Solid-State Fermentation With Lactic Acid Bacteria Improves Protein Digestibility in Sorghum

IntroductionSorghum is a gluten-free cereal grain valued for its resilience to water and nutrient stress and efficient agronomic performance. However, its use in human food applications remains limited due to nutritional constraints and reduced protein digestibility. Solid-state fermentation (SSF) represents a promising strategy for improving sorghum nutritional quality by modifying its macronutrient composition and reducing antinutritional components. The objective of this study was to evaluate the effect of SSF on protein digestibility in multiple sorghum grain varieties using homofermentative and heterofermentative lactic acid bacteria (LAB) as starter cultures.MethodsThree whole-grain sorghum varieties (White, Sumac, and Black) were subjected to SSF using commercially available LAB strains: Pediococcus acidilactici, Leuconostoc mesenteroides, and a co-culture of both. Fermentations were conducted at 30°C for 72 h at two moisture levels (30% and 50%). Microbial growth was monitored throughout fermentation. Crude protein content, in vitro protein digestibility, and phytic acid concentration were determined at the end of fermentation and compared with unfermented controls. Data were analyzed using factorial analysis of variance (ANOVA), followed by post-hoc pairwise mean comparisons and contrasts, when appropriate.ResultsMoisture level significantly (p < 0.05) influenced fermentation outcomes with treatments fermented at 30% moisture showing higher microbial counts and greater improvements in protein digestibility compared to those fermented at 50% moisture. All fermented samples exhibited significantly higher protein digestibility than their unfermented controls (p < 0.05). Protein digestibility increased from 13.6% to 20.5% in White sorghum, from 12.6% to 17.2% in Sumac sorghum, and from 15.6% to 23.2% in Black sorghum following fermentation. Phytic acid content was significantly reduced across all treatments (p < 0.05), with decreases ranging from 38% to 61%; the greatest reductions were observed in samples fermented with the LAB co-culture.SignificanceThese findings demonstrate that SSF with LAB can greatly enhance protein digestibility and reduce phytic acid content in sorghum grains. Improving sorghum nutritional quality through SSF may expand its application in human food products, supporting the development of nutrient–dense, gluten–free foods from climate–resilient crops.