Effect of nutrient compositions in peat hydrolysate on protein and biomass yields of Candida tropicalis

Abstract

Research was conducted to study the effect of nutrient compositions, at different levels, added in peat hydrolysates on biomass yields and protein of Candida tropicalis. Samples of Minnesota sphagnum peat were hydrolyzed by boiling at 100°C with 1-1 H2SO4 solutions to produce peat hydrolysates which can support the growth of yeast. Peat hydrolysates were adjusted to pH 5.5 and mixed with mineral nutrients (NH4NO3, NaH2PO4 + Na2HPO4, KCl, and MgSO4) and glucose. Among the single nutrients tested, glucose produced the most significant enhancement of biomass yields, followed by NH4NO3, NaH2PO4 + Na2HPO4, KCl, and MgSO4. NH4NO3 was found to be the most important single nutrient affecting protein accumulation in yeast cells, followed by glucose > NaH2PO4 + Na2HPO4 > KCl > MgSO4. However, protein and biomass production was significantly (P ≤ 0.05) greater for combined nutrients than for any single-nutrient enrichment. The level of residual reducing sugars in peat hydrolysate was inversely proportional to cell counts and optical densities. Addition of high concentrations of nutrients delayed the time of reaching to stationary phase in optical density, cell counts, and pH of yeast cultures. In general, as nutrients were increased, significant (P ≤ 0.05) increases in productivity and cell density were observed. However, specific growth rate decreased with increasing nutrient concentrations. It was concluded that nutrient amendments containing supplementary sources of C/N/P/K/S = 400:36:3.3:3.8:1 are most suitable for biomass production and the biosynthesis of protein by C. tropicalis.