The Soy Protein Research Committee(Japan)

BIOCHEMICAL AND NUTRITION STUDIES ON THE HEAT-INDUCED COMPLEX OF SOYBEAN PROTEIN ISOLATE AND WHEY PROTEIN CONCENTRATE

Masao KANAMORI and Hiroshi DOI

Faculty of Agriculture, Kyoto Prefectural University

Nutr. Sci. Soy Protein, Jpn. 5, 5-12, 1984.

Soybean protein isolate (SPI) is a by-product of an oil industry and whey protein concentrate (WPC) is a by-product of cheese making industry. Discard of these proteins causes pollution problems. These proteins have a good characteristics as a food protein. For example, SPI has a hypocholesterolemic effect and WPC is an excellent quality protein in nutrition. Development of usage of both proteins is expected. It was tried to make the protein preparation having effective characteristics of SPI and WPC in this paper. A mixture of SPI and WPC was heated at 80Åé for 30 min in water, and then lyophilized. The physical properties of the heated mixture (HM) were different from those of SPI and WPC in solubility and gelation by heating. It is considered from the results of gel filtration of each protein that heat treatment caused re-arrangement of protein subunit of SPI and WPC. HM was easily hydrolyzed by trypsin and pepsin compared with SPI. Rats fed the diet containing 20% HM as a protein source showed a good growth curve. Serum cholesterol level of rats fed HM diet was lower than that of rats fed SPI or WPC diet. A functional impairment of liver or small intestine was not detected in rats fed HM diet, when activities of serum cholinesterase, leucine aminopeptidase in liver and small intestine and alkaline phosphatase in small intestine were measured.

FUNCTION OF A HIGHLY PHOSPHORYLATED SOYBEAN PROTEIN AT THE ACIDIC RANGE

Makoto KITO ¹, Hiroshi NARITA ¹,Motohiko HIROTSUKA ² and Hitoshi TANIGUCHI ²

¹ Research Institute for Food Science, Kyoto University
² Fuji Oil Co., Ltd

Nutr. Sci. Soy Protein, Jpn. 5, 13-17, 1984.

Acid precipitated soybean protein (Soybean Protein Isolate, SPI) was phosphorylated with POCl3 under an alkaline condition. The amount of incorporated phosphorus was 14É g per mg of SPI. When the molecular weight of the SPI was taken as 360,000 daltons, the mol ratio of phosphorus to protein was about 140. Amino acid analysis for the phosphorylated SPI suggested that the type of phosphate bound to the protein was ortho-phosphoric acid, and that the phosphorylated amino acid residues were lysine and histidine. The association of phosphate to SPI was stable for more than 2 weeks at pH>5.0. The functions of phosphorylated SPI were examined at various pH. The high solubility of phosphorylated SPI at pH >3.0 did not decrease the emulsifying ability and gel forming ability, even in the acidic range when compared with the neutral range, whereas the SPI lost most solubility and functionality at pH <5.5. There was no difference between the digestibility of phosphorylated SPI and SPI. These results suggested that phosphorylated SPI is a very useful food material possessing good functional properties throughout a wide pH range.

EXTRACTION OF BEANY ODOR COMPOUNDS FROM SOY PROTEIN SOLUTION OF VARIED IONIC STRENGTH WITH MIXED SOLVENTS

Seiichi HOMMA, Ko AIDA and Masao FUJIMAKI

Department of Nutrition and Food Science, Ochanomizu University

Nutr. Sci. Soy Protein, Jpn. 5, 18-21, 1984.

Fujipro R and soybean protein isolate freshly prepared from soybean meal were dissolved in pH 7 phosphate buffer of varied ionic strength (0.1, 0.01 and 0.001). These protein solutions were extracted with mixed solvent of ether-ethanol. The ether extract was subjected to GLC for the determination of n-hexanal and n-hexanol as the indexes of beany odor. Protein solubility was determined by the biuret method. Percentages of extracted n-hexanal and n-hexanol were 94% (É : 0.001) and ca. 100%, respectively, in the aqueous extracts freshly prepared from defatted soybean meal. Extracted n-hexanal was larger in the protein solution of small ionic strength, and there was no effect of ionic strength on the extraction of n-hexanol. The solubility of the treated soy protein was decreased to 88% (É : 0.001), and the larger the ionic strength is, the smaller the protein solubility is. n-Hexanal and n-hexanol in the soy protein isolate prepared decreased by 40% and 5%, respectively, compared with those in the aqueous extract. Extractable n-hexanal and n-hexanol in the soy protein isolate were 25% and 50%, respectively. Total n-hexanal and n-hexanol were decreased to 57% and 8% through dialysis with pH 7.6 phosphate buffer (É : 0.001). Extractable n-hexanal and n-hexanol in Fujipro R were 30% and 80%, respectively.

IMPROVEMENT OF FLAVOR IN COOKING OF SOY PROTEIN ISOLATE

Yoko TAKEI and Toshizo KIMURA

Department of Home Economics, Osaka Kyoiku University

Nutr. Sci. Soy Protein, Jpn. 5, 22-27, 1984.

Supplementation of soy protein to cereal proteins has been recognized to be effective to nutritional improvement of their protein quality, although soy protein has a peculiar odor. To investigate preferable utilization of soy protein in nutrition and cooking, taste of cookies, which were partially substituted SPI for wheat flour, was estimated by sensory evaluation, and removal of unpleasant odor from soybean products was studied. The cookie substituted SPI for 10% of wheat flour was more preferable than that substituted for more than 20% of wheat flour. The soy protein : wheat protein ratio in the preferable cookie was approximately 1:1, demonstrating definitely the supplementary effect of soy protein on wheat protein in animal experiments. An addition of phospholipids to defatted soybean was suggested to be effective for removal of the unpleasant odor during the isolation process of soy protein.

STRUCTURE AND NUTRITIONAL PROPERTY OF SOY PROTEIN WITH COVALENTLY SUPPLEMENTED METHIONINE

Soichi ARAI

Faculty of Agriculture, The University of Tokyo

Nutr. Sci. Soy Protein, Jpn. 5, 28-30, 1984.

L-Methionine was covalently attached to a soy protein isolate (SPI) by modification with papain under the conditions we reported previously [J Agric. Food Chem. (USA), 27, 52 (1979)Ån. The three kinds of enzymatically modified proteins, EMP4, EMP7, and EMP11 which attached methionine at 3.9%, 6.8% and 10.7% levels, respectively were obtained. Any of these products had a molecular weight of approximately 2,000Å`13,000 daltons, with a polymerized methionine sequence at the C-terminal. EMP11, for example, was found to have a methionine tetramer at the C-terminal. Feeding tests with rats demonstrated that the methionine tetramer attached covalently to EMP11 was as bioavailable as free methionine, whereas a synthesized methionine polymer with a degree of polymerization of 4Å`6, when formulated non-covalently in SPI, was less bioavailable. The significance of covalently attaching methionine to SPI is discussed from a food and nutritional point of view.

DIFFERENTIAL INDUCIBILITY OF THREONINE IMBALANCE OF L-METHIONINE AND OLIGO-L-METHIONINE SUPPLEMENTED TO A 8% CASEIN OR 10% SOY PROTEIN ISOLATE DIET IN RATS

Shuhachi KIRIYAMA, Takanori KASAI, Hideyuki CHIJI, Koichi HARAYAMA and Keiko NISHINO

Faculty of Agriculture, Hokkaido University

Nutr. Sci. Soy Protein, Jpn. 5, 31-37, 1984.

When a 8% casein basal diet was supplemented with free L-methionine (Met) at the levels of 0.02, 0.04, 0.06, 0.08, 0.1, 0.2, 0.3 and 0.6% of diet, body weight gain of weanling male rats of the Sprague-Dawley strain was increased with increasing levels of Met, showing a maximal supplementary effect at the 0.2% level. However, Met supplementation to the 8% casein diet consistently produced fatty liver. Liver fat began to accumulate when the Met level added reached 0.1% of diet, resulting in most severe fatty liver at the 0.2% Met level. On the other hand, supplementation of enzymatically synthesized oligo-L-methionine (a mixture of hexa- and hepta-peptides of Met as determined with FAB-MS, abbreviated as OM) to the 8% casein diet did not produce fatty liver due to "threonine imbalance" until the supplementary level was increased up to 0.2% of diet in one experiment and 0.3% of diet in other two experiments, although OM was as effective on body weight gain as free Met at all corresponding supplementary levels. Neither Met nor OM exerted consistent effect on plasma cholesterol concentration. The addition of 3% free Met to a low casein diet usually causes severe growth retardation. Nevertheless, toxicity due to 3% OM addition was very weak. When supplemented to a 10% SPI-based diet, Met significantly improved growth rate of weanling rats to the same extent as observed in the low casein diet. In contrast to the case of low casein diet, supplementary effect of OM was significantly smaller in the SPI diet than that of Met, although the addition of OM improved growth slightly, but significantly above the 0.2% level. OM-supplementation led to decreased plasma cholesterol levels. To improve nutritive value of food proteins, we tried to convert glycine residues in peptide chains to essential amino acids in situ. As preliminary experiments, salicylideneglycinatoaquocopper (II) (Sal-Gly-Cu) was heated with various alkyl halides (methyl iodide, isopropyl chloride, isopropyl bromide, isobutyl bromide, benzyl chloride, benzyl bromide, bromoacetic acid, and 2-chloroethyl methylsulfide) in DMF or DMSO in the presence of KOH or EtONa. Valine produced from Sal-Gly-Cu and isopropyl bromide, the yield becoming higher by EtONa than by KOH (1 to 2% of Gly). Leucine and phenylalanine were obtained from isobutyl bromide and benzyl chloride with yield of about 1%. The conversion into Met was not achieved from a reaction with 2-chloroethyl methyl sulfide. Generally, alkyl bromides seemed to be better reagents than chlorides.

SOLUBILITY OF CALCIUM AND IRON IN THE SMALL INTESTINAL CONTENTS OF RATS RECEIVING SOY PROTEIN ISOLATE AND THE RELATION TO THEIR ABSORPTION

Hiroshi NAITO, Ryuichiro SATO and Tadashi NOGUCHI

Faculty of Agriculture, The University of Tokyo

Nutr. Sci. Soy Protein, Jpn. 5, 38-42, 1984.

Solubility and absorption of Ca and Fe in the small intestinal contents of rats receiving a diet containing casein or soy protein isolate (SPI) were examined. These amounts were higher in casein group, which was exclusively located in distal small intestine. The absorption of 40Ca and 45Ca measured by a ligated ileal loop technique was also higher in casein group. These results were further confirmed by measuring 45Ca femur uptake as well as comparing between caseinphosphopeptide (CPP) and tryptic SPI peptides instead of respective proteins, suggesting that the observed superiority in Ca absorption of casein in essentially due to the luminal formation of CPP, and SPI had no effect. The situation of Fe in these problems seemed to be ambiguous. One-day balance test of 59Fe showed no significant difference between two groups, whereas there was much less amount of Fe in the luminal contents from SPI-fed rats.

GASTROINTESTINAL DIGESTION OF SOYBEAN PROTEIN (Part 1)

Kazuo IWAI and Tohru FUSHIKI

Faculty of Agriculture, Kyoto University

Nutr. Sci. Soy Protein, Jpn. 5, 43-47, 1984.

Digestion process of soy bean 11S globulin was studied. In order to clear the digestion process of the 11S globulin specifically, the disappearance of its native antigenicity was employed as an indication of denaturation and digestion. The prepared antiserum for soybean 11S globulin recognized the overall protein molecule and did not react with its each subunit. The antigenic determinants of soy bean 11S globulin were highly sensitive to conformational change in the protein molecule. None of the 11S globulin molecule which has some part of the antigenic determinants was detected by double immunodiffusion technique. The gel filtration of partially heat-denatured 11S globulin indicated that only intact 11S globulin has an antigenic activity. Thus, heat and acid denaturation destroyed the reactivities of all antigenic determinants of a 11S globulin at once. The experiments of protease digestion in vitro showed that native 11S globulin was hardly digested by pepsin at pH 2.7 and pancreatin 1 : 25. And once denatured soybean 11S globulin was rapidly digested by the proteases under the same conditions. These results suggested that the denaturation of native soybean 11S globulin was a rate-limiting step in overall digestion, and the disappearance of its antigen was a useful indication of the initial process of the digestion.

SELENOMETHIONINE IN SOYBEAN PROTEINS AND ITS INTESTINAL ABSORPTION

Kyoden YASUMOTO ¹, Tetsuya SUZUKI ¹ and Munehiro YOSHIDA ²

¹ Research Institute for Food Science, Kyoto University
² Department of Public Health, Kansai Medical University

Nutr. Sci. Soy Protein, Jpn. 5, 48-52, 1984.

Selenium contents of soybean flakes, protein concentrates, protein isolates, and protein subfractions were determined fluorometrically. On dry weight basis, selenium content exceeded the level of 0.5 É g per g protein in soybean flakes, whereas it ranged from 0.24 to 0.45 g per g protein in the protein concentrates and the protein isolates. Similar values were obtained for the selenium content of the subfractions of proteins extracted from soybean flakes with 0.03 M tris-HCl buffer of pH 8.0. Several lines of evidence suggested that selenium occurs in soybean proteins largely in the form of or in close association with selenomethionine. The intestinal absorption of selenomethionine, selenocystine and sodium selenite was examined by using ligated intestine of rats. Among the tested selenium compounds selenomethionine disappeared most rapidly from the intestinal loop. Presented experimental data are consistent with the notion that selenium in soybean proteins occurs largely, if not entirely, as selenomethionine, which is readily absorbable from the intestinal lumen and nutritionally effective in retaining glutathione peroxidase activity in rats.

CALCIUM UTILIZATION IN PREGNANT RATS FED SOY PROTEIN ISOLATE

Yoshiaki NIIYAMA and Sadaichi SAKAMOTO

Department of Nutrition, School of Medicine, The University of Tokushima

Nutr. Sci. Soy Protein, Jpn. 5, 53-58, 1984.

Effects of different sources in dietary protein and calcium on calcium utilization were investigated in pregnant rats by an apparent balance method. Pregnant rats of the SpragueDawley strain, weighing about 190g, were fed one of the four combinations of diets containing SPI or casein and crystalline CaCO3 or egg shell. Protein and calcium in diets were maintained at levels of 20% and 0.6%, respectively. All groups of pregnant rats showed gradual increases in their food consumption throughout pregnancy, except for terminal 2 or 3 days. Total food consumption during pregnancy was influenced only by the dietary proteins, not by sources of dietary calcium. However, food efficiency was affected by both factors. Efficiency of the diet containing SPI and egg shell was the lowest. There were no differences in calcium content of fetuses from four groups of dams. Regardless of dietary calcium sources, pregnant rats receiving casein diets retained about 700 mg of calcium during pregnancy with 36 to 38% of apparent absorption rates. On the other hand, absorption rate and retention in rats receiving SPI were influenced appreciably by the calcium source in diets. Rats receiving diets containing crystalline CaCO3 and egg shell retained about 500 mg and 800 mg of calcium, respectively, during pregnancy and calcium content in femur from the latter animals was high. Reasons why a combination of SPI and egg shell resulted in an increased calcium utilization are obscure, and have to be studied further.

EFFECT OF DIETARY PROTEIN ON VITAMIN E TRANSFER BETWEEN BLOOD AND TISSUES IN RATS

Kayo MOURI and Osamu IGARASHI

Institute of Environmental Science for Human Life, Ochanomizu University

Nutr. Sci. Soy Protein, Jpn. 5, 59-62, 1984.

This experiment was carried out to elucidate the influence of nutritional status of rats upon vitamin E transfer among serum, erythrocyte, liver, kidney, lung and muscle. To elucidate this relationship between vitamin E transfer and nutritional status, we investigated the effect of dietary protein. As to the effect of dietary protein, we observed the quantity and quality of proteins, such as the effect of milk casein and SPI. The following results were obtained. When the rats were fed at levels of 10 and 20% protein in diets for 6 weeks, the concentrations of Éø-tocopherol in serum and liver were not different each other. However, the concentrations of Éø-tocopherol in erythrocyte, kidney, lung and muscle were significantly decreased in rats fed 10% protein diet. The level of serum cholesterol in rats fed 10 and 20%milk casein diets was not different each other. The rats fed SPI showed lower concentration of Éø-tocopherol in serum, liver, erythrocyte, kidney, lung and muscle than the rats fed milk casein at the same level. The level of serum cholesterol in rats fed SPI was lower than the rats fed milk casein. Then, it may be concluded that both quantity and quality have an effect on vitamin E transfer.

CHANGES OF GLUTATHIONE CONTENT AND É¡- GLUTAMYL TRANSPEPTIDASE ACTIVITY OF LIVERS OF RATS FED ON ISOLATED SOY PROTEIN DIETS

Misako TANIGUCHI

Department of Food and Nutrition, Nakamura Gakuen College

Nutr. Sci. Soy Protein, Jpn. 5, 63-66, 1984.Å@

Weanling male rats (Wistar strain) were fed on the diet containing 10 or 20% SPI for 3 weeks, and glutathione content and É¡-glutamyl transpeptidase (É¡-GTP) activity of the livers were determined, comparing with those of control rats which were fed on the laboratory chow (Oriental CRF-1), respectively. Glutathione content of the livers of rats fed on 10% SPI diet decreased to about 40% of that of control rats, whereas that of kidney or blood plasma was not much changed by the diet. Supplement of cysteine or methionine to 10% SPI diet did not alter the glutathione content significantly, but the addition of methionine resulted in decrease of É¡-GTP activity which was remarkably increased by 10% SPI diet. Close similarities between the changes of É¡-GTP and alkaline phosphatase activities were shown among 10 and 20% SPI diet groups, except cysteine-supplemented diet group, in which É¡-GTP activity remained at the high level and alkaline phosphatase activity decreased significantly towards the control value. No change of the activity of either glutathione reductase or glutathione peroxidase was observed in 10 and 20% SPI diet groups.

THE EFFECTS OF SOY PROTEIN ON CELLULAR IMMUNOLOGIC RESPONSE

Yasuo KISHINO and Satoru MORIGUCHI

Department of Nutrition, School of Medicine, The University of Tokushima

Nutr. Sci. Soy Protein, Jpn. 5, 67-70, 1984.

We measured phagocytosis of opsonized sheep red blood cells (SRBC) by alveolar macrophages (AM) of rats fed diets containing 5 and 20% of soy protein and casein, respectively, for 3 weeks. After in vitro treatment with a macrophage-activating factor (MAF), such as lymphokines, AM from the 5 and 20% soybean protein groups showed a greater enhancement of phagocytic activity than AM from the casein group, which was not enhanced in 5% casein diet. When methionine was added to soy protein diet MAF showed a slight increase of phagocytic ability compared to that of soybean protein diet only. This observation suggests that soybean protein exerts the phagocytic action of alveolar macrophage in the presence of MAF, even when fed on 5% level of soybean protein.

SUPPLEMENTATION OF SULFUR AMINO ACIDS TO A DIET CONTAINING SOY PROTEIN ISOLATE ÅF EFFECTS ON CHOLESTEROL AND ASCORBIC ACID METABOLISM IN RATS FED A PCB CONTAINING DIET

Akira YOSHIDA and Hiroaki ODA

School of Agriculture, Nagoya University

Nutr. Sci. Soy Protein, Jpn. 5, 71-74, 1984.

Nutritional quality of food proteins is usually evaluated based on growth rate and nitrogen balance of animals. Activities of tissue enzymes, turnover rate of tissue components and some other criteria are also used sometimes. We previously reported the increase in urinary excretion of ascorbic acid and in serum level of cholesterol due to dietary xenobiotics such as PCB, DDT and others is greatly affected by dietary level, and quality of proteins. Generally, these metabolic responses due to dietary xenobiotics are more significant when animals were fed the better quality or higher level of dietary proteins. However, those metabolic responses were comparatively low when the animals were fed diets containing soy proteins. Sulfur-containing amino acids are the first limiting in soy protein, and the specific role of sulfur amino acids for the responses to the xenobiotic intake was suggested. In the present report, the effects of supplementation of methionine, cystine and inorganic sulfate on the changes in cholesterol and ascorbic acid metabolism in rats due to PCB feeding were investigated. Male young rats of the Wistar strain were used and the basal diet contained 10% of soy protein isolate as a sole protein source and adjusted the total sulfur content to be 0.3%. In case of methionine supplementation, rats showed the maximum growth rate when the diets contained 0.5% of total sulfur amino acids. However, the urinary excretion of ascorbic acid, and the serum level of cholesterol were significantly higher in rats fed the 0.8% of sulfur containing amino acid diet with 300 ppm PCB. Supplementation of cystine did not improve the growth rate of animals but the urinary excretion of ascorbic acid and serum cholesterol were significantly increased by supplementation with 0.2% of cystine. The addition of inorganic sulfate affected on neither growth rate nor the metabolic responses to the xenobiotic. These results confirmed the specific requirement of sulfur amino acids for the maximum responses to the xenobiotics over the maximum growth rate. Sulfate conjugation would not have any specific role for those metabolic responses to PCB. Biochemical mechanism of specific effect of sulfur amino acids is to be clarified.

HYPOCHOLESTEROLEMIC EFFECT OF SOY PROTEIN ISOLATE IN RATS (V)

Michihiro SUGANO, Kazunari TANAKA, Ikuo IKEDA and Katsumi IMAIZUMI

Kyushu University School of Agriculture

Nutr. Sci. Soy Protein, Jpn. 5, 75-78, 1984.

Considering the small intestine as an important synthetic site for lipoproteins, the effects of dietary protein sources on the intestinal synthesis in vitro of cholesterol and apoA-I and on the concentration of these components in the mesenteric lymph were studied in rats fed isolated soybean protein or casein. Soybean protein caused reduction of the apoA-I concentration in the lymph as well as the de novo synthesis of apoA-I in the small intestinal segment. The intestinal HMG-CoA reductase activity was high in animals fed soybean protein, whereas the lymph cholesterol level was comparable. The concentration of biliary cholesterol in rats fed soybean protein was significantly higher. These results indicate that the intestine together with the liver plays an important role in the hypocholesterolemic effect of soybean protein in relation to casein.

THE EFFECT OF NEW PROPLUS SA ON PLASMA AND LIPOPROTEIN LIPIDS

Haruo NAKAMURA ¹, Emiko MIYAZIMA ¹, Toshitsugu ISHIKAWA ², Norio TADA ² and Naoki SUZUKI ²

¹ National Defense Medical College
² Jikei University School of Medicine

Nutr. Sci. Soy Protein, Jpn. 5, 79-82, 1984.

Three grams of New Proplus SA was administered to 3 hypercholesterolemic and 3 normocholesterolemic subjects to investigate the efficacy of this fibre on plasma and lipoprotein lipids. In hypercholesterolemic subjects, mean plasma total cholesterol decreased from 257.7 mg/100 ml to 221.0 mg/100 ml (14.2%). This change was reflected by the reduction of LDL-cholesterol, however, HDL2- and HDL3-cholesterol were remained unchanged. In normocholesterolemic subjects, plasma and lipoprotein lipids did not change significantly. This fibre ingestion was confirmed to be useful for the control of hypercholesterolemia in clinical field.

INFLUENCE OF SOY PROTEIN ISOLATE ON GLUCOSE TOLERANCE IN MAN

Seiki NAMBU ¹, Masayuki MATSUSHITA ¹, Hideki KOH ₁, Shigeki FUJII ¹, Yasuko NISHIOHEDA ¹, Motoo TSUSHIMA ¹, Teruaki NARUKAWA ², Michio FURUSAWA ² and Tadao NAKANO ²

¹ Division of Atherosclerosis and Metabolism, Department of Internal Medicine, National Cardiovascular Center
² Division of Nutritional Education, National Cardiovascular Center

Nutr. Sci. Soy Protein, Jpn. 5, 83-87, 1984.

Seven male and one female hospitalized subjects (mean age 58 years, range 49-71 years), six with non-insulin dependent diabetes mellitus and two with normoglucose tolerance, were standardized on a diet (1000 kcal/day) for 5weeks preceding the soy protein isolate diet (SP diet). Then all subjects were given an isocaloric SP diet containing 23 g of soy protein isolate (37% of total protein content) for one week. Seventy-five g oral glucose tolerance test (OGTT) and arginine infusion test were carried out before and after the SP diet treatment. Three hundreds ml of 10% L-arginine were infused at a constant rate over 30 minutes. Before, during and 60 minutes after infusion, blood samples were drawn for determination of glucagon and C-peptide reaction (CPR). The results obtained were as follows : 1)áî Glucose during 180 minute OGTT was significantly increased by 10% after the SP diet (p<0.05). However, response of insulin (IRI) and CPR to glucose load, and ‡”IRI/‡”glucose ratio in OGTT were not significantly different before and after the SP diet.2) ‡”Glucagon/‡”C-peptide ratios both during arginine infusion and thereafter on the SP diet were significantly raised as compared with pre-diet(p<0.01). However, ‡”glucagon was not modified by the SP diet treatment. 3)Basal plasma glucagon levels were significantly decreased in the SP diet (p<0.05). These results suggest that impaired glucose tolerance by SP diet might be derived from the unbalance of ƒ¿-cell and ƒÀ-cell functions in islets stimulated by arginine.

EFFECT OF METHIONINE SUPPLEMENTATION TO SOY PROTEIN ISOLATE ON SHORT - TERM NITROGEN BALANCE IN ADULT MEN

Kyoichi KISHI, Midori MAEGAWA, Shigeru YAMAMOTO and Fujiko SHIZUKA

Department of Nutrition, School of Medicine, The University of Tokushima

Nutr. Sci. Soy Protein, Jpn. 5, 88-93, 1984.

Soybean protein has been believed to be deficient in sulfur-containing amino acids and the protein nutritional value is improved by the addition of methionine in the growing rat. In the present study effective level of methionine supplementation to soy protein isolate (SPI) was evaluated by a short-term nitrogen balance method at two levels of nitrogen intake in 12 healthy young men. There were two 11-day experimental diet periods allowing a 3-day free-choice, adequate diet period between them. Methionine was added to SPI during the second diet period. One period consisted of one protein-free day followed by a 10-day low protein diet period. The nitrogen intake levels of SPI (Fujipro R) were 60 and 90 mg N/kg/day and L-methionine was supplemented at 1.0 and 1.5% of SPI. Mean nitrogen balance was Å|17.9Å}5.1 mg N/kg/day (n=5) at 60 mg N/kg/day and was Å|19.4Å}5.6 mg N/kg/day (n=5) when 1.0% methionine was added, indicating no beneficial effect. When the intake of SPI nitrogen was increased to 90 mg N/kg/day, apparent nitrogen balance was nearly zero (+1.55Å}10.1 mg N/kg/day, n=7). But again we found no improvement in nitrogen balance by supplementing either 1.0 or 1.5% methionine. It was appeared that sulfur-containing amino acids of well-manufactured SPI were not limiting for adults in this short-term nitrogen balance study.

EFFECT OF SUPPLEMENTING METHIONINE TO SOY PROTEIN ISOLATE ON THE PROTEIN UTILIZATION IN MALE ADULT HUMANS

Tetsuzo TAKAHASHI and Tetsuo YAMADA

Institute of Health and Sports Sciences, University of Tsukuba

Nutr. Sci. Soy Protein, Jpn. 5, 94-98, 1984.

The effect of supplementing 1.0 or 1.5% of L-methionine to soy protein isolate on the protein utilization was examined by nitrogen balance method in five healthy young men. The nitrogen balance was improved by addition of methionine in four of the subjects, but one subject showed quite the opposite tendency. As to the effect of the amount of methionine supplemented, there was no significant difference between 1.0 and 1.5% in the improvement of nitrogen balance.

NUTRITIVE EFFECTS OF L - METHIONINE SUPPLEMENT TO THE SOY PROTEIN ISOLATE IN HUMAN BODY

Hideo KOISHI, Toyoko OKUDA and Hiroko MIYOSHI

Faculty of the Science of Living, Osaka City University

Nutr. Sci. Soy Protein, Jpn. 5, 99-103, 1984.

Nutritive effects of L-methionine supplement to the soy protein isolate (SPI) were examined on 5 male adult human subjects. The experimental diets were composed of following 3 diets, one-day protein free diet, three-day low protein habitual diet and seven-day low protein SPI diet containing 99 mg N/kg/day. The 3 kinds of diets were given without interruption (first experiment). Three days after the first experiment, the second experiment, in which the SPI diet was supplemented with L-methionine at a level of 1.0 or 1.5% of protein, was repeated. There were no significant differences between the SPI diet and SPI + Met diet on nitrogen balance, availability of food energy, blood protein status or plasma cholesterol concentration.

SUPPLEMENTARY EFFECT OF LIMITING AMINO ACID ON THE UTILIZATION OF SOY PROTEIN ISOLATE IN HUMAN ADULTS

Kayoko KANEKO and Goro KOIKE

Kagawa Nutrition College

Nutr. Sci. Soy Protein, Jpn. 5, 104-108, 1984

Supplementary effect of L-methionine on the utilization of SPI was evaluated in young women by the nitrogen balance method. Seven female students were given SPI in the first experimental period and SPI supplemented with 1% methionine in the second period immediately after a menstruation as the sole source of protein. After one day on protein-free diet, each subject received a low protein, conventional diet for five days, then the following five days a low protein, semisynthetic diet containing 0.5 g/kg/day of SPI or SPI supplemented with methionine in each experimental period, respectively. Energy intake was approximately maintenance level of 37.3+2.8 kcal/kg/day. Nitrogen balance was calculated from the intake, fecal N excretion and the mean of urinary N excretion of the last four experimental days when urinary N excretion achieved a constant level. Mean values of N balance in SPI period and methionine supplemented period were both negative, and there was no significant difference between two values. Blood analysis were carried out before and after SPI period and after methionine supplemented period. Urinary urea and ammonia excretions were measured throughout the experimental days. Blood and urine analyses were not affected by the methionine supplementation.

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