Production of schizosaccharomyces sp. HL biomass fron supernatant of anaerobically fermented pig waste and its use as feed additives

Abstract

Surface culture of yeast on the supernatant from anaerobically fermented pig waste was attempted. The utilization of the yeast biomass produced from the supernatant as feed additives has been also studied. Volatile fatty acids (VFA) concentrations of supernatats after anaerobic fermentation at 30$^\circ$C for 4 days were 6.16, 9.24 and 14.63 g/l when the pig wastes contained 5.3, 8.2 and 14.3\% w/w solids, respectively. VFA composition of supernatant was acetic 43\%, propionic 15\%, butyric 23\%, valeric 9\%, isovaleric 6\% and isobutyric 4\% on the weight basis. VFA production rate increased about two times as the temperature rose by 10$^\circ$C from 20$^\circ$C to 40$^\circ$C The pH value of supernatant decreased from neutral region to 6.3 during anaerobic fermentation irrespective of dilution ratio of pig waste and temperature. A yeast strain, growing rapidly into stable thick pellicle on the supernatant with pH lowered by adding sulfuric acid, was isolated and identified as $\underline{\mbox{Schizosaccharomyces}}$ Sp. HL. $\underline{\mbox{Schiz}}$. sp. Hl was close to $\underline{\mbox{Schiz}}$. $\underline{\mbox{japonicus}}$ by the characteristics to form true septate hyphae and asci containing six to eight globose ascospores, but there were considerable differences between two yeasts in cell size and carbon compounds that can be fermented or assimilated. The yeast pellicle in non-wrinkled phase was good as inoculum in the surface culture using the supernatant as medium. The yeast grew in dispersed state throughout the nonwrinkled phase. The growth of contaminated bacteria in the supernatant could be inhibited by lowering pH with sulfuric acid. The yield of yeast dry matter (DM) and that per gram VFA tended to increase as pH decrease to the value higher than the critical pH below which growth of the yeast was strongly inhibited. The minimum pH of supernatant at which the yeast can grow without inhibition rose as VFA concentration of the supernatant increa...