Bioactive compounds of fresh tea shoots plucked in different seasons: Optimization of extraction of polyphenols

Abstract

In this study, the effects of harvest year and period on the total polyphenol (TP), radical scavenging activity (RSA), total flavonoid (TF) and ascorbic acid (AA) contents of fresh tea leaves were investigated. Extraction of polyphenols from the tea leaf was optimized using the response surface methodology (RSM). The effect of the independent variables ((solvent concentration, extraction time and solid to solvent (S/S) ratio)) on TP and RSA was studied using Box-Behnken design (BBD). The results showed that extraction parameters selected were significant in the extraction procedure regarding TP and RSA (p < 0.05). The optimum extraction conditions were obtained as 1/60.86 of S/S ratio, 84.65% of ethanol concentration and the extraction time of 50 min. As a result of the extraction of tea leaves under optimum conditions, the TP, RSA and TF contents of the leaves harvested in September in 2020 were found to be higher. In addition, the individual phenolic compounds of these leaves were analyzed by high performance liquid chromatography (HPLC) and epigallocatechin gallate (EGCG) was detected the most (57.52 mg/g DM). After in-vitro digestion of the same samples, TP and RSA values were significantly decreased, mostly at intestinal stage (p < 0.05), and the bioaccessibility of the polyphenols was determined as 48.98%. As a result of AA analysis by HPLC of the, the highest contents for 2019 and 2020 were observed in the leaves harvested in May (41.92 mg/100 g DM) and those in July (38.55 mg/100 g DM), respectively.