Abstract
Pigmented sorghum with high content of tannins were studied in this work. Tannins bind to proteins and reduce their availability. A hydrothermal treatment was carried out to reduce tannins. A control sample of non-pigmented pericarp variety was used. After the treatment, grains were milled, and a part was separated for wholegrain flour elaboration. Several determinations were done after treatment: tannins (T), total antioxidant capacity (TAC) and total polyphenols (TPP) content. TPP and TAC in wholegrain pigmented sorghum were 3.9 to 12.3 and 2.3 to 3.5 times higher than those of non-pigmented sorghum, respectively. In all sorghum varieties the extractions of TPP decreased with milling. TAC in flour increased 3.3 times the initial value for non-pigmented sorghum, whereas for the other sorghum samples it increased slightly from 1.1 to 1.3 times the initial value. In flours there was a noticeable reduction in T, with respect to the wholegrain. It was possible to conclude that the hydrothermal treatment allowed lower levels of tannins than those established in the Codex for both wholegrain sorghum and flour. This reduction makes it possible to obtain flour which may be suitable for food processing and the recovery of tannins for other uses.
Highlights
Sorghum (Sorghum bicolor (L.) Moench) is the fifth most important cereal crop in the world after wheat, rice, corn and barley (Singh et al, 2011), being an excellent source of energy used for both animal and human feed (Carvalho Teixeira et al, 2016)
It was possible to conclude that the hydrothermal treatment allowed lower levels of tannins than those established in the Codex for both wholegrain sorghum and flour
For unmilled sorghum (UMS) (Figure 1), it is observed that pigmented sorghum T contains more polyphenols than the rest of the samples (0.40%), while non-pigmented sorghum shows the lowest value (
Summary
Sorghum (Sorghum bicolor (L.) Moench) is the fifth most important cereal crop in the world after wheat, rice, corn and barley (Singh et al, 2011), being an excellent source of energy used for both animal and human feed (Carvalho Teixeira et al, 2016). The world consumption of this cereal is considerable (Althwab et al, 2015) and it is probably due to the ability of the grain to grow over extensive agro-ecological zones (Girard et al, 2018; Taylor et al, 2014) This cereal has nutrients common to all varieties, including several minerals, vitamins and amino acids (Althwab et al, 2015). In pigmented sorghum, condensed tannins, belonging to the group of polyphenols, become important In this variety, a positive correlation between total phenolic content and proanthocyanidin, flavan-4-ols and 3-deoxyanthocyanidins (condensed tannins) has been reported. 55% of polyphenols correspond to proanthocyanidin 18% to flavan-4-ols and 7.5% to 3-deoxyanthocyanidins (Dicko et al, 2005) From this previous study, analyzing tannin content in pigmented sorghum through polyphenol determination leads to a good estimation. The Codex Alimentarius Standard states that wholegrain and flour of sorghum cannot contain more than 0.5% and 0.3% tannins, respectively
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