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Factors affecting production of mold mycelium and protein in synthetic media
Abstract:
The effects of certain cultural conditions on the yield of dry mycelium, protein, and total amino acid content of Rhizopus oligosporus Saito (NRRL 2710), Rhizopus rhizopodiformis (Cohn apud Lichtheim) Zopf (NRRL 6246), and Absidia corymbifera (Cohn) Sacc. et Trotter (NRRL 6247) were studied. The yield of mycelium was found to significantly increase as the spore inoculum was increased from 187,500 to 2,250,000 spores. But the total amino acids (grams/liter) did not change significantly, whereas the percentage of crude protein decreased. An inoculum containing approximately 750,000 spores/ml was used in all of the other experiments. Mycelial production was highest at 37 degrees C for all three molds. However, the best temperature for percentage of crude protein and total amino acids varied with the organism. The mycelial yield and total crude protein of R. oligosporus showed some significant changes as the C/N ratio was increased in 3% glucose medium. In a synthetic medium having a 15:1 C/N ratio, the strains of R. oligosporus, R. rhizopodiformis, and A. corymbifera had better yields from falactose than glucose, not only in dry mycelium but also in total crude protein (grams/liter) and total amino acids (grams/liter). R. oligosporus grew very well on several ammonium salts. but the maximum yield of dry mycelium, total crude protein (grams/liter), and total amino acids (grams/liter) occurred with ammonium sulfate. The optimum pH for both Rhizopus species was 4.0, although R. oligosporus grew equally well at pH 3.0 and slightly less at pH 5.0. The highest yield of mycelium for A. corymbifera was obtained in a medium with an initial pH of 8.0. It was calculated that a fermenter chanrged with an adequate medium and 1,000 lb (about 450 kg) of R. oligosporus or A. corymbifera cells could produce 88 or 90 lb of protein (on a dry-weight basis) per h if the product was removed continuously.
Insights
Optimizing Rhizopus oligosporus and related fungi cultivation involves adjusting spore inoculum, temperature, and C/N ratio for maximal mycelial and protein yield. Fermentation studies indicate potential for continuous protein production.
Area of Science:
- Microbiology and Biotechnology
- Food Science and Technology
- Biochemical Engineering
Background:
- Rhizopus species are crucial in food fermentation and biotechnology.
- Understanding optimal growth conditions is key for maximizing biomass and protein production.
- Previous research has explored various aspects of Rhizopus cultivation, but comprehensive optimization is ongoing.
Purpose of the Study:
- To investigate the impact of cultural conditions on the yield of dry mycelium, protein, and amino acids in Rhizopus oligosporus, Rhizopus rhizopodiformis, and Absidia corymbifera.
- To determine optimal parameters for maximizing biomass and protein content for industrial applications.
- To evaluate the potential for continuous protein production using these fungal strains.
Main Methods:
- Cultivation of R. oligosporus, R. rhizopodiformis, and A. corymbifera under varying spore inoculum concentrations, temperatures, carbon-to-nitrogen (C/N) ratios, carbon sources (galactose vs. glucose), nitrogen sources (ammonium sulfate), and pH levels.
- Measurement of dry mycelial yield, crude protein content, and total amino acid concentration.
- Fermentation modeling to estimate continuous protein production rates.
Main Results:
- Increased spore inoculum significantly enhanced mycelial yield but decreased crude protein percentage.
- Optimal temperature for mycelial production was 37°C for all strains, but protein and amino acid optimization varied.
- Galactose generally yielded better results than glucose for mycelium, protein, and amino acids; ammonium sulfate was the preferred nitrogen source for R. oligosporus; optimal pH varied by species (4.0 for Rhizopus, 8.0 for A. corymbifera).
Conclusions:
- Cultural conditions, including spore inoculum, temperature, C/N ratio, carbon source, nitrogen source, and pH, significantly influence the yield and composition of Rhizopus and Absidia species.
- Optimized fermentation parameters can lead to substantial biomass and protein production.
- Continuous fermentation of R. oligosporus or A. corymbifera holds potential for efficient protein production, with calculated yields of 88-90 lb per hour per 1,000 lb of cells.