Irvin E. Liener

Implications of antinutritional components in soybean foods

There are a number of components present in soybeans that exert a negative impact on the nutritional quality of the protein. Among those factors that are destroyed by heat treatment are the protease inhibitors and lectins. Protease inhibitors exert their antinutritional effect by causing pancreatic hypertrophy/hyperplasia, which ultimately results in an inhibition of growth. The lectin, by virtue of its ability to bind to glycoprotein receptors on the epithelial cells lining the intestinal mucosa, inhibits growth by interfering with the absorption of nutrients. Of lesser significance are the antinutritional effects produced by relatively heat stable factors, such as goitrogens, tannins, phytoestrogens, flatus-producing oligosaccharides, phytate, and saponins. Other diverse but ill-defined factors appear to increase the requirements for vitamins A, B12, D, and E. The processing of soybeans under severe alkaline conditions leads to the formation of lysinoalanine, which has been shown to damage the kidneys of rats. This is not generally true, however, for edible soy protein that has been produced under milder alkaline conditions. Also meriting consideration is the allergenic response that may sometimes occur in humans, as well as calves and piglets, on dietary exposure to soybeans.

Determination of available lysine in proteins

Abstract A simple and rapid method has been developed to determine the available lysine content of proteins and protein foodstuffs involving the use of the reagent 2,4,6-trinitrobenzenesulfonic acid (TNBS). Close agreement was found between the observed and expected lysine values for a number of representative proteins. In the case of protein foodstuffs the available lysine values determined with TNBS were similar to values obtained with the more commonly used Carpenter method which employs fluorodinitrobenzene.

The photometric determination of the hemagglutinating activity of soyin and crude soybean extracts.

Abstract A photometric procedure for measuring the hemagglutinating activity of soyin and crude soybean extracts is described. This method is based on the observation that rabbit erythrocytes sediment at a rate which is proportional to the concentration of the hemagglutinin. Hemagglutinating activity is calculated from absorbance measurements of the suspension of unsedimented cells after a given time. This technique was found to have potential value for predicting the nutritive value of soybean meals subjected to various degrees of heat treatment.

A rapid procedure for the large scale purification of elastase and cathepsin g from human sputum

A procedure is described which permits the rapid isolation of large amounts of elastase and cathepsin G from purulent sputum. This procedure involves: (1) digestion of sputum with DNase, (2) extraction of the insoluble residue that remains with 1 M NaCl, pH 8, (3) affinity chromatography on Sepharose-bound Trasylol, and (4) separation of the two enzymes by chromatogrphy on CM-Sephadex. Starting with 500 g of sputum it was possible to isolate 175 mg of each of these two enzymes within 7 to 10 days. Active site titration indicated both enzymes to be at least 97% pure. Disc gel electrophoresis in the presence and absence of SDS and amino acid sequence of the N-terminal region support the conclusion that the elastase and cathepsin G isolated from sputum are identical to the same enzymes isolated directly from the leukocytes of human blood.

Some physical and chemical properties of a phytohemagglutinin isolated from Phaseolus vulgaris.

Abstract The phytohemagglutinin (lectin) of the wax bean (Phaseolus vulgaris) has been purified by a sequence of steps involving fractionation with ammonium sulfate and successive chromatography on DEAE- and CM-cellulose. The purified wax bean hemagglutinin was shown to be homogeneous by ultracentrifugal analysis and electrophoresis on polyacrylamide gel. Wax bean hemagglutinin had an s°20,w value of 5.37 S and its molecular weight, calculated from sedimentation equilibrium data, was 132 000. In addition to amino acids, wax bean hemagglutinin contained 10.4 % covalently bound carbohydrate which was identified and quantitated by gas chromatography of the acetylated alditols. Mannose was the predominant sugar with lesser amounts of glucosamine, galactose, arabinose, xylose, and fucose also being present. The physicochemical properties of wax bean hemagglutinin differ in several respects from those of other phytohemagglutinins which have been reported by previous workers.

In vitro and in vivo studies on the digestibility of the major storage protein of the navy bean (Phaseolus vulgaris).

Fraction G1, the major storage protein of the navy bean (P. vulgaris), was subjected to in vitro digestion with pepsin, trypsin, or chymotrypsin. Based on measurements of the release of free amino groups, G1 appeared to be markedly resistant to digestion unless subjected to heat treatment. Molecular weight determinations by sedimentation equilibrium and amino acid analysis, however, indicated that G1 had in fact undergone limited proteolysis and a reduction in size, from 140,000 to 120,000, as a result of exposure to either trypsin or chymotrypsin. Disc gel electrophoresis in the presence of sodium dodecylsulfate also revealed significant changes in subunit composition. Native G1 was composed of two subunits, 43,000 and 49,000, in a ratio of 1:2, whereas trypsinor chymotrypsin-modified G1 had subunits of 22,500 and 30,000, in a ratio of 4:1.

Note on the determination of chymotrypsin and chymotrypsin inhibitor activity using casein.

Abstract A method is described which enables one to obtain a linear relationship between the activity of chymotrypsin on casein and the concentration of the enzyme. This method has been applied to an evaluation of the chymotrypsin inhibitor activity of crude soybean extracts.

The purification of human serum α1-antitrypsin by affinity chromatography on concanavalin A

α1-Antitrypsin (α1-AT) has been isolated from human serum by a two-step procedure which involves chromatography on DEAE-Sephadex followed by affinity chromatography on insolubilized concanavalin A. This protein appeared to be homogeneous when examined by electrophoresis on cellulose acetate and double immunodiffusion; minor contaminants, however, were detected by gel electrophoresis and immunoelectrophoresis. This procedure is readily adaptable to the large-scale purification of α1-AT and should facilitate further studies on the physicochemical and biological properties of α1-AT and its genetic variants.

A study of the proteolytic system of Tetrahymena pyriformis W I. Purification and partial characterization of the constituent proteinases

Abstract The proteolytic activity of the cell-free supernatant solutions of cultures of Tetrahymena pyriformis grown on a medium containing 2% proteose-peptone was considerably depressed by the incorporation of 1% glucose. The proteinases produced in the presence and absence of glucose were purified by fractionation with (NH 4 ) 2 SO 4 , treatment with bentonite, and repeated electrophoresis on a vertical starch column. An intracellular proteinase was isolated by preliminary fractionation of the cytolyzed cellular extract with (NH 4 ) 2 SO 4 followed by chromatography on carboxymethylcellulose. Each of these three enzymes were characterized with respect to their specific activity, pH for optimal activity, N-terminal amino acid residue, molecular weight and sedimentation behavior. The implications of these findings in relation to the mechanism of enzyme synthesis are briefly considered.

The USDA trypsin inhibitor study. IV. The chronic effects of soy flour and soy protein isolate on the pancreas in rats after two years

In two year feeding trials, histologic changes in the pancreas of the Wistar rat were evaluated after chronic dietary exposure to raw and heated, dehulled, defatted soy flour and soy protein isolates which provided a range of trypsin inhibitor (TI) concentrations from 93 to 1271 mg/100 g diet. Also investigated was the nutritional interaction of level of dietary protein with the development of pancreatic pathology. Graded levels of TI were achieved from mixtures of raw and heated soy flour or protein isolate. Dietary protein levels were 10%, 20%, and 30%; the two higher levels obtained in some diets through casein supplementation. A total of 26 diets, including casein controls, were fed to groups of 40 male rats. Growth rates with these diets were commensurate with protein quality and level. Mortality rates tended to be slightly greater in the higher protein diets, and rats fed only raw soy as a source of protein survived well.