Wanying Yao1, Jun Zhu1, Bo Sun2, Xiao Wu3, and Curtis Miller1. (1) Bioproducts and Biosystems Engineering, University of Minnesota, 1390 Eckles Avenue, St Paul, MN 55108, (2) Food College, NorthEast Agricultural University, MUCAI Street No.59, Harbin, 150030, China, (3) Southern Research and Outreach Center, University of Minnesota, 35838 120th Street, Waseca, MN 56093
Recycling the nitrogen source in dairy manure (rich in amino acids, peptides and protein) could supply a potentially economic nitrogen for biochemicals production, e.g., organic acids and provides an alternative for waste treatments. Thus, a viable process featuring low-cost culture media is desired to enhance the economic production of L-lactic acid, a useful organic acid utilized in food, pharmaceutical, and chemical industries. In this study, the potential use of the nitrogen source in dairy manure was evaluated for L-lactic acid by Rhizopus oryzae NRRL 395. Six levels of extracted protein (0.21, 0.42, 0.84, 1.68, 2.52, and 3.36 g/L) and six levels of protein hydrolysates (degree of hydrolysis of 6.9%, 17.2%, 25.9%, 33.8%, 36.1%, and 36.7%) from dairy manure, were investigated for the influence on L-lactic acid yield and the correlation with biomass yield and mycelia morphology. Increases in extracted protein from 0.21 to 1.68 g/L led to an increase in L-lactic acid concentration from 6.48 to 57.7 g/L. However, further increases beyond 1.68 g/L did not present continuing increases in L-lactic acid yields. The highest biomass was obtained at a nitrogen concentration of 2.52 g/L. At a nitrogen level of 0.42 g/L (hydrolysates) with DH ranging from 33.8% to 36.7%, L-lactic acid yield of 0.53–0.56 g/L was achieved, with a 13–14% yield of fungal biomass. The results indicated that using the manure crude protein at appropriate nitrogen levels could achieve productivity of L-lactic acid parallel to that of using (NH4)2SO4 and stimulated the biomass accumulation. The same results were obtained for protein hydrolysates.
