Microbial Bioprocessing of Sunflower Protein Extracts: Nutritional, Techno-Functional and Bioactive Outcomes of Lactobacillus helveticus and Bacillus subtilis Fermentation Products

Fermentation has significant potential for valorizing de-oiled sunflower meal (DSM) protein for human consumption. Here, DSM extracts were fermented for 48 h with Lactobacillus helveticus B-4526 and Bacillus subtilis B-3387, and their nutritional, bioactive, and techno-functional properties were evaluated. DSM extract supported the growth of both organisms, with cell numbers increasing by >1.5 log CFU/mL for B. subtilis and approximately 1 log CFU/mL for L. helveticus. During fermentation, B. subtilis degraded protein bands in the 23–46 kDa range, whereas L. helveticus promoted protein aggregation due to acidification, which may have reduced protein solubility. Antioxidant activities (DPPH, ABTS, and CUPRAC assays) and ACE-inhibitory activity increased in both fermentations, with B. subtilis showing the strongest effect. FTIR analysis indicated fermentation-induced alterations in the protein secondary structure. The total amino acid content decreased after B. subtilis fermentation but remained similar after L. helveticus fermentation. Phytic acid present in the meal decreased as a result of extraction/fermentation workflow. B. subtilis fermentation improved solubility at pH 4.0 but reduced foaming and emulsifying properties. Both fermentations decreased the oil-holding and water-holding capacities. Overall, this study underscores the need to match the fermenting microorganism to the desired outcome, as enhancements in one property often involve trade-offs with others.