Smartphone-based digital images as a low-cost and simple colorimetric approach for the assessment of total phenolic contents in several specific Vietnamese dried tea products and their liquors.

The total phenolic contents (TPCs) represent the bioactive substances and antioxidant capacities of flora products. The present study employed digital images from a smartphone to determine the TPCs in tea products and their liquors. Various parameters related to the portable home-made colorimetric analysis box design were optimized to achieve the most favorable capturing condition. The proposed method performance was evaluated, which agreed with the Appendix F of AOAC (2016). In comparison with the standard UV-vis, no statistical differences (t-tests, P = 95 %) were observed, and there were advantages of simplicity, portability, sample volume reduction, decreased analysis time, low-cost operation, especially the potential to be used by tea producers, managers, and consumers to quickly analyze the TPCs. The results demonstrate the descending TPCs orders of green > white > oolong > black teas (recoveries of 95-98 %) and the increase of TPCs in tea liquors regarding the rising brewing temperature and duration.