The Soy Protein Research Committee(Japan)
QUALITY OF SOY PROTEIN ISOLATE AND THE EFFECT OF SULFUR AMINO ACID SUPPLEMENTATION ON THE PROTEIN UTILIZATION IN GROWING RATS
Goro INOUE, Kyoichi KISHI and Ikuko YAGI
Department of Nutrition, School of Medicine, The University of Tokushima
Nutr. Sci. Soy Protein, Jpn. 1, 6-9, 1980.
Soybean protein isolate has been known to be limiting in sulfur amino acids. Thus, the effect of supplementing isolated soy protein with L-methionine or L-cystine on body weight gain and protein utilization was investigated in growing rats.
Male rats of Wistar strain weighing about 100g were freely given 10% isolated soy protein diet (Fujipro R) with or without 0.05 (methionine only), 0.1, 0.2 and 0.3% L-methionine or L-cystine supplementation for three weeks. Control rats were received 10% lactalbumin diet.
PER, NPR and NPU (from carcass N) of soy protein and lactalbumin were 2.63, 3.56, 50 and 3.94, 4.80, 76, respectively. Supplementation of 0.05% methionine to the soy protein had no effect on food intake and weight gain. The addition of 0.1-0.3% methionine resulted in an increase in body weight gain similar to that obtained in lactalbumin. However, cystine supplementation to soy protein had adverse effects on food intake and body weight gain. The quality of soy protein was significantly improved by methionine supplementation in a dose-response manner approaching that of lactalbumin hut even at the highest level of methionine addition it was still lower than that of lactalbumin.
It was concluded that nutritive value of soy protein isolate was about 70% relative to that of lactalbumin and that the addition of 0.1% methionine was effective to bring body weight gain to that of lactalbumin.
LIMITING AMINO ACIDS OF SOY PROTEIN ISOLATE AND THEIR SUPPLEMENTARY EFFECTS
Michio YAMAGUCHI, Masako IWAYA and Motoyoshi MIYAZAKI
National Institute of Nutrition
Nutr. Sci. Soy Protein, Jpn. 1, 10-15, 1980.
This study dealt with nutritional evaluation of the soy protein isolate (SPI) "Fujipro R" with special regard to supplementary effects of its limiting amino acids for growing rats.
In the first experiment, the nutritive value of SPI was compared with those of whole egg protein and casein. The nutritive value was much inferior to those of the two reference proteins in spite of its high true digestibility, i.e. about 96%. The biological value of SPI was estimated to be about 60.
In the second experiment, the supplements of Met and Thr to SPI improved the body weight gain and protein efficiency ratio (PER) nearly upto the values of whole egg protein. But further improvement was not observed by additional supplement of Lys.
In the third experiment, the supplements of all essential amino acids to SPI did not increase the nutritive value any more. The nutritive values of SPI and the steam-heated SPI were almost identical to that of the steam-heated original soybean meal irrespective of the amino acid supplements. These results indicate that SPI contains no detectable trypsin inhibitor and it was prepared maintaining the nutritive value of the original soy protein.
Biochemical examination on several blood components, which was conducted in the three experiments, gave favourable results to the Met and Thr supplement group on the whole.
From these results it can be concluded that the limiting amino acids of SPI are mostly represented by Met and Thr, and the nutritive value is most highly qualified when its limiting amino acids are supplied by other food proteins.
SUPPLEMENTAL EFFECT OF SOY PROTEIN ISOLATE TO WHITE RICE
Tetsuzo TAKAHASHI
Institute of Health and Sport Science, The University of Tsukuba
Nutr. Sci. Soy Protein, Jpn. 1, 16-19, 1980.
Nitrogen balance measurements were made with five healthy young men, each of them consumed three different experimental diets for ten, eight and eight days in randomized order. The expenmental diets provided approximately 42 kcal/kg/day of energy and 80 mg/kg/day of nitrogen, although different in nitrogen sources. White rice, soy protein isolate or white rice supplemented with soy protein isolate with the ratio of 66% rice N and 34% soy N was used as the nitrogen source. As the results, no significant supplemental effect of soy protein isolate to white rice on the nitrogen balance was observed, due to the large individual variation.
EFFICIENCY OF UTILIZATION OF SOY PROTEIN ISOLATE IN PREGNANT RATS
Yoshiaki NIIYAMA and Sadaichi SAKAMOTO
Department of Nutrition, School of Medicine, The University of Tokushima
Nutr. Sci. Soy Protein, Jpn. 1, 20-23, 1980.
Pregnant rats of the Sprague-Dawley strain, weighing about 190 g, were fed 10% or 6% soy protein isolate (SPI) diet for 21 days. To calculate the BV, NPU or nitrogen balance index (NBI), nitrogen intake and nitrogen output in urine and feces during the period were determined. Endogenous and metabolic nitrogen were measured on pregnant rats receiving protein-free diet and ovarian steroids. On days 16 and 22 of pregnancy animals were autopsied and body nitrogen and free amino acids in plasma were determined.
Similar experiments were performed on the pregnant rats receiving whole egg protein (WEP) and both results were compared.
BVs of the SPI at the levels of 10% and 6% were 47 and 64 in pregnant rats and 42 and 56 in non-pregnant rats, respectively. These values correspond to approximately 65% to 70% of values for WEP. Utilization efficiencies of both proteins in pregnant animals were 10 to 15% higher than those in non-pregnant animals. Although the respective values were different, NPU and NBI of SPI in pregnant rats were about 30% lower than those of WEP.
Free essential amino acids except threonine in plasma from pregnant rats eating 6% SPI fell markedly, due mainly to reduced food intake in this group. However, plasma amino acid concentrations in rats fed 10% SPI were comparable to those in rats receiving WEP, indicating that qualitative deficit of the SPI did not reflect on the plasma aminogram.
HYPOCHOLESTEROLEMIC EFFECT OF SOY PROTEIN ISOLATE IN RATS
Michihiro SUGANO and Yasuo NAGATA
Laboratory of Nutrition Chemistry, Kyushu University
Nutr. Sci. Soy Protein, Jpn. 1, 24-30, 1980.
The effect of the soy protein isolate and casein, both given at the 20% level for 3 to 4 weeks, on serum cholesterol was compared in male rats. The effect of soy protein on serum cholesterol was easily modified by the type of diet. Soy protein exerted a hypocholesterolemic effect in a cholesterol-free low fat (1% corn oil) diet, when the lowering action appeared independent of the strain of the rat or the feeding pattern. Although the decrease in serum cholesterol appeared greater in Éø-lipoproteins than in É¿-lipoproteins, the proportion of the former to total cholesterol remained almost unchanged. The concentration of serum apo A-I was significantly lower in rats given the vegetable protein. Rats given soy protein excreted significantly more feces and fecal neutral sterols. The serum amino acid pattern did not reflect the difference in dietary protein. Addition of cholesterol to the diets modified the serum aminogram, the decrease in threonine being most marked in both protein groups.
EFFECT OF DIETARY SOYBEAN PROTEINS ON PLASMA CHOLESTEROL, URINARY ASCORBIC ACID AND LIVER MICROSOMAL MIXED FUNCTION OXIDASE SYSTEM IN RATS WITH OR WITHOUT RECEIVING PCB.
Akira YOSHIDA, Norihisa KATO and Takeshi TANI
Department of Agricultural Chemistry, Nagoya University
Nutr. Sci. Soy Protein, Jpn. 1, 31-35, 1980.
Exposure of rats to PCR or other xenobiotics results in an increase in activity of liver microsomal mixed function oxidase system, plasma cholesterol and urinary ascorbic acid. Experiments were designed to study the effect of dietary quality of protein on these metabolic responses to dietary addition of PCB, with special reference to nutritional characteristics of soybean and isolated soybean proteins.
The experimental diets contained whole egg protein, casein, fish protein, soy protein isolate, defatted soyflour, wheat gluten, corn gluten or gelatin, fed at 10% of the diet. In general, nutritional values of proteins correlated with the activity of mixed function oxidases, plasma level of cholesterol and the urinary ascorbic acid. However, in the aninials fed soy proteins, especially soy protein isolate, with PCB, mixed function oxidase activity, plasma level of cholesterol and urinary ascorbic acid were apparently lower than those expected from the nutritional values. Supplementation of methionine to the soy protein diets significantly elevated those values. These results indicate the nutritional specificity of soy proteins for the metabolic changes by the intake of the xenobiotics, and these characteristic features of soy proteins probably due to its relatively low content of sulfur amino acids. Sulfur amino acids may play a specific role in the metabolic responses to xenobiotics.
EFFECT OF SOY PROTEIN ISOLATE ON PLASMA LIPID CONCENTRATION IN RELATIVELY FATTY PMD PATIENTS
Yoshiaki NIIYAMA
Department of Nutrition, School of Medicine, The University of Tokushima
Nutr. Sci. Soy Protein, Jpn. 1, 36-38, 1980.
Four patients with progressive muscular dystrophy (PMD), who are relatively fatty, were supplied a diet containing about 65g of protein including abou 10g of soy protein isolate (SPI) for 40 days. They consumed daily about 1200 kcal and 53g of protein in which about 5g of SPI contained. Changes in TG, phospholipid and HDL-cholesterol in plasma during 40-day period were not observed, however, concentration of cholesterol tended to reduce and that of NEFA decreased markedly. Concentration of free amino acids in plasma did not change. Concentrations of TG, phospholipid, cholesterol and free amino acids, particularly essential amino acids, in plasma before receiving the SPI were low, suggesting that subjects were in malnourished state despite they look as fatty.
EVALUATION OF NUTRITIVE VALUE OF SOY PROTEIN ISOLATE USING HEPATIC ORNITHINE DECARBOXYLASE ACTIVITY AS A MARKER
Shin-ichi HAYASHI, Tamio NOGUCHI and Yasuko MURAKAMI
Department of Nutrition, Jikei University School of Medicine
Nutr. Sci. Soy Protein, Jpn. 1, 39-42, 1980.
We have previously shown that dietary induction of hepatic ornithine decarboxylase (ODC) depended not only on the quantity but also on the nutritive value of dietary protein. In the present study we attempted to evaluate nutritive value of soy protein isolate by ODC activity of liver and other tissues of the rat. Feeding 50% casein diet caused marked induction of ODC activity in liver, kidneys or skin in 5 hours while 50% zein diet had only negligible effect. Soy protein isolate produced ODC induction of intermediate degree in all the tissues. Relative growth rate obtained with 10% soy protein isolate was 77% of that with casein, while supplementation of 1 or 2% methionine to soy protein isolate improved the value to 95 or 108%, respectively. Methionine supplementation similarly improved hepatic xanthine oxidase level. When tested at 30% protein level, supplementation of 1% methionine slightly improved ODC level of three rat tissues. Unexpectedly, however, supplementation of 2% methionine significantly depressed the ODC levels. The reason for the discrepancy between these parameters remains to be elucidated.
EFFECT OF SOY PROTEIN ISOLATE ON LIPID METABOLISM
Kiyoshi ASHIDA
Department of Food Science, Sugiyama-Jogakuen University
Nutr. Sci. Soy Protein, Jpn. 1, 43-47, 1980.
Two experiments were conducted to clarify the effect of soybean protein isolate on the lipid metabolism in rats of various strains. In the first experiment, five weeks old male rats of the Wistar strain and the Charles River CD strain were fed 15% hydrogenated coconut oil diets containing casein or soy protein isolate with or without cholesterol for 10 days. Dietary cholesterol led to an increase in plasma cholesterol. Plasma cholesterol level was slightly higher with soybean protein isolate than with casein in rats of both strains regardless of the existence of cholesterol in the diets. Wistar rats tended to have greater amounts of carcass lipid than Charles River CD regardless of diet. Soybean protein isolate-fed rats tended to have greater carcass lipid than casein-fed rats. Soybean feeding resulted in an increase in liver lipid in CD rats, but no differences were observed in Wistar rats. In the second experiment, five weeks old male rats of the Fischer strain, the Donryu strain, the SHR strain, the Charles River strain and the Wistar strain were fed 15% hydrogenated coconut oil diets containing casein or soybean protein isolate and starch or sucrose for 10 days. The replacement of starch by sucrose caused an elevation in plasma cholesterol in all strains used. Plasma cholesterol level was higher with soybean protein isolate than with casein in Charles River CD rats, Wistar rats and SHR, but no difference in plasma cholesterol was found in Fischer rats and Donryn rats.
COMPARATIVE STUDIES ON THE GOITROGENIC ACTIVITIES OF DEFATTED SOYBEAN AND SOYBEAN PROTEIN ISOLATE
Shuichi KIMURA
Department of Food Chemistry, Faculty of Agriculture, Tohoku University
Nutr. Sci. Soy Protein, Jpn. 1, 48-50, 1980
Nowadays and in future, soybean must be an important foodstuff as the protein source and health foods, because it has been iccognized that the soybean protein has an adequate amino acid pattern and that this foodstuff reduced serum cholesterol level according to the recent reports.
However, soybean has also some defects which are due to trypsin inhibitors and goitrogenic substances.
In a previous study, we showed that soybean contained goitrogenic substances which affect the thyroid function and that some of those elements were sapogenols and isoflavonoides.
Present study is undertaken to examine the goitrogenic substances in soybean protein isolate as compared with defatted soybean.
An enlargement of the thyroid was observed in the rats fed on isolated soybean protein diet; the thyroid weighed about 26.7mg/100g body weight.
This value is higher than 21.4mg/100g body weight which is obtained from rats fed on control diet (iodine deficient diet). However, this is almost equal to that of defatted soybean.
It is considered easily that the iodine level of soybean protein isolate is decreasing in the same way as the goitrogenic substances. So, equal thyroid weight in rats fed on defatted soybean and soybean protein isolate does not always mean the same amounts for goitrogenic substances, because it was well known that the degree of enlargement of thyroid depends upon the level of iodine content of diet.
The assay experiments of goitrogenic substances are progressing now using the method of chromatography.