Processing and product characteristics for textured soy flours,concentrates and isolates

During the last 25 years, the development of processes to provide textural properties in soy proteins has greatly increased the market potential for soy protein products. Many different processes based on soy flour, concentrates and isolates have been developed. They have ranged from products to be used in extension of meats to meat analogs themselves. The real success of new processes is measured by their success in the commercial marketplace. The most successful products have been based on thermoplastic extrusion of soy flour. More recently, second generation products made by the thermoplastic extrusion of soy protein concentrates have been introduced. These products have less flavor, wider variety of functional characteristics and greatly reduced flatulence characteristics compared to textured soy flour products. This paper describes processes used to texturize soy proteins and characteristics of the various products. Product characteristics, functionally and economics are key factors in deciding which product to use in end-product formulations. The wide variety of textured soy proteins available provides a product for each individual need.     

Oilseed protein concentrates and isolates

Much attention has been focused on the oilseed crops as an alternate and largely untapped source of food protein in an endeavor to provide needed nourishment for large segments of the world’s expanding population. A significant part of this attention has been devoted to the practical concentration and isolation of the proteins of several oilseeds. As a result of intensive effort during the last decade, soy protein concentrates and isolates are now commercial commodities which are gaining increasing acceptance as useful functional and nutritional ingredients for food. This report is concerned with a brief review of the commercial processing, product characteristics and food utilization of soy protein concentrates and isolates. In addition, pertinent comments on the concentrates and isolates of other oilseed are included. One of 21 papers presented at the Symposium, “Oilseed Processors Challenged by World Protein Need,” ISF-AOCS World Congress, Chicago, September 1970.     

Rheological properties of emulsions containing modified soy protein isolates

The feasibility of replacing common emulsifiers with soy protein isolates (SPI) in low-calorie salad dressings was evaluated. Structural modifications of SPI were obtained by thermal-acidic treatment with or without neutralization (TH1.6N and TH1.6, respectively). Modification of flow properties of TH1.6 and TH1.6N emulsions by thermal treatment and different protein concentrations was evaluated through shear stress vs. shear rate measurements in a rotational viscometer. TH1.6N isolates generated emulsions with higher shear stress and apparent viscosity than those prepared with TH1.6. Heated TH1.6N emulsions at 10% protein gave the highest values of shear stress and plastic flow behavior. These emulsions had high consistency, viscosity, and elasticity. TH1.6N isolates had lower emulsifying capacity than TH1.6, probably due to the higher protein aggregation produced during neutralization, which prevented protein unfolding. These isolates would be suitable for the preparation of stable emulsions with adequate consistency and elasticity.     

Chemical,functional, and nutritional properties of sunflower protein products

Sunflower flours and protein concentrates have potential food uses because of their high protein content, white color, bland flavor, and absence of antinutritive factors. Procedures have been developed for removal of chlorogenic acid which forms green and brown colors under alkaline pH, and selection for low chlorogenic acid cultivars is underway in plant breeding programs. Further research is needed on dehulling techniques and possible problems associated with high levels of sugars in sunflower flour. Sunflower flours and concentrates have excellent fat absorption, oil emulsification, and whipping properties. Wieners supplemented with sunflower products showed low shrinkage during the smokehouse treatment and low cooking losses due to high fat and water absorptions. Sunflower-supplemented wieners did score poorly in peelability and organoleptic tests. Sunflower proteins had an excellent amino acid balance except for low lysine content and, in feeding trials with rats, showed high protein efficiency ratios when blended with legume or meat proteins.     

Electrophoretic and functional properties of mustard seed meals and protein concentrates

Defatted meals and protein concentrates from five varieties of mustard seeds (four Brassica spp. and one Sinapis alba) were analyzed for polypeptide composition and functional properties. Nonreducing gel electrophoresis showed that Brassica seeds lacked the 135- and 50-kDa polypeptides that were present in the seeds of the S. alba variety. On the other hand, the 29-kDa polypeptide found in the Brassica seeds was absent from the seed of the S. alba variety. Under reducing conditions, the 135 kDa was not detected in the S. alba variety and the intensity of the 50-kDa polypeptide was severely reduced; in contrast, the intensity of the 29-kDa polypeptide in the Brassica seeds was not affected. Meals from yellow seeds had significantly higher (P≤0.05) protein contents than meals from the brown seeds. The emulsifying activity indexes (EAI) of meals and protein concentrates from the Brassica seeds were significantly higher (P≤0.05) than those obtained for similar products from S. alba sees. It was concluded that the disulfide-bonded 50- and 135-kDa polypeptides may have contributed to increased rigidity of S. alba meal proteins, which resulted in poor EAI when compared to the Brassica meals, which do not contain these polypeptides.     

Textural properties of cheese analogs containing proteolytic enzyme-modified soy protein isolates

Cheese analogs were prepared from untreated or proteolytically modified soy protein isolates (SPIs), replacing 60% of casein, to explore their potential to replace higher-priced milk proteins. Quality attributes of cheese analogs were evaluated by texture profile analysis with the Instron and melting spread. Compared with commercial milk-based cheeses, ranging from hard-type (Cheddar) to soft-type products (Mozzarella), textural properties of cheese analogs were markedly different; they were harder and more fracturable with no measurable adhesiveness. The use of enzyme-modified SPI significantly (P < 0.05) lowered both hardness and fracturability of cheese analogs and also brought about adhesiveness, all of which fell within the range observed for dairy cheeses. Although melting spread of cheese analogs was improved by the use of enzyme-modified SPI, it was still inferior to those of dairy cheeses and needed further improvement. Treatments of SPI with alcalase and trypsin were more influential in modifying textural properties of the resulting cheese analogs than those with other proteases studied.     

Thermal and mechanical properties of plastics molded from urea-modified soy protein isolates

Soy protein has been considered as a potential alternative of some petroleum polymers in the manufacture of plastics. The purpose of this investigation was to characterize the thermal and mechanical properties of plastics made from urea-modified soy protein. Soy protein isolate was separated from the defatted soy flour, modified with various urea concentrations, and compression-molded into plastics. Differential scanning calorimetry showed that the temperatures of denaturation and the enthalpies of denaturation of the modified soy protein decreased as urea concentrations increased above 1 M. At the same urea concentration, molded plastics made from the modified soy proteins showed a similar temperature of denaturation as the modified soy protein, but a lower enthalpy of denaturation. Tensile strength and Young's modulus of the molded plastics from the modified soy proteins increased as urea concentration increased and reached their maximum values at 8 M urea modification. Both storage modulus and glass transition temperature of the plastics from the modified soy proteins increased as urea concentration increased. The plastics made from the 2 M urea-modified soy proteins showed improvements in elongation, tough fracture behavior, and water resistance. The urea may function as a denaturant, a plasticizer, and a filler.     

Analysis of products, mechanisms of reaction, and some functional properties of soy protein hydrolysates

Soybean protein isolates were hydrolyzed with papain, bromelain, cucurbita, hieronymin, and pomiferin. The highest hydrolysis rate for cucurbita and the lowest for papain was detected at 720 min. Gel filtration, reversed-phase liquid chromatography, and electrophoresis showed that the action of each protease was different. Pomiferin acted on the native structure of β-conglycinin and glycinin, generating a large number of small hydrolysis products with hydrophilic and hydrophobic characteristics. The hydrolysates obtained with cucurbita showed residual structures that were almost intact and very similar to the substrate and contained a low number of small peptides. The hydrolyzates obtained with papain, bromelain, and hieronymin had hydrolysis products with structures similar to the partially hydrolyzed native isolate. The molecular masses of these products were similar to or lower than the controls. Polypeptides of low molecular mass were also detected. The prevalence of one-by-one and zipper mechanisms was suggested for cucurbita and pomiferin, respectively. For the other proteases both mechanisms were likely to coexist. The solubility of hydrolysates and their ability to form and stabilize foams correlated well with the structural properties and with the suggested mechanisms of hydrolysis. The best properties were presented by the hydrolysates prepared with cucurbita. Foaming ability for pomiferin hydrolysates was as high as that for unhydrolyzed soy isolate, but the foams were extremely unstable.     

Production and functional characteristics of protein concentrates

Protein concentrates derived from common dry beans (Phaseolus vulgaris L.) may improve world protein resources, reduce on-site preparation time and expense and provide improved nutrition. Several different methods have been studied for the production of these concentrates, including alkali extraction and isoelectric precipitation, ultrafiltration, air-classification and salt extraction under high salt concentrations. Recent studies using solid-solid dry roasting, pin milling and air-classification resulted in the following percent mass fractions: hull/fiber (10%), coarse/starch (70%) and fine/protein (20%). Results indicated that the protein fractions were approximately 45–50% protein, low in raffinose and stachyose and hadtrypsin inhibitor activity reduced to about half of that of raw beans. Nitrogen Solubility Index (NSI) ranged from 33–70% and was associated with the thermal conditions applied during dry roasting. The flours had a bland flavor without the bitter off-flavors which have traditionally limited the use of dry beans in formulated foods. Most minerals and phytic acid tended to be associated with protein flour; however, although iron may have been bound to phytic acid, its absorption by anemic rats was not hindered by the presence of endogenous phytic acid. These flours produced acceptable products when incorporated into cookies, doughnust, quick breads and leavened doughs. Presented at the 78th American Oil Chemists' Society Annual Meeting, May 27–21, 1987, New Orleans, LA.     

Enzymatic modification of soy protein concentrates by fungal and bacterial proteases

Solubility, foaming capacity and foam stability of denatured soy protein concentrate obtained from toasted flour were improved by proteolysis with fungal or bacterial proteases. Emulsifying capacity was unchanged, but emulsion stability decreased; bacterial protease highly improved oil absorption. Also, the bacterial protease was able to solubilize more protein and gave products which foamed more than those obtained with the fungal enzyme. However, the stabilizing properties of the bacterial modified soy protein concentrate at the air/water or oil/water interface were inferior. By limited hydrolysis up to degree of hydrolysis 10% most functional properties were improved without greatly reducing emulsion stability and water absorption.     

Partially hydrolyzed rapeseed protein isolates with improved functional properties

Limited rapeseed protein hydrolysates ranging from 3.1 to 7.7% hydrolysis were produced from isoelectric-precipitated protein isolate. Water absorption, oil absorption, whippability, foam capacity and stability, emulsifying activity, and emulsion stability of the hydrolysates were determined. All protein hydrolysates showed better functional properties than the original protein isolate. Foam and emulsion stability decreased as the degree of hydrolysis increased. The hydrolysate with the lowest degree of hydrolysis showed the best functional properties. These improved functional properties make rapeseed protein hydrolysates a useful product to be used in foods such as breads, cakes, ice creams, meat products, desserts, and salad dressings.     

Chemical lipophilization of soy protein isolates and wheat gluten

Chemical modification of soy protein isolate and wheat gluten can be used to investigate the influence of the chemical composition and the structure of the proteins on the final product properties and to adjust these properties to meet specific demands. Proteins were lipophilized by adding different levels of lauroyl chloride to aqueous protein dispersions. At optimum reaction conditions, incorporation rates of lauroyl chains to the protein were 400 and 300 μmol/g proteins for soy protein isolate and wheat gluten, respectively. The study showed that it was possible to lipophilize proteins in an aqueous medium, even with the protein significantly high in concentration.     

Lipid components that reduce protein solubility of soy protein isolates

A lipid fraction from a commercial soy protein isolate (SPI), previously found to be detrimental to SPI solubility, was analyzed by size-exclusion liquid chromatography, by high-performance liquid chromatography (HPLC), and for chemical composition. The molecular weight of most of this material was greater than 1,100 daltons. This lipid fraction was water-soluble yet required a strong nonpolar solvent mixture to elute it from a C₁₈ HPLC column. The lipid material was alkaline (pH 8.7) and composed of 3.0% nitrogen, 1.6% phosphorus, 17.5% nonvolatile crude fatty acids primarily hydroxylated), 10.4% long-chain bases, 9.9% hexuronic acid, 3.2% hexosamine, and 6.6% total sugar. The molecular weight, chemical composition, and physical characteristics (solubility characteristics, surfactant characteristics, and appearance) of this material were all similar to those reported for phytoglycolipid.     

Nonpolar-volatile lipids from soy protein isolates and hexane-defatted flakes

Lipid extracts from two samples of commercial soy protein isolates (SPI) and two samples of commercial hexane-defatted flakes were fractionated by silici acid-column chromatography. The material eluted with 100% chloroform was collected, further fractionated by silica solid-phase extractions, and analyzed by gas chromatography-mass spectroscopy by using mass spectra, retention times of authentic standards, and Kovats indices for identification. Thirty-eight compounds were identified and quantitated in the lipid fractions from soy protein isolates (SPI); 23 of these are reported for the first time as components of SPI. An additional 13 compounds are reported for the first time as components of hexane-defatted soybean flakes. The major classes of compounds reported for the first time associated with SPI include: butyl, methyl, and ethyl esters of fatty acids; phenols, diphenyls and phenyl esters; and abietic acid derivatives. Dehydroabietinal at 0.180 to 0.191 ppm of the protein isolates was the most abundant aldehyde in the SPI lipid extracts. The third most abundant aldehyde found in SPI after dehydroabietinal and hexanal was 2-butyl-2-octenal (0.065 to 0.086 ppm). Dehydroabietic acid methyl ester was present in SPI (0.309 to 0.459 ppm). Dehydroabietene (0.628 ppm) and abietatriene (0.396 ppm) were tentatively identified in one sample of hexane-defatted flakes.     

Processing edible peanut protein concentrates and isolates to inactivate aflatoxins

Experiments were conducted to study the efficacy of some oxidizing or other reactive chemicals for destruction of aflatoxins in conjunction with the aqueous extraction process for the production of peanut protein concentrates and/or isolates directly from contaminated raw peanuts. The chemicals tested included acetone, isopropyl alcohol, methylamine, hydrogen peroxide, benzoyl peroxide, ammonia gas, and sodium hypochlorite. Among these chemicals, hydrogen peroxide, benzoyl peroxide, and sodium hypochlorite showed very effective destruction of aflatoxins during the aqueous extraction process of infected peanuts. However, the use of benzoyl peroxide may pose some difficulties because it is not readily soluble in the aqueous suspensions. It was therefore concluded that aflatoxins can be effectively destroyed during the aqueous processing of peanuts by properly utilizing either sodium hypochlorite or hydrogen peroxide to produce either peanut protein concentrates or isolates.     

Changes of isoflavones during processing of soy protein isolates

Soy protein isolate (SPI) is a widely used food ingredient and is made by extracting soy flour (SF) under slightly alkaline pH, followed by precipitation, washing, and drying. Soy foods and foods containing soy protein ingredients have great potential in the prevention of cardiovascular diseases and cancers. These health benefits have been attributed to isoflavones in soy protein ingredients. However, the current processing techniques were developed many years ago without this knowledge. The objective of this study was to investigate the mass balance of different isoflavones during manufacturing of SPI and to provide basic information to assist further development efforts leading to preservation of soy isoflavones in soy protein ingredients. The study revealed that only about 26% of the total isoflavones in SF remained in SPI. The percentages of total isoflavones lost during extraction, precipitation, and washing were 19, 14, and 22%, respectively. Washing was the step where most isoflavones were lost. The isoflavone profile of the SPI was different from that of SF. The former contained much more aglucones (genistein and daidzein), while the latter had almost none. The high content of aglucones in SPI was probably due to the hydrolysis of glycosides.     

Improvement of nutritional value and functional properties of soybean glycinin by protein engineering

Glycinin is one of the predominant storage proteins of soybean.To improve its functional properties (heat-induced gelationand emulsification) and/or nutritional value, the A_1aB_1b proglycininsubunit was modified on the basis of genetically variable domainssuggested from the comparison of amino acid sequences of glycinin-typeglobulins from various legumes and nonlegumes and the relationshipsbetween the structure and the functional properties of glycinin.Thus, nucleotide sequences corresponding to each of the variabledomains were deleted from the cDN A encoding the A_1aB_1b proglycinin,and a synthetic DNA encoding four continuous methionines wasinserted into the cDNA region corresponding to each of the variabledomains. Expression plasmids carrying the modified cDNAs wereconstructed and expressed in Escherichia coli strain JM105.Some of the modified proteins were accumulated as soluble proteinsin the cells at a high level and self-assembled. They exhibitedfunctional properties superior to those of the native glycininfrom soybean, which establishes the possibility of creatingtheoretically designed novel glycinins with high food qualities.     

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.