The Soy Protein Research Committee(Japan)

CHANGES IN LIPIDS OF SOY PROTEIN ISOLATE DURING STORAGE

Masao FUJIMAKI and Seiichi HOMMA

Department of Nutrition and Food Science, Ochanomizu University

Nutr. Sci. Soy Protein, Jpn. 8, 5-8, 1987.

Soy products, defatted soy meal and soy protein isolate, were allowed to stand at 40Åé for 1 and 3 months under relative humidity (RH) 30 and 70%. Trace amounts of lipids in these soy products were extracted with 86% ethanol. The extracted lipids were applied on a silicic acid column, and then successively eluted with chloroform (simple lipid), acetone (glycolipid) and methanol (phospholipid). The amount of glycolipid fraction of soy protein isolate was almost similar to that of defatted soy meal. This fraction was analyzed by TLC on silica gel, and 7 spots were detected with alpha-naphthol reagent. The storage condition of RH 70% resulted in the increase of the amount of glycolipid fraction of the defatted soy meal. The amounts of glucose and galactose in this fraction were found to be slightly reduced compared to the control. It follows that the increased amount of this fraction was due to the oxidized products eluted in the glycolipid fraction and that glycolipid stored was rather stable against autooxidation. The phospholipid fraction was analyzed by TLC and detected with Dittmer's reagent. Four phospholipids, namely phosphatidyl-choline, phosphatidyl-ethanolamine, phosphatidyl-inositol and phosphatidic acid were found in both samples. Their amounts were large in phosphatidyl-choline. The amount of phospholipid fraction of defatted soy meal was reduced by storage at 70% RH. Distinct degradation was found in the phospholipids of defatted soy meal and soy protein isolate stored under 70% RH. The degradation of lipids was more remarkable in defatted soy meal than in soy protein isolate, and it is due to lipoxygenase which would catalyze the oxidation of lipids under high RH.

GENERATION OF GRASSY BEAN FLAVORS DURING PROCESSING OF SOYBEANS ÅFCONTRIBUTION OF HYDROPEROXIDE LYASE ACTIVITY TO N - HEXANAL FORMATION IN SOYBEAN

Teruyoshi MATOBA ¹,Hiroshi HIDAKA ²,Makoto KITO ²,Keisuke KITAMURA ³ and Norihiko KAIZUMA ³

¹ Department of Food Science and Nutrition, Nara Women 's University
² Research Institute for Food Science, Kyoto University
³ Department of Agriculture, Faculty of Agriculture, Iwate University

Nutr. Sci. Soy Protein, Jpn. 8, 9-11, 1987.

A hydroperoxide (HPO) lyase which catalyzes the specific cleavage of 13-L-hydroperoxy- cis-9, trans-11-octadecadienoic acid (13-L-c,t-HPO) to form n-hexanal was found in the homogenates of the soybeans such as Glycine max var. Suzuyutaka (normal type) and lipoxygenase (L) deficient mutant seeds (L-1 null, L-2 null, L-3 null). A carbonyl compound which was formed from 13-L-c,t-HPO and 13-DL-c,t-HPO by the enzyme was n-hexanal. The enzyme was specific to the L isomer of 13-c,t-HPO. 9-D-t,c-HPO was not available for the enzyme reaction. Km and Vmax values of the enzyme for 13-L-c,t-HPO were apparently similar among all the seeds. Apparent Vmax value of the homogenate from L-2 null seed for linoleic acid was considerably lower (1/3 Å` 1/4) than those in the other seeds. It is concluded that a rate-determining step of n-hexanal formation from linoleic acid in L-2 null seed is a step of 13-L-c,t-HPO formation by lipoxygenase.

STUDIES ON PRODUCTION OF TOFUYO USING SOY PROTEIN ISOLATEÅFPREPARATION OF SOY PROTEIN GEL

Masaaki YASUDA and Kyuichiro NAGAMATSU

College of Agriculture, University of the Ryukyus

Nutr. Sci. Soy Protein, Jpn. 8, 12-16, 1987.

Tofuyo is a unique fermented soybean food in Okinawa prefecture, Japan, and is made from tofu (soybean curd) with koji, salt, and awa-mori (distilled liquor). It was learned that the texture of tofu affects the quality of tofuyo. As preparation of tofu is complicated and it is difficult to make uniform quality of tofuyo, it is needed to establish a simple, new method in this food processing. We took notice of soy protein isolate (SPI) having gel-forming ability in order to cover the weakness in this processing. We first examined conditions in preparing soy protein gel (SP-Gel) and then, tried to use the gel instead of tofu itself for the tofuyo production. Optimum conditions for the quality of the SP-Gel were affected by chemical properties and quantities of coagulant, amount of moisture, and heating temperature and duration when the SP-Gel was prepared by deflating the mixture of the SPI, soybean oil, water and coagulant and by heating in the casing. Found were 68 to 70% of moisture, 1.38g of calcium sulfate for 100g of SPI, and 60 minutes heating at 80Åé as best condition for the SP-Gel preparation. The SP-Gel was characterized as follows; hardness: 20.3 Å~ 104 dyne/cm2, jelly strength: 17.5 Å~ 105 dyne/cm2, and texture: suitable elasticity and fine texture. However, the tofuyo prepared from the best gel above mentioned did not have smooth texture and was not good for taste. Therefore, it was found that good gel in physical properties was not necessarily suited for the tofuyo production of the best quality. The best quality of tofuyo was obtained with the SP-Gel which was prepared by increasing calcium sulfate up to 3.68g for 100g of SPI (hardness: 26.0 Å~ 104 dyne/cm2, jelly strength: 12.9 Å~ 105 dyne/cm2).

ANISOTROPIC FREEZE - TEXTURING OF FOOD PROTEINSÅF APPLICATION TO SOY PROTEIN

Soichi ARAI

Faculty of Agriculture, The University of Tokyo

Nutr. Sci. Soy Protein, Jpn. 8, 17-19, 1987.

We proposed a new process for freeze-texturing using Erwinia ananas cells as heterogeneous ice nuclei. The bacterial cells, when added to isotropic aqueous dispersions or hydrogels of proteins, converted the bulk water into directional ice crystals at a subzero temperature, not lower than -5Åé, with formation of anisotropically textured products. Aqueous dispersions of SPI and soybean curd were used as materials to be textured. These were each mixed with a small mass of the bacterial cells and slowly cooled to -5Åé in an air bath. The frozen materials were vacuum-dried before setting the resulting textures by steaming for 2 min at 1 atm, if necessary, forming flake-like textures. Slicing the textured products at right angles to the lamellas of the flakes gave fibrous products.

ATTEMPTS TO MICROENCAPSULATE POLYUNSATURATED FATTY ACID USING SOY PROTEIN AND OTHERS AS WALL MATERIALS

Fumio IBUKI, Mari NAKAMURA and Kimikazu IWAMI

Faculty of Agriculture, Kyoto Prefectural University

Nutr. Sci. Soy Protein, Jpn. 8, 20-24, 1987.

Various food proteins were examined for their antioxidant effects in powder model systems (40Åé, Aw=0.6Å`0.7). The peroxide value of gliadin-based samples was kept at a marginal level during a month of storage. Gliadin was not so much effective to antioxidation at low and middle Aws as at high Aw. SPI and SPT-5 also exhibited potent antioxidant effects, but their effects at high Aw were less than those at low and middle Aws. With respect to the 60% ethanol-extractable component of SPI, its antioxidant effects at different Aws had a resemblance to each other and were scarcely affected by dialysis before evaporation to dryness. This implies that the presence of active substances with low molecular weight is not necessarily involved in the function of SPI or its component as antioxidant. The effect of gliadin that was not so good as antioxidant at low Aw, was markedly improved by means of spray-drying. The same effect is expected to hold for SPI microcapsules, which were not only prepared by spray-drying but also by freeze-drying. Their availability is under investigation.

STUDY ON QUANTITATION OF HEAT DENATURED SOY PROTEINÅFDEVELOPMENT OF A NOVEL METHOD FOR QUANTITATION OF HEAT DENATURED SOY PROTEIN BY UTILIZING PEPTIDE FRAGMENT FROM SUBUNIT OF SOY 11S GLOBULIN AS ANTIGEN IN ENZYME LINKED IMMUNOSORBENT ASSAY

Kyoden YASUMOTO, Miki SUDO and Tetsuya SUZUKI
Research Institute for Food Science, Kyoto University

Nutr. Sci. Soy Protein, Jpn. 8, 25-30, 1987.

A high specificity and sensitivity of enzyme linked immunosorbent assay (ELISA) was availed to work out a quantitative procedure for heat denatured soy protein at microgram level. The procedure is based on the immunoreactivity of peptide fragment(s) to anti-11S globulin antibody. Anti-11S globulin antibody was raised in rabbits. The peptide fragment(s) which was reactive against rabbit anti-11S globulin antibody was prepared by a combination of ion exchange, gel permeation, and reversed-phase chromatographies subsequent to heat treatment and tryptic digestion of 11S globulin. An immunoreactive fraction thus obtained was used for calibration in ELISA. Food samples were autoclaved, digested with trypsin and then subjected to ELISA for quantitation of added soy protein. A quantitative difference was observed in immunoreactivity against anti-11S globulin antibody among soybean varieties. However, food proteins other than soy bean showed little, if any, immunoreactivity in present system. This novel method appears to be a useful technique in quantitating heat denatured soy protein in various processed foods.

BIOAVAILABILITY OF ZINC AFFECTED WITH SOYBEAN PROTEIN - PHYTATE

Hiroshi NAITO, Tadashi NOGUCHI, Syoko SHINODA and Akio TAKENAKA

Department of Agricultural Chemistry, Faculty of Agriculture, The University of Tokyo

Nutr. Sci. Soy Protein, Jpn. 8, 31-33, 1987.

The interaction of soybean protein and phytate on the bioavailability of zinc was investigated. Overnight-fasted rats were fed a diet containing phytate-free 20% SPI and 65Zn, and tissues uptake of radioactivities after 3 hr of dose was compared with those fed a diet containing 0.35% phytate. The presence of phytate depressed the absorption of zinc, irrespective of protein source (casein or SPI) and of state of phytate (intrinsically contained or addition of sodium phytate). On the other hand, solubility in the small intestinal tract of labeled zinc in rats fed SPI was not altered in the presence of phytate, whereas dietary casein added with phytate depressed the solubilization of zinc. These results suggest that zinc is not insolubilized with phytate in SPI, probably due to the formation of soluble protein-phytate-zinc complex, but the absorption of zinc is markedly inhibited with phytate unrelated to the luminal solubility of the metal. It was also confirmed that SPI per se did not affect the absorption of zinc, suggesting that the availability of zinc may be improved by removal of phytate in SPI.

CALCIUM AND ZINC 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. 8, 34-39, 1987.

Bioavailabilities of dietary calcium and zinc were examined using a balance method in pregnant rats fed one of diets containing 10 and 20% SPI with or without 0.3% methionine supplementation (named as l0SM, 20SM, 10S and 20S, respectively). Levels of dietary calcium and zinc were about 0.4% and 35 ppm, respectively. Results obtained were as follows: 1) Anorexia in the 10S group of rats in late pregnancy was improved by methionine supplementation. This resulted in the comparable nitrogen retention and fetal growth with those in 20S or 20SM group. 2) Bioavailabilities of calcium and zinc were higher in the 20S group than in the 10S group. Methionine supplementation to the 10S diet resulted in an increased utilization of dietary calcium or zinc, however, this was not a case in 20% SPI diet. 3) Total nitrogen retention during entire period of pregnancy correlated positively with total calcium retention, dependent on the dietary protein levels. However, total nitrogen retention related positively to total zinc retention, independent of protein levels in diets, indicating that both nutrients may be stored in same organs and tissues. 4) From the results of present and previous studies from our laboratory, we concluded that total amounts of calcium and zinc retention primarily generally depended on their amounts ingested.

EFFECTS OF HIGH SPI DIET ON CALCIUM METABOLISM

Kayoko KANEKO ¹ and Goro KOIKE ²

¹ Yokohama National University
² Kanagawa Nutrition College

Nutr. Sci. Soy Protein, Jpn. 8, 40-45, 1987.

After 5 days of basal diet period (protein intake 55 g/day), seven female students were given a high protein diet (100g protein/day) containing 340g meat (meat diet) or 105g SPI (SPI diet) for 9 days. Other six subjects were given a high protein diet containing meat or SPI added 160g apple (meat+apple diet and SPI+apple diet) for 9 days. Urine and feces of last 4 days of each experimental period were collected and urinary pH, titratable acid. Ca, P, S, K and ammonia excretion and fecal Ca, P, S excretion were measured. Dietary intakes of S-containing amino acids in basal diet, meat diet and SPI diet were 1.82g, 3.72g and 3.03g, respectively. Meat diet improved the absorption of Ca and increased urinary Ca excretion compared with those of basal diet period. In SPI diet period Ca absorption and urinary excretion of Ca were as much as those of basal diet period. Ca balances were -37Å}62 mg/day in meat diet period, -45Å}30mg/day in SPI diet period and -58Å}37mg/day in basal diet period. In meat+apple diet period fecal Ca excretion increased, Ca absorption decreased and urinary Ca excretion decreased to the level of basal diet period. Addition of apple to high SPI diet did not affect Ca absorption or urinary excretion of Ca.

EFFECTS OF EPA AND SPI ON PLASMA LIPIDS AND PLATELET FUNCTION IN SHRSP

Meng-Tsan CHIANG, Michio KOMAI and Shuichi KIMURA

Faculty of Agriculture, Tohoku University

Nutr. Sci. Soy Protein, Jpn. 8, 46-51, 1987.

Epidemiological studies suggest that high dietary intake of eicosapentaenoic acid (EPA), a precursor of the trienoic prostaglandins, is associated with low incidence and reduced extent of myocardial infarction. A highly concentrated EPA (78% of EPA, ethylester form), manufactured from sardine oil, was administered to SHRSP (stroke-prone spontaneously hypertensive rats) for 4 weeks. Casein or SPI (soy protein isolate) was used as protein source in the experimental diet. In the experiment using casein diet, significant decreases in blood pressure, triglyceride and cholesterol in plasma and platelet count in SHRSP were observed at 4 weeks after EPA treatment, but no significant difference was found in SPI diet. Also a similar effect of EPA on plasma lipid level and platelet aggregation was observed in Wistar-Kyoto (WKY). Platelet count in WKY was observed to be contrast to SHRSP after EPA treatment. WKY fed casein diet with EPA supplement had higher platelet count than those fed diet without EPA supplement. The reason for this contrast phenomenon is not clear. The supplement of methionine to SPI diet induced the lowering effect of EPA on the blood pressure, triglyceride, cholesterol, platelet count and platelet aggregation. Besides, the ratio of EPA to arachidonic acid in plasma was higher in rats fed methionine supplemented SPI diet than those fed the diet without methionine. These facts suggest that the amino acid profile is related to the effective utilization of EPA.

DIGESTIBILITY OF SOYBEAN PROTEIN AND BIOAVAILABILITY OF THE CONSTITUENT AMINO ACIDS

Kazuo IWAI and Masako HIGUCHI

Faculty of Agriculture, Kyoto University

Nutr. Sci. Soy Protein, Jpn. 8, 52-58, 1987.

Presence of antinutritional factors, such as trypsin inhibitor and lectin, and in vitro digestion of these factors in soybean and soybean protein isolates were examined. Hemagglutinating activity, which was strongly detected in raw soybean, was not detected in soybean protein isolates. Trypsin inhibitory activity was detected in several preparations of the soybean protein isolates, but the inhibitory activity was only approximately 10% of that present in the raw soybean. Purified soybean trypsin inhibitor was rapidly inactivated by pepsin. When soybean extract was digested with pepsin, inactivation of the trypsin inhibitory activity was much less than that observed in digestion of purified soybean trypsin inhibitor. Consequently, trypsin inhibitor in raw soybean was suggested not to be inactivated by passage through the stomach and thus affect the intestinal digestion of protein. Growth experiments with defatted soybean meal, autoclaved soybean meal and amino acid supplemented soybean meal were carried out at 10% protein level in growing rats. Raw soybean diet depressed the growth of rats, but autoclaved soybean diet improved body weight gains of the rat. The supplement of 0.3% L-methionine to the raw soybean meal resulted in significant increase in PER and NPU as compared with raw soybean diet; NPU was comparable to that obtained by autoclaved soybean diet but slightly lower than that from casein diet. Further improvement was observed by additional supplement of threonine and valine. NPU of the supplemented soybean diet was not statistically different from the value obtained by casein diet, thus suggesting that supplementation of methionine, threonine and valine to raw soybean improves the nutritional value of soybean protein.

DIFFERENTIAL EFFECTS OF OLIGO - L - METHIONINE SUPPLEMENTED TO VARIOUS DIETARY PROTEINS AND EXOCRINE PANCREATIC ENZYME SECRETION IN RATS

Shuhachi KIRIYAMA, Hideyuki CHIJI and Xiaohong YIN

Hokkaido University

Nutr. Sci. Soy Protein, Jpn. 8, 59-63, 1987.

When oligo-L-methionine (OM, a mixture of hexa- and hepta-peptides) was supplemented to an 8% casein- and a 10% soybean protein isolate (SPI) diets (8C and 10S), supplementary effect of OM was observed only in 8C diet. In order to clarify the cause of the differences, we compared the digestibility of OM by measuring the increments of Met concentration in the portal blood plasma 30 min after refeeding diets containing various protein sources with or without added OM to 30 hr-fasted rats. Dietary protein sources used here were rice powder, wheat gluten, defatted peanut powder, potato protein isolate and defatted-powder from tuna, salmon, scallop and cod meats. Also, the supplemental effect of 0.3% OM and 0.3% Met was studied on the Met-limited diets containing three proteins (6.2% cod, 8% potato and 7.5% gluten) in which each essential amino acid (EAA) content was equalized to the 8C diet by the addition of EAA except for Met. The supplementation of OM to a low cod protein diet did not improve the growth rate. When OM was supplemented to a low potato protein diet, the growth rate was significantly improved, but the weight gain was lower than that of rats fed the Met-supplemented diet. On the other hand, supplementation of OM to a low gluten diet significantly increased the growth rate, it being the same as that of rats fed the Met-supplemented diet. The different growth-promoting effect of OM supplemented to three diets roughly paralleled with the degree of increments of Met concentration in portal blood in rats refed diets containing various proteins with and without added 3% OM. From the present and previous results, we concluded that the digestibility of OM is dependent on the dietary protein source which changes exocrine pancreatic enzyme secretion.

EFFECT OF SOY PROTEIN ISOLATE ON PROTEINURIA IN ADULT RATS

Hidemichi EBISAWA, Tomoko OZEKI and Yoshiaki FUJITA

Nutrition Research Laboratory, Tokyo Metropolitan Institute of Gerontology

Nutr. Sci. Soy Protein, Jpn. 8, 64-69, 1987.

Effect of soy protein isolate on proteinuria in male adult rats was examined in relation to dietary protein levels and changes in free amino acids in serum and kidney. In experiment 1, animals were fed 8 g/day of 5, 10, 15, 40 and 60% protein diets containing lactalbumin (LA; control group) or soy protein isolate (SPI) for 8 weeks from 90 days of age. In experiment 2, two groups (proteinuria group) received 16 g/day of 20% protein diet containing LA or SPI and other two groups (normal group) 8 g/day of 40% protein diet instead of 20% protein diet for 6 months from 3 months of age, respectively Results showed that 1) under restricted dietary energy, urinary protein excretion increased with dietary protein levels, irrespective of dietary protein sources, but the increasing rate was lower in SPI group than LA group, 2) the appearance of proteinuria was related to significant increase in threonine, cystine, tyrosine and arginine in serum and methionine and histidine in kidney.

IMPROVEMENTS OF THE PROTEIN QUALITY OF SOYBEAN WHEY

Kyoichi KISHI ¹, Sachiko TERAI ¹, Fujiko SHIZUKA ¹,Yasuhiro KIDO ¹ and Goro INOUE ²

¹ Department of Nutrition School of Medicine, The University of Tokushima
² Koshien University

Nutr. Sci. Soy Protein, Jpn. 8, 70-75, 1987.

In the previous paper we reported that the digestibility of soybean whey protein (pH 4.5 supernatant of soybean meal) heated at 168Åé for two minutes was lower than that of soy protein isolate (SPI) in rats and human. In the present study we investigated the digestibility and the efficiencies of utilization of soybean whey protein (SWP) in mice in relation to the temperature and time of heating, water content of SWP, browning reaction, the activities of trypsin inhibitor (TI) and hemagglutinin (HA), dialysis treatment and amino acid supplementation. Mice fed untreated SWP lost weight and died at 3 to 7 days of feeding. TI activity and the digestibility of SWP were about 800 mg/g of crude protein and 50%, respectively. Heating of SWP destroyed TI and HA to the same extent as SPI and improved the digestibility but not as good as SPI. The inactivation of TI and the improvement in digestibility were less by dry heating than by moist heating. And browning reaction was more evident in dry heating. Proper heat treatment of SWP brought about better growth than SPI in mice. SWP caused hypertrophy of the pancreas, the small intestine and large intestine. Dialysis by ultrafiltration membrane (molecular weight cut-off; 14,000 and 50,000) had no effect on the digestibility of SWP.

EFFECTS OF SOYBEAN PROTEIN ON TRIGLYCERIDE SYNTHESIS AND DEGRADATION IN RAT LIVER

Nobuko IRITANI ¹, Akemi SUGA ¹, Hitomi FUKUDA ¹,Akihiko KATSURADA ¹ and Takehiko TANAKA ²

¹ Tezukayama Gakuin College
² Osaka University Medical School

Nutr. Sci. Soy Protein, Jpn. 8, 76-78, 1987.

Hepatic lipogenic enzyme induction and triglyceride level were markedly decreased by dietary soybean protein (Iritani, N. et al., 1986, J. Nutr., 116, 190Å`197). Rats fed a fat-free diet containing casein or soybean protein were intraperitoneally injected with tritiated water and time courses for the incorporation of tritiated water into triglycerides in liver and plasma were followed for 6 days. The incorporation plateau was reached in 1 day in the casein group and 2 days in the soybean group. The incorporation on plateau was about twice more in the casein group than in the soybean group. The incorporation was decreased 3 days after the injection and the decreasing rates were similar between the casein and soybean protein groups. The incorporation of Åm3HÅn palmitic acid into triglycerides was similar between the groups. Therefore, it is suggested that the triglyceride lowering effects by soybean protein are not due to triglyceride degradation but to triglyceride synthesis (ascribed to fatty acid synthesis).

EFFECT OF SOY PROTEIN ISOLATE ON SERUM APOPROTEIN IN MAN

Seiki NAMBU ¹, Masako WAKI ¹,Hideki KOH 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. 8, 79-82, 1987.

It is well-known that soy protein affects both plasma cholesterol and triglyceride levels. This study was conducted to clarify the mechanism of triglyceride lowering action of soy protein. Method: Six inpatients were divided into two groups according to plasma triglyceride level. Initially, patients with type IV hyperlipemia were given 1481 kcal/day and those with normolipemia were given 1860 kcal/day. Then, both groups were shifted to respective isocaloric diet containing 25 g of SPI for 2 weeks. Results: Serum triglyceride levels were significantly decreased with the increase in HDL-cholesterol in type IV patients. On the other hand, serum triglyceride levels were also decreased in patients with normolipemia, but decrease in HDL-cholesterol was slight. Though apo CII was decreased in five of six patients, apo CII/E ratio was increased by soy protein rich diet. As apo CII and E are the major apoproteins in VLDL, decrease in apo CII means that VLDL catabolism was improved by soyprotein diet. It was very important result to increase in apo CII/E ratio by soy protein diet. We concluded that one of the mechanisms of action of soy protein was to repair the remnant of VLDL in the liver.

CHARACTERISTIC EFFECT OF SOY PROTEIN ISOLATE ON CHOLESTEROL METABOLISM IN RATS

Akira YOSHIDA and Yoshifumi OKUMURA

School of Agriculture, Nagoya University

Nutr. Sci. Soy Protein, Jpn. 8, 83-88, 1987.

In previous report, we indicated that the serum level of cholesterol in rats fed a 15% soyprotein isolate (SPI) was significantly lower than that of rats fed a casein or rice protein diet. In the presence of 1% of cholesterol or 300 ppm of PCB in diet also showed the similar result. In the present study, we investigated the effect of dietary proteins on the excretion of bile acids and neutral steroids in feces and bile. The effects on the activity of HMG-CoA (the rate limiting enzyme of cholesterol synthesis) of liver microsomes were also examined. The excretion of fecal neutral and acidic steroids was significantly higher in rats fed SPI diet as compared with that of casein diet group. However, the fecal excretion of neutral and acidic steroids of rice protein diet group was also similarly higher as SPI diet group though the serum level of cholesterol in rats of rice protein diet group was significantly higher than that of SPI diet group. Similar results were obtained in the presence of dietary cholesterol (exogenous hypercholesterolemia) or PCB (endogenous hypercholesterolemia). These results suggest the importance of other factor(s) than the lowering absorption of cholesterol and bile acids by SPI. The HMG-CoA reductase activity of liver microsomes in rats fed either SPI or rice protein diet was significantly higher than that of casein diet group reflecting the lower absorption of cholesterol. When 300 ppm of PCB was added to the diet, liver microsomal HMG-CoA reductase activity was significantly induced in casein or rice protein diet group. However, in SPI diet group, this induction of HMG-CoA reductase activity was not observed. This would be a factor involved in the lowering mechanism of serum level of cholesterol in SPI diet group in the endogenous hypercholesterolemia.

EFFECTS OF SOY PROTEIN ON FECAL STEROL EXCRETIONS

Junko YAMASHITA, Miwako KAMIMURA and Shin-ichi HAYASHI

Department of Nutrition, The Jikei University School of Medicine

Nutr. Sci. Soy Protein, Jpn. 8, 89-92, 1987.

Effects of soy protein isolate (SPI) on plasma cholesterol level and fecal sterol excretions were studied in male ICR mice. Mice were fed various experimental diets for 3 weeks starting at 4 weeks of age and then subjected to the above determinations. A part of mice were treated with goldthioglucose, a hyperphagia- and obesity-inducing agent, before the feeding experiment. In goldthioglucose-treated mice, a good correlation was observed between body weight and plasma cholesterol level and both high-fat casein and high-fat SPI diets caused a marked hypercholesterolemia of the same degree. The latter results were confirmed in normal mice, too. The amount of fecal neutral sterol excretions (coprostanol plus cholesterol) were not increased by SPI compared with casein. These results were in marked contrast with previous results obtained in other experimental animals, such as rabbits and rats, although correlation between reduced fecal sterol excretion and hypercholesterolemia appears to exist in mice, too. A substantial hypocholesterolemic effect of SPI was observed, however, when mice were fed low-fat diets.

EFFECTS OF SOY PROTEIN ISOLATE ON FECAL STEROL EXCRETION AND PLASMA CHOLESTEROL IN YOUNG MEN

Toyoko OKUDA, Hiroko MIYOSHI, Yumiko YAMAMOTO, Toshie ASADA,
Mayumi UEDA, Natumi HAYAKAWA and Hideo KOISHI

Faculty of the Science of Living, Osaka City University

Nutr. Sci. Soy Protein, Jpn. 8, 93-97, 1987.

The effects of the substution of soy protein isolate for milk protein in diets on plasma cholesterol levels and fecal neutral sterol excretion, were examined on 5 healthy young men. The experimental diets contained 25% of energy as fat, 67% as carbohydrate and 8% as protein. The intakes of energy and protein were about 43 kcal/kg/day and 0.8 g/kg/day, respectively. The cholesterol intake was 23 mg/kg/day from egg yolk. The subjects were fed a milk diet and then a soy protein isolate (SPI) diet for 2 weeks each. There was a 6-day break period between both diets. In the milk diet, half of protein was composed of skim milk and in the SPI diet it was substituted with SPI. During the milk diet period, total and LDL-cholesterol and É¿-lipoprotein levels in plasma were significantly increased, but they were unchanged during the SPI diet period. The SPI diet, compared to the milk one, produced a significant increase in the fecal excretion of lipid, cholesterol and neutral sterol without any changes in fecal weight. These data suggest that the increased excretion of fecal neutral sterol may in part account for the hypocholesterolemic effect of soy protein.

EFFECT OF PLANT AND ANIMAL PROTEINS SUPPLEMENTED WITH METHIONINE ON PLASMA CHOLESTEROL LEVEL IN RATS

Keiichiro MURAMATSU, Kimio SUGIYAMA and Akio OHISHI

Faculty of Agriculture, Shizuoka University

Nutr. Sci. Soy Protein, Jpn. 8, 98-103, 1987.

The effect of methionine supplementation to high cholesterol diets containing one of casein, lactalbumin, SPI and wheat gluten at a 25% level on plasma and liver lipid levels and fecal steroid excretion was investigated in growing rats. The plasma cholesterol level was casein>SPI > lactalbumin ÅÜ wheat gluten in rats fed diets unsupplemented with methionine. Dietary addition of 0.8% methionine resulted in about 2-fold concentration of plasma cholesterol in rats fed casein and lactalbumin diets, whereas methionine addition rather decreased and did not affect plasma cholesterol level in rats fed SPI and wheat gluten diets, respectively. Although addition of 0.8% choline chloride also increased plasma cholesterol level of rats fed a casein diet, it did not affect plasma cholesterol level of rats fed a SPI diet. Addition of methionine to SPI diet significantly increased fecal excretion of bile acids. There was a correlation between fecal excretion of cholesterol and plasma cholesterol level, but there was also a significant correlation between cystine content of proteins and plasma cholesterol level. It is suggested that the differential response of dietary proteins to methionine addition is ascribed to different glycine content of proteins.

HYPOCHOLESTEROLEMIC EFFECT OF SOY PROTEIN ISOLATE IN RATS (VIII)ÅFEFFECT OF PROTEIN DIGESTS ON SERUM CHOLESTEROL

Michihiro SUGANO, Yukio YAMADA and Katsuko YOSHIDA

Kyushu University School of Agriculture

Nutr. Sci. Soy Protein, Jpn. 8, 104-107, 1987.

Soy protein isolate was digested in vitro successively by two microbial protease and the digest was separated by centrifugation into low molecular (soluble) and high molecular (insoluble) fractions. These fractions as well as total hydrolysate were fed to rats at the 20% level, either as a weight basis or a protein basis, of the cholesterol-enriched diet. The total hydrolysate was significantly hypocholesterolemic than the soluble fraction, although the efficacy was far less than that of intact protein. The hypocholesterolemic effect paralleled to the magnitude of fecal steroid excretion. The insoluble fraction exhibited a markedly greater hypocholesterolemic activity than the intact protein. The results suggest that the peptides produced during the gastrointestinal digestion are at least responsible for the cholesterollowering effect of soy protein.

The soy protein protein reserch(Japan)