The effect of hot air, vacuum and microwave drying on drying characteristics, rehydration capacity, color, total phenolic content and antioxidant capacity of Kumquat (<i>Citrus japonica</i>)

OZCAN-SINIR, Gulsah; OZKAN-KARABACAK, Azime; TAMER, Canan Ece; COPUR, Omer Utku

doi:10.1590/fst.34417

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Food Science and Technology

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Original Article • Food Sci. Technol 39 (02) • Apr-Jun 2019 • https://doi.org/10.1590/fst.34417 copy

The effect of hot air, vacuum and microwave drying on drying characteristics, rehydration capacity, color, total phenolic content and antioxidant capacity of Kumquat (Citrus japonica)

Authorship SCIMAGO INSTITUTIONS RANKINGS

Abstract

Sliced kumquats were dried by using three different drying methods, microwave (375 W), hot air (70 and 80 °C), and vacuum (70 and 80 °C with 100 and 300 mbar) to determine drying characteristics, antioxidant capacity and total phenolic content and color. All color parameters (L, a, b, C_ab, ΔE and h° ) changed depending on the drying methods. Page and Modified Page models are the best fitted drying methods with the highest value of R² (0.9994) and the lowest values of RMSE (0.000635-0.000735) and χ² (0.000010-0.000013) compared to other models. Effective moisture diffusivity values for dried kumquats ranged from 1.54 × 10^-8 to 8.24 × 10^-8 in vacuum drying at 70 °C-300 mbar and microwave drying at 375 W, respectively. In comparison to the fresh sample, the dried samples showed an increase in both total phenolic content and antioxidant capacity. The total phenolic content (3095.71 ± 101.41 mg GA/100g d.w) and antioxidant activity (10.51 ± 0.19 µmol TE/g d.w) with DPPH assay showed the highest levels for the vacuum drying at 70 °C-100 mbar method. Microwave dried samples had the highest antioxidant activity with CUPRAC assay as (17.58 ± 0.63 µmol TE/g d.w.). This study indicated that microwave drying and vacuum drying at 70 °C-100 mbar were able to yield high-quality kumquat slices.

Keywords:
kumquat; drying methods; drying characteristics; rehydration; antioxidant capacity

Model name	Model	References
Page	MR = exp(-ktⁿ)	Sarsavadia et al. (1999) Sarsavadia, P. N., Sawhney, R. L., Pangavhane, D. R., & Singh, S. P. (1999). Drying behaviour of brined onion slices. Journal of Food Engineering, 40(3), 219-226. http://dx.doi.org/10.1016/S0260-8774(99)00058-8. http://dx.doi.org/10.1016/S0260-8774(99...
Modified Page	MR= exp [(-kt)ⁿ]	Overhults et al. (1973) Overhults, D. D., White, G. M., Hamilton, M. E., & Ross, I. J. (1973). Drying soybeans with heated air. Transactions of the ASAE. American Society of Agricultural Engineers , 16(1), 195-200. http://dx.doi.org/10.13031/2013.37459. http://dx.doi.org/10.13031/2013.37459 ...
Logarithmic	MR = a exp(-kt) + c	Yagcioglu (1999) Yagcioglu, A. (1999). Drying technique of agricultural products (Faculty of Agriculture Publications, Vol. 536). Bornova: Ege University.
Lewis	MR = exp(-kt)	Doymaz (2006) Doymaz, I. (2006). Drying kinetics of black grapes treated with different solutions. Journal of Food Engineering, 76(2), 212-217. http://dx.doi.org/10.1016/j.jfoodeng.2005.05.009. http://dx.doi.org/10.1016/j.jfoodeng.20...
Handerson ve Pabis	MR = a exp(-kt)	Westerman et al. (1973) Westerman, P. W., White, G. M., & Ross, I. J. (1973). Relative humidity effect on the high temperature drying of shelled corn. Transactions of the ASAE. American Society of Agricultural Engineers, 16(6), 1136-1139. http://dx.doi.org/10.13031/2013.37715. http://dx.doi.org/10.13031/2013.37715 ...

Model name		Model coefficients		R²	RMSE	X²
Page	MW-375 W	n	1.4539	0.9994	0.000635	0.000010
	MW-375 W	k	0.0136
	air drying 70 °C	n	1.4084	0.9940	0.004870	0.000296
	air drying 70 °C	k	0.0015
	air drying 80 °C	n	1.4117	0.9912	0.006326	0.000500
	air drying 80 °C	k	0.0017
	vacuum 70 °C-100 mbar	n	1.1870	0.9975	0.002709	0.000099
	vacuum 70 °C-100 mbar	k	0.0036
	vacuum 70 °C-300 mbar	n	1.2334	0.9779	0.006542	0.000699
	vacuum 70 °C-300 mbar	k	0.0021
	vacuum 80 °C-100 mbar	n	1.3524	0.9954	0.003739	0.000201
	vacuum 80 °C-100 mbar	k	0.0023
	vacuum 80 °C-300 mbar	n	1.2304	0.9925	0.004301	0.000284
	vacuum 80 °C-300 mbar	k	0.0026
Modified page	MW-375 W	n	1.4553	0.9994	0.000735	0.000013
	MW-375 W	k	0.0514
	air drying 70 °C	n	1.4084	0.9940	0.004870	0.000296
	air drying 70 °C	k	0.0100
	air drying 80 °C	n	1.4117	0.9912	0.006326	0.000500
	air drying 80 °C	k	0.0110
	vacuum 70 °C-100 mbar	n	1.1870	0.9975	0.002891	0.000112
	vacuum 70 °C-100 mbar	k	0.0087
	vacuum 70 °C-300 mbar	n	1.2334	0.9779	0.006803	0.000756
	vacuum 70 °C-300 mbar	k	0.0069
	vacuum 80 °C-100 mbar	n	1.3524	0.9954	0.003782	0.000206
	vacuum 80 °C-100 mbar	k	0.0112
	vacuum 80 °C-300 mbar	n	1.2304	0.9925	0.004426	0.000301
	vacuum 80 °C-300 mbar	k	0.0079
Logarithmic	MW-375 W	k	0.0496	0.9701	0.007194	0.001318
	MW-375 W	a	1.0661
	air drying 70 °C	k	0.0141	0.9473	0.038968	0.021693
	air drying 70 °C	a	1.3013
	air drying 80 °C	k	0.0164	0.9512	0.042941	0.026342
	air drying 80 °C	a	1.3633
	vacuum 70 °C-100 mbar	k	0.0114	0.9726	0.028996	0.012717
	vacuum 70 °C-100 mbar	a	1.2442
	vacuum 70 °C-300 mbar	k	0.0095	0.9125	0.031448	0.017621
	vacuum 70 °C-300 mbar	a	1.3425
	vacuum 80 °C-100 mbar	k	0.0160	0.9723	0.032961	0.017383
	vacuum 80 °C-100 mbar	a	1.3408
	vacuum 80 °C-300 mbar	k	0.0105	0.9634	0.027636	0.012907
	vacuum 80 °C-300 mbar	a	1.2872
Lewis	MW-375 W	k	0.0445	0.9598	0.005966	0.000820
	air drying 70 °C	k	0.0123	0.9291	0.024350	0.006588
	air drying 80 °C	k	0.0263	0.9323	0.026902	0.008041
	vacuum 70 °C-100 mbar	k	0.0103	0.9604	0.016112	0.003141
	vacuum 70 °C-300 mbar	k	0.0082	0.8925	0.018321	0.005061
	vacuum 80 °C-100 mbar	k	0.0141	0.9556	0.019578	0.005018
	vacuum 80 °C-300 mbar	k	0.0094	0.9493	0.016757	0.003955
Henderson and Pabis	MW-375 W	k	0.0508	0.9808	0.004735	0.000543
	MW-375 W	a	1.0826
	air drying 70 °C	k	0.0143	0.9524	0.035940	0.016146
	air drying 70 °C	a	1.3335
	air drying 80 °C	k	0.0165	0.9541	0.041634	0.021667
	air drying 80 °C	a	1.3876
	vacuum 70 °C-100 mbar	k	0.0114	0.9726	0.024535	0.008093
	vacuum 70 °C-100 mbar	a	1.2442
	vacuum 70 °C-300 mbar	k	0.0095	0.9148	0.030401	0.015096
	vacuum 70 °C-300 mbar	a	1.3573
	vacuum 80 °C-100 mbar	k	0.0149	0.9749	0.022479	0.007276
	vacuum 80 °C-100 mbar	a	1.2483
	vacuum 80 °C-300 mbar	k	0.0106	0.9650	0.026219	0.010562
	vacuum 80 °C-300 mbar	a	1.3011

Drying conditions	L	a	b	ΔE	*C_ab*	h°
fresh	61.04 ± 0.15^a	16.27 ± 0.03^e	63.52 ± 0.18^cd	-	65.57 ± 0.16^d	75.63 ± 0.06^a
MW-375 W	17.84 ± 0.57^e	8.60 ± 0.14^f	26.36 ± 0.65^g	7.79 ± 0.11^d	27.73 ± 0.65^g	71.92 ± 0.21^e
air drying 70 °C	51.61 ± 1.37^d	20.80 ± 0.71^b	57.16 ± 0.55^f	8.45 ± 0.19^c	60.83 ± 0.27^f	70.00 ± 0.81^g
air drying 80 °C	58.74 ± 0.13^b	19.02 ± 0.06^d	63.70 ± 0.03^c	3.44 ± 0.10^e	66.48 ± 0.01^c	73.37 ± 0.05^cd
vacuum 70 °C-100 mbar	59.11 ± 0.20^b	20.57 ± 0.05^bc	72.19 ± 0.22^a	8.62 ± 0.44^c	75.06 ± 0.23^a	74.09 ± 0.03^b
vacuum 80 °C-100 mbar	53.19 ± 0.24^c	18.65 ± 0.07^d	61.84 ± 0.26^e	3.24 ± 0.17^e	64.59 ± 0.27^e	73.22 ± 0.01^d
vacuum 70 °C-300 mbar	59.42 ± 0.48^b	20.19 ± 0.14^c	69.84 ± 0.27^b	35.47 ± 0.57^a	72.70 ± 0.29^b	73.88 ± 0.05^bc
vacuum 80 °C-300 mbar	53.62 ± 0.19^c	21.63 ± 0.08^a	62.93 ± 0.24^d	10.76 ± 0.15^b	66.54 ± 0.25^c	71.03 ± 0.02^f

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[1] * Corresponding author: azimeozkan@uludag.edu.tr