In our series of studies aimed at improving food proteins by enzymatic hydrolysis and resynthesis (plastein reaction), we first isolated and identified a series of bitter peptides occurring in a peptic hydrolysate of soybean protein. We then applied the plastein reaction to the bitter hydrolysate and succeeded in debittering it. We also found that the papain-catalyzed resynthesis reaction permitted covalent incorporation of added amino acid esters. This led to improving the functional and nutritional properties of food proteins, giving rise to peptide surfactants with considerable oil-emulsifying capacity and modified peptides with balanced amino acid compositions. The products we then developed are exemplified by a low-phenylalanine, high-tyrosine peptide for patients with phenylketonuria. The products aiso include peptides with maximized branched-chain amino acids and minimized aromatic amino acids as well as those with an enriched glutamine content. Recently, we extended our studies to analysis of cereal allergens and the design of hypoallergenic foods. Our first success was the design of rice grains with removed allergenic prateins. The process for producing this kind of functional food was subsequently industrialized, and the product “Fine Rice” was approved as the first “food far specified health use” by the Japan Ministry of Health and Welfare. This was followed by the current study, aimed at producing a hypoallergenic wheat flour preparation by controlled enzymatic hydrolysis. In this study, we have determined a major epitope unit (Gln-Gln-Gln-Pro-Pro) of glutenin origin and also developed a haptenic peptide that may be usable as an antiallergenic factor for patients with wheat-associated atopic dermatitis. An important aspect of these studies is that we took special care not to jeopardize acceptability or palatability, which is one of the most important considerations when dealing with food.

View full abstract

We compared dietary minerals measured directly from food cooked following the therapeutic diet menu for patients with mild renal disease with those calculated from a food table, to estimate the loss of minerals due to cooking. The results obtained were as follows: 1) The percentage of the measured to the calculated values ranged from 62-67% for K and Fe, to 77-81% for Na, P, Mg and Mn, and 90% for Ca. The measured values for Zn and Cu were similar to the calculated values. 2) We also estimated the differences between the measured and calculated values for various cooking methods. More minerals were lost after boiling or soaking in water than following thin slicing or squeezing. The loss of K was largest among the minerals studied. In making therapeutic diets, such as a low K diet, selection of cooking methods to avoid mineral loss is important in addition to selection of low-K foods.

View full abstract

The nutritional effect of a milk protein hydrolysate (MPH) consisting of di-and tripeptides was compared with that of milk protein (MP) in Mann-Williamson (MW) rats which had been treated surgically to bypass bile and pancreatic secretions into the ileum. During 3 days, from the 3rd to the 5th day after the operation, the biological value and nitrogen balance in MW rats fed the MPH diet (MPH group) were significantly higher than those in rats fed the MP diet (MP group). The level of 3-methylhistidine and the ratio of 3-methylhistidine/creatinine in the urine of the MPH group were significantly lower than those in the MP group. Furthermore, serum protein, total protein and albumin levels in the MPH group were significantly higher than those in the MP group. These results indicate that MPH may be utilized more effectively than MP in the absence of bile and pancreatic juice in the small intestine.

View full abstract

α-Glucosidase inhibitory activity of D-xylose and the duration of its activity were examined in rats without restraint and under unanesthetized conditions using a portal cannulation method. The inhibitory effect of D-xylose on the digestion and absorption of sucrose was estimated from the suppression of the elevation of portal plasma glucose after administration of D-xylose and sucrose. The duration of the inhibitory effect of D-xylose was measured as the duration of suppression of the elevation of the portal glucose level in rats that received continuous intragastric infusion of sucrose. D-Xylose suppressed the elevation of portal glucose after administration of sucrose and suppressed it slightly after administration of maltose. The durations of the inhibitory effect of D-xylose were 25 min and 50 min in rats receiving 0.12g/ kg and 0.24g/kg D-xylose, respectively. This is the first animal model used for measuring the duration of the inhibitory effect of an α-glucosidase inhibitor without restraint and under unanesthetized conditions. This should be useful for basic studies of α-glucosidase inhibitor in rats.

View full abstract

The effects of oleic acid on the concentrations of plasma lipids with special reference to the rates of lipid secretion from the liver were investigated in male Wistar rats. In Exp. 1, rats weighing about 90g were fed a test diet containing 15% (wt%) corn, high-oleic sunflower, sunflower, higholeic safflower or safflower oil for 2 weeks, and the lipid concentrations in the plasma and liver were determined. The concentrations of total cholesterol and triacylglycerol in the plasma of rats fed the high-oleic sunflower oil and high-oleic safflower oil diets were higher than those of rats given the corn oil, sunflower oil and safflower oil diets. The concentration of liver total cholesterol was low in rats fed the high-oleic sunflower oil diet and high in rats given the safflower oil diet, compared with that in rats fed the corn oil diet. Liver triacylglycerol concentrations were not different among the dietary groups. In Exp. 2, the rates of lipid secretion from the liver after Triton WR-1339 injection were estimated in rats fed the corn oil or high-oleic safflower oil diet for 2 weeks. The secretion rates of cholesterol and triacylglycerol in rats fed the high-oleic safflower oil diet were not different from those of rats given the corn oil diet. These results suggest that the elevation of plasma lipid concentrations in rats fed the diet rich in oleic acid is not directly related to the rate of lipid secretion from the liver.

View full abstract

Several tannins such as (+) -catechin, (-) -epicatechin and penta-O-galloyl glucose (PGG) have been well characterized as antimutagens or anticarcinogens in previous studies. The present studies were carried out to examine the antimutagenic activities of a hydrolysable tannin, eugeniin, which is contained in certain crude drugs and has high antiviral activity. The antimutagenic activity was tested by the Ames method against the respective mutagenicity of Trp-P-1, Trp-P-2 and an activated form of Trp-P-2 (act. Trp-P-2), which were metabolized by S9 Mix, or 1-nitropyrene (1-NP) toward Salmonella typhimurium TA98. Addition of 65μg of eugeniin or 50 μg PGG into each plate caused a decrease of about 50% in the mutagenicity on Trp-P-1, respectively. Eugeniin also markedly suppressed the mutagenicity of Trp-P-1, Trp-P-2, act. Trp-P-2 or 1-NP. The antimutagenicity against act. Trp-P-2 and 1-NP was higher than that against Trp-p-1 or Trp-P-2 (+S9 Mix). Therefore, it was concluded that eugeniin reacted directly against each of the mutagens used, and strongly interfered with their mutagenic activities. These results suggest that the antimutagenic activity of eugeniin is essentially due to desmutagenicity.

View full abstract