Single-cell protein, concentrates

Grant (58), single-cell protein concentrates by McElwain et al. (59), and fish protein by Groninger and Miller (60) and Chen et al. (61). Succinylated fish myofibrillar protein had rapid rehydration and good dispersion characteristics at neutral pH (60). Succinylation of fish protein concentrate improved its emulsifying capacity and emulsion stability (61). 

In general, nonconventional protein foods must be competitive with conventional plant and animal protein sources on the bases of cost delivered to the consumer, nutritional value to humans or animals, functional value in foods, sensory quality, and social and cultural acceptability. Also, requirements of regulatory agencies in different countries for freedom from toxins or toxic residues in single-cell protein products, toxic glycosides in leaf protein products, pathogenic microorganisms, heavy metals and toxins in fish protein concentrates, or inhibitory or toxic peptide components in synthetic peptides must be met before new nonconventional food or feed protein products can be marketed. 

Loop reactors are particularly suitable as bioreactors to produce, for example, single-cell protein (96). In this process, single yeast or bacteria ceUs feeding on methanol multiply in aqueous culture broths to form high value biomass at 35—40°C, 20 kg/m ceU concentrations, and specific growth rates of... 

Two broad areas of application for xylanolytic enzymes have been identified (1). The first involves the use of xylanases with other hydrolytic enzymes in the bioconversion of wastes such as those from the forest and agricultural industries, and in the clarification and liquification of juices, vegetables and fruits. For these purposes, the enzyme preparations need only to be filtered and concentrated as essentially no further purification is required. Several specific examples of applications involving crude xylanase preparations include bioconversion of cellulosic materials for subsequent fermentation (2) hydrolysis of pulp waste liquors and wood extractives to monomeric sugars for subsequent production of single cell protein (3-5). Xylose produced by the action of xylanases can be used for subsequent production of higher value compounds such as ethanol (6), xylulose (7) and xyIonic acid (8-9). 

Figure 3. Strategies for optimization of continuous culture for production of single-cell protein. Top, under continuous culture isotherm with a fixed value for carbon source feed concentration. D is the dilution rate of maximum productivity. Bottom, comparison of isotherm for fixed substrate feed concentration. So, with that for fixed oxygen transfer rate, OTR (curves show the maximum cell concentration for a given OTR and cell yield).

The strategy for optimizing single-cell protein production is based not only on a dilution rate that will give a low residual substrate concentration and high conversion yield, but also that will operate with the maximum cell density permitted by the oxygen transfer rate. Simultaneously, it is important to prevent accumulation of residual methanol to achieve both high yields and process stability. 

Spent solids ate often pressed to recover occluded liquid. The press liquor may be recycled to the leaching system as part of the vent feed, or it may be concentrated and ad(M back to the pressed solids, which are then dried to produce by-products, such as animal feed. The pressed solids may be combined with fuel and burned. If the pressing removes sufficient water, the solids can provide substantial net fuel value. In some cases spent solids can be chemically hydrolyzed or treated with microorganisms to generate fermentable sugars, single-cell proteins, or other valuable products. 

Table 5.7 Maximum permissible concentrations of single cell protein (SCP) in air of workplace and the atmosphere...

Table 5.8 Maximum permissible concentrations (PDKs) of Candida yeast strains approved by the FSU Ministry of Health for use in the production of single cell protein...

The protein content of bacteria is higher than that of yeasts and contains higher concentrations of the sulphur-containing amino acids but a lower concentration of lysine. Single-cell protein (SCP) contains unusually high levels of nucleic acids, ranging from 50 g/kg DM to 120 g/kg DM in yeasts and from 80 g/kg DM to 160 g/kg DM... 

Researchers are attempting to bolster traditional protein sources and to develop entirely new proteins, with their efforts centered around the following approaches and protein sources (1) improvement of traditional sources through gene tic manipulation, (2) fortification with synthetic nutrients, or addition of protein concentrates from fish, oilseeds, and other foods, (3) use of the versatile soybean, and (4) development of single cell protein technology. 

Interferons [alFN, piFN and ylFN]. Interferons are a family of glycosylated proteins and are cytokines which are produced a few hours after cells have been infected with a virus. Interferons protect cells from viral infections and have antiviral activities at very low concentrations ( 3 x 10 M, less than 50 molecules are apparently sufficient to protect a single cell). Double stranded RNA are very efficient inducers of IFNs. There are three main types of IFNs. The aIFNs are synthesised in lymphocytes and the piFNs are formed in infected fibroblasts. The a and P families are fairly similar consisting of ca 166 to 169 amino acids. Although ylFNs are also small glycosylated proteins (ca 146 amino acids), they are different because they are not synthesised after viral infections but are produced by lymphocytes when stimulated by mitogens (agents that induced cell division). 

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