Ikuo Ohara

Interaction of MSG taste with nutrition: Perspectives in consummatory behavior and digestion

Studies in the taste system of mammals indicate that monosodium glutamate (MSG) produces a unique taste sensation termed umami. As a derivative of glutamic acid, MSG is a naturally occurring nutrient in many foods; its commercial use to improve food palatability for humans is well documented. Behavioral studies with experimental animals have revealed that preference for MSG in solutions and selection of MSG-flavored diets can be explained by sensory means with no appreciable effects on preference by postingestive consequences. However, preference for umami-flavored fluids is reduced by feeding rats low-protein diets or low quality protein. MSG-flavored diets, initially unpreferred, were subsequently highly selected. However, the adulteration of diets by MSG either did not or only slightly increased food intake. In light of the significant contribution of MSG to diet taste, apparently as a signal coupled to dietary proteins, physiological studies have been initiated to reveal its role as a stimulator of the cephalic phase of pancreatic exocrine secretion. Modified sham-feeding experiments with dogs have shown that oral stimulation by MSG produced significant stimulation of both pancreatic flow and protein output in conscious dogs.

Elemental diets for liver diseases

ABSTRACT OF THE DISCLOSURE An elemental diet for therapy of liver diseases comprises amino acids, carbohydrates, fats, vitamins and minerals, and in particular contains at least isoleucine, leucine, valine, phenylalanine, tyrosine, tryptophan, theronine, glycine, serine and arginine, so that (a) the molar ratio of (isoleucine + leucine + valine + arginine)/ (phenylalanine + tyrosine + tryptophan) is 50 - 60; (b) the molar ratio of (isoleucine + leucine + valine + arginine)/ (glycine + serine + threonine) is 4 - 5; and (c) the molar ratio of arginine / (glycine + serine + threonine) is 0.8 - 1O

Effects of modified rice bran on serum lipids and taste preference in streptozotocin-induced diabetic rats.

The present study was designed to determine whether or not the administration of modified rice bran could improve streptozotocin (STZ)-induced diabetes. Taste preferences were also compared in diabetic and control rats. Male Sprague-Dawley rats were divided into control and diabetic groups. A single STZ injection, 65 mg per kg body mass i.p., induced diabetes. Rats were given free access to commercial diet and water for 2 months and modified rice bran (0.5 g per kg body mass) was administered daily by stomach tube. Two-bottle-choice preference tests between aqueous solutions of either 5 mM citric acid, 27 mM monosodium glutamate, 0.016 mM quinine, or 0.82 mM saccharin in deionized water were conducted in the experimental period. Blood was collected and serum levels of glucose, insulin, triglycerides, total cholesterol, HDL-cholesterol, urea nitrogen, total protein, albumin, and zinc were measured. Serum triglycerides and total cholesterol decreased with the administration of modified rice bran, although serum insulin and glucose remained low and high, respectively. Water intake was also reduced by the modified rice bran, which suggests that polyuria induced by STZ improved. Diabetic rats showed significant aversion to citric acid and quinine when compared with control rats. Modified rice bran can be useful as a dietary fiber supplement for the treatment of diabetes. In addition, high taste sensitivity for sourness and/or bitterness is a characteristic of STZ-induced diabetes.

Influence of zinc supplementation to diets at graded levels of protein on taste sensitivity, morphological changes of tongue epithelia and serum zinc concentration in growing rats.

OBJECTIVE We previously reported dietary protein was needed to maintain normal taste function and low serum zinc concentration led due to protein insufficiency [1], but generally zinc has been known to improve taste dysfunction. The present study was designed to determine whether zinc supplementation is effective in maintaining normal taste function at different levels of dietary protein. METHODS Sixty weanling rats were given free access to one of six diets: protein-free, 2.5% and 8% purified egg protein (PEP), and 10 ppm zinc supplementation at each protein level for 28 days. Preference tests between aqueous solution of 1, 2, 5 or 10 mmol/L NaCl vs. deionized water were conducted on days 14, 17, 20 and 23, respectively. Blood was collected for the measurements of serum zinc concentration, and the tongue of each rat was excised for observation by electron microscopic scanning. The number of fungiform papillae with normal taste pores and also the number of rats with abnormal morphological changes on tongue epithelia were recorded. RESULTS In basal diet groups, the rats fed 8% and 2.5% PEP diets discriminated 2 mmol/L NaCl liquid, while those fed the protein-free diet discriminated only the highest concentration of 10 mmol/L in this experiment. Serum zinc concentration and the ratio of fungiform papillae with normal taste pores increased with increasing dietary protein level. Abnormal morphological changes of tongue epithelia were observed in the protein-free diet group whether or not it contained additional zinc. No significant differences were observed between the basal and zinc supplemented diets at the other protein levels in the other parameters. CONCLUSION These results suggest that adequate dietary protein is more important in maintaining normal taste function and zinc supplementation did not improve taste function when dietary protein was suboptimal.

The effect of palatability and feeding conditions on digestive functions in rats

OBJECTIVE Information concerning various post prandial gastrointestinal functions modulated by taste stimulation is rather limited. Thus, effects of different types of palatability and feeding condition on digestive functions were studied. METHODS Male Sprague-Dawley rats were divided into two different feeding groups, meal feeding and ad libitum. In meal feeding, the daily feeding period was shortened gradually and was restricted eventually only 3 hours. In ad libitum feeding, food was freely available for 24 hours until experiment. After each rat in both feeding groups was fed 8.29 mM saccharin or 1.28 mM quinine flavored diet as a taste stimulant for 15 minutes, changes of gastric and intestinal nitrogen and pH and pancreatic amylase activities were compared with meal feeding vs ad libitum feeding. RESULTS In meal feeding, no difference was observed between before and after taste stimulation or between saccharin and quinine flavored diets on gastric and intestinal nitrogen contents, pH in the stomach and in the small intestine, and amylase activity. On the other hand, in ad libitum feeding, intestinal nitrogen contents tended to stagnate until 60 minutes after tasting quinine, although there was little difference between saccharin and quinine diets on gastric nitrogen contents. Gastric juice was hardly secreted before tasting (pH 6.2) and then pH in the stomach changed to become more acid following taste stimulation. Although amylase secreted in small intestine was hardly secreted before tasting, activities after tasting saccharin were increased immediately and lasted until 120 minutes. Amylase activity in rats fed the quinine diet, however, showed slower increase and faster recovery than that in rats fed the saccharin diet. CONCLUSIONS The results confirmed that various postingestive functions after taste stimulation depend on feeding conditions and it suggests that the ad libitum feeding condition is more appropriate than meal feeding on the experiment related to gustatory response.

The timing of protein feeding and dietary protein levels affect taste preference, serum zinc concentration and glossal epithelial morphology in growing rats

OBJECTIVE The present study investigated the effect of timing of protein feeding on taste preference, serum zinc concentration and morphological changes of tongue epithelia. METHODS Weanling rats were fed one of three diets: protein-free and 2.5 or 8% purified egg protein (PEP) diets for 14 days (first feeding period). Rats in each group were further subdivided into three dietary treatments, totaling nine groups and fed one of the same three diets for 14 days (second feeding period). Preference tests between 3 or 6 mmol/L NaCl vs. deionized water were conducted in both feeding periods. At the end of each period, blood and tongue were collected for the measurement of serum zinc concentrations and morphological observations. RESULTS The rats fed the protein-free diet in the first feeding period did not discriminate 3 mmol/L NaCl from deionized water in both feeding periods, even though adequate protein was administered in the second feeding period. The rats fed the 2.5 or 8% PEP diet in the first feeding period discriminated 3 mmol/L NaCl from deionized water regardless of the protein levels in the diet during the second feeding period. Serum zinc concentration was proportionate to protein content in the diet at the end of each feeding period (p < 0.001), and low serum zinc concentration was restored by protein feeding. Abnormal changes of tongue epithelia were observed only in the rats fed the protein-free diet throughout the two feeding periods. CONCLUSIONS The results suggest that protein nutrition immediately after weaning is important to maintain normal taste function.

Optimal protein level is required for normalization of taste sensitivity in rats

Abstract The influence of levels of dietary protein on taste sensitivity for sodium chloride and zinc status was studied in rats. Animals were given free access to one of seven graded levels of purified egg protein (PEP) diets for 28 days. Preference tests for the solution of sodium chloride (0.86 and 8.56 mmol/L) versus deionized water were conducted on days 19 and 21. Feces, urine and blood were collected for assay of zinc concentrations. Only the rats fed the 8% PEP diet discriminated low concentration of 0.86 mmol/L sodium chloride solution. The rats fed another diets discriminated only high concentration of 8.56 mmol/L sodium chloride solution. Twenty percent PEP diet-fed group did not discriminate both concentrations of sodium chloride. Zinc in serum concentration (r=0.89, p