The effect of pre- and post-harvesting techniques on phenolics, antioxidant activities and key enzyme inhibitions of commercially available ready-to-drink teas

Tea, the world's most popular beverage, is prepared using different pre- and post-harvesting techniques, leading to its unique sensory characteristics and bioactive ingredients. However, knowledge about the impact of these processing methods on the phenolic compositions and health properties of commercially available ready-to-drink teas is limited. To fill this research lacuna, the phenolic compositions, antioxidant potentials, and inhibitory activities against the key enzymes relevant to non-communicable diseases including hyperlipidemia (lipase), type II diabetes (α-amylase, α-glucosidase, and dipeptidyl peptidase-IV), and Alzheimer's disease (acetylcholinesterase, butyrylcholinesterase, and β-secretase) of eleven commercially available ready-to-drink teas were investigated. The results indicated that pre-harvest shading led to higher contents of catechin, epicatechin gallate, chlorogenic acid, and 3,4-dihydroxybenzoic acid, while fermentation significantly increased rutin content, which, in turn, led to higher total phenolic contents. Antioxidants in shaded tea tended to follow a hydrogen atom transfer (HAT)-based mechanism, while the single electron transfer (SET)-based mechanism was a preferable reaction pathway for antioxidants in fermented teas. The ability to inhibit key enzymes was more pronounced in fermented teas than in shaded tea, potentially attributed to the biological activities of certain phenolics, either individually or working together as effective inhibitors. The addition of flavors (honey lemon, kyoho grape, watermelon, and roasted rice) led to higher contents of catechins than the original green tea (without added flavor), while the contents of other general phenolics varied, leading to similar or higher TPCs. Antioxidant potentials and enzyme inhibitions varied for different ready-to-drink tea varieties. The knowledge from this research will benefit the development of ready-to-drink teas with particular phenolics and health-related properties. • Pre-harvesting shading increased HAT-based antioxidant activities. • Post-harvesting fermentation increased TPCs and key enzyme inhibitions. • Addition of flavors led to relatively high contents of catechins. • Additional roasted rice lowered phenolic contents and biological properties.