Effect of selected lactic acid bacteria fermentation on sorghum techno-functional properties

Sorghum is a climate-resilient, gluten-free crop with a high presence of bioactive components. However, sorghum proteins (kafirins) are highly hydrophobic and poorly digestible. Moreover, sorghum starch is trapped in the protein matrix and has poor technological performances. Consequently, the formulation of good quality leavened bread with sorghum flour is challenging. Fermentation is a sustainable biotechnology that can improve the nutritional and technological functionalities of cereals. This study aimed to evaluate the effect of fermentation of sorghum flour with lactic acid bacteria (LAB) strains (Lactobacillus delbruekii subsp. bulgaricus, Lacticaseibacillus casei, Leuconostoc spp.), which were selected according to their proteolytic, flavour and exopolysaccharides (EPS)-producing activities. To assess the growth capacity of bacteria on sorghum flour, the sourdough's pH, total titratable acidity, and bacterial count were analysed. Colour and antioxidant activity by DPPH assay were also analysed. The sourdough's rheological properties, thermal properties by differential scanning calorimetry and proton molecular mobility by 1HNMR, were evaluated. All LAB strains showed excellent growth capacity on sorghum substrate, reaching values of up to 109 CFU gE−1, and pH between 4.0 and 4.3. The samples showed a pH-induced colour change, probably affecting the phenolic compound, with an increase in a*, b* and L* values, with a resultant change from a greyish to a more pinkish colour. Fermentation changed the gelatinization properties of the samples and showed an increase in viscosity probably due to changes in the protein and starch fractions, and the possible production of EPS. These results demonstrate that the fermentation with the LAB strains studied may be a potential strategy to improve sorghum-based bread.