Tuesday, April 20, 2010
LL Conference Facility (Hilton Clearwater Beach)
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.