The new insight into the influence of fermentation temperature on quality and bioactivities of black tea

This study aimed to figure out the optimum fermentation temperature by analyzing the major chemical constituents of black tea and its antioxidant activities, inhibitory activities against alpha-amylase, a-glucosidase and glucose uptake. Sensory evaluation revealed 28 degrees C-fermented black tea showed best sensory quality with highest scores for aroma (6.5) and taste (29.8). With increasing fermentation temperature, polyphenols, polysaccharides, (-)-epigallocatechin, (+)-catechin, theaflavins and thearubigins decreased significantly, while amino acids, soluble sugars and volatiles increased when temperature increased up to 31 degrees C. Furthermore, black tea fermented at 28 degrees C showed strongest DPPH radical scavenging ability, anti-lipid peroxidation and inhibitory effect on alpha-glucosidase activity with IC50 value of 17.72 mu g/mL, 1.49 mg/mL and 21.69 mu g/mL respectively. While 25 degrees C-fermented black tea showed highest inhibition rate of glucose uptake in Caco-2 cells. The results demonstrate that appropriately lowering fermentation temperature could improve both sensory quality and bioactivity of black tea.