Consumption of fruits rich in antioxidant substances such as phenolic compounds and vitamin C is inversely associated with risks of non-communicable diseases [ 1]. Main compounds of phytochemicals that can contribute to the total antioxidant capacity of the plant include polyphenols and vitamins (C and E) [ 2]. Phenolic compounds from plants belong to a class of bioactive components with antioxidant activities [ 3,4,5,6,7]. Several epidemiological studies suggest that antioxidant-rich plants play a protective role in health and disease [ 8], and their consumption has lowered the risk of cancer [ 9], heart disease, and hypertension [ 10]. Antioxidants function through protection mechanisms at several levels within cells in human body by inhibiting the formation of free radical species, intercepting radicalchained reactions, converting existing free radicals into less harmful molecules and repairing oxidative damage [ 11].

Peach (Prunus persica L.) is one of the most important fruit crops in the Rosaceae family. In Georgia is increasing peach production year by year. There is 20.5% quantitative growth observed in the last 4 years. Demand for this product has increased in the market.

There are many varieties of peach fruits, showing different organoleptic qualities and economic values [ 12]. Peach fruits contain an abundance of phytochemicals, such as lipids, vitamins, nucleotides, phenolics (phenolic acids and flavonoids), carotenoids, triterpenes and alkaloids [ 13]. The content of these phytochemicals in peach fruits is not only dependent on peach cultivars and climatic conditions, but also related to fruit ripeness [ 14].

Ascorbic acid, Folin-Ciocalteu reagent, TPTZ-2,4,6-Tris (2-pyridyl)-s- triazine, sodium carbonate, sodium acetate, ferric (III) chloride and ethanol were purchased from Sigma-Aldrich (Steinheim, Germany). All other reagents were commercially available at the local market and were of analytical grades.

Three commercially produced peach (Prunus persica L.) Fairtime and O´henry, grown in the village of Jighaura (WGS84 41° 55′ 25″ N, 44° 46′ 35″ E 41.923611, 44.776389), were selected for study. The test samples were kept in the fridge chamber at the temperature of 0-1⁰C and the relative humidity of 90–95 %. Initially, during and at the end of storage the antioxidant properties of peach fruit of each variety were examined and compared.

The total phenolic compound content was determined using a 1.0 mL aliquot of diluted sample extract, which was vortexed with 10 mL distilled water and 1.0 mL Folin-Ciocalteau reagent [ 15]. After equilibrating at room temperature the solutions were mixed with 4 mL of 7.5% (w·v^-1) Na2CO3. The absorbance values of the samples and standards were measured spectrophotometrically at 765 nm, with a 10 mm path length cell and the TPC was calculated as mg of gallic acid equivalents per 100 gram fresh sample weight.

The ferric reducing antioxidant power (FRAP) assay was carried out as previously described by (Benzie and Strain, 1996). The experiment was carried out at 37 °C. In the FRAP assay, the reductants (“antioxidants”) in the sample reduce the Fe(III)/tripyridyltriazine complex to the blue ferrous form, with an increase in absorbance at 593 nm. The final results were expressed as mg ascorbic acid equivalents (AAE) per 100 gram fresh weight (mg AAE100 g^-1 FW) [ 16].

The data represents the mean of three replicates ± standard deviation (SD). Data were subjected to the t-test. All calculations were performed with Microsoft Excel (Version 4, statistical functions, Microsoft Corp., Redmond, WA, USA).

Various fruit and vegetable show high correlation between the total polyphenols and antioxidant activity [ 17]. However, this correlation may vary depending on a specific phenolic compound in a genotype. The correlation may also change depending on fruit maturity, storage condition, etc. [ 18].

At the beginning of storage, the total polyphenols and antioxidant activity were measured in peaches of different varieties in order to determine the correlation between the total polyphenols and antioxidant activity and impact of variety characteristics. The results show a relatively high content of total polyphenols in Fairtime variety (136.17mg/100g) while in O’Henry peaches it is 120.31mg100g^-1. The same is true for the antioxidant activity levels which reach 223.36 mg AAE100 g^-1 FW and 200.12 mg AAE100 g^-1 FW respectively (Table 1).

The research also analyzed the changes in the total polyphenols in different varieties. The research shows that total polyphenols in both varieties decrease during the storage but with different intensity. There is a more intensive decrease in Fairtime peaches after 45 days of storage. The content of total polyphenols in these peaches was reduced to 89.36mg100g^-1 which means 34.3% reduction. At the end of the storage period the decrease is 55.52% reaching 60.56mg100g^-1. There is a similar decrease in O’Henry peaches with less intensity. After 45 days of storage the decrease in this variety was 32.77% and after 90 days - 50.24% (Table 2).

The research studies the changes in the antioxidant activity by varieties. The results demonstrate decreased antioxidant activity in both varieties (Table 3).

The levels of decrease are similar in both varieties after 45 days of storage. However, at the end of the storage period there is a more significant difference between the varieties in terms of antioxidant activity decrease. In O’Henry peaches it is decreased by 49.78%, while in Fairtime – by 46.12%.

The study and comparison of the changes in total polyphenols and antioxidant activity allowed us to determine the correlation between the total polyphenols and antioxidant activity in fruit. In the stored Fairtime peaches the decrease in total polyphenols was 55.52 % and the decrease in antioxidant activity was 46.12% while in O’Henry peaches they are 50.52% and 49.78% respectively. The results, therefore, show a correlation between the total polyphenols and antioxidant activity (Figure 1).

The positive correlation is stronger in Fairtime peaches (R²=0.9927) compared to O’Henry peaches (R²=0.9789). However, both varieties have quite high positive correlation.

The conducted research shows a common pattern of 45-50% decrease of total polyphenols and antioxidant activity in stored peaches. The positive correlation between them is quite strong and the intensity of the process depends on a variety and its genotype.

Funding

The project was supported by LEPL Scientific-research center of Agriculture (SRCA), Agricultural University of Georgia and Biotechnology center.

Conflicts of interest

The authors have declared no conflicts of interest related to this study.