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Vietnam has diverse and long-established tea plantations but scientific data on the characteristics of Vietnamese teas are still limited. Chemical and biological properties including total polyphenol and flavonoid contents (TPCs and TFCs), antioxidant activities (DPPH, ABTS, FRAP, and CUPRAC), as well as the contents of caffeine, gallic acid, and major catechins, were evaluated for 28 Vietnamese teas from North and South Vietnam. Higher values of TPCs and TFCs were found for green (non-oxidised) and raw Pu'erh (low-oxidised) teas from wild/ancient tea trees in North Vietnam and green teas from cultivated trees in South Vietnam, as compared to oolong teas (partly oxidised) from South Vietnam and black teas (fully oxidised) from North Vietnam. The caffeine, gallic acid, and major catechin contents depended on the processing, geographical origin, and the tea variety. Several good Pearson's correlations were found (r2 > 0.9) between TPCs, TFCs, the four antioxidant capacities, and the content of major catechins such as (–)-epicatechin-3-gallate and (–)-epigallocatechin-3-gallate. Results from principal component analysis showed good discriminations with cumulative variances of the first two principal components varying from 85.3% to 93.7% among non-/low-oxidised and partly/fully oxidised teas, and with respect to the tea origin. [ABSTRACT FROM AUTHOR]

• A home-made colorimetric analysis box equipped with a smartphone was designed. • Advantages of simplicity, portability, reduced-volume, and low cost are obtained. • No statistical differences were observed between the proposed and UV–vis methods. • TPCs in tea liquors are proportional to the rising brewing temperature and time. • The proposed methods can be applied for other criteria and used by tea manufacturers. 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. [ABSTRACT FROM AUTHOR]