.1111/jfpp.14254...
; Ferreira et al., 2019aFerreira, M. V. S., Cappato, L. P., Silva, R., Rocha, R. S., Cucinelli, R. P. C. No., Tavares, M. I. B., Esmerino, E. A., Freitas, M. Q., Bissagio, R. C., Ranadheera, S., Raices, R. S. L., Silva, M. C., & Cruz, A. G. (2019a). Processing raspberry-flavored whey drink using ohmic heating: physical, thermal and microstructural considerations. Food Research International, 123, 20-26. http://dx.doi.org/10.1016/j.foodres.2019.04.045. PMid:31284969.
http://dx.doi.org/10.1016/j.foodres.2019...
; Hardinasinta et al., 2019Hardinasinta, G., Salengke, S., Juaedi, M., & Mursalim, M. (2019). Ohmic heating characteristics and degradation kinetics of anthocyanin in mulberry juice. IOP Conference Series: Earth and Environmental Science, 355(1), 012094. http://dx.doi.org/10.1088/1755-1315/355/1/012094.
http://dx.doi.org/10.1088/1755-1315/355/...
; Loypimai et al., 2015Loypimai, P., Moongngarm, A., Chottanom, P., & Moontree, T. (2015). Ohmic heating-assisted extraction of anthocyanins from black rice bran to prepare a natural food colourant. Innovative Food Science & Emerging Technologies, 27, 102-110. http://dx.doi.org/10.1016/j.ifset.2014.12.009.
http://dx.doi.org/10.1016/j.ifset.2014.1...
; Makroo et al., 2017Makroo, H. A., Saxena, J., Rastogi, N. K., & Srivastava, B. (2017). Ohmic heating assisted polyphenol oxidase inactivation of watermelon juice: effects of the treatment on pH, lycopene, total phenolic content, and color of the juice. Journal of Food Processing and Preservation, 41(6), e13271. http://dx.doi.org/10.1111/jfpp.13271.
http://dx.doi.org/10.1111/jfpp.13271...
; Mercali et al., 2015Mercali, G. D., Gurak, P. D., Schmitz, F., & Marczak, L. D. F. (2015). Evaluation of non-thermal effects of electricity on anthocyanin degradation during ohmic heating of jaboticaba (Myrciaria cauliflora) juice. Food Chemistry, 171, 200-205. http://dx.doi.org/10.1016/j.foodchem.2014.09.006. PMid:25308660.
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, 2013Mercali, G. D., Jaeschke, D. P., Tessaro, I. C., & Marczak, L. D. F. (2013). Degradation kinetics of anthocyanins in acerola pulp: comparison between ohmic and conventional heat treatment. Food Chemistry, 136(2), 853-857. http://dx.doi.org/10.1016/j.foodchem.2012.08.024. PMid:23122136.
http://dx.doi.org/10.1016/j.foodchem.201...
; Sarkis et al., 2013Sarkis, J. R., Jaeschke, D. P., Tessaro, I. C., & Marczak, L. D. F. (2013). Effects of ohmic and conventional heating on anthocyanin degradation during the processing of blueberry pulp. Lebensmittel-Wissenschaft + Technologie, 51(1), 79-85. http://dx.doi.org/10.1016/j.lwt.2012.10.024.
http://dx.doi.org/10.1016/j.lwt.2012.10....
, 2019Sarkis, J. R., Jaeschke, D. P., Mercali, G. D., Tessaro, I. C., & Marczak, L. D. F. (2019). Degradation kinetics of anthocyanins in blackberry pulp during ohmic and conventional heating. International Food Research Journal, 26(1), 87-97.; Yildiz et al., 2009Yildiz, H., Bozkurt, H., & Icier, F. (2009). Ohmic and conventional heating of pomegranate juice: effects on rheology, color, and total phenolics. Food Science & Technology International, 15(5), 503-512. http://dx.doi.org/10.1177/1082013209350352.
http://dx.doi.org/10.1177/10820132093503...
). Salari & Jafari (2020)Salari, S., & Jafari, S. M. (2020). The influence of ohmic heating on degradation of food bioactive ingredients. Food Engineering Reviews, 12(2), 191-208. http://dx.doi.org/10.1007/s12393-020-09217-0.
http://dx.doi.org/10.1007/s12393-020-092...
conducted a review on the results of various studies and concluded that the effects of ohmic heating on the degradation of phenolic compounds and anthocyanin are not consistent since some researchers reported that ohmic heating resulted in higher degradation compared to conventional heating, while others reported that ohmic heating resulted in lower phenolic and anthocyanin degradation or similar to that of conventional heating.

Castro et al. (2004)Castro, I., Teixeira, J. A., Salengke, S., Sastry, S. K., & Vicente, A. A. (2004). Ohmic heating of strawberry products: electrical conductivity measurements and ascorbic acid degradation kinetics. Innovative Food Science & Emerging Technologies, 5(1), 27-36. http://dx.doi.org/10.1016/j.ifset.2003.11.001.
http://dx.doi.org/10.1016/j.ifset.2003.1...
reported that the magnitude of the electric field applied did not affect ascorbic acid degradation in the strawberry product. The same trend was reported by Mercali et al. (2015)Mercali, G. D., Gurak, P. D., Schmitz, F., & Marczak, L. D. F. (2015). Evaluation of non-thermal effects of electricity on anthocyanin degradation during ohmic heating of jaboticaba (Myrciaria cauliflora) juice. Food Chemistry, 171, 200-205. http://dx.doi.org/10.1016/j.foodchem.2014.09.006. PMid:25308660.
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for their study on jaboticaba juice. However, other studies reported that higher electric field resulted in higher degradation of anthocyanin in blackberry pulp (Sarkis et al., 2019Sarkis, J. R., Jaeschke, D. P., Mercali, G. D., Tessaro, I. C., & Marczak, L. D. F. (2019). Degradation kinetics of anthocyanins in blackberry pulp during ohmic and conventional heating. International Food Research Journal, 26(1), 87-97.) and ascorbic acid in tropical fruit pulp (Athmaselvi et al., 2017Athmaselvi, K. A., Kumar, C., & Poojitha, P. (2017). Influence of temperature, voltage gradient and electrode on ascorbic acid degradation kinetics during ohmic heating of tropical fruit pulp. Journal of Food Measurement and Characterization, 11(1), 144-155. http://dx.doi.org/10.1007/s11694-016-9381-5.
http://dx.doi.org/10.1007/s11694-016-938...
). The degradation kinetics of some bioactive compounds during ohmic heating also differ among products. The rate constant for anthocyanin from acerola pulp (Mercali et al., 2013Mercali, G. D., Jaeschke, D. P., Tessaro, I. C., & Marczak, L. D. F. (2013). Degradation kinetics of anthocyanins in acerola pulp: comparison between ohmic and conventional heat treatment. Food Chemistry, 136(2), 853-857. http://dx.doi.org/10.1016/j.foodchem.2012.08.024. PMid:23122136.
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) showed higher value compared to that of jaboticaba juice (Mercali et al., 2015Mercali, G. D., Gurak, P. D., Schmitz, F., & Marczak, L. D. F. (2015). Evaluation of non-thermal effects of electricity on anthocyanin degradation during ohmic heating of jaboticaba (Myrciaria cauliflora) juice. Food Chemistry, 171, 200-205. http://dx.doi.org/10.1016/j.foodchem.2014.09.006. PMid:25308660.
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). These results indicate that the stability of anthocyanin is relatively different in different products. Therefore, it is important to determine the effect of ohmic heating process on the stability of bioactive compounds in the scarcely studied exotic fruits such as bignay fruit. This kind of study can form an important step towards the development of commercial processes at industrial scale. Therefore, the objectives of this study were: (1) to evaluate the effects of ohmic heating on antioxidant activity and degradation kinetics of phenolic, anthocyanin, and flavonoid compounds in bignay juice, and (2) to obtain electrical conductivity of bignay fruit juice during ohmic heating.

2 Materials and methods

2.1 Sample preparation

Freshly harvested bignay fruits were obtained from a local market in Makassar, South Sulawesi, Indonesia. The fruits were washed and sorted based on maturity level and fruits with good maturity, distinguished by their black-purplish color, were used in this study. The selected fruits were crushed using a commercial juicer (Philips HR1832) and then filtered to separate the pulp from the juice. The single strength juice obtained was stored at -20 °C until used.

2.2 Ohmic heating experiments

Ohmic heating experiment was conducted using a laboratory-scale static ohmic heater as illustrated in our previous study (Hardinasinta et al., 2019Hardinasinta, G., Salengke, S., Juaedi, M., & Mursalim, M. (2019). Ohmic heating characteristics and degradation kinetics of anthocyanin in mulberry juice. IOP Conference Series: Earth and Environmental Science, 355(1), 012094. http://dx.doi.org/10.1088/1755-1315/355/1/012094.
http://dx.doi.org/10.1088/1755-1315/355/...
). The experiment was conducted at three levels of temperature (70, 90, 110 °C) and 2 mL of sample was drawn from the ohmic heater at different heating time (0, 15, 30, 45 min). The prolonged heating time was used to bring about appreciable changes in the bioactive compounds in the juice samples so as to obtain an appropriate fit for the degradation kinetics model. During ohmic heating, temperature, electric field strength, and electric current were recorded using a data logger (CR1000 Campbell Scientific, Inc., Logan - Utah,).

2.3 Electrical conductivity measurement

The electrical conductivity of bignay juice during ohmic heating was determined using Equation 1,

σ = L A . I V (1)

where L is the distance between electrodes (m), A is the cross-section area of the ohmic heating chamber (m2), I is current consumption (A), and V is applied voltage (V).

2.4 Chemical analysis

Chemical analysis were carried out to determine total phenolic, anthocyanin, and flavonoid contents as well as antioxidant activity. Chemicals used in the analysis were analytical grade and all measurements were carried out in triplicate.

2.5 Total phenolic content

Prior to analysis, stock solutions of control and ohmically treated juice samples were prepared by dilution of 0.1 mL of the samples with 10 mL of methanol/water (6:4, v/v) solution. The Folin-Ciocalteu method was used to determine total phenolic content of each sample based on the procedure described by Tezcan et al. (2009)Tezcan, F., Gultekin-Ozguven, M., Diken, T., Özçelik, B., & Erim, F. B. (2009). Antioxidant activity and total phenolic, organic acid and sugar content in commercial pomegranate juices. Food Chemistry, 115(3), 873-877. http://dx.doi.org/10.1016/j.foodchem.2008.12.103.
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with some modification. From the stock solution, 0.5 mL of aliquot was mixed with 1.5 mL of Folin Ciocalteu reagent (7.5%) and 1.2 mL of Na2CO3 (7.5%). Distilled water was then added to the mixture to reach a total volume of 5 mL. The mixture was allowed to rest for 90 min at room temperature before measurement of absorbance was carried out. The absorbance of the samples was measured using UV-Vis Spectrophotometer (UV-1800, Shimadzu, Japan) at 760 nm and the results of measurements were expressed in gallic acid equivalent (GAE). Standard curve was prepared by diluting gallic acid in methanol/water (6:4, v/v) with five different concentrations ranging from 2-10 ppm and the absorbance of each solution was measured using the same wavelength (760 nm).

2.6 Anthocyanin content

Total monomeric anthocyanin was determined using the pH differential assay as described by Jiang et al. (2013)Jiang, D. Q., Guo, Y., Xu, D. H., Huang, Y. S., Yuan, K., & Lv, Z. Q. (2013). Antioxidant and anti-fatigue effects of anthocyanins of mulberry juice purification (MJP) and mulberry marc purification (MMP) from different varieties mulberry fruit in China. Food and Chemical Toxicology, 59, 1-7. http://dx.doi.org/10.1016/j.fct.2013.05.023. PMid:23727333.
http://dx.doi.org/10.1016/j.fct.2013.05....
. This method measures color difference of two samples obtained by reacting samples with a buffer solution at two different pH levels. The preparation of the samples was carried out as follow. Each of the control and ohmically treated juice sample was pipetted 50 μL into two glass vials. A 100-fold dilution was carried out for each sample by adding potassium chloride (0.025 M) buffer solution at pH 1.0 to one of the vial and sodium acetate (0.4 M) buffer solution at pH 4.5 to the other vial. The preparation of the buffer solution was based on the standard method by (Association of Official Analytical Chemists, 2005Association of Official Analytical Chemists – AOAC. (2005). AOAC official method 2005.02: total monomeric anthocyanin pigment content of fruit juices, beverages, natural colorants, and wines. Journal of AOAC International, 88, 1269.). The diluted samples were placed in a dark room for 20 min and the absorbance of each sample was measured using 520 and 700 nm wavelength. Total absorbance of the samples was calculated using Equation 2:

A = A 520 A 700 p H 1,0 A 520 A 700 p H 4,5 (2)

where A520 is the absorbance at the wavelength of 520 nm, and A700 is the absorbance at the wavelength of 700 nm. Total anthocyanin content was determined using Equation 3,

A n t h o c y a n i n m g L = A × M W × D F × 10 3 ε × l (3)

where A is total absorbance, MW is the molecular weight of cyanidin-3-glucoside (445.2 g/mol) as the standard, DF is the dilution factor, ɛ is the molar absorption capacity (29,600 l/mol.cm), and l is the cuvette length (1 cm).

2.7 Flavonoid content

Analysis of flavonoid content was carried out using Thin Layer Chromatography (TLC) assay (Altemimi et al., 2015Altemimi, A., Watson, D. G., Kinsel, M., & Lightfoot, D. A. (2015). Simultaneous extraction, optimization, and analysis of flavonoids and polyphenols from peach and pumpkin extracts using a TLC-densitometric method. Chemistry Central Journal, 9(1), 39. http://dx.doi.org/10.1186/s13065-015-0113-4. PMid:26106445.
http://dx.doi.org/10.1186/s13065-015-011...
). A 20 × 20 cm TLC plates pre-coated with silica gel 60 F254 (Merck, Germany) was divided into four pieces of equal size (5 × 20 cm) and then dried in an oven at 110 °C for 20-30 min before use. Standard solution was prepared using rutin (250 ppm). The mixture of ethyl acetate: formic acid: water (10:2:3 v/v/v) was used as solvent for the separation process. The chromatography chamber was filled with 10 mL solvent and allowed to saturate for 30-40 min before used. The standard solution was dotted on the TLC plate in five different volumes of 0.1, 0.5, 1.0, 2.0, and 4.0 μL followed by 2 μL of samples with a distance of 1 cm each. The plate was placed inside the chamber in a straight horizontal position and then covered to allow the separation process. The reading of peak area was performed using a densitometer (Camag TLC 3 scanner, Switzerland) at the wavelength of 245 nm according to the spot reference from the standard solution. From the peak area of the standard spot, the calibrating curve of rutin was acquired and used to determine the flavonoid content of the juice samples.

2.8 Antioxidant activity

Antioxidant activity measurements were carried out using two different approaches, i.e. 2,2 Diphenyl-1-picrylhydrazyl (DPPH) assay and 2,20-azino-bis (3-ethylbenzthiazonline-6-sulfonic acid) (ABTS) assay.

2.9 DPPH method

The DPPH radical-scavenging activity was determined based on the method described in Kenny et al. (2013)Kenny, O., Smyth, T. J., Hewage, C. M., & Brunton, N. P. (2013). Antioxidant properties and quantitative UPLC-MS analysis of phenolic compounds from extracts of fenugreek (Trigonella foenum- graecum) seeds and bitter melon (Momordica charantia) fruit. Food Chemistry, 141(4), 4295-4302. http://dx.doi.org/10.1016/j.foodchem.2013.07.016. PMid:23993618.
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with several modifications. The DPPH solution was prepared by the dilution of 8 mg DPPH (Sigma-Aldrich) in 50 mL of methanol. Juice samples (5 mg) were diluted in 5 mL of methanol to obtain stock solution of the sample. A series of five different sample concentrations ranging from 75-375 ppm were prepared by pipetting 15, 30, 45, 60, and 75 μL of the stock solution across the 96-well plate, followed by the addition of 75 μL DPPH solutions. Methanol was then added into the well to reach the final volume of 200 μL. The mixture was kept in the dark for 30 minutes at room temperature to allow optimum reaction to occur. The absorbance of each sample was measured at the wavelength of 515 nm using ELISA plate reader (ELx808 BioTek, Vermont, USA). The results were expressed in IC50 value.

2.10 ABTS method

The ABTS assay was performed based on the method illustrated in Jorjong et al. (2015)Jorjong, S., Butkhup, L., & Samappito, S. (2015). Phytochemicals and antioxidant capacities of Mao-Luang (Antidesma bunius L.) cultivars from Northeastern Thailand. Food Chemistry, 181, 248-255. http://dx.doi.org/10.1016/j.foodchem.2015.02.093. PMid:25794747.
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with modifications. To obtain the ABTS reagent, a 7.4 mM ABTS solution and a 2.6 mM potassium persulfate solution were required. ABTS solution was prepared by diluting 0.018 g of ABTS in 5 mL of methanol while potassium persulfate solution was obtained by mixing 4.6 mg of potassium persulfate with 5 ml methanol. Both solutions were mixed with the ratio of 1:1 (v/v) and the final volume was made up to 25 mL with methanol. The reagent was incubated in the dark for 12-16 hours before use. Sample preparation procedure was similar to the DPPH method mentioned above, except for the volume of ABTS used (125 μL) and the wavelength at which the absorbance was measured (650 nm).

2.11 Degradation kinetic measurement

The rate constant for degradation of a compound due to heat treatments can be determined using first-order kinetic as represented in Equation 4.

C = C o e k t (4)

In the above equation, C0 (mg/L) is initial concentration of the compound, C is concertation at time t, and k is the rate constant. The time required to reduce the concentration of a compound to one-tenth of its initial concentration is denoted as decimal reduction time (D-value). This value was determined using Equation 5. Another parameter that is often used to describe the rate of degradation of a compound is the half-time (t1/2) which represents the time needed to reduce the concentration of the compound to one-half of its initial concentration (Equation 6).

D = l n 10 k (5)
t 1 / 2 = l n 2 k (6)

Temperature dependence of degradation rate of compounds can be derived from the Arrhenius equation as shown in Equation 7.

k T = k 0 e x p E a R T (7)

In the above equation, k is the degradation rate constant at temperature T (in K), Ea is the activation energy (kJ/mol), and R is the universal gas constant (8.314 x 10-3 kJ/mol.K).

2.12 Statistical analysis

The IC50 value was analyzed using the trial version of Prism 8.0 (GraphPad Software, San Diego, CA-USA). Other statistical analyses were performed using R Studio software (RStudio PBC, Boston, MA-USA).

3 Results and discussions

3.1 Electrical conductivity of bignay juice

Electrical conductivity is a substantial aspect affecting the heat generation inside the product and consequently it can significantly influence the design process. Figure 1 shows the change in electrical conductivity of bignay fruit juice during ohmic heating. The electrical conductivity of bignay juice increased linearly from 0.128 to 0.390 S/m as temperature increased from 32 °C to 110 °C. The relationship between temperature and electrical conductivity is given in Equation 8 with R2 > 0.9986.

Figure 1
Electrical conductivity of bignay fruit juice during ohmic heating.
σ = 0.0034 T + 0.0111 (8)

This result is in accordance with the results reported by other researches which indicated that electrical conductivity increased linearly with temperature (Palaniappan & Sastry, 1991Palaniappan, S., & Sastry, S. K. (1991). Electrical conductivity of selected juice: influences of temperature, solid content, applied voltage, and particle size. Journal of Food Process Engineering, 14(4), 247-260. http://dx.doi.org/10.1111/j.1745-4530.1991.tb00135.x.
http://dx.doi.org/10.1111/j.1745-4530.19...
; Srivastav & Roy, 2014Srivastav, S., & Roy, S. (2014). Changes in electrical conductivity of liquid foods during ohmic heating. International Journal of Agricultural and Biological Engineering, 7(5), 133-138. http://dx.doi.org/10.3965/j.ijabe.20140705.015.
http://dx.doi.org/10.3965/j.ijabe.201407...
).

The result obtained in this study is comparable to the results of previous studies conducted on blueberry and strawberry pulp with the electrical conductivity of 0.79-3.86 mS/cm (0.079-0.386 S/m) at 30-82 °C and 0.001-0.004 S/cm (0.1-0.4 S/m) at 20-100 °C, respectively (Castro et al., 2004Castro, I., Teixeira, J. A., Salengke, S., Sastry, S. K., & Vicente, A. A. (2004). Ohmic heating of strawberry products: electrical conductivity measurements and ascorbic acid degradation kinetics. Innovative Food Science & Emerging Technologies, 5(1), 27-36. http://dx.doi.org/10.1016/j.ifset.2003.11.001.
http://dx.doi.org/10.1016/j.ifset.2003.1...
; Mercali et al., 2011Mercali, G. D., Sarkis, J. R., Jaeschke, D. P., Tessaro, I. C., & Marczak, L. D. F. (2011). Physical properties of acerola and blueberry pulps. Journal of Food Engineering, 106(4), 283-289. http://dx.doi.org/10.1016/j.jfoodeng.2011.05.010.
http://dx.doi.org/10.1016/j.jfoodeng.201...
). The electrical conductivity of bignay juice can be considered optimum for ohmic heating processing since electrical conductivity in the range of 0.1-5 S/m is considered optimum for ohmic heating by several researchers (Proctor, 2018Proctor, A. (2018). Alternatives to conventional food processing (2nd ed., Vol. 53). Cambridge: Royal Society of Chemistry.; Salari & Jafari, 2020Salari, S., & Jafari, S. M. (2020). The influence of ohmic heating on degradation of food bioactive ingredients. Food Engineering Reviews, 12(2), 191-208. http://dx.doi.org/10.1007/s12393-020-09217-0.
http://dx.doi.org/10.1007/s12393-020-092...
). Beside temperature and ionic compounds, electrical conductivity also depends on the applied electric field, free water content, and solid content of the product (Castro et al., 2003Castro, I., Teixeira, J. A., Salengke, S., Sastry, S. K., & Vicente, A. A. (2003). The influence of field strength, sugar, and solid content on electrical conductivity of strawberry products. Journal of Food Process Engineering, 26(1), 17-29. http://dx.doi.org/10.1111/j.1745-4530.2003.tb00587.x.
http://dx.doi.org/10.1111/j.1745-4530.20...
; Icier & Ilicali, 2004Icier, F., & Ilicali, C. (2004). The effects of concentration on electrical conductivity of orange juice concentrates during ohmic heating. European Food Research and Technology, 220(3-4), 406-414. http://dx.doi.org/10.1007/s00217-004-1043-x.
http://dx.doi.org/10.1007/s00217-004-104...
; Varghese et al., 2014Varghese, K. S., Pandey, M. C., Radhakrishna, K., & Bawa, A. S. (2014). Technology, applications and modelling of ohmic heating: a review. Journal of Food Science and Technology, 51(10), 2304-2317. http://dx.doi.org/10.1007/s13197-012-0710-3. PMid:25328171.
http://dx.doi.org/10.1007/s13197-012-071...
).

3.2 Change in bioactive compounds during heating

Fresh bignay juice contained 1202.5 mg GAE/100 mL total phenolic, 426.6 mg/100 mL anthocyanin, and 3.78 mg/100 mL flavonoid. The total phenolic content obtained was comparable to the results reported in Butkhup & Samappito (2008)Butkhup, L., & Samappito, S. (2008). Analysis of anthocyanin, flavonoids, and phenolic acids in tropical bignay berries. International Journal of Fruit Science, 8(1-2), 15-34. http://dx.doi.org/10.1080/15538360802365913.
http://dx.doi.org/10.1080/15538360802365...
, while anthocyanin content in this study was higher than the anthocyanin content of bignay juice described in Chaikham et al. (2016)Chaikham, P., Prangthip, P., & Seesuriyachan, P. (2016). Ultra-sonication effects on quality attributes of maoberry (Antidesma bunius L.) juice. Food Science and Technology Research, 22(5), 647-654. http://dx.doi.org/10.3136/fstr.22.647.
http://dx.doi.org/10.3136/fstr.22.647...
. On the contrary, a study conducted by Jorjong et al. (2015)Jorjong, S., Butkhup, L., & Samappito, S. (2015). Phytochemicals and antioxidant capacities of Mao-Luang (Antidesma bunius L.) cultivars from Northeastern Thailand. Food Chemistry, 181, 248-255. http://dx.doi.org/10.1016/j.foodchem.2015.02.093. PMid:25794747.
http://dx.doi.org/10.1016/j.foodchem.201...
reported higher flavonoid content compared to the result found in this study. The influence of temperature and time during ohmic heating was shown in Figure 2 below. Each type of compound possessed different behavior when exposed to both treatments. Statistical analysis was used to further determine the interaction between the observed bioactive compounds and the treatment used.

Figure 2
Degradation of bioactive compounds during ohmic heating; (a) Phenolic content; (b) Anthocyanin content; (c) Flavonoid content

Total phenolic in bignay juice decreased during ohmic heating at all temperatures with the highest reduction occurred at 110 °C. Significant degradation was observed during heating from ambient temperature to the targeted treatment temperatures. During constant temperature period (up to 45 minutes holding time at treatment temperatures), we found insignificant change in phenolic content. Previous studies reported that degradation of phenolic content occurred during ohmic heating of watermelon juice (Makroo et al., 2017Makroo, H. A., Saxena, J., Rastogi, N. K., & Srivastava, B. (2017). Ohmic heating assisted polyphenol oxidase inactivation of watermelon juice: effects of the treatment on pH, lycopene, total phenolic content, and color of the juice. Journal of Food Processing and Preservation, 41(6), e13271. http://dx.doi.org/10.1111/jfpp.13271.
http://dx.doi.org/10.1111/jfpp.13271...
) and sugarcane juice (Brochier et al., 2016Brochier, B., Mercali, G. D., & Marczak, L. D. F. (2016). Influence of moderate electric field on inactivation kinetics of peroxidase and polyphenol oxidase and on phenolic compounds of sugarcane juice treated by ohmic heating. Lebensmittel-Wissenschaft + Technologie, 74, 396-403. http://dx.doi.org/10.1016/j.lwt.2016.08.001.
http://dx.doi.org/10.1016/j.lwt.2016.08....
). Ohmic heating of sugarcane juice at varying frequencies demonstrated no further degradation that occurred after time zero. The phenolic content of watermelon juice decreased significantly during the first 30 seconds of heating while the reduction of this compound became insignificant afterward. Another study which evaluate the effect of heating method on fruit juice indicated no significant difference between ohmic and conventional heating in terms of total phenolic content (Brochier et al., 2016Brochier, B., Mercali, G. D., & Marczak, L. D. F. (2016). Influence of moderate electric field on inactivation kinetics of peroxidase and polyphenol oxidase and on phenolic compounds of sugarcane juice treated by ohmic heating. Lebensmittel-Wissenschaft + Technologie, 74, 396-403. http://dx.doi.org/10.1016/j.lwt.2016.08.001.
http://dx.doi.org/10.1016/j.lwt.2016.08....
; Yildiz et al., 2009Yildiz, H., Bozkurt, H., & Icier, F. (2009). Ohmic and conventional heating of pomegranate juice: effects on rheology, color, and total phenolics. Food Science & Technology International, 15(5), 503-512. http://dx.doi.org/10.1177/1082013209350352.
http://dx.doi.org/10.1177/10820132093503...
). However, the study conducted for pomegranate juice reported that phenolic content increased after processing both with ohmic and conventional heating (Yildiz et al., 2009Yildiz, H., Bozkurt, H., & Icier, F. (2009). Ohmic and conventional heating of pomegranate juice: effects on rheology, color, and total phenolics. Food Science & Technology International, 15(5), 503-512. http://dx.doi.org/10.1177/1082013209350352.
http://dx.doi.org/10.1177/10820132093503...
). An increase in phenolic compounds after thermal treatment was also observed in sajor-caju extract (Saad et al., 2014Saad, W. Z., Hashim, M., Ahmad, S., & Abdullah, N. (2014). Effects of heat treatment on total phenolic contents, antioxidant and anti- inflammatory activities of pleurotus sajor-caju extract. International Journal of Food Properties, 17(1), 219-225. http://dx.doi.org/10.1080/10942912.2011.619290.
http://dx.doi.org/10.1080/10942912.2011....
) and jambolana pulp (Branco et al., 2016Branco, I. G., Moraes, I. C. F., Argandoña, E. J. S., Madrona, G. S., dos Santos, C., Ruiz, A. L. T. G., de Carvalho, J. E., & Haminiuk, C. W. I. (2016). Influence of pasteurization on antioxidant and in vitro anti-proliferative effects of jambolan (Syzygium cumini (L.) Skeels) fruit pulp. Industrial Crops and Products, 89, 225-230. http://dx.doi.org/10.1016/j.indcrop.2016.04.055.
http://dx.doi.org/10.1016/j.indcrop.2016...
). The different trends reported by various researchers can be due to varying processing conditions applied to the products. For instance, Cappato et al. (2018aCappato, L. P., Ferreira, M. V. S., Moraes, J., Pires, R. P. S., Rocha, R. S., Silva, R., Cucinelli, R. P. C. No., Tavares, M. I. B., Freitas, M. Q., Rodrigues, F. N., Calado, V. M. A., Raices, R. S. L., Silva, M. C., & Cruz, A. G. (2018a). Whey acerola-flavoured drink submitted Ohmic Heating: Bioactive compounds, antioxidant capacity, thermal behavior, water mobility, fatty acid profile and volatile compounds. Food Chemistry, 263, 81-88. http://dx.doi.org/10.1016/j.foodchem.2018.04.115. PMid:29784332.
http://dx.doi.org/10.1016/j.foodchem.201...
, bCappato, L. P., Ferreira, M. V. S., Pires, R. P. S., Cavalcanti, R. N., Bisaggio, R. C., Freitas, M. Q., Silva, M. C., & Cruz, A. G. (2018b). Whey acerola-flavoured drink submitted Ohmic Heating processing: Is there an optimal combination of the operational parameters? Food Chemistry, 245, 22-28. http://dx.doi.org/10.1016/j.foodchem.2017.10.019. PMid:29287363.
http://dx.doi.org/10.1016/j.foodchem.201...
) described that the quality of whey acerola-flavored drink was highly affected by the voltage and electric frequency used during ohmic heating. In regard to phenolic compound, the worst operating condition was reported at 60 V - 60 Hz combination, while the highest retention was reported at 25 V - 1000 Hz combination (Cappato et al., 2018aCappato, L. P., Ferreira, M. V. S., Moraes, J., Pires, R. P. S., Rocha, R. S., Silva, R., Cucinelli, R. P. C. No., Tavares, M. I. B., Freitas, M. Q., Rodrigues, F. N., Calado, V. M. A., Raices, R. S. L., Silva, M. C., & Cruz, A. G. (2018a). Whey acerola-flavoured drink submitted Ohmic Heating: Bioactive compounds, antioxidant capacity, thermal behavior, water mobility, fatty acid profile and volatile compounds. Food Chemistry, 263, 81-88. http://dx.doi.org/10.1016/j.foodchem.2018.04.115. PMid:29784332.
http://dx.doi.org/10.1016/j.foodchem.201...
). The types of phenolic compounds contained in the product also affect the change in the phenolic compound during heating. Xu et al. (2007)Xu, G., Ye, X., Chen, J., & Liu, D. (2007). Effect of heat treatment on the phenolic compounds and antioxidant capacity of citrus peel extract. Journal of Agricultural and Food Chemistry, 55(2), 330-335. http://dx.doi.org/10.1021/jf062517l. PMid:17227062.
http://dx.doi.org/10.1021/jf062517l...
, described that free phenolic acid fraction in citrus peel extract increased after thermal treatment while the phenolic acid found in the form of ester, glycoside, and ester-bound fractions decreased during heating.

Anthocyanin is known to be susceptible to several environmental factors such as temperature, pH, light, and oxygen (Loypimai et al., 2016Loypimai, P., Moongngarm, A., & Chottanom, P. (2016). Thermal and pH degradation kinetics of anthocyanins in natural food colorant prepared from black rice bran. Journal of Food Science and Technology, 53(1), 461-470. http://dx.doi.org/10.1007/s13197-015-2002-1. PMid:26787965.
http://dx.doi.org/10.1007/s13197-015-200...
; Moreno et al., 2016Moreno, J., Gonzales, M., Zúñiga, P., Petzold, G., Mella, K., & Muñoz, O. (2016). Ohmic heating and pulsed vacuum effect on dehydration processes and polyphenol component retention of osmodehydrated blueberries (cv. Tifblue). Innovative Food Science & Emerging Technologies, 36, 112-119. http://dx.doi.org/10.1016/j.ifset.2016.06.005.
http://dx.doi.org/10.1016/j.ifset.2016.0...
). The same trend was observed in this study where anthocyanin in the treated bignay juice degraded significantly (p < 0.05). Ohmic heating at 70 °C for 45 minutes retained 93.7% of anthocyanin in the treated bignay juice, while heating at 90 °C and 110 °C for 45 minutes caused degradation in the order of 21% and 62% respectively. Similar trend was reported for blackberry pulp, where anthocyanin showed better retention at lower temperatures (70-75°C) compared to that at higher temperatures (80-90 °C) which showed degradation for up to 40% (Sarkis et al., 2019Sarkis, J. R., Jaeschke, D. P., Mercali, G. D., Tessaro, I. C., & Marczak, L. D. F. (2019). Degradation kinetics of anthocyanins in blackberry pulp during ohmic and conventional heating. International Food Research Journal, 26(1), 87-97.). Although anthocyanin content of bignay juice decreased during ohmic heating for 45 minutes, the reduction was statistically insignificant (p > 0.05). Degradation of anthocyanin also occurred during thermal treatment of plump juice (Turturicǎ et al., 2018Turturicǎ, M., Stǎnciuc, N., Murean, C., Râpeanu, G., & Croitoru, C. (2018). Thermal degradation of plum anthocyanins: comparison of kinetics from simple to natural systems. Journal of Food Quality, 2018, 1-10. http://dx.doi.org/10.1155/2018/1598756.
http://dx.doi.org/10.1155/2018/1598756...
), sour cherry concentrate (Zoric et al., 2014Zoric, Z., Dragovi-uzelac, V., Pedisic, S., Kurtanjek, Z., & Garofulic, I. E. (2014). Kinetics of the degradation of anthocyanins, phenolic acids and flavonols during heat treatments of freeze-dried sour cherry marasca paste. Food Technology and Biotechnology, 52(1), 101-108.), and jamun fruit juice (Shaheer et al., 2014Shaheer, C. A., Hafeeda, P., Kumar, R., Kathiravan, T., Kumar, D., & Nadanasabapathi, S. (2014). Effect of thermal and thermosonication on anthocyanin stability in jamun (Eugenia jambolana) fruit juice. International Food Research Journal, 21(6), 2189-2194.). Sarkis et al. (2013)Sarkis, J. R., Jaeschke, D. P., Tessaro, I. C., & Marczak, L. D. F. (2013). Effects of ohmic and conventional heating on anthocyanin degradation during the processing of blueberry pulp. Lebensmittel-Wissenschaft + Technologie, 51(1), 79-85. http://dx.doi.org/10.1016/j.lwt.2012.10.024.
http://dx.doi.org/10.1016/j.lwt.2012.10....
compared anthocyanin degradation due to ohmic and conventional heating of blueberry pulp and reported that ohmic heating at high voltage (200 and 240 V) caused higher degradation than conventional heating. Similar trend was also reported by Sarkis et al. (2019)Sarkis, J. R., Jaeschke, D. P., Mercali, G. D., Tessaro, I. C., & Marczak, L. D. F. (2019). Degradation kinetics of anthocyanins in blackberry pulp during ohmic and conventional heating. International Food Research Journal, 26(1), 87-97. who studied anthocyanin degradation in blackberry pulp. Meanwhile, ohmic heating conducted at lower voltages (25, 45, and 60 V) provided no significant difference in anthocyanin degradation compared to that of conventional heating (Ferreira et al., 2019aFerreira, M. V. S., Cappato, L. P., Silva, R., Rocha, R. S., Cucinelli, R. P. C. No., Tavares, M. I. B., Esmerino, E. A., Freitas, M. Q., Bissagio, R. C., Ranadheera, S., Raices, R. S. L., Silva, M. C., & Cruz, A. G. (2019a). Processing raspberry-flavored whey drink using ohmic heating: physical, thermal and microstructural considerations. Food Research International, 123, 20-26. http://dx.doi.org/10.1016/j.foodres.2019.04.045. PMid:31284969.
http://dx.doi.org/10.1016/j.foodres.2019...
; Mercali et al., 2015Mercali, G. D., Gurak, P. D., Schmitz, F., & Marczak, L. D. F. (2015). Evaluation of non-thermal effects of electricity on anthocyanin degradation during ohmic heating of jaboticaba (Myrciaria cauliflora) juice. Food Chemistry, 171, 200-205. http://dx.doi.org/10.1016/j.foodchem.2014.09.006. PMid:25308660.
http://dx.doi.org/10.1016/j.foodchem.201...
).

In contrast to the phenolic and anthocyanin degradation, the degradation of flavonoid in bignay juice is more time-dependent. The degradation of flavonoid was 36%, 51%, and 60% after 45 min of heating at 70, 90, and 110°C, respectively. Prolong heating time significantly affected the destruction of flavonoid content (p<0.05), while the influence of temperature was not significant (p>0.05). Thermal treatment applied to two types of flavonoids (fisetin and quercetin) showed similar behavior where the concentration of both compounds decreased in a time-dependent manner (Wang & Zhao, 2016Wang, J., & Zhao, X. (2016). Degradation kinetics of fisetin and quercetin in solutions affected by medium pH, temperature and co-existing proteins. Journal of the Serbian Chemical Society, 81(3), 243-253. http://dx.doi.org/10.2298/JSC150706092W.
http://dx.doi.org/10.2298/JSC150706092W...
). The same time-dependent behavior was also reported from a study on flavonoid in white grape juice as affected by High Voltage Atmospheric Cold Plasma (Pankaj et al., 2017Pankaj, S. K., Wan, Z., Colonna, W., & Keener, K. M. (2017). Effect of high voltage atmospheric cold plasma on white grape juice quality. Journal of the Science of Food and Agriculture, 97(12), 4016-4021. http://dx.doi.org/10.1002/jsfa.8268. PMid:28195339.
http://dx.doi.org/10.1002/jsfa.8268...
) except that the flavonoid content increased during the treatment.

3.3 Degradation kinetics of anthocyanin and flavonoid

The first-order kinetic models were used to describe the degradation kinetics of anthocyanin and flavonoid in bignay juice in terms of the k, t1/5, D, and Ea values and the results are shown in Table 1. These models have been applied widely in defining the kinetics of degradation of compounds for their mathematical simplicity. These models are widely used to obtain the degradation rate constants which are the main parameters that describe the time and temperature dependence of compounds’ stability during heating (Sarkis et al., 2019Sarkis, J. R., Jaeschke, D. P., Mercali, G. D., Tessaro, I. C., & Marczak, L. D. F. (2019). Degradation kinetics of anthocyanins in blackberry pulp during ohmic and conventional heating. International Food Research Journal, 26(1), 87-97.). Applications of first-order kinetics model to determine the thermal degradation of anthocyanin have been reported for black mulberry juice (Fazaeli et al., 2013Fazaeli, M., Hojjatpanah, G., & Emam-Djomeh, Z. (2013). Effects of heating method and conditions on the evaporation rate and quality attributes of black mulberry (Morus nigra) juice concentrate. Journal of Food Science and Technology, 50(1), 35-43. http://dx.doi.org/10.1007/s13197-011-0246-y. PMid:24425885.
http://dx.doi.org/10.1007/s13197-011-024...
), purple potato (Nayak et al., 2011Nayak, B., Berrios, J. D. J., Powers, J. R., & Tang, J. (2011). Thermal degradation of anthocyanins from purple potato (Cv. Purple Majesty) and impact on antioxidant capacity. Journal of Agricultural and Food Chemistry, 59(20), 11040-11049. http://dx.doi.org/10.1021/jf201923a. PMid:21800848.
http://dx.doi.org/10.1021/jf201923a...
), juçara and “Italia” grapes (Peron et al., 2017Peron, D. V., Fraga, S., & Antelo, F. (2017). Thermal degradation kinetics of anthocyanins extracted from juçara (Euterpe edulis Martius) and “Italia” grapes (Vitis vinifera L.), and the effect of heating on the antioxidant capacity. Food Chemistry, 232, 836-840. http://dx.doi.org/10.1016/j.foodchem.2017.04.088. PMid:28490147.
http://dx.doi.org/10.1016/j.foodchem.201...
), while modeling of flavonoid degradation with first-order kinetics equation can be found in studies on the effects of heat on plump extract (Turturicǎ et al., 2016Turturicǎ, M., Stănciuc, N., Bahrim, G., & Râpeanu, G. (2016). Effect of thermal treatment on phenolic compounds from plum (prunus domestica) extracts: a kinetic study. Journal of Food Engineering, 171, 200-207. http://dx.doi.org/10.1016/j.jfoodeng.2015.10.024.
http://dx.doi.org/10.1016/j.jfoodeng.201...
), black rice flour extract (Bolea et al., 2016Bolea, C., Turturicǎ, M., Stănciuc, N., & Vizireanu, C. (2016). Thermal degradation kinetics of bioactive compounds from black rice flour (Oryza sativa L.) extracts. Journal of Cereal Science, 71, 160-166. http://dx.doi.org/10.1016/j.jcs.2016.08.010.
http://dx.doi.org/10.1016/j.jcs.2016.08....
), and mandarin slices (Akdaş & Başlar, 2015Akdaş, S., & Başlar, M. (2015). Dehydration and degradation kinetics of bioactive compounds for mandarin slices under vacuum and oven drying conditions. Journal of Food Processing and Preservation, 39(6), 1098-1107. http://dx.doi.org/10.1111/jfpp.12324.
http://dx.doi.org/10.1111/jfpp.12324...
).

Table 1
Kinetics parameters of anthocyanin and flavonoid degradation in bignay juice during ohmic heating.

The results shown in Table 1 indicate that the degradation rate constant (k-value) for anthocyanin in bignay fruit juice ranged from 0.0016 to 0.0213. Comparable values were reported from studies on anthocyanin degradation in blackberry (Sarkis et al., 2019Sarkis, J. R., Jaeschke, D. P., Mercali, G. D., Tessaro, I. C., & Marczak, L. D. F. (2019). Degradation kinetics of anthocyanins in blackberry pulp during ohmic and conventional heating. International Food Research Journal, 26(1), 87-97.), jaboticaba (Mercali et al., 2015Mercali, G. D., Gurak, P. D., Schmitz, F., & Marczak, L. D. F. (2015). Evaluation of non-thermal effects of electricity on anthocyanin degradation during ohmic heating of jaboticaba (Myrciaria cauliflora) juice. Food Chemistry, 171, 200-205. http://dx.doi.org/10.1016/j.foodchem.2014.09.006. PMid:25308660.
http://dx.doi.org/10.1016/j.foodchem.201...
), and acerola fruit juice (Mercali et al., 2013Mercali, G. D., Jaeschke, D. P., Tessaro, I. C., & Marczak, L. D. F. (2013). Degradation kinetics of anthocyanins in acerola pulp: comparison between ohmic and conventional heat treatment. Food Chemistry, 136(2), 853-857. http://dx.doi.org/10.1016/j.foodchem.2012.08.024. PMid:23122136.
http://dx.doi.org/10.1016/j.foodchem.201...
). The k-values reported in these studies ranged from 0.00155-0.0051 min-1 for blackberry pulp at 70-90 °C (Sarkis et al., 2019Sarkis, J. R., Jaeschke, D. P., Mercali, G. D., Tessaro, I. C., & Marczak, L. D. F. (2019). Degradation kinetics of anthocyanins in blackberry pulp during ohmic and conventional heating. International Food Research Journal, 26(1), 87-97.), from 0.0017-00075 min-1 for jaboticaba juice at 70-90 °C (Mercali et al., 2015Mercali, G. D., Gurak, P. D., Schmitz, F., & Marczak, L. D. F. (2015). Evaluation of non-thermal effects of electricity on anthocyanin degradation during ohmic heating of jaboticaba (Myrciaria cauliflora) juice. Food Chemistry, 171, 200-205. http://dx.doi.org/10.1016/j.foodchem.2014.09.006. PMid:25308660.
http://dx.doi.org/10.1016/j.foodchem.201...
), and from 0.0059-0.0197 min-1 for acerola pulp processed at 75-90°C (Mercali et al., 2013Mercali, G. D., Jaeschke, D. P., Tessaro, I. C., & Marczak, L. D. F. (2013). Degradation kinetics of anthocyanins in acerola pulp: comparison between ohmic and conventional heat treatment. Food Chemistry, 136(2), 853-857. http://dx.doi.org/10.1016/j.foodchem.2012.08.024. PMid:23122136.
http://dx.doi.org/10.1016/j.foodchem.201...
). Contrary to anthocyanin, research evaluating the degradation kinetics of flavonoid compounds during ohmic heating is still limited. However, compared to the degradation rate constant of flavonoid in other products using other heating methods, the results obtained in this study provide lower degradation rate constant. For instance, microwave processing of York cabbage at 400-800 W resulted in k-values of 0.144-0.197 (Jaiswal & Abu-Ghannam, 2013Jaiswal, A. K., & Abu-Ghannam, N. (2013). Degradation kinetic modelling of color, texture, polyphenols and antioxidant capacity of York cabbage after microwave processing. Food Research International, 53(1), 125-133. http://dx.doi.org/10.1016/j.foodres.2013.04.007.
http://dx.doi.org/10.1016/j.foodres.2013...
) while the k-value for catechin (included in flavonoid group) under ultrasonic treatment at 28-135 kHz were in the range of 0.0099-0.0182 min-1 (Zhu et al., 2018Zhu, Y., Sun, J., Xu, D., Wang, S., Yuan, Y., & Cao, Y. (2018). Investigation of (+)-catechin stability under ultrasonic treatment and its degradation kinetic modeling. Journal of Food Process Engineering, 41(8), e12904. http://dx.doi.org/10.1111/jfpe.12904.
http://dx.doi.org/10.1111/jfpe.12904...
). Comparable k-values (0.012 to 0.025 min-1) were reported for flavonoid in plump extract heated thermally at 70-110°C (Turturicǎ et al., 2016Turturicǎ, M., Stănciuc, N., Bahrim, G., & Râpeanu, G. (2016). Effect of thermal treatment on phenolic compounds from plum (prunus domestica) extracts: a kinetic study. Journal of Food Engineering, 171, 200-207. http://dx.doi.org/10.1016/j.jfoodeng.2015.10.024.
http://dx.doi.org/10.1016/j.jfoodeng.201...
). The results shown in Table 1 also indicate that flavonoid degradation rates were relatively higher than those of anthocyanin. This finding was validated by the significantly smaller half time (t1/2) value for flavonoid which indicate that the time required to degrade 50% of flavonoid in bignay fruit juice is significantly shorter than that of anthocyanin. Comparable t1/2 values for anthocyanin (129-447 min) were reported in blackberry pulp treated by ohmic heating (Sarkis et al., 2019Sarkis, J. R., Jaeschke, D. P., Mercali, G. D., Tessaro, I. C., & Marczak, L. D. F. (2019). Degradation kinetics of anthocyanins in blackberry pulp during ohmic and conventional heating. International Food Research Journal, 26(1), 87-97.).

The effect of temperature on the degradation rate constant was significant as shown in Table 1. It can be observed that the k-value for anthocyanin degradation at 110 °C was more than 10 times the k-value at 70 °C. On the other hand, the k-value for flavonoid degradation was only double as temperature was increased from 70 °C to 110 °C. Consequently, the activation energy (Ea) of anthocyanin degradation was significantly higher than that of flavonoid (Figure 3). Based on the Ea values, anthocyanin is much more thermally stable than flavonoid since its Ea value was about 3.5 times the Ea value of flavonoid. A closer examination to the data in Table 1 indicates that at 70oC, the degradation rate constant for flavonoid was about 6.7 times that of anthocyanin, while at 90 °C the value was about 2.8. On the other hand, at 110oC, the degradation rate constant for flavonoid was about 0.98 that of anthocyanin. These values indicate that at the lower treatment temperature (70 and 90 °C), anthocyanin was much more stable that flavonoid while at the highest treatment temperature (110 °C) the degradation rate constants of the two compounds were almost identical. Therefore, overall, anthocyanin in bignay fruit juice is much more stable during ohmic heating compared to flavonoid. This trend can also be seen from the slopes of the curves in Figure 2. For the effect of temperature on anthocyanin degradation, results of statistical analysis indicate that degradation of anthocyanin in bignay fruit juice was significantly higher at 90 and 110 °C than that at 70 °C (p<0.05). The activation energy for degradation of anthocyanin found in this study was comparable to those reported for blackberry pulp (67 kJ/mol) and acerola pulp (74.83 kJ/mol) (Mercali et al., 2013Mercali, G. D., Jaeschke, D. P., Tessaro, I. C., & Marczak, L. D. F. (2013). Degradation kinetics of anthocyanins in acerola pulp: comparison between ohmic and conventional heat treatment. Food Chemistry, 136(2), 853-857. http://dx.doi.org/10.1016/j.foodchem.2012.08.024. PMid:23122136.
http://dx.doi.org/10.1016/j.foodchem.201...
; Sarkis et al., 2019Sarkis, J. R., Jaeschke, D. P., Mercali, G. D., Tessaro, I. C., & Marczak, L. D. F. (2019). Degradation kinetics of anthocyanins in blackberry pulp during ohmic and conventional heating. International Food Research Journal, 26(1), 87-97.).

Figure 3
Arrhenius plot of ln k vs. 1/T for the kinetic degradation of anthocyanin and flavonoid in bignay fruit juice.

It is interesting to note that the Ea value for degradation of flavonoid in bignay fruit juice during ohmic heating as found in this study as comparable to those reported previously for sour cherry marasca paste with Ea value of 18.1 kJ/mol (Zoric et al., 2014Zoric, Z., Dragovi-uzelac, V., Pedisic, S., Kurtanjek, Z., & Garofulic, I. E. (2014). Kinetics of the degradation of anthocyanins, phenolic acids and flavonols during heat treatments of freeze-dried sour cherry marasca paste. Food Technology and Biotechnology, 52(1), 101-108.), plump extract with Ea value of 18.0 ± 2.0 kJ/mol and black rice flour with Ea value of 15.80 ± 1.50 kJ/mol (Bolea et al., 2016Bolea, C., Turturicǎ, M., Stănciuc, N., & Vizireanu, C. (2016). Thermal degradation kinetics of bioactive compounds from black rice flour (Oryza sativa L.) extracts. Journal of Cereal Science, 71, 160-166. http://dx.doi.org/10.1016/j.jcs.2016.08.010.
http://dx.doi.org/10.1016/j.jcs.2016.08....
; Turturicǎ et al., 2016Turturicǎ, M., Stănciuc, N., Bahrim, G., & Râpeanu, G. (2016). Effect of thermal treatment on phenolic compounds from plum (prunus domestica) extracts: a kinetic study. Journal of Food Engineering, 171, 200-207. http://dx.doi.org/10.1016/j.jfoodeng.2015.10.024.
http://dx.doi.org/10.1016/j.jfoodeng.201...
). Another important bioactive compound that has been reported to have comparable Ea value was ascorbic acid in pineapple juice with Ea vaalues ranged from 14.22 to 29.78 kJ/mol (Dhakal et al., 2018Dhakal, S., Balasubramaniam, V. M., Ayvaz, H., & Rodriguez-Saona, L. E. (2018). Kinetic modeling of ascorbic acid degradation of pineapple juice subjected to combined pressure-thermal treatment. Journal of Food Engineering, 224, 62-70. http://dx.doi.org/10.1016/j.jfoodeng.2017.12.016.
http://dx.doi.org/10.1016/j.jfoodeng.201...
) and ascorbic acid in strawberry pulp with Ea value of 21.36 kJ/mol (Castro et al., 2004Castro, I., Teixeira, J. A., Salengke, S., Sastry, S. K., & Vicente, A. A. (2004). Ohmic heating of strawberry products: electrical conductivity measurements and ascorbic acid degradation kinetics. Innovative Food Science & Emerging Technologies, 5(1), 27-36. http://dx.doi.org/10.1016/j.ifset.2003.11.001.
http://dx.doi.org/10.1016/j.ifset.2003.1...
).

3.4 Changes in antioxidant activity

The antioxidant activity of bignay fruit juice is expressed as IC50 with lower value implies higher antioxidant activity. The IC50 value of bignay fruit juice ranged from 0.106-0.168 mg/mL for DPPH method and 0.131-0.161 mg/mL for ABTS method. Comparable range of antioxidant activity was reported for black plump (71.30 - 114.69 μg/mL) and Litchi chinensis fruit pulp (0.102 mg/mL) (Prakash et al., 2011Prakash, D., Upadhyay, G., Pushpangadan, P., & Gupta, C. (2011). Antioxidant and free radical scavenging activities of some fruits.". . Journal of Complementary & Integrative Medicine, 8(1), 23. http://dx.doi.org/10.2202/1553-3840.1513. PMid:22754941.
http://dx.doi.org/10.2202/1553-3840.1513...
; Baliga et al., 2011Baliga, M. S., Bhat, H. P., Baliga, B. R. V., Wilson, R., & Palatty, P. L. (2011). Phytochemistry, traditional uses and pharmacology of Eugenia jambolana Lam. (black plum): a review. Food Research International, 44(7), 1776-1789. http://dx.doi.org/10.1016/j.foodres.2011.02.007.
http://dx.doi.org/10.1016/j.foodres.2011...
). Antioxidant activity of bignay fruit juice obtained from both DPPH and ABTS methods slightly decreased after undergoing heating for 45 min (Figure 4). However, the overall effect of ohmic heating duration on the reduction of antioxidant activity measured using both DPPH and ABTS methods was statistically insignificant (p > 0.05). Results of statistical analysis indicate that the effect of temperature on antioxidant activity was significant (p < 0.05) based on the measurement results using the DPPH method but insignificant based on measurement results from the ABTS method. It is important to note that based on the results obtained from the DPPH method, bignay fruit juice heated by ohmic heating at 90 and 110 °C provided higher antioxidant activity than that at 70 °C (p < 0.05). In fact, the antioxidant activity of ohmically heated bignay juice at 90 °C exhibited no significant difference from that of fresh bignay fruit juice in our previous study (Hardinasinta et al., 2020Hardinasinta, G., Mursalim, M., Muhidong, J., & Salengke, S. (2020). Determination of some chemical compounds of bignay (Antidesma bunius) fruit juice. Food Science and Technology. In press. http://dx.doi.org/10.1590/fst.27720.
http://dx.doi.org/10.1590/fst.27720...
). This implies that higher temperature showed a positive effect on antioxidant activity. Increased in antioxidant activity of food product at higher temperature or after thermal treatment has been reported by other researchers (Alizadeh & Aliakbarlu, 2020Alizadeh, O., & Aliakbarlu, J. (2020). Effects of ultrasound and ohmic heating pretreatments on hydrolysis, antioxidant and antibacterial activities of whey protein concentrate and its fractions. Lebensmittel-Wissenschaft + Technologie, 131, 109913. http://dx.doi.org/10.1016/j.lwt.2020.109913.
http://dx.doi.org/10.1016/j.lwt.2020.109...
; Jaramillo-Flores et al., 2003Jaramillo-Flores, M. E., González-Cruz, L., Cornejo-Mazón, M., Dorantes-álvarez, L., Gutiérrez-López, G. F., & Hernández-Sánchez, H. (2003). Effect of thermal treatment on the antioxidant activity and content of carotenoids and phenolic compounds of cactus pear cladodes (Opuntia ficus-indica). Food Science & Technology International, 9(4), 271-278. http://dx.doi.org/10.1177/108201303036093.
http://dx.doi.org/10.1177/10820130303609...
; Jeong et al., 2004Jeong, S. M., Kim, S. Y., Kim, D. R., Jo, S. C., Nam, K. C., Ahn, D. U., & Lee, S. C. (2004). Effect of heat treatment on the antioxidant activity of extracts from citrus peels. Journal of Agricultural and Food Chemistry, 52(11), 3389-3393. http://dx.doi.org/10.1021/jf049899k. PMid:15161203.
http://dx.doi.org/10.1021/jf049899k...
; Keenan et al., 2010Keenan, D. F., Brunton, N. P., Gormley, T. R., Butler, F., Tiwari, B. K., & Patras, A. (2010). Effect of thermal and high hydrostatic pressure processing on antioxidant activity and colour of fruit smoothies. Innovative Food Science & Emerging Technologies, 11(4), 551-556. http://dx.doi.org/10.1016/j.ifset.2010.07.003.
http://dx.doi.org/10.1016/j.ifset.2010.0...
; Kusznierewicz et al., 2008Kusznierewicz, B., Śmiechowska, A., Bartoszek, A., & Namieśnik, J. (2008). The effect of heating and fermenting on antioxidant properties of white cabbage. Food Chemistry, 108(3), 853-861. http://dx.doi.org/10.1016/j.foodchem.2007.11.049. PMid:26065745.
http://dx.doi.org/10.1016/j.foodchem.200...
; Mannozzi et al., 2019Mannozzi, C., Rompoonpol, K., Fauster, T., Tylewicz, U., Romani, S., Dalla Rosa, M., & Jaeger, H. (2019). Influence of pulsed electric field and ohmic heating pretreatments on enzyme and antioxidant activity of fruit and vegetable juices. Foods, 8(7), 247. http://dx.doi.org/10.3390/foods8070247. PMid:31288407.
http://dx.doi.org/10.3390/foods8070247...
; Nayik & Nanda, 2016Nayik, G. A., & Nanda, V. (2016). Effect of thermal treatment and pH on antioxidant activity of saffron honey using response surface methodology. Journal of Food Measurement and Characterization, 10(1), 64-70. http://dx.doi.org/10.1007/s11694-015-9277-9.
http://dx.doi.org/10.1007/s11694-015-927...
; Sharma et al., 2015Sharma, K., Ko, E. Y., Assefa, A. D., Ha, S., Nile, S. H., Lee, E. T., & Park, S. W. (2015). Temperature-dependent studies on the total phenolics, flavonoids, antioxidant activities, and sugar content in six onion varieties. Journal of Food and Drug Analysis, 23(2), 243-252. http://dx.doi.org/10.1016/j.jfda.2014.10.005. PMid:28911379.
http://dx.doi.org/10.1016/j.jfda.2014.10...
). Mannozzi et al. (2019)Mannozzi, C., Rompoonpol, K., Fauster, T., Tylewicz, U., Romani, S., Dalla Rosa, M., & Jaeger, H. (2019). Influence of pulsed electric field and ohmic heating pretreatments on enzyme and antioxidant activity of fruit and vegetable juices. Foods, 8(7), 247. http://dx.doi.org/10.3390/foods8070247. PMid:31288407.
http://dx.doi.org/10.3390/foods8070247...
reported that antioxidant activity of carrot and apple juice preheated at 80 °C was higher than those preheated at 40 and 60 °C. There are several postulates have been proposed for this trend such as the disruption of chemical bonds, formation of chemical reaction products that provide scavenging activity, and inactivation of oxidative enzymes (Keenan et al., 2010Keenan, D. F., Brunton, N. P., Gormley, T. R., Butler, F., Tiwari, B. K., & Patras, A. (2010). Effect of thermal and high hydrostatic pressure processing on antioxidant activity and colour of fruit smoothies. Innovative Food Science & Emerging Technologies, 11(4), 551-556. http://dx.doi.org/10.1016/j.ifset.2010.07.003.
http://dx.doi.org/10.1016/j.ifset.2010.0...
; Kusznierewicz et al., 2008Kusznierewicz, B., Śmiechowska, A., Bartoszek, A., & Namieśnik, J. (2008). The effect of heating and fermenting on antioxidant properties of white cabbage. Food Chemistry, 108(3), 853-861. http://dx.doi.org/10.1016/j.foodchem.2007.11.049. PMid:26065745.
http://dx.doi.org/10.1016/j.foodchem.200...
; Mannozzi et al., 2019Mannozzi, C., Rompoonpol, K., Fauster, T., Tylewicz, U., Romani, S., Dalla Rosa, M., & Jaeger, H. (2019). Influence of pulsed electric field and ohmic heating pretreatments on enzyme and antioxidant activity of fruit and vegetable juices. Foods, 8(7), 247. http://dx.doi.org/10.3390/foods8070247. PMid:31288407.
http://dx.doi.org/10.3390/foods8070247...
; Nayik & Nanda, 2016Nayik, G. A., & Nanda, V. (2016). Effect of thermal treatment and pH on antioxidant activity of saffron honey using response surface methodology. Journal of Food Measurement and Characterization, 10(1), 64-70. http://dx.doi.org/10.1007/s11694-015-9277-9.
http://dx.doi.org/10.1007/s11694-015-927...
; Sharma et al., 2015Sharma, K., Ko, E. Y., Assefa, A. D., Ha, S., Nile, S. H., Lee, E. T., & Park, S. W. (2015). Temperature-dependent studies on the total phenolics, flavonoids, antioxidant activities, and sugar content in six onion varieties. Journal of Food and Drug Analysis, 23(2), 243-252. http://dx.doi.org/10.1016/j.jfda.2014.10.005. PMid:28911379.
http://dx.doi.org/10.1016/j.jfda.2014.10...
).

Figure 4
Antioxidant activity of bignay juice during ohmic heating represented as IC50 value; (a) DPPH method; and (b) ABTS method.

4 Conclusions

The present study demonstrates that an insignificant change in total phenol occurred during ohmic heating of bignay juice, while anthocyanin and flavonoid contents tended to decrease. Activation energy for the degradation of anthocyanin was much higher than that of flavonoid which suggests that anthocyanin in bignay fruit juice is much more stable during heating compared to flavonoid. The degradation rate constants at 70 and 90 °C for the two compounds indicate that anthocyanin is much more stable at the lower temperature treatment (70 and 90 °C) but these compounds have almost the same destruction rate constant at 110 °C. Antioxidant activity of bignay fruit juice showed a significant increase after undergoing ohmic heating even though the natural bioactive compounds contained in the juice decreased during ohmic heating.

  • Practical Application: Production of antioxidant rich bignay fruit juice using ohmic heating technology.

References

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Publication Dates

  • Publication in this collection
    12 Mar 2021
  • Date of issue
    2022

History

  • Received
    20 Nov 2020
  • Accepted
    05 Jan 2021
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