Iy Hamdan

Yield depression in methanol-utilizing batch cultures

SummaryYield depression, as opposed to growth inhibition, in batch cultures of methanol-utilizing microorganisms is discussed. Under conditions where the yield coefficient varies, the effect on oxygen demand has been predicted for exponentionally growing cultures.

CHEMOSTAT OPTIMIZATION OF BIOMASS PRODUCTION OF A MIXED BACTERIAL CULTURE UTILIZING METHANOL

SummaryA continuous culture technique was used to optimize the medium composition and growth conditions of a mixed bacterial culture utilizing methanol. The improved medium resulted in satisfactory growth, high-yield coefficients and gave a product containing reduced polysaccharide concentrations. Optimal growth and biomass yields occurred at pH 6.8 a temperature of 37° C and dissolved oxygen at >20% saturation. The maximum growth rate was 0.58 h−1 and maximum biomass yield 0.48 g g−1. The protein content of the product ranged between 81%–83%, and nucleic acid content between 10%–12%, increasing with growth rate. The amino acid profile of the mixed culture product met and, in some cases, exceeded the UN Food and Agricultural Organization standard, indicating a good source of feed protein.

LARGE-SCALE PRODUCTION OF BACTERIAL BIOMASS FROM METHANOL FOR USE AS MILK-REPLACER

SummaryA mixed methanol-utilizing bacterial culture was utilized to produce bacterial biomass as milk replacer. This culture comprised three pure strains: KISRI-5 (NCIB 12135), KISRI-512 (NCIB 12137) and KISRI-5112 (NCIB 12138). Optimal concentrations of methanol (15 g 1−1) and medium elements as well as optimal growth conditions, e.g., pH (6.8), temperature (38°C), dissolved oxygen and dilution rate, were established. The maximum biomass yield coefficient obtained under optimized conditions was 0.48 g g−1.· Large-scale production was successfully carried out in a 1500 1 fermenter under chemostat conditions. A good product was obtained having high true protein content (59–62%) and low polysaccharides (5%) without microbial contamination.

Reduction of nucleic acid content in cell biomass of methanol-utilizing mixed bacterial culture by heat treatment

SummaryA heat treatment method to reduce nucleic acid content in cell biomass of a mixed methanol-utilizing bacterial culture was studied. Maximum nucleic acid reduction in the bacterial cells was achieved by using heat shock at 65°C for 5–10 min followed by 2 h incubation at 55°C and 7.2±0.2 pH. In this treatment, 81–85% nucleic acid content was removed from the cells without affecting their true protein content and essential amino acids profile.