Valorization of sweet potato peel biomass for lactic acid production in solid-state fermentation and control of abiotic bacteria in goat meat

Sweet potato peel, a lignocellulosic residue, was used as a sugar source for lactic acid production in solid-state fermentation. The dried sweet tuber peels were heated at 80, 90, and 100 °C for 15, 30, and 60 min. They were steamed three times, first at 68.9 KPa for 15 to 60 min, then at 86.2 KPa for 15 to 60 min, and lastly at 103.4 KPa for 15 to 60 min. Compared with the 15 min treatment, the steam treatment significantly improved the reducing sugar content after 60 min from 190.4 ± 2.2 to 245.4±3.5 mg/g biomass. Enzymatic hydrolysis afforded 29.5 g/L total sugars, including 22.7 g/L glucose, 3.5 g/L disaccharides, 0.1 g/L arabinose, and 3.2% xylose. The pretreated substrate was used as a solid medium to produce lactic acid in solid-state fermentation via Lactobacillus plantarum MTCC1325. Central composite rotatory design (CCRD) was used to optimize lactic acid production to improve the lactic acid yield. Fermentation of sweet potato peel hydrolysate by L. plantarum yielded 85.6 g lactic acid/kg substrate, which was an overall fourfold increase compared with that of the unoptimized medium. Compared with the untreated control, goat meat treated with 1.25% to 5% lactic acid presented a reduced aerobic bacteria count (p<0.001). These studies imply that the sweet potato peel substrate is a promising biomass for the production of lactic acid in the food industry.