Comparison of the phenolic contents, antioxidant activity and volatile compounds of different sorghum varieties during tea processing.

Sorghum grain is rich in phenolic compounds and has the potential to be developed into functional beverages such as sorghum grain tea, in which the health benefits and flavour are the important quality attributes to be considered in tea product development. Therefore, this study investigated the effect of grain tea processing steps on the phenolic contents, antioxidant activity and aroma profile (volatile compounds) of MR-Buster (red-coloured) and Shawaya Short Black 1 (black-coloured) sorghum and the results compared with those for our previously reported Liberty (white-coloured) sorghum. Tea processing had significant impacts on sorghum polyphenols and volatile compounds, but the effect and level varied among sorghum varieties. The phenolic contents and antioxidant activity in these three sorghum varieties were consistent in both raw grain and grain tea samples and in the order Shawaya Short Black 1 > MR-Buster > Liberty. However, the volatile profiles (both individual and grouped volatiles) were significantly different between sorghum varieties, and the abundance and diversity of the volatile compounds of the tea samples were in the order Liberty > MR-Buster > Shawaya Short Black 1. Black-coloured sorghum with high phenolic content and antioxidant activity is more suitable for making sorghum tea considering the health benefits. In terms of the aroma intensity and diversity, white-coloured sorghum could be the ideal material. However, future study is needed to determine the key volatile compounds that positively contribute to the aroma. This work provides important insights into the selection of grain materials for sorghum grain tea production. © 2019 Society of Chemical Industry.