Facilities available for preparation of various protein products from oilseeds, cereals and grains. These include:
Capabilities exist for process design of commercial facilities for production of protein products used in meat, dairy, beverage and bakery applications.
I. Soy Protein Concentrates
Soy protein concentrates are prepared by removing soluble sugars from defatted soy flakes or flours. The remaining components are mainly proteins and insoluble polysaccharides.
By the removal of soluble sugars from defatted flakes , the protein content of the resulting soy product is increased and the undesirable oligosaccharides, which cause flatulence, are eliminated. Flatus is gas formed in the gut by bacterial fermentation of nondigestible carbohydrates. During extraction, most sucrose and most nondigestible oligosaccharides consisting of stachyose, raffinose, and a small amount of other carbohydrates are not removed. Sucrose and the total nondigestible oligosaccharides each constitute 8% of defatted flakes.
Different leaching methods are available to remove soluble sugars to yield concentrates. The basic approach is to extract the sugars while not solubilizing the protein portion. The major parameters in leaching or fractionation that affect yield and product quality are the starting material, extracting solvent, and extracting conditions.
Soy concentrate can be prepared from full-fat flakes produced by employing hexane as the oil-extracting solvent.
The amount of heat treatment during the preparation of defatted flakes influences the quality as well as yield of soy protein concentrate. Excessive toasting of defatted flakes, as indicated by a lower Nitrogen Solubility Index (NSI), reduces the amount of soluble sugars leached, resulting in a lower protein content in the final product. In addition, heating of flakes reduces the rate of soluble leaching. Because extraction is a continuous process, slow leaching has a major impact on production speed.
There are three common processes for manufacturing soy protein concentrate: aqueous alcohol wash, acid wash, and hot water leaching. In general, concentrate preparation involves countercurrent extraction.
1. Aqueous Alcohol Process
This process is commonly employed for producing commercial soy protein concentrates. Soluble sugars along with a small amount of soluble proteins are extracted by 50 to 70% aqueous alcohol. Due to the denaturation of protein by aqueous alcohol, most of the proteins become insoluble and remain with the insoluble polysaccharide. The alcohol was recovered by flash desolventizing.
The preferred alcohol concentration is 60% by weight. Soy proteins appear to be least soluble in about 50% aqueous alcohol; their solubility increases on either side of that concentration. Excess water in the extraction solvent is to be avoided because of additional energy costs for removal and because an extremely wet soy protein cake tends to agglomerate, clogging the process system. The aqueous alcohol removed by evaporation from the alcohol water soy solubles is recycled to the extraction step.
The nitrogen solubility of soy protein concentrate made by the aqueous alcohol process is low, in the NSI range of 5 to 10. This low NSI is not necessarily related to functionality because the denaturation mechanism is different from that of toasting used to produce low-NSI soy meals. However, extraction with aqueous alcohol removes objectionable flavor and color to yield desirable soy protein concentrate products.
2. Acid Wash Process
The majority of soy proteins are globulins, which are insoluble in water in the regions of their isoelectric points. By the washing of defatted soy flakes with water near the isoelectric point of pH 4-5, soluble sugars are removed from the matrix of proteins and polysaccharide. After acid-water washing, the remaining materials are adjusted to near neutrality and dried. Usually, these products are spray-dried. Because some of the soy proteins are soluble at pH 4-5 , there is a reduction in the protein yield.
The acid wash process yields soy protein concentrate products with a relatively high NSI (about 65-75%) because severe denaturation steps are not introduced in the process and the proteins are neutralized before drying.
3. Hot Water Leaching Process
Proteins, including soy proteins, are easily denatured by heat and become insoluble in water. Moist heat is more effective for denaturation than dry heat. With water of high temperature, the small molecular weight materials, including soluble sugars, are extracted from the insoluble protein and polysaccharide matrix.
4. Other Processes
Another modified, "second-generation" soy protein concentrate of improved functionality is produced by successive pressure and cavitation, such as centrifugal homogenation at elevated temperatures and slightly alkaline pH, a high-NSI soy protein concentrate can be obtained from one that originally had a low NSI value. The highly soluble soy concentrate has functional properties similar to those of milk protein's.
II. Manufacture of Isolated Soy Protein
It includes aqueous extraction of soluble proteins and carbohydrates from defatted soybean flakes or soy flour; separation of the insoluble residue, followed by precipitation of protein at mildly acidic conditions; separation and removal of the soluble carbohydrates, proteins, and salts; and washing and drying of the protein. The protein can be neutralized and further processed into isolates with a variety of forms and functional properties.
III. SOY ISOLATE
Soybean flour is added to deionized water. The temperature and pH of the mixture during the extraction is kept at 55 degrees C. The pH of the mixture is kept at 8.5 - 9.5 using NaOH. After an hour the mixture is pumped into a centrifuge to separate the solids and the liquids. The liquid is held in a container while the solids were extracted again. (The difference between the beginning balance and the balance after centrifugation is attributed to the extra water used to clean the centrifuge baskets.) The solid residue is re-extracted using the same conditions. The proteins are precipitated out by HCI by bringing the pH to 4.55. All of the liquid fractions are pasteurized at 65 degrees C for a hour. The solution was then pumped into the centrifuge to separate the solids and the liquids. Then, separated solids are neutralized and spray dried to produce protein isolates.