Solid-State Fermentation of Sorghum by Aspergillus oryzae and Aspergillus niger: Effects on Tannin Content, Phenolic Profile, and Antioxidant Activity.

Sorghum contains antioxidants such as tannins. However, these are considered antinutritional factors since they are responsible for the low digestibility of proteins and carbohydrates. Nevertheless, these can be extracted by solid-state fermentation (SSF). Therefore, this study aimed to evaluate the effects of SSF from Aspergillus oryzae and Aspergillus niger Aa210 on the tannin contents, phenolic profiles determined by HPLC-MS, and antioxidant activities (ABTS, DPPH, and FRAP) of two genotypes of sorghum. The results showed that with SSF by A. niger Aa210, a higher tannin content was obtained, with yields of 70-84% in hydrolyzable tannins (HT) and 33-49% in condensed tannins (CT), while with SSF by A. oryzae the content of HT decreased by 2-3% and that of CT decreased by 6-23%. The extracts fermented by A. niger at 72 and 84 h exhibited a higher antioxidant activity. In the extracts, 21 polyphenols were identified, such as procyanidins, (+)-catechin, (-)-epicatechin, scutellarein, arbutin, and eriodictyol, among others. Therefore, SSF by A. niger was an efficient process for the release of phenolic compounds that can be used as antioxidants in different food products. It is also possible to improve the bioavailability of nutrients in sorghum through SSF. However, more studies are required.

Sorghum (Sorghum bicolor L.) as a potential source of bioactive substances and their biological properties.

Sorghum is the fifth cereal most produced in the world after wheat, rice, maize, and barley. In some regions, this crop is replacing maize, due to its high yield, resistance to drought and heat. There are several varieties of sorghum, whose coloration varies from cream, lemon-yellow, red, and even black. Pigmented sorghum grain is a rich source of antioxidants like polyphenols, mainly tannins, which have multiple benefits on human health such as, antiproliferative properties associated with the prevention of certain cancers, antioxidant activities related to the prevention of associated diseases to oxidative stress, antimicrobial and anti-inflammatory effects, it also improves glucose metabolism. Despite having these types of compounds, it is not possible to assimilate them, their use in the food industry has been limited, since sorghum is considered a food of low nutritional value, due to the presence of anti-nutritional factors such as strong tannins which form complexes with proteins and iron, thus reducing their digestibility. Based on these restrictions that this product has had as food for humans, the analysis of this review emphasizes the valorization of sorghum as a source of bioactive substances and the importance they confer on human health because of the biological potential it has.