Enhanced lactic acid production with indigenous microbiota from date pulp waste and keratin protein hydrolysate from chicken feather waste

A substantial amount of keratin, a key protein with excellent material-forming properties, can be sustainably extracted from chicken feathers, which are commonly discarded in the poultry industry. The keratin protein found in chicken feathers can serve as a nitrogen source and a pH regulator for microbes. In this study, the use of indigenous bacteria and extracted keratin protein hydrolysate from chicken feathers as a nitrogen source improved lactic acid production from date pulp waste by fermentation. After six days of optimal dark fermentation time at pH 6, the maximum concentration of L-lactic acid (46.2 g/L) was obtained with keratin protein hydrolysate and date pulp waste substrate. Under the same conditions, the value was 2.12 times higher than that of the date pulp waste substrate (21.7 g/L) without the addition of keratin protein hydrolysate. Under optimal conditions, volumetric lactic acid productivity and yield were 7.7 g/L/day and 0.3 g/g substrate, respectively. Keratin protein hydrolysate proved to be the most effective neutralizing agent for L-lactic acid production at a concentration of 6 g/L. The combination of keratin protein hydrolysate and date pulp waste was studied for the first time as a substrate for lactic acid production. Keratin protein hydrolysate was found to buffer pH changes during fermentation. Poultry and plant by-products are usually available in agriculturally challenged areas. Therefore, this study provides an excellent opportunity to recycle waste and improve the overall circular economy of such agro-industrial complexes.