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For producing quality SCP one has to take care in every step. The first and foremost important is the selection of microorganisms. The selected microorganism should be fast growing, wide substrate utilizing capacity, should be non-pathogenic and do not produce any type of toxin, should produce protein not only of high quality but also good quantity and contain limited quantity of nucleic acid etc.
The next step would be selection of sub-stratum. The sub stratum is not only cheaper, but readily utilizable. The organisms employed do not contribute for liberation of toxic substances. Then the growing condition of organism should be ambient and do not required any additional requirements. The incubation period should be short and downstream process should be simple and in apposition to yield pure protein with minimum number of steps.
The purification and drying of protein should be a simple and should not affect the quality of protein. If protein is deficient in some respects that can be improved by supplementation of required substances. Thus the post-harvest stage of SCP should do simple and amenable for processing. This will help to get a quality SCP and will be useful as feed additive for other purposes.
1. Bel Process:
Dairy industry generates over 100 million tonnes of whey each year. This byproduct of cheese manufacture has pollution load with a chemical oxygen demand (COD) of 60 g of O2 per liter. Whey contains approximately 45 g/L lactose and 10 g/L protein. Hence, it is particularly suitable for SCP utilizing lactose utilizing yeast, Kluyvermyces lactis or K. marxianus. Bel industries in France has developed Bel process with the aim of reducing the pollution load of dairy industry waste, while simultaneously producing most acceptable SCP.
2. Pekilo Process:
This process began operating in 1975 and was the first commercially continuously operating process for the production of a filamentous fungal protein. This process was developed in Finland for utilization of spent sulphite waste liquor derived after wood processing that contains monosaccharides and acetic acid. Supplement of other carbon sources, usually molasses and whey added prior to inoculation with paecilomyces varotii.
This continuous process is operated aseptically and produces over 10,000 tonnes of SCP a year from bio 360 m3 fermenters. The dried pekilo protein containing up to 59% crude protein is used in the preparation of compounded animal feed.
3. Bioprotein Process:
Bioprotein process developed in 1990 by Norferm uses methane rich natural gas, as a sole carbon and energy source for the growth of Methylococcus capsulates. A mixture of heterobacteria is also present which helps to stabilize the process. This manufacturing plant is at Tedbergoden in Norway.
This highly aerobic continuous fermentation is performed in a loop fermenter with a medium containing ammonia, minerals and methane obtained from North Sea gas fields. The biomass is continuously harvested by centrifugation and ultrafiltration prior to inactivation and spray drying. The final product contains 70% protein and currently marketed as pronin. It is approved for use as fish and animal feed but may be used as human foods in the future.
4. Pruteen Process:
Attempts to develop methanol based processes were made in Europe, the former society union, Japan and the USA. They involved bacterial species (Hyphomicrobium, Methylococcus, Methylophilus and Methylotrophus), yeasts (Candida boidinii, Pichia angusta and P.pastorn) and even filamentous fungi (Gliocladium deliquescans, paecilomyces variotii and Trichoderma linganus).
The most adventurous process was developed by ICI in UK in 1980. This process used the methylotrophic bacterium, M.methylotrophus, to produce a feed protein for chicken and pigs called pruteen. It is a world largest continuous aerobic bioprocess system involving 3000 m3 pressure cycle airlift fermenter with inner loop and working fluid volume of 1.5 × 106 L. capable of producing upto 50,000 tonnes of pruteen protein (Fig. 16.4).
5. Quorn Production:
The RHM company developed process for production of mycoprotein utilizing Fusarium vevenatum in 1964, known as Quorn, a food grade SCP. Following a joint venture with ICI, UK, 1000 tonnes of quorn are now produced each in the 40 m3 airlift fermenter that was formerly used as pruteen pilot fermenter. This fermenter is operated continuously at 30°C and pH 6.0.
Food grade wheat starch is used to control the pH and acts as nitrogen source. Oxygen is supplied as sterile compressed air and if it goes below, byproducts are formed resulting in unacceptable flavour and aroma. During fermentation biomass doubles for every 4-5 hrs.
The filamentous structure of harvested organism is a critically important factor related to eating quality. Mycoprotein is different from other noval bacterial and yeast protein because of its microfilamentous structure which can be partially digested to resemble the microfibrils of meat. This enables it to be processed and flavored to form meat substitute foods that have a meat texture.
The fungal biomass generated contains 10% RNA which is too high for human consumption. RNA levels can be reduced by a thermal shock at 40°C for 30 min. which kills the organism and activates organisms to secrete RNA ases. This results in the breakdown of RNA into nucleotides that diffuse out of cells into the medium. Thus RNA concentration is reduced to an acceptable level of less than 2% (W/W). Following RNA reduction the mycelium is continuously harvested by vacuum filtration. The filter cake formed is a mat of inter fungal hyphae which can be frozen as sheets into various shapes, granulated or powdered.
6. Symba Process:
The symba process was developed in Sweden to produce SCP for animal feed from potato processing wastes to make it more attractive and economical. The process was developed with two microorganisms that grow in symbiotic association (Fig. 16.5).
The yeast (Saccharomycosis fibuligera) which produces copious amount of amylases necessary for starch degradation, while Candida utilis utilizes resultant sugars. The process is operated in two stages. In the first stage S. fibuligera is grown in a small reactor on the sterilized waste supplemented with a nitrogen source and phosphate. At this point starch is hydrolysed.
The resulting broth is then pumped into second larger fermenter of 300 m capacity where both organisms are present. However, C.utilis dominates and constitutes 90% of the final product. The symba process operates continuously and the pollution load of the waste is reduced by 90%. Resultant protein rich biomass (45% protein) is concentrated by centrifugation and finally spray or drum dried (Fig. 16.5).
7. The Waterloo Process:
Production of SCP from waste biomass is based on the cellulolytic fungus chaetomium cellulolyticum. It utilizes agricultural wastes, crop residues and forestry residues (wood, saw dust, paper pulp and mill sludges) for SCP production. It was developed by university of Waterloo, Ontario, Canada.
The process operation involves the following steps:
1. Thermal and/or chemical pretreatment of cellulosic materials.
2. Aerobic fermentation of pretreated materials with nutrient supplements with C.cellulolyticum. The SCP produced is recovered by the usual process.
This fermentation process has several advantages such as:
(a) The raw material is cheap.
(b) The process employs low cost technology operation, efficient mass and energy exchanges.
(c) By products like methane can be obtained.
(d) SCP is satisfactory as animal feed protein rations in terms of safety, digestibility and nutritive value.
8. High-Rate Algal Ponds (HRAP):
This was developed at Technion-sherman Environmental Engineering Research Centre, Haifa, Israel. In this process algal SCP is produced to supplement animal feed in conjunction with the treatment of sewage in HRAP. This system involves symbiotic interaction between algae and bacteria. The decomposition of sewage by bacteria releases CO2 which is utilized by algae for photosynthesis. Algae grow by utilizing solar radiation, CO2 and releases O2 which is utilized by bacteria for sewage decomposition. The biomass thus produced will serve as SCP.
This process has several advantages such as:
1. Waste water treatment with less cost and producing useful biomass.
2. It is non-aseptic process which does not require sterilization or additional carbon source.
3. Less oxygen is required thus reducing the aeration costs.
4. Sludge treatment is not required.
However, this process has a limited utility where solar radiation is not abundantly available. Further, for algal pond large land area is required.