The gas environment is solid‐substrate fermentations of rice significantly affected levels of biomass and enzyme formation by a fungal species screened for high amylase production. Constant oxygen and carbon dioxide partial pressures were maintained at various levels in fermentations by Aspergillus oryzae. Control of the gas phase was maintained by a “static” aeration system admitting oxygen on demand and stripping excess carbon dioxide during fermentation. Constant water vapor pressures were also maintained by means of saturated salt solutions. High Oxygen pressures stimulated amylase productivity significantly. On the other hand, amylase production was severely inhibited at high carbon dioxide pressures. While relatively insensitive to oxygen pressure, maximum biomass productivities were obtained at an intermediate carbon dioxide pressure. High oxygen transfer rates were obtained at elevated oxygen pressures, suggesting, in view of the stimulatory effect of oxygen on amylase production, a stringent oxygen requirement for enzyme synthesis. Solid‐substrate fermentations were highly advantageous as compared with submerged cultures in similar gas environments. Not only were amylase productivities significantly higher, but the enzyme was highly concentration in the aqueous phase of the semisolid substrate particles and could be extracted in a small volume of liquid. Results of this work suggest that biomass and product formation in microbial processes may be amenable to control by the gas environment. This is believed to offer an interesting potential for optimizing selected industrial fermentation processes with respect to productivity and energy consumption.
Investigation of the effects of selected enzymatic pretreatments of alfalfa leaves on plant protein recovery by mechanical expression of cell contents showed significantly higher crude protein recoveries for enzymatically treated extracts as compared with untreated samples. Protein recovery increases were seen for leaves pretreated with a buffered cellulase and a cellulase‐pectinase mixture. However, protein recoveries were not increased by pretreatment with a pectinase or a phospholipase. The increases were partly due to nonspecific buffer effects associated with leaching or osmotic shock and were pH dependent. The increases were also partly due to specific enzymatic effects which appear to result from structural degradation of plant tissue, as seen in electron micrographs, leading to enhanced cell rupture and release of cytoplasmic materials. The effect of enzymatic pretreatment is thought to result in accelerated senescence by degrading major structural components which provide rigidity and mechanical strength in plant tissue. This may be primarily related to the degradation of structural polysaccharides of the cell wall and middle lamella.
Controlled gas environments were maintained by a novel aeration system in solid substrate fermentations for enhanced protein recovery from pressed alfalfa residues. High oxygen pressures stimulated biomass and enzyme production by an Aspergillus species, isolated from alfalfa, which produced cellulase and pectinase activities in growth‐associated metabolism. High carbon dioxide pressures also stimulated enzyme production, but had less effect on biomass production, as estimated from the dissimilation of plant solids. Cellulase and pectinase activities were generally related to protein recoveries. Recoveries were up to 50% higher than those obtained by mechanical extraction, with maximum recoveries of nearly 70% of crude protein contents. Proteins not recovered at high cellulase and pectinase activities were believed to be in structurally bound forms not amenable to recovery by non‐proteolytic enzymes. Buffering at pH8 and autoclaving of residues prior to fermentation had little effect on protein recoveries. Controlled gas environments are seen to offer an interesting potential for optimizing industrial fermentation processes for the production of microbial enzymes.
SummarySolid-substrate fermentations for extraction of protein from pressed alfalfa residues with Aspergillus sp. QM 9994, Asper~illrrs nigc'r QM 877. and Rliizopus !iigric ( 1 1 1~ QM 387 were conducted in shake flasks. Upon reimbibing and second pressing. total protein recovery from alfalfa was increased from 47.2% for control samples and up to 64.5% for fermented samples. Analysis of juice from fermented samples indicated the presence of cellulase as well as pectinase activities. Dialysis cultures of cellulaseproducing fungi showed that total biomass production and solids consumption were much higher than those of a mutant strain lacking the ability to produce cellulase. indicating significant utilization of cellulosic materials in alfalfa. The biomass yields in the former case ranged from 39-47% based on total solids consumption. Since some of the cellulosic and other carbohydrate constituents in alfalfa may be converted into fungal protein. final alfalfa residues following protein extraction in a commercial process would be less bulky for storage and handling and would be more digestible as a nonruminant animal feed.
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