## 4 Discussion
Tea aroma compounds are not always present in free form; some are in glycosidically bound form, so-called glycosides, which are more soluble in water but are less reactive than their corresponding aglycone (non-sugar part), and glycosides also synthesize volatile compounds in the presence of glycosidase during tea manufacture [39]. Alcoholic aroma compounds in black tea are often derived from glycosides and \(\beta\)-primeveroside; although \(\beta\)-primeveroside is about three times more abundant than \(\beta\)-glucoside, \(\beta\)-primeveroside decreases more than glucoside, which means that primeveroside highly contributes to the aroma formation of tea [40]. It was found that the withering process triggers stressful conditions for the fresh leaves, then \(\beta\)-primeverosidase and \(\beta\)-glucosidase residing in the cell wall become in contact with their respective substrates (\(\beta\)-primeveroside and \(\beta\)-glucose, respectively) residing in the vacuole [39; 40; 41]. Terpenoid volatile derivatives such as geraniol, linalool, linalool oxides, volatile phenylpropanoids/benzoids viz. benzyl alcohol, and phenylethyl alcohol [39] increased significantly (_p_ < 0.05) with an increase in withering time up to WT10. The accumulation of these terpenoid volatiles compounds correlated with the upregulation in genes responsible for the biosynthesis of terpenoid volatile constituents in tea during withering, through the plastitial methyl-erythriol phosphate (MEP) and cytosolic mexulonic acid (MVA) pathways [8]. Alcohol-based volatiles were dominant compounds and increased as withering time extended, with an apparent peak at WT10. Alcohol dehydrogenase aids in converting aldehydes from primary fatty acids into alcohols, and alcohol compounds impart a floral-fruit aroma in black tea [39; 40]. Phenylalanine is converted to phenylacetaldehyde, then reduced to phenylethyl alcohol [29]. Usually, the hydrolysis of glycosides and de novo biosynthesis of volatile compounds and their precursors cause the accumulation of volatile compounds during withering [8]. DPPH was used to analyze the antioxidant activity due to its potential to attract the proton from the antioxidant [42]. The decrease in antioxidants was due to the diminution of flavan-3 ol/catechins, which are the core source of antioxidants in green tea because of their higher number of hydroxyl groups [38]. The outcomes of this study reveal that total polyphenol, total flavonoids, catechins, and total theflavins positively correlated with the black tea antioxidant activity (Figure S2). However, the contents of all the compounds mentioned above decreased with an increase in withering time, which was the main reason for the decrement in antioxidants. Theaflavins in black tea act as a powerful antioxidant, like catechins in green tea [43]. Thus, the theaflavins content is associated with the antioxidant activity of black tea. \(\alpha\)-amylase and \(\alpha\)-glucosidase play an essential role in the degradation of starch into glucose [16]. \(\alpha\)-amylase digests a complex molecule of carbohydrate into disaccharides and oligosaccharides; \(\alpha\)-glucosidase catalyzes the formation of glucose and its absorption in the small intestine [44]. Therefore, inhibition of \(\alpha\)-amylase and \(\alpha\)-glucosidase activity will impede postprandial hyperglycemia by reducing the synthesis of absorbable monosaccharides viz. glucose, after consuming a carbohydrate-based diet. Consequently, the glucose content in the bloodstream is maintained in nearly the normal range [14]. The reduction in inhibitory activity is due to the decrement in gallated catechins, theaflavins, and flavonoids, which exhibit potent inhibitory effects against \(\alpha\)-amylase and \(\alpha\)-glucosidase activities [13; 45]. The observed different degree of inhibition signifies that there is a specific interaction involved in tea extract with \(\alpha\)-amylase and \(\alpha\)-glucosidase [45].