Assisted extraction using green technologies and conventional solvent extraction method: a comparison of the phenolic content and profile of sorghum and their antioxidant activity

The use of sorghum in food has been limited due to the presence of tannins, considered anti-nutritional factors. However, these compounds can be extracted using green technologies. The objective of this study was to compare the tannin content, the phenolic profile, and the antioxidant activity of sorghum extracts obtained using ultrasound and microwave technologies, against conventional solvent extraction. Ground grains of the sorghum genotypes (LES 5 and GB) were studied; optimization of the extraction processes in terms of condensed tannin (CT) content by ultrasound and microwave was performed. In the extraction of CT using ultrasound, a higher yield of 82.40% was obtained, followed by microwave extraction with 73.10% compared to solvent extraction. Sorghum extracts obtained with green technologies exhibited higher antioxidant activity in vitro compared to solvent extraction, this activity was positively correlated with CT concentration. The phenolic profile of the extracts was determined by HPLC-MS, finding compounds such as flavonoids theaflavin 3,3'-O-digallate and sinensetin and feruloyl tartaric acid, it is also the first time that they have been reported in sorghum. In general, green technologies turned out to be more efficient regarding tannin yield, number of phenolic compounds, and antioxidant activity. This study provides an alternative to detoxify the sorghum grain by releasing the tannins present and using them as antioxidants, nevertheless, more studies are required.