Carotenoids are related to the colour and lipid content of the pequi (Caryocar brasiliense Camb.) pulp from the Brazilian Savanna

Carotenoids are related to the colour and lipid content of the pequi ( Caryocar brasiliense Camb.) pulp from the Brazilian Savanna

Débora Melo Ribeiro^I; Daniela Canuto Fernandes^I; Aline Medeiros Alves^II; Maria Margareth Veloso NavesII, ^*

^IDepartment of Nursing, Nutrition and Physiotherapy, University Pontifical Catholic of Goiás – PUC-GO, Goiânia, GO, Brazil

^IISchool of Nutrition, Federal University of Goiás – UFG, Goiânia, GO, Brazil, e-mail: [e-mail], [e-mail]

ABSTRACT

This study investigated the colour, proximate composition, bioactive compounds (phenolic and carotenoid contents), and antioxidant activity of the pulp of pequi from different regions of the Brazilian Savanna. The colour parameters and the lipid and carotenoid contents of the pulp were significantly different between the samples. The lipid content ranged from 135.4 to 322.5 g/kg. The pequi pulp showed high total phenolic content (1.8 to 3.3 mg GAE/g). The carotenoid amount ranged from 37 to 187 µg/g. The carotenoid content was significantly correlated with the colour and lipid content of the pequi pulp. The antioxidant activity showed a mean IC₅₀ value of 197.9 µg/mL. The pequi pulp is rich in phenolic compounds and carotenoids and has a good antioxidant activity. Its colour is influenced by the carotenoid content, which can be predicted by regression models using routine colour parameters.

Keywords:Caryocar brasiliense Camb.; native fruits; Savanna; bioactive compounds; antioxidant capacity.

1 Introduction

The Brazilian Savanna (Cerrado) is the second largest biome in Brazil and is located mainly in the mid-western region of the country. The Brazilian Savanna has several fruit-bearing species with a great potential for agricultural and technological uses (Carvalho et al., 2009; Castro et al., 1999). Among these native fruits, pequi (Caryocar brasiliense Camb.) is the most expressive example; its pulp has an intense colour that ranges from light yellow to dark orange and a striking and peculiar flavour (Geőcze et al., 2013).

Pequi pulp is often consumed and appreciated by the population of the Brazilian Savanna, either in its homemade or industrial form, and its harvest period varies from September to February (Araújo, 1995). In addition to its gastronomic and technological potentials, studie suggests that pequi has a good antioxidant potential (Morais et al., 2013). However, research regarding the carotenoid and phenolic contents of its pulp is limited in number and sample stratification since sampling has been restricted to a small area of the Cerrado or even reduced to a single plant (Azevedo-Meleiro & Rodriguez-Amaya, 2004; Rodriguez-Amaya et al., 2008).

The lack of sample stratification is an important limitation in food research, mainly for native fruits, since studies on the biodiversity of the Brazilian Savanna have shown that there is a great variability of physical (Moura et al., 2013; Vera et al., 2005) and chemical (Czeder et al., 2012) properties of the native fruits from different area of the biome. Therefore, this study tested the hypothesis that there are differences in colour, chemical properties and antioxidant activity of pequi fruits from different regions of the Brazilian Savanna, and that these properties are interrelated. Thus, the present study analysed and compared the colour and chemical and antioxidant properties of pequi fruit samples from five different regions of the Brazilian Savanna, and the correlations among the variables were tested.

2 Materials and methods

2.1 Fruit sampling

Five fruit samples were obtained from native pequi plants from different regions of the Brazilian Savanna: North (latitude: 08° 32' 20", longitude: 48° 30' 21"), South (latitude: 16° 51' 39", longitude: 44° 54' 50"), West (latitude: 15° 51' 57", longitude: 56° 04' 37"), East (latitude: 15° 59' 42", longitude: 44° 16' 12"), and Central (latitude: 16° 37' 08", longitude: 48° 44' 38"). These areas are representative of the production of the native pequi from the Cerrado biome. The samples were obtained in different months, according to the harvest period in each region: North - October 2010; Central - December 2010; South - December 2010; East - January 2011; West - January 2011. The fruits acquired were newly collected and at optimum maturity for commercial use.

2.2 Pequi pulp colour analysis

The colour analysis was performed with 30 pequi fruits from each savanna region, randomly selected from a total of 50 kg. This analysis, which was performed in peeled fruits using a Sphere Colorimeter - Color Quest II (Hunter Lab, Reston, VA, USA) to determine the following CIE (Commission Internationale de l'éclairage) parameters: L* (whiteness or brightness), a* (redness/greenness), and b* (yellowness/blueness) (Lancaster et al., 1997). Colour intensity (chroma) (Equation 1) and hue angle (Equation 2) were calculated using the following equations (McGuire, 1992):

Chroma (C) = (a*² + b*²)^½ (1)

Hue angle (h) = tan ^{- 1} (b*/a*) (2)

2.3 Chemical analyses of the pequi pulp

Sample preparation

For the chemical analyses, the pequi fruits were peeled and pulped manually using a stainless steel knife. Then, the fruit pulp was ground and homogenized in a food processor HL-3253 (Walita, São Paulo, Brazil), packaged in opaque bags, and stored at - 45°C until analyses. For the analyses of the total phenolic and carotenoid content, whole fruits were frozen and stored at - 45°C until analysis.

Proximate composition

The following analyses were performed: moisture (Association of Official Analytical Chemists, 2002); total nitrogen, according to the micro-Kjeldahl method and converted into protein using the factor 6.25 (Association of Official Analytical Chemists, 2002); total lipids, extracted using the technique of Bligh and Dyer (1959) and subsequently measured by gravimetry; ash, by burning in an oven at 550°C; and total dietary fibre (Association of Official Analytical Chemists, 2002). The total carbohydrates were estimated by difference, subtracting the values obtained for moisture, protein, fat, ash and fibre from one hundred. The energy value of the samples was estimated based on the proximate composition data, considering the Atwater conversion factors, which are 4, 4, and 9 kcal/g for protein, carbohydrate, and lipid, respectively (Merril & Watt, 1973). The analyses were performed in triplicate.

Fatty acid composition

To determine the fatty acid composition, the samples were extracted as described by Folch et al. (1957) and esterified according to Hartman & Lago (1973). Fatty acids were separated by Finnigan Focus GC gas chromatography (Thermo, Austin, TX, USA) with a flame ionization detector and capillary column (RESTEK, Bellefonte, PA, USA - polyethylene glycol crossbond - 30 m x 0.25 mm) of fused silica. The running conditions were: carrier gas - hydrogen (2 mL/min); make up gas - nitrogen (28 mL/min); and hydrogen (30 mL/min), and synthetic air (300 mL/min) in order to maintain the detector flame. The injection volume was 1 µL and split ratio of 2:98. Retention time, peak area, and area relative percentage values were obtained using the Chrom Quest 4.1 software. Fatty acids were identified and quantified by reference to the calibration curve prepared with standard methyl esters of fatty acids (Sigma Aldrich). The analyses were performed in triplicate.

Total phenolic content

The total phenolic content was determined by the method described by Swain & Hillis (1959) using the Folin-Ciocalteu's reagent. The extract was obtained as follows: first extraction with 9.52 M acetone, followed by a second extraction with 12.33 M methanol. Then, the extract (0.6 mL) was added to 5.0 mL of distilled water, and 1.0 mL of the Folin-Ciocalteu's phenol reagent and 1.0 mL of 0.24 M sodium carbonate were added to the mixture. The mixture was agitated and incubated at 25°C for 30 min. The absorbance at 700 nm was measured using a spectrophotometer V-630 (JASCO, Tokyo, Japan). A standard curve of gallic acid was drawn, and absorbance was converted to phenolic content in terms of mg of gallic acid equivalents (GAE) per g of pulp. The analyses were performed in triplicate.

Total carotenoid content

The total carotenoid content of the pequi pulp was analysed according to the method described by Higby (1962). The extractions were performed using 25 mL of cold acetone and 1.0 g of pulp mixed with 0.1% of butyl hydroxy toluene (BHT). The residue was re-extracted until it became colourless. The extracts were transferred to petroleum ether, and the filtrates were combined in a separatory funnel and washed with distilled water. The water phase was discarded, and sodium sulphate was added as a desiccant. The ether phase was transferred to a 100 mL volumetric flask and brought to volume with petroleum ether. The absorbance of the extracts was measured from 250 to 700 nm in a spectrophotometer. To determine the total carotenoid content, the highest value of absorbance detected was considered. The total carotenoid content was calculated using the absorbance of anteraxantin at 1 g/mL, which has an extinction coefficient of 2350 (Chisté & Mercadante, 2012). The analyses were performed in triplicate.

2.4 Evaluation of antioxidant activity of the pequi pulp

The antioxidant activity of the pequi pulp was measured using a 2,2-diphenyl-1-picrylhydrazyl (DPPH•)-free radical scavenging assay, according to the method of Brand-Williams et al. (1995) with some adaptations. The extraction experiments were conducted using 50 mL of ethanol and 2.5 g of pulp. Then, 1.5 mL of a 0.05 mM DPPH• solution was added to the extracts. The decrease in the absorbance at 517 nm at 0, 1, 2, 3, 4, 5, 10, 15, and 20 min of the reaction was measured using a spectrophotometer V-630 (JASCO, Tokyo, Japan). The decrease in the sample absorbance readings was related to the control (without the extract), and the percentage of DPPH• discoloration was estimated. Based on this value, the IC₅₀ (concentration of the sample required to inhibit 50% of the radical) was calculated. BHT was used as a standard. The analyses were performed in triplicate.

2.5 Statistical analysis

The values of colour, proximal composition, total phenolic, carotenoid content, and antioxidant activity obtained were submitted to variance analysis, and the comparisons between the means were performed by the Tukey test. The coefficient of correlation r was calculated to assess the correlations between the variables. Statistical calculations were performed using the Statistica software (Stat Soft Inc., 7.0 version, 2004, Tulsa, USA). A significance level of 5% was adopted.

3 Results and discussion

3.1 Pequi pulp colour

The fruits from the North and Central regions showed higher values of L* (mean= 70.8) and lower values of a* (mean= 23.7), which indicate lighter coloured and less red fruits. In contrast, the fruits from the East region were darker and redder (Table 1). There was a positive correlation between L* and the parameter a* (p= 0.001). The pequis from the North region showed the highest b* values. The lowest values were observed in fruits from the East and Central regions (Table 1). The variation in this parameter is due to the great amplitude of the yellow colour of the pequi pulp. The parameter C ranged from 75 to 115 and was positively correlated with the parameter b* (p= 0.006). The hue angles of the pequi pulps ranged from approximately 55° to 80°, indicating a fruit colour from orange-red to intense yellow since lower hue angle values corresponded to more orange-red pulps and higher hue angles corresponded to more yellow pulps. There are no studies on the CIE parameters of pequi pulps in the literature.

3.2 Chemical characteristics of pequi pulp

The pequi pulp showed moisture content greater than 500 g/kg and protein content less than 30 g/kg (Table 2), similar values to those reported for other pulps of exotic fruits (Clerici & Carvalho-Silva, 2011). There was a significant variation in the lipid content of the pequi pulps (approximately 147 to 322 g/kg); however, a narrower range of lipid content for the C. brasiliense - 200 to 330 g/kg - has been reported in the literature (Lima et al., 2007; Vera et al., 2007). The wide variation observed in the lipid content of the pequi pulps is most likely due to different genetic profiles in the same pequi species. The monounsaturated fats were the most prevalent among the fatty acids in all samples, mainly oleic acid (Table 3). The energy values found in this study varied according to the lipid content of the fruits. The fruits from the West region showed the highest energy values (greater than 3000 kcal/kg), which is compatible with the literature (Lima et al., 2007). On the other hand, lower energy values of approximately 1500 kcal/kg (Table 2) were found for the pequi fruit, which represent lighter pulps than that of the cited study (3584 kcal/kg). The pequi pulps also had high percentage of total dietary fibre, mainly insoluble fibre (Table 2). A portion of 20 g of pequi pulp provides around 10% of the Dietary Reference Intake (DRI) for dietary fibre (Institute of Medicine, 2005). The pequi pulp contains low levels of carbohydrates, ranging from 6.0 (Central region) to 70.2 g/kg (East region) (Table 2).

The fruits from the Central region had the highest value of total phenolic content (Table 4), which is higher than the previously reported value (2.09 mg GAE/g) (Lima et al., 2007). The phenolic content found in the pequi pulp in this study is comparable with that of the other exotic fruits, such as blackberry, cactus pear, and mangaba (Clerici & Carvalho-Silva, 2011).

Regarding the total carotenoid content, values ranging from 37 (North region) to 187 µg/g (East region) were found (Table 4). The only previous study on the total carotenoid content in pequi fruits of the same species investigated in the present study reported an intermediate value, 72.5 µg/g (Lima et al., 2007). The identification and quantification of the carotenoids of the C. brasiliense are an important tool to clarify the differences found in the present study, as recently reported for the Caryocar villosum (Chisté & Mercadante, 2012; Chisté et al., 2012). There was a linear and positive correlation between the carotenoid and lipid contents of the pequi pulp (r= 0.67, p= 0.002), confirming the lipophilic nature of carotenoids (Amorim-Carrilho et al., 2014).

It is important to note that the great variation of the physical and chemical characteristics of the pequi fruits from the different regions studied may occur due to differences in the climate, soil fertility and pH, annual rainfall, and other environmental conditions observed in the Brazilian Savanna biome (Novaes et al., 2013).

3.3 Antioxidant activity

All extracts showed the ability to sequester the free radical DPPH (Table 4). The fruits from the East and West regions showed higher antioxidant activity than the fruits from the other regions. These values are comparable with those of other exotic fruits (Dembitsky et al., 2011). A lower antioxidant activity (IC₅₀ = 298 µg/mL) than those found in the present study (Table 4) was reported for the pulp + seed of the pequi fruit (Roesler et al., 2007).

3.4 Relationship between colour parameters and carotenoid content

According to the r coefficient values (Table 5), there are strong significantly (p<0.001) correlations between luminosity and the carotenoid content and between the hue angle and carotenoid content in the pequi pulp. In addition, a significant correlation between the carotenoid content and the parameters a* and b* was observed. These correlations are a useful tool for the technological and commercial uses of the pequi pulp because the equations presented in Table 5 can predict the carotenoid content using routine colour parameters.

4 Conclusions

Colour and the lipid and carotenoid contents are influenced by the native region of the pequi fruit. The carotenoid content is positively related to the colour and the lipid content of the pequi pulp. The pequi pulp is rich in phenolic compounds and carotenoids, and it has good antioxidant activity. The regression models developed enable the prediction of the total carotenoid content of the pequi pulp using routine colour parameters.

Acknowledgements

The authors are grateful to CNPq and CAPES (Brazil) for the financial support, to professor Dr. Ronaldo Veloso Naves, School of Agronomy (UFG), for his guidance in collecting the pequi fruit, and to Dr. Tânia S. Agostini-Costa, Embrapa Cenargen, Brasília-DF, Brazil, for her assistance in the carotenoid analysis.

Received: 29 Apr., 2014

Accepted: 09 July, 2014 (006369)

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Publication Dates

• Publication in this collection
  09 Sept 2014
• Date of issue
  Sept 2014

History

• Accepted
  09 July 2014
• Received
  29 Apr 2014