Current status of soy protein functionality in food systems

Much of the research discussed in this paper deals with the effects of processing treatments on the physicochemical and functional properties of total soy protein isolate, 7S and 11S components and/or their subunits. This is new and exciting information that should become significant for future developments within the soy protein ingredient manufacture and utilization field. However, these researchers generally failed to provide adequate experimental details concerning methodologies employed to prepare, characterize and utilize soy proteins, their components and subunits in functionality studies. There is also an obvious need to devise and implement the use of more uniform and/or standardized methodologies for this kind of work in the future. Presented at the 78th American Oil Chemists' Society Annual Meeting, May 17–21, 1987, New Orleans, LA.     

Nutritional aspects of soy protein products

This paper is concerned with the nutritional properties of the soybean and of various food products derived from it. Although primary consideration is given to the protein, cognizance is made of other nutrients such as vitamins and minerals. Much of our knowledge concerning the nutritional properties of the soybean has been derived from experiments with animals, and such knowledge is frequently directly applicable to human nutrition. Nutritional experiments with human subjects pose special problems, the most difficult of which is acceptability. People will not eat a certain food simply “because it is good for them.” Thus, the most serious hurdle to be overcome in the development of products containing soybean proteins is frequently not a nutritional one but one of consumer acceptance.     

Uses of soy protein in mixed protein systems to meet nutritional needs

Soya products can be introduced into animal protein food systems to supplement animal protein. This can serve to increase the total protein available to target populations. Nutritional studies have demonstrated that mixtures of soya protein and meat or soya protein and fish are of a biological quality similar to that of meat or fish protein when fed alone. Soya products also can be used in mixed protein systems with vegetable proteins to complement amino acids. Many studies with human subjects have demonstrated the utility of soya products in a variety of soya-cereal foods that can serve as the major source of protein for infants and children.     

Use of spun soy protein in meat systems

Fabricated products made with spun protein analogues, even at 50% levels, are very similar to their all meat counterparts and have high acceptability. The flavor and texture problems associated with many other meat extenders which restrict their use to 10–30% can be overcome by use of spun protein analogues. These spun protein analogues are very adaptable to applications with sectioned and formed products and in some cases actually improve product quality.     

Nutritional aspects in textured soy proteins

Textured soy protein products have found extensive use in pet foods and many human foods. They extend and complement meats in formulated foods. Numerous feeding tests with people and experimental animals show that biological values are high and protein efficiency ratios compare favorably with pure meat products. By careful processing of the textured soy products, high quality, safe, low cost protein food can be prepared. Textured soy proteins are an excellent example of man’s creative ability to engineer a supplementary food that is nutritious, palatable, and economical.     

Nutritional evaluation and acceptance of a novel spun protein food

Spun vegetable proteins have been widely discussed in recent years, mainly for two reasons. First, they are often associated with the idea of an analog, which in our view is outdated. It is indeed illusory to want to imitate a product such as meat, which is a highly complex material and one for which the consumer has a considerable emotional attachment. Second, the actual technique of spinning is often disparaged on the supposition that its cost is prohibitive, which our experience leads us to dispute, and for the reason that its effects are antinutritional, which we will examine further in detail. “Food should nourish while pleasing the taste,” said Tremolieres (1). This definition of food as needing to nourish and to please will serve as a basis for this paper. A new food must, in fact, first and foremost contain no toxic or antinutritional substances. Moreover, a food can only be considered as such in the context, and as a function of its capacity to satisfy a given nutritional need. Last, and above all, it can only be considered as a food if it is judged to be good, and acceptably priced. So we see that it would be unreasonable to separate the concept of nutrition from that of acceptability. The two notions are inextricably linked when it is a matter of creating a new food, which is what we are proposing to do.     

Requirements for foods containing soy protein in the food for peace program

Under the Food for Peace Program, whole grains, milled wheat flour, milled rice, soybean oil, soybean flour, nonfat dry milk, soyacontaining blended food supplements, and soya-fortified processed foods are provided by the U.S. to needy people abroad to alleviate malnutrition. These commodities are used in maternal/child health programs, school feeding, food for work projects and disaster relief. The wide diversity of nutritional requirements and traditional food preferences has led to development of nine soya-containing food types, which are used in the PL-480 Title II donation program as blended food supplements or fortified processed foods. Research studies have led to the development of product specifications. Blended food supplements include the standardized mixtures of corn-soya-milk (CSM), instant CSM, wheat-soy blend and whey-soy drink mix. These foods, developed to fulfill the nutritional requirements of preschool children, contain from 17.5 to 29.7% either toasted-defatted or equivalent full-fat soya flour, along with vitamins and minerals. In addition, 4–19% soya oil is added to improve caloric density. These products contain 19 or 20% minimum protein and 6 or 19% minimum fat content. Fortified processed foods include soya-fortified bulgur (SFB), soya-fortified bread wheat flour (SFWF), soya-fortified cornmeal (SFCM), soya-fortified sorghum grits (SFSG), and soya-fortified rolled oats (SFRO). These foods contain toasted soya flour, grits, or flakes added at 12–15% levels. Fortified foods are generally consumed by people other than infants.     

Nutritional value and economic aspects of fortification of foods of plant origin with soy protein

The protein requirements of children and adults are reviewed in comparison with the protein qualities of several foods with and without added soy. The economic considerations greatly favor soy containing foods for equivalent nutrition.     

Nutritional effectiveness of soy cereal foods in undernourished infants

These studies show that a variety of cereal-soy foods can be the major or only source of protein in the diet of growing infants and children. These included various combinations of cornmeal and soy flour, with and without added dry skim milk or methionine; a wheat flour-wheat concentrate mixture or whole wheat flour with soy flour; oat and soy flours; and a corn-wheat-soy flour macaroni. Apparent absorption of nitrogen from each of these mixtures was similar, averaging 76.3±0.6 (SEM) % of intake, but was inferior to that from casein in the same children, which averaged 86.8±0.4% of intake. Apparent retentions of nitrogen averaged 26.6±0.8 and 33.8±1.0% of intake respectively, with all but one of the soy-cereal combinations being similar. This one had a mean retention equal to that from casein, possibly as the result of “instantizing” of the cornmeal which probably resulted in increased availability of dietary energy. For all the mixtures, nitrogen retention was influenced by the efficiency of nitrogen absorption, suggesting that processing methods can improve the nutritional quality of these foods.     

Phytate-calcium interactions with soy protein

Solubilities of mixtures of soy protein isolate, calcium and phytate were determined as a function of pH and molar ratio of the components. Below the isoelectric point, phytate and protein solubility profiles paralleled each other, indicating some type of protein-phytate interaction. Addition of phytate shifted the isoelectric point and the minimum solubility to lower values. Between the isoelectric point and pH 6.5, the complex apparently dissociates; addition of phytate results in an increase in the maximum solubility of the phosphorus and the protein, as well as a shift in their solubility profiles. Calcium has no apparent effect on protein solubility in this pH region. Higher pH (>6.5) results in the formation of ternary protein-calcium-phytate complexes and a significant drop in calcium and phosphorus solubility, probably due to formation of insoluble calcium phytate salts.     

Adhesion strength of sodium dodecyl sulfate-modified soy protein to fiberboard

Thermal and rheological properties of sodium dodecyl sulfate (SDS)-modified soy protein isolate (SPI) adhesives were studied using differential scanning calorimetry (DSC) and rheometry. The ordered structure of native SPI was denatured as SDS concentration increased, and thermal stability of native SPI decreased at high SDS concentration. The enthalpy of SPI denaturation decreased significantly with increasing SDS concentration. Apparent viscosity of the SPI adhesives increased as SDS concentration increased. The SPI adhesives modified by high concentrations of SDS exhibited characteristics of a Newtonian-type flow. The SDS-modified SPI adhesives were applied to fiberboard, and effects of SDS concentration, press conditions, and assembly time on bond strength were investigated. Shear strength of the SPI adhesives increased with SDS concentration, reaching its maximum value at 3 wt% of SDS, and then decreased significantly. The shear strength increased as press time and/or press temperature increased. High press temperature (100 °C) and long press time (5 min) are needed to achieve relatively good adhesion properties. The shear strength also increased as assembly time increased. The shear strength of the SDS-modified SPI adhesives decreased after soaking in water for 24 h.     

Removal of phytate from soy protein

Phytate, as a minor constituent of soybeans, has been reported to interfere with the dietary mineral absorption of mammals. Commercial soy protein isolate contains 2-3% tightly bound phytate. Practifrom soy protein materials. However, in this reported process, the phytate content was reduced to extremely low levels using commercially feasible processing techniques. The first step of this process was the extraction of water soluble components from soy flakes using routine commercial procedures. In the second step, the extract was adjusted to pH 11.6 at 28 C to insolubilize the phytate. The phytate was removed by centrifugation or vacuum filtration. Neutralization followed the phytate removal. The temperature and pH are critical for phytate removal but also must be carefully controlled to prevent protein degradation. Lysinoalanine was not detected nor was cysteine or other amino acids found to be degraded. The third step of this process was purification of the protein. In this case, the low phytate soy extract was purified by Ultrafiltration until permeate equivalent to 1/2 times the volume of the extract was collected. The phytate and phosphorus contents of the resulting soy protein isolate were 0.1 and 0.2%, respectively, compared to 2.6 and 0.8 for typical commercial soy protein isolate. The PER was significantly better than an acid isolate prepared from the same soy flakes or the commercial soy isolate tested. The retenate obtained after purification by Ultrafiltration was a translucent liquid with a protein content of 5-6%. This protein was in a very soluble form and was stable to heat.     

Regulatory approach of industrialized countries to accommodate use of soy protein

Government bodies worldwide are moving toward accepting soy proteins in their food supplies. There is a trend toward food laws that allow countries to take advantage of unique nutritional, functional and economic benefits soy protein has to offer. This is a world precedent, soundly based on broad experiences and firmly backed by scientific research and development. There is no longer any need to postpone this important decision to allow soy protein in the food supply. The most critical question at this point should be: “What steps can be taken now to properly incorporate and take advantage of soy protein in the national food supply? Regulations recognizing the benefits of soy protein in the food system need not be complex. A reasonable approach to food legislation attempts: (a) to allow the production of properly labeled, safe, wholesome foods, recognizing new developments in modern food technology; (b) to ensure the nutritional value of foods; (c) to provide sufficient information and understanding to help the consumer make a wise purchase decision; and (d) to adopt controls as required to promote honesty and fair dealing in the marketplace.     

Position of soy protein processors in relation to laws and regulations

Soy protein products in the U.S. fall under the regulatory powers of the Food and Drug Administration as far as processing plants are concerned. The U.S. Department of Agriculture controls their use in meat and poultry products. Many states have separate regulations. The industry is expected to know federal and state regulations and interpret them for the customer. Difficulties arise for the processor when there are so many different state, Food and Drug Administration, U.S. Department of Agriculture, and foreign regulations that affect the products. This Conference might spearhead world-wide cooperation in the development of future regulations.     

大豆蛋白乳液胶粘剂的研制

由于以石化原料合成的胶粘剂在生产和使用过程中会对环境带来不良影响,近年来采用可再生资源,如大豆蛋白合成环保型胶粘剂已成为发展趋势。以尿素和亚硫酸钠改性大豆分离蛋白(SPI),并与醋酸乙烯酯(VAc)等复合单体在过硫酸铵(APS)引发下进行接枝共聚反应,合成了性能较好的VAc/SPI接枝共聚乳液胶粘剂,降低了原料成本。通过正交实验研究了不同的反应条件对该乳液胶粘剂性能的影响,优化的反应条件是采用半连续乳液聚合工艺,以改性SPI自身作为保护胶体,改性剂尿素的浓度为3mol/L,复合单体与SPI的质量比为2.0:1,反应温度为68℃,共聚反应时间为4～5h。由此制得的乳液胶粘剂具有良好的综合性能。