Bioprocessing of Damaged Wheat Grain Into PHB Using Lactobacillus Fermentation Following Optimized Acid Hydrolysis

This study establishes a sustainable strategy for poly(3-hydroxybutyrate) (PHB) biosynthesis by utilizing damaged wheat grain (DWG) as an alternative, non-food agro-industrial substrate. The integrated approach involves the systematic optimization of HCl-mediated hydrolysis followed by microbial fermentation using Lactobacillus species. Hydrolysis parameters, including time, acid-to-sample ratio, HCl concentration, and substrate loading, were evaluated to maximize reducing sugar (RS) release while suppressing the formation of fermentation inhibitors. Optimal nutrient recovery was achieved at 45 min, 20% w/v acid-to-sample ratio, 6% w/v HCl, and 20% w/w substrate loading, yielding 336.66 ± 1.14 mg glucose equivalent/g RS and 4.67% ± 0.07% w/w protein. Under these optimized conditions, inhibitory concentrations of acetic acid, formic acid, furfural, and 5-HMF were effectively restricted to 2.36, 6.95, 0.49, and 1.17 mg/g, respectively. Subsequent fermentation of the refined hydrolysate by a consortium of Lactobacillus plantarum, Lactobacillus murinus, and Lactobacillus casei was conducted. At 30°C with a 6% inoculum level over 96 h, FH12 achieved a maximum PHB titer of 1.85 ± 0.42 g/L. These results demonstrate the potential of converting low-value agro-wastes into biopolymers via optimized lactic acid bacteria fermentation, providing a viable pathway for circular bioeconomy applications.