Chapter SAQ 4.3 Choose the correct completion to the following statement. In the production of Chlorella spp for SCP from molasses, bioreactors rather than lagoons are used because 1)molasses-based medium is darkly coloured and would not allow sunlight to penetrate lagoons 2) the CO2 required for growth can be more efficiently dissolved in fermentors 3)lagoon systems containing molasses-based medium would become heavily contaminated by bacteria 4)bioreactors give higher biomass yields than lagoons 4.7 SCP from carbohydrates Carbohydrates derived from plant biomass are plentiful and are renewable. They thus form an excellent substrate for SCP production by heterotrophs. Such carbohydrate can be in the form of sugars, which are readily used by microbial cells, or starch, pectin and cellulosic material, which require hydrolysis to sugars before they are available for cell uptake and use. Hydrolysis of starch can be carried out by chemical or enzymatic treatment to produce sugars for a fermentation medium, or by enzymes produced in situ by an amylase-producing organism growing in or on the starch substrate Cellulosic quantities of such materials available for sCP production (or other fermentation processes)are given in Table 4. 4. Note the importance of grain-derived products
74 Chapter 4 Choose the correct completion to the following statement. In the production of Chlorella spp for s8 from molasses, bioreactors rather than lagoons are used because: 1) molasses-based medium is darkly coloured and would not allow sunlight to 2) the COZ required for growth can be more efficiently dissolved in fermentors; 3) lagoon systems containing molasses-based medium would become heavily 4) bioreactors give higher biomass yields than lagoons. penetrate lagoons; contaminated by bacteria; 4.7 SCP from carbohydrates Carbohydrates derived from plant biomass are plentiful and are renewable. They thus form an excellent substrate for s8 production by heterotrophs. Such carbohydrates can be in the form of sugars, which are readily used by microbial cells, or starch, pectin and cellulosic material, which require hydrolysis to sugars before they are available for cell uptake and use. Hydrolysis of starch can be carried out by chemical or enzymatic treatment to produce sugars for a fermentation medium, or by enzymes produced in situ by an amylaseproducing organism growing in or on the starch substrate. Cellulosic material is solid and is normally used in solid-substrate fermentations. The estimated quantities of such materials available for SCP production (or other fermentation processes) are given in Table 4.4. Note the importance of grainderived products
Source Quantity (x10° tonnes per your) ugars Molasses 93 1.5 (USA) Sulphite waste liquor 12-2 Glucose(from starch) Starch Wastes from vegetable processing agasse(sugar Wheat bran Rice st Corn(maize)wastes Urban refuse(paper/cardboard 152 Table 4.4 Approximate world (or USA)availability of carbohydrate substrates 4.7.1s yeasts Yeasts are the product of many of the sCP processes based on sugars. This is because yeasts can use many different sugars, they have been used traditionally in foods and they have most of the desirable characteristics for SCP. Each process differs slightly accordin ing to the nature of the substrate and th nism used, but in pri systems are similar. The experience you gained in earlier sections should enable you to answer the following SAQ
Single cell protein 75 Lpe SOUrCe Chantlty (x 10' tonner per ywr) Sugars: Starch: :ellulosics: Molasses Whey Sulphite waste liquor Glucose (from starch) Wastes from fruit processing Wastes from vegetable processing Bagasse (sugar cane fibre) Wheat bran Wheat straw Rice straw Corn (maize) wastes Urban refuse (paperkardboard) Woodnorestry wastes 9.3 1.5 (USA) 12-2 1 06 58 864 599 1 93 152 61 Table 4.4 Approximate world (or USA) availability of carbohydrate substrates 4.7.1 Sugars Yeasts are the product of many of the SCP processes based on sugars. This is because yeasts can use many different sugars, they have been used traditionally in foods and they have most of the desirable characteristics for SCP. Each process differs sli tly systems are similar. The experience you gained in earlier sections should enable you to answer the following SAQ. yeasts according to the nature of the substrate and the organism used, but in principle afthe
apter SAC 4.4 The diagram below is a flow diagram of an sCP process from carbohydrate, with the letters A-Krepresenting various operations, inputs and outputs. Using the list given, fit in appropriate operations, inputs or outputs at points A-K to complete FILTRATI Biomass slurry dried SCP cell separation continuous heat sterilisation continuous fermentation minerals(phosphate/sulphate) molasses Molasses is a by-product of sugar refining, mostly from beet or cane, and contains 35-50% sucrose and small quantities of nitrogen. It is used as sweeteners in the food industry and as a fermentation medium for the production of bakers yeast, ethanol and other products. For sCP production, the molasses is diluted to 4-6% sucrose supplemented with phosphate and sterilised by continuous heat sterilisatio conbnuous Continuous processes are run in aerated fermentors with ammonia addition, producing food-grade Candida utilis and Saccharomyces cerevisiae Systems operate at dilution rates 0.2-0.3 h"at pH.5-4-5 at 25-35C. Yeasts are recovered by centrifugation, washed, dried by drum or spray drying and packaged. The product contains about 45% protein and is used as a high protein food supplement, particularly in Taiwan, South Africa and the former Ussr
76 Chapter 4 The diagram below is a flow diagram of an SB process from carbohydrate, with the letters A-K representing various operations, inputs and outputs. Using the list given, fit in appropriate operations, inputs or outputs at points A-K to complete the flow diagram. mobses Molasses is a by-product of sugar rdining, mostly from beet or cane, and contains 35-50% suame and small quantities of nitrogen. It is used as sweeteners in the food industry and as a fermentation medium for the production of bakers yeast, ethanol and other products. For SCP production, the molasses is diluted to 44% sucrose, supplemented with phosphate and sterilised by continuous heat sterilisation. Continuous processes are run in aerated fermentors with ammonia addition, producing food-grade Candida utilis and Sacchmomyces cerm*siae. Systems operate at dilution rates 0.2-0.3 h-’ at pH 3.545 at 25-35°C. Yeasts are recovered by centrifugation, washed, dried by drum or spray drying and packaged. The product contains about 45% protein and is used as a high protein food supplement, particularly in Taiwan, South Africa and the former USSR. -tim~~us Culture
Single cell prote ∏ Presented below are four flow diagrams representing processes for washing the concentrated yeast suspension(the suspension concentrated from the fermentation medium by centrifugation). Which of these processes do you think rould be suitable for washing the ye Concentrate Concentrated water 2) Concentrated d Resuspension Spray Drying Dried Concentrated Concentrated R esuspens Ultrafiltration suspension water Rotary vacuum Yeast cake Methods I and 4 are appropriate methods of washing yeast cells. Yeast cells can be concentrated by centrifugation, so method 1 achieves washing Method 4 makes use of rotary vacuo the fact that concentrated yeast cells can be de-watered using a rotary vacuum filter which can incorporate washing. In order to filter yeast cells the filter would first have be coated (pre-coated)with a layer of material such as starch granules, to decrease the effective size of the filter. Method 2 does not achieve washing, as medium components would be dried with the yeast and not removed in the water Method 3 is not suitable for concentrating large volumes of yeast cells as ultrafilters would become blocked by dense yeast suspension whey Whey is the effluent from cheese manufacture, and contains about 5% lactose and about 1% protein. About half of the global production is used as a feed supplement but th rest is unused. The BOD can be as high as 70,000 mg or, which requires reduction by iological treatment ( which is costly) prior to disposal For sCP processes the valuable deprotination Protein from the whey is first recovered by precipitation or ultrafiltration, and the deproteinised whey used in processes such as described for molasses. The yeasts used
Single cell protein n Presented below are four flow diagrams representing processes for washing the concentrated yeast suspension (the suspension concentrated from the fermentation medium by centrifugation). Which of these processes do you think would be suitable for washing the yeast suspension? rI Methods 1 and 4 are appropriate methods of washing yeast cells. Yeast cells can be concentrated by centrifugation, so method 1 achieves washing. Method 4 makes use of the fact that concentrated yeast cells can be dewatered using a rotary vacuum filter which can incorporate washing. In order to filter yeast cells the filter would first have to be coated (pre-coated) with a layer of material such as starch granules, to decrease the effective size of the filter. Method 2 does not achieve washing, as medium components would be dried with the yeast and not removed in the water. Method 3 is not suitable for concentrating large volumes of yeast cells as ultrafilters would become blocked by dense yeast suspension. Whey is the effluent from cheese manufacture, and contains about 5% lactose and about 1% protein. About half of the global production is used as a feed supplement but the rest is unused. The BOD can be as high as 70,000 mg 02 1-’, which rrquires reduction by biological treatment (which is costly) prior to disposal. For SCP processes the valuable protein from the whey is first recovered by precipitation or ultrafiltration, and the deproteinised whey used in processes such as described for molasses. The yeasts used rotary vacuum filter whey depmtination