Abstract
Sorghum (Sorghum bicolor) is an important cereal grain, especially in Africa, which contains a wide range of nutrients and bioactive phytochemicals. Its full potential is limited by variables such as membrane bound phenolic compounds, a lack of key amino acids (e.g., lysine, methionine, and tryptophan), and high concertation of anti-nutrients (phytate, saponins, and condensed tannins), which reduce its nutrient and mineral bioavailability, contributing to malnutrition. Sorghum grains are milled into flour and subjected to lactic fermentation in the Southern African region to produce ting, a sourdough that can be boiled into a gruel (motogo) or a porridge (Bogobe), served as either a weaning food or at major ceremonies. This study was aimed at optimizing the ting fermentation (from whole and dehulled sorghum) as well as identifying the fermentation microbial community of the obtained samples. The optimization was achieved through using the central composite design (CCD) in response surface methodology (RSM). The fermentation microbial community was identified using a metagenomic analysis in which the 16S bacterial rRNA was sequenced using an Illumina MiSeq using the primer pair 5'-AGGGTTTGATCTGGC-3' and 3'-CGTAACAAGGTAACC-5', and the quantitative insights into microbial ecology (Qiime2) version 2019.10. The nutritional content (B-group vitamins, proximate and mineral composition, amino acids), as well as health-promoting properties (phenolic compound analysis and antioxidant activities - ABTS (2-azino-bis-3-ethylbenzothiazoline-6-sulphonic acid) and DPPH (1, 1-diphenyl-2-picrylhydrazyl) assays were also investigated. These results were subjected to statistical analysis using the Duncan method from the IBM SPSS statistics software, with a significance of variance of p ≤ 0.05. The optimum conditions obtained were 37.3°C over 81.9 H, 22.7°C over 79.9 H, 37.8°C over 81.9 H and 26.1°C over 77.8 H for whole white sorghum, dehulled white sorghum, whole brown sorghum, and dehulled brown sorghum respectively. The data obtained indicated Lactobacillus bacteria were dominant in the whole white and dehulled brown optimally fermented ting, bacteria from the genus Erwinia were dominant in the whole brown and dehulled white optimally fermented ting and an unknown bacterial species was the most dominant for all the raw sorghum samples including for both whole and dehulled brown and white samples. The fermentation optimization rssulted in improved nutritient and phytochemical content. The optimized fermentation was statistically significant (p ≥ 0.05) for B-complex vitamins, where vitamins B1, B6 showed an increase in concentration respectively, while vitamin B3 decreased. The effects of optimized fermentation were found to be statistically insignificant on the mineral content, proximate composition and antioxidant
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activity (ABTS and DPPH) of both whole and dehulled samples. Additionally, the antioxidant activity of fermented samples was higher than that of the raw samples. Furthermore, dehulled samples exhibited lower concentrations of both nutritional and health promoting compounds owing to the absence of the bran. Thus, the optimized fermentation of sorghum whole grains improved both the nutrtional composition as well as the health promoting properties of ting.
Keywords: Dehulling, Lactic acid bacteria (LAB), Lactic fermentation, Next generation sequencing (NGS), Response surface methodology (RSM), Sorghum, Whole grains (WG)