关于单细胞蛋白的综述（英文版）
Single-cell protein (SCP) typically
mixed protein extracted from pure refers to sources of or mixed cultures of algae , yeasts , fungi or bacteria (grown on agricultural wastes) used as a substitute for protein-rich foods, in human and animal feeds. Single-cell proteins develop when microbes ferment waste materials (including wood, straw, cannery, and food-processing wastes, residues from alcohol production, hydrocarbons, or human and animal excreta). [10] The problem with extracting single-cell proteins from the wastes is the dilution and cost. They are found in very low concentrations, usually less than 5%. Engineers have developed ways to increase the concentrations including centrifugation, flotation, precipitation, coagulation, and filtration, or the use of semi-permeable membranes.
The single-cell protein must be dehydrated to approximately 10% moisture content and/or acidified to aid in storage and prevent spoilage. The methods to increase the concentrations to adequate levels and the de-watering process require equipment that is expensive and not always suitable for small-scale operations. It is economically prudent to feed the product locally and soon after it is produced.
Some contaminants can produce mycotoxins . Some bacterial SCP have amino acid profiles different from animal proteins. Yeast and fungal proteins tend to be deficient in methionine .
Microbial biomass has a high nucleic acid content, and levels must be limited in the diets of monogastric animals to
increased plasma levels of uric acid , which can cause gout and kidney stones . Uric acid can be converted to allantoin , which is excreted in urine. Nucleic acid removal is not necessary from animal feeds but is from human foods. A temperature hold at 64 °C inactivates fungal proteases and allows RNases to hydrolyse RNA with release of nucleotides from cell to culture broth.
Large-scale production of microbial biomass has many advantages over the traditional methods for producing proteins for food or feed. 1. Microorganisms have a high rate of multiplication and, hence, rapid succession of generations (algae: 2–6 hours, yeast: 1–3 hours, bacteria: 0.5–2 hours)
2. They can be easily genetically modified for varying the amino acid composition.
3. A very high protein content 43–85% in the dry mass.
4. They can utilize a broad spectrum of raw materials as carbon sources, which include even waste products. Thus, they help in the removal of pollutants also.
5. Strains with high yield and good composition can be selected or produce relatively easily.
6. Microbial biomass production occurs in continuous cultures and the quality is consistent, since the growth is independent of seasonal and climatic variations.
7. Land requirements is low and is ecologically beneficial.
8. A high solar-energy-conversion efficiency per unit area.
9. Solar energy conversion efficiency can be maximized and yield can be enhanced by easy regulation of physical and nutritional factors. - 2 -
10. A lgal culture can be done in space that is normally unused and so there is no need to compete for land.
Although SCP shows very attractive features as a nutrient for humans there are many problems that deter its adoption on global basis. These problems are high concentration of nucleic acids which is 6-10% which elevates serum uric acid levels and becomes cause of kidney stone formation. About 70-80% of total Nitrogen is present in amino acids while rest occurs in nucleic acids and this concentration of nucleic acid is higher than conventional protein which is characteristic of all fast growing organisms. The problem associated with high concentration of nucleic acid is increase in uric acid concentration in the blood causing heath problems like gout and kidney stone. Another problem is presence of cell wall which is non digestible, in case of algae and yeast, there may be unacceptable color and flavors, cells of organisms must be killed before consumption, there is chance of skin reaction from taking foreign proteins and gastrointestinal reactions may occur resulting in nausea and vomiting. SCP obtained from algae is not suitable for human consumption because they are rich in chlorophyll. SCP from yeast and fungi has high nucleic acid content. SCP obtained from bacteria also has high nucleic acid content, high risk of contamination during the production process and cell recovery also causes many problems. - 3 -
关于单细胞蛋白的综述（英文版）
Single-cell protein (SCP) typically
mixed protein extracted from pure refers to sources of or mixed cultures of algae , yeasts , fungi or bacteria (grown on agricultural wastes) used as a substitute for protein-rich foods, in human and animal feeds. Single-cell proteins develop when microbes ferment waste materials (including wood, straw, cannery, and food-processing wastes, residues from alcohol production, hydrocarbons, or human and animal excreta). [10] The problem with extracting single-cell proteins from the wastes is the dilution and cost. They are found in very low concentrations, usually less than 5%. Engineers have developed ways to increase the concentrations including centrifugation, flotation, precipitation, coagulation, and filtration, or the use of semi-permeable membranes.
The single-cell protein must be dehydrated to approximately 10% moisture content and/or acidified to aid in storage and prevent spoilage. The methods to increase the concentrations to adequate levels and the de-watering process require equipment that is expensive and not always suitable for small-scale operations. It is economically prudent to feed the product locally and soon after it is produced.
Some contaminants can produce mycotoxins . Some bacterial SCP have amino acid profiles different from animal proteins. Yeast and fungal proteins tend to be deficient in methionine .
Microbial biomass has a high nucleic acid content, and levels must be limited in the diets of monogastric animals to
increased plasma levels of uric acid , which can cause gout and kidney stones . Uric acid can be converted to allantoin , which is excreted in urine. Nucleic acid removal is not necessary from animal feeds but is from human foods. A temperature hold at 64 °C inactivates fungal proteases and allows RNases to hydrolyse RNA with release of nucleotides from cell to culture broth.
Large-scale production of microbial biomass has many advantages over the traditional methods for producing proteins for food or feed. 1. Microorganisms have a high rate of multiplication and, hence, rapid succession of generations (algae: 2–6 hours, yeast: 1–3 hours, bacteria: 0.5–2 hours)
2. They can be easily genetically modified for varying the amino acid composition.
3. A very high protein content 43–85% in the dry mass.
4. They can utilize a broad spectrum of raw materials as carbon sources, which include even waste products. Thus, they help in the removal of pollutants also.
5. Strains with high yield and good composition can be selected or produce relatively easily.
6. Microbial biomass production occurs in continuous cultures and the quality is consistent, since the growth is independent of seasonal and climatic variations.
7. Land requirements is low and is ecologically beneficial.
8. A high solar-energy-conversion efficiency per unit area.
9. Solar energy conversion efficiency can be maximized and yield can be enhanced by easy regulation of physical and nutritional factors. - 2 -
10. A lgal culture can be done in space that is normally unused and so there is no need to compete for land.
Although SCP shows very attractive features as a nutrient for humans there are many problems that deter its adoption on global basis. These problems are high concentration of nucleic acids which is 6-10% which elevates serum uric acid levels and becomes cause of kidney stone formation. About 70-80% of total Nitrogen is present in amino acids while rest occurs in nucleic acids and this concentration of nucleic acid is higher than conventional protein which is characteristic of all fast growing organisms. The problem associated with high concentration of nucleic acid is increase in uric acid concentration in the blood causing heath problems like gout and kidney stone. Another problem is presence of cell wall which is non digestible, in case of algae and yeast, there may be unacceptable color and flavors, cells of organisms must be killed before consumption, there is chance of skin reaction from taking foreign proteins and gastrointestinal reactions may occur resulting in nausea and vomiting. SCP obtained from algae is not suitable for human consumption because they are rich in chlorophyll. SCP from yeast and fungi has high nucleic acid content. SCP obtained from bacteria also has high nucleic acid content, high risk of contamination during the production process and cell recovery also causes many problems. - 3 -