Anti-Hyperglycemia Properties of Tea (Camellia sinensis) Bioactives Using In Vitro Assay Models and Influence of Extraction Time

Tea (Camellia sinensis) has well-known health benefits, which are attributed to its polyphenolic metabolites. This research explored the potential of regular tea consumption and influence of extraction time typically used in daily consumption of tea, as a therapeutic dietary support for potential management of early stage type 2 diabetes using in vitro assay models. Extraction times of 2 and 5 minutes were compared. The 5-minute extraction time had significantly higher total phenolic content compared with the 2-minute extraction time. Choice Darjeeling 5-minute extraction yielded the highest amount of total phenolics (299.6 +/- 5.9 mg/g), followed by Tazo Black 5-minute extraction (240 +/- 9.7 mg/g), whereas Bigelow Green 2-minute extraction had the lowest total phenolic content (53 +/- 8.2 mg/g). 1,1-Diphenyl-2-picrylhydrazyl scavenging-linked antioxidant activity was high (81-91%) for all types evaluated, and for most samples it was influenced by the extraction time. Similarly, high in vitro a-glucosidase inhibition was observed in almost all the samples assayed, and for most samples the 5-minute extraction had significantly higher inhibition compared with the 2-minute extraction time. The most fermented teas showed highest a-amylase inhibition: Choice Darjeeling 5-minute extraction had the highest inhibition (84.1%), followed by Tazo Black 5-minute extraction (71.6%). Angiotensin converting enzyme inhibition was not observed in any sample. Overall, the 5-minute extraction time was found to have more relevance for potential benefits for managing hyperglycemia than the 2-minute procedure. This research suggests that tea offers an attractive potential strategy to regulate postprandial hyperglycemia toward an overall dietary support for type 2 diabetes management.