Soybean processing. Sirichai Songsermpong, Ph.D. Department of Food Science and Technology Kasetsart University

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1 Soybean processing Sirichai Songsermpong, Ph.D. Department of Food Science and Technology Kasetsart University Soybean is regarded as one of the cash crops for the farmers and the important material for the food industry. It contains high nutritional values especially protein and lipid and other functional substances such as isoflavones which can prevent cancer. It is widely processed to many products such as soymilk, tofu, soybean oil, textured vegetable protein and others. 1. Soybean composition Raw soybean contains 11.1% moisture, 34.0% protein, 18.7% oil, 31.4% carbohydrate, 4.7% crude fiber and 4.8% ash. It can be said that soybean is a rich source of complete protein which contains a significant amount of essential amino acids. Soybean oil contains high amounts of essential fatty acids around percent of unsaturated fatty acids, especially linoleic (C 18:2) and linolenic (C 18:3) acids. Lecithin, a widely used surfactant, is also a by product that can be extracted from the raw oil. Carbohydrate in soybean can be water soluble carbohydrates which are sugars such as sucrose, raffinose and stachyose and water insoluble carbohydrates such as Arabinan and pectic substances which contains bigger molecules of sugars. Soybean contains high potassium phosphorus and calcium. Soybean is a good source of thiamine, riboflavin and nicotinic acid. 2. Soy products 2.1 Soymilk Soymilk can be made from the whole grain, from soy protein isolate and from full fat soy flour. The process to make soymilk from whole grain includes water extraction and emulsification. The soymilk can be pasteurized, canned and UHT. The pasteurized soymilk was done by cleaning of soybean, soaking in water or sodium bicarbonate 0.5% in water, grinding with water, filtering by using a cloth filter or a filter press or a decanter. The soymilk is added with water to the required solid content, boiled and added with some sugar. The industry will add soybean oil and emulsifiers and homogenize the soymilk to reduce the size of oil droplets in order to prevent fat separation during storage for long time. The soymilk is heated to boil and packaged in the container. This product is called pasteurized soymilk which can be stored in the refrigerator for only 1 week. If the soymilk is heated and filled in can and heat processed by the steam in a retort at the suitable temperature and time (such as 116C for 20 minutes) and then cool down to 35 C. This product is called sterilized soymilk or canned or bottled soymilk and can be stored for a long time at least 2 years. If the soymilk is heated to 140 C for 3 seconds and cooled down in a tubular heat exchanger in a continuous mode and packaged in a sterile package in a sterile room. This product is called U.H.T soymilk and can be stored for a long time such as 6-8 months. Soymilk can be transformed to soymilk powder by using a spray drier or vacuum drier.

2 2.2 Tofu There are many types of tofu such as hard tofu, medium tofu and soft tofu in plastic tube. All tofu has a similar process except using different salts to precipitate the protein. Hard tofu use magnesium sulfate or magnesium chloride. Medium tofu use calcium sulfate and soft tofu in plastic tube use glucono delta lactone or calcium sulfate. The temperature and concentration of protein and salt concentration has to be optimized to obtain a good quality tofu. Tofu can be processed further such as fermented tofu, fried tofu and many products. The process for making the fermented tofu is soaking the hard tofu in the salt and citric acid solution and baked the tofu at 100 degree celcius for minutes and cool down to room temperature. Adding the mold Actinomucor elegan and incubating at 20 C for 3-7 days. The mold will grow on the tofu. The tofu will be filled in the jar and brine solution together with the wine and seasoning agent will be added and fermented for 1-2 months. 2.3 Dried bean curd sheet Dry bean curd sheet is made by boiling the concentrated soymilk in the shallow pan which is heated by the water bath of temperature C. A film is developed on the surface of the soymilk. Using a bamboo stick, the sheet is removed and dried. The dry bean curd can be prepared for many kinds of dishes. 2.4 Soy sauce and soy paste The fermentation process was done by mixing of roasted wheat flour and cooked soybean with green mold of Aspergillus oryzae type to digest the starch to sugars and protein to amino acids in the dry state (Koji) and the action of the yeast and lactic acid bacteria in the liquid salt solution (Moromi) to become a dark soy paste. The soy paste is pasteurized by boiling and hot filled in the jar. If the soy paste is filtered by using a plate and frame filter press or using thick cheese cloth, it will become the soy sauce. The soy sauce is boiled and hot filled in the bottle. The soy sauce and soy paste can be stored for longer than 1 year because they are acid foods, ph lower than 4.6 and salt concentration is higher than 18%. 2.5 Others Boiled soybean, roasted soybean, baked soybean, sprouts are widely home made and consumed. Full fat soy flour is made by cleaning the whole soybean and heated about C, removing the seed coat and then grinding the seed into flour. This flour can be used to produce the products that can be made from the soybean such as soymilk, tofu, soy sauce etc. Tempeh is another product from Indonesia which is made from soybean. Tempeh is made of whole soybeans which are softened by soaking and dehulling and cooking. The spore of mold Rhizopus oligosporus is mixed. The beans are spread into a thin layer and are allowed to ferment for 24 to 36 hours at room temperature around 30 C for hours. It can be eaten by cooking, frying and other preparations. 3. Soybean oil extraction The production process starts from the preparation of soy flake, the solvent extraction and the refining process.

3 Soy flake preparation starts from cleaning, cracking, adding moisture to soften the meat and flaking by using rollers until the thickness is about 0.01 inch. Solvent extraction of soybean oil is used in the commercial production. Hexane is widely used in the extraction in a rotocel continuous extractor. Counter current extraction with many extraction units was designed to completely remove the oil content in the seed. The flake is conveyed by a screw conveyer in the rotocel and was extracted by the solvent coming from the next unit. The oil is removed step by step until the flake is conveyed to the last extraction unit. Fresh hexane is sprayed in the last unit and extracts the oil until the flake contains less than 0.5% of oil. Hexane and oil which is called miscella is transferred to the previous extraction unit and so on. The defatted flake is conveyed out of the extraction unit by a screw conveyer. The miscella is transferred out and filtered and heated to remove the hexane out of the oil. Hexane vapor is condensed to liquid and used again and again. The soy flake is heated to remove hexane and hexane is condensed to liquid for reuse. Refining process contains 4 steps. Degumming: water is used to remove the gums and lecithin in raw oil. Neutralizing: caustic soda is used to neutralized the fatty acid which become soap. The soap is removed out of the oil by a centrifuge. Bleaching: the oil is bleached with Fuller s earth and activated carbon to absorb the colorant in oil. Deodorization: the oil is stripped with steam to remove the volatile materials under vacuum. The residual free fatty acids and odor substance are removed during this step. The antioxidants such as BHA, BHT and citric acid are added to preserve the oil during storage and consumption. Some manufacturers used nitrogen gas to preserve the oil to prevent oxidation of oil. The soybean oil should have the specific gravity of (20C), refractive index of , water less than 0.2%, impurity less than 0.5% and mineral content should be in the limit according to CODEX standards. The soybean meal has to be heated to remove hexane, cooked to destroy the trypsin inhibitor and dried. Soybean 100 kg will yield the soybean meal of 72 kg. It can be said that soybean meal is the main product for this industry and soybean meal is the important raw material for animal feed because it has high protein content almost 50%. 4. Soy Protein Concentrate The protein from defatted soy meal was extracted by the aqueous alcohol. Adding dilute acid to precipitate the protein and washing the protein with water and drying. This protein is called soy protein concentrate. The concentration of protein is %. 5. Soy Protein Isolate The soy protein Isolate is made by extraction of protein by using dilute alkali. The extract was adjusted the ph to 4.5 which is the isoelectric point of the protein to precipitate the protein. The protein is washed with water until neutral and then dried. The protein content in SPI is around %. 5. Flavored sauce This sauce is made from the acid hydrolysis of soy meal. It is a chemical process. The soy meal is mixed with water and hydrochloric acid 4-5 Normal. The digestion was done in a stainless steel tank with high pressure and temperature of C and cooled down. Adding sodium hydroxide to adjust the ph to 4.5 and

4 filtering the sediment. The sauce is then aged to achieve a characteristic flavor for 2-4 weeks and then filtered and pasteurized at the temperature about 90 C and hot filled. 6. Texturized Vegetable protein The raw material to make texturized vegetable protein is defatted soy meal. The defatted soy meal powder is mixed with water to adjust the moisture content to 12% and is extruded in the single screw extruder. The soy meal is heated, cooked and pressurized in the barrel by the compression of the screw and barrel. The melt is extruded out of the die and is cut by a cutter to small pieces. The extrudates are dried by a continuous drier at the temperature of 70 C for 15 minutes. The extrudates are packed in a polyethylene bag. This TVP is similar to meat analog and mostly welcomed by vegetarians and other people. Soybean processing in Thailand is continuing to grow however the soybean production is slowly increased. Import from abroad is increasing. The consumers need green, clean and healthy food. Therefore, the production of soybean and soybean products need to be adapted to the organic, good agricultural practiced soybean with the concern of the environment. It can be said that soybeans feed the world.

5 Mungbean processing Sirichai Songsermpong, Ph.D. Department of Food Science and Technology Kasetsart University Mungbean is a cash crop for the farmers and a raw material to make starch and noodle for human consumption and protein for animal feed. It contains a high amount of starch and protein. The starch has the most viscous properties of all the other starches which exhibit good property for making noodle and other products that require strength. Researchers are now interested in making the biodegradable film sheet and composites from this starch. Moreover, every part of mungbean plant is useful. The plant is a food fertilizer. The seed is used for food preparation such as sprouts, dahl (mungbean split) and dahl products for desserts and snacks. The seed is extracted for starch for human and protein and fiber can be fed to animal. Processing of mungbean can add value to the bean, reduce the attack from insect and make the full use of the seed. 1. Mungbean composition Mungbean contains 11.5% moisture, 23.4% protein, 1.3% fat, 60.3% carbohydrate, and 3.5% ash. The starch is the major component of mungbean. Thailand is the major processor of mungbean starch and noodle. Songsermpong et al. developed the processing machine and process for making mungbean starch and noodle and make mungbean sauce from the mungbean protein for the local markets during working at Postharvest Engineering Research Group, Agricultural Engineering Division, Department of Agriculture in 1992 and transferred the technology to the King s project in Sakonnakorn, Narathiwad and Chacherngsao provinces and Chainart field crops research center. 2. Production of mungbean starch Mungbean is cleaned to remove the spoiled seeds and foreign matters. The mungbean is soaked in water for at least 6 hours. The soaked mungbean is grinded with water at the ratio of seed:water 1:3 by weight. The slurry was filtered by using a screen of 200 mesh sieve. The mungbean fiber and the slurry are separated continuously. The slurry is settled in the tank for 2 hours to sediment the starch. The protein water on the top is decanted. The starch still has a green color which needs to be washed with clean water and decanted. The starch is cleaned at least four times until white. The moist starch is dried by the sun or using a tray drier until the moisture content is less than 14%. The protein water is boiled and adjusted the ph to 4.5 or using magnesium sulfate to precipitate the protein. The protein is filtered by a thick cheese cloth and dried by the sun or a hot air drier which is called mungbean protein isolate. In order to use the protein to make mungbean sauce, new process is developed. The mungbean hull is removed by splitting the seed and soaking in water. The hull will be removed. Another method is to use the small scale rice mill to remove the seed coat. Preparation of seed coat is needed to loosen the hull by soaking the seed in water for 6 hours and dried. The seed passes through the whitener, set up the suitable gap between the rubber and the stone roller mill. The seed is splitted and the hull is removed. The splitted seed is almost free of hull and is the material to make starch and protein. The starch is cleaned easily and the protein color is yellow and has

6 less smell, better than the first process which the protein is green and has a grass or chlorophyll smell. 3. Production of mungbean noodle Dried mungbean starch is separated into 2 parts 4.5% and 95.5% by weight. The small Part (4.5%) is mixed with 10 times of water (4.5 g of starch mixed with 45 g of water) and heated to gelatinized the starch. The gelatinized starch is mixed with the large part of dried mungbean starch (95.5 g). Then water is mixed little by little until the mixture can flow in treads. The mixture is poured in the bucket which has many big holes of 9 mm. The mixture is pressed by hand to pass the holes in treads to the boiling water and the noodle is cooked and cooled down by using cool water continuously. The noodle is then frozen in a freezer for 6 hours and then thawed in water. The stick noodle can be separated by hand easily and then dried by sun drying on the bamboo stick or on the tray. The mungbean noodle should have the moisture content lower than 14%. It is packaged in the polyethylene bags and sealed. Mungbean noodle is popular for making noodles and other products. Some people call glass noodle as the appearance is transparent as glass. 4. Production of mungbean sauce from mungbean protein The mungbean protein after precipitation is washed with water and then mixed with the roasted wheat flour. The mold Aspergillus oryzae is mixed with the mixture and put on the bamboo tray. The fermentation is done for 3 days. The molds will grow and digest the starch and protein. The Koji is removed from the bamboo tray in the jar and the salt solution of 20% is added in the jar and covered tightly. The fermentation is done for 3 months by yeast and lactic acid bacteria. The sauce is filtered by using a thick filter cloth or a plate and frame filter press. The clear sauce is boiled and hot filled in the bottle and cooled down. The mungbean sauce can be stored for 1 year with a good quality. The mungbean starch can be processed further to desserts and snacks. It has a high potential to mix with plastics or poly lactic acid to become biodegradable plastics which is the trend for environment friendly packaging. The potential for this plastic is very high. The researcher at Department of Packaging and Materials, Faculty of Agro-Industry, Kastsart University are now studying forming many kinds of products from the mixture of this starch and poly lactic acid such as sheets, films, bags, trays, cups and other containers with success.