The effects of restraint stress on immune function were studied using diet-induced obese mice. C57BL/6J female mice 4 weeks of age were fed for 9 weeks on a control diet (control group) or a high-fat diet (obese group). Mice in each group were further divided into two groups: a stress (+) group that was subjected to restraint stress for 12h, and a stress (-) group that was subjected to only fasting. Mice in these four groups received intraperitoneal immunization with ovalbumin (OVA) immediately after restraint or fasting. The serum leptin concentration in the obese group was high, and was further increased by restraint stress. In both diet groups, the number of splenocytes and the lymphocytic proliferative response to LPS stimulation were decreased by stress loading. On the other hand, both IL-2 and IL-4 production in response to OVA stimulation were increased by restraint stress. A high-fat diet decreased the OVA-specific antibody titer and the value was lowest in the obese-stress (+) group. Thus, an antigen-specific immunoreaction can be changed by stress loading. Moreover, it is possible that leptin may have an influence on immune function in obese individuals subjected to stress.

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We obtained ACE inhibitory hydrolysis products from egg yolk protein by enzyme digestion. The egg yolk protein was digested with four types of proteases (Bioprase-SP-15FG, Denapsin, Denazyme AP, and papain; Nagase ChemteX). These hydrolysis products were assayed for their effect on ACE inhibitory activity in vitro. The hydrolysis product obtained by digestion with Bioprase-SP-15FG showed the most potent inhibitory activity (IC₅₀=33.2μg/mL) and had a strong hypotensive effect when administered orally to spontaneously hypertensive rats (1, 000mg/kg). One of the active products against ACE activity was purified by reverse-phase HPLC and identified as Ile-Tyr with an IC₅₀, value of 2.4μM (0.71μg/mL).

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We compared nutrient intakes estimated from the 4th revised edition of the Standard Tables of Food Composition in Japan (4th) with those estimated from the 5th revised edition (5th). The influence of revision of the Standard Tables of Food Composition revision on nutrient intake estimations was examined. Nutrient intakes were calculated from the 4th using data on food intake in a three-day dietary record in a community of 2, 110 men and women aged 40-82 years. Nutrient intakes were then recalculated using the 5th food code converted from the 4th food code. The nutrient intakes estimated by the 4th and the 5th were then compared. Mean differences (5th-4th) and mean percentage difference [{(5th-4th)/4th}×100] between nutrient intakes calculated from the 4th and the 5th ranged from -2.1mg (-16%; iron) to 1, 132μg (31%; carotene), and these differences were significant for all nutrient intakes except protein and retinol. Coefficients of correlation between the nutrient intakes estimated from the 4th and the 5th ranged from 0.934 (carotene) to 0.996 (energy and protein), which were highly significant. However, regression analysis showed a significant systematic error in the nutrient intakes estimated from the 4th and the 5th code.

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In contemporary society characterized by high stress and an aging population, nutritional neuroscience has become a highlighted field for maintenance of health and longevity. Humans are exposed to various kinds of stressors from birth to death, and these affect body metabolism, endocrine function, neuronal function, and the central nervous system and immune system. Brain metabolism and function are acutely regulated by nutrient availability in the diet, because many pathways of brain nutrient metabolism are controlled by precursor availability in the brain. Availability of nutrients to brain cells is influenced by the concentration of nutrients in plasma, and by the rate of nutrient transport through the blood-brain barrier (BBB). Brain function also affected by food components. We have been examining the effects of nutrition, stress, and certain types of diseases on brain amino acid metabolism, protein synthesis and certain forms of behavior such as appetite, sleep, mood, memory-learning ability, performance and motor activity. If treatments that modify central neurotransmission can produce changes in brain function and behavior, then there is every reason to anticipate that at least some nutrients-those that affect neurotransmitter synthesis-will also prove to be behaviorally active. The formation and release of a number of brain neurotransmitters-among them acetylcholine, serotonin and catecholamines-have been shown to depend on the brain levels of their precursor molecules (choline, and the amino acids tryptophan and tyrosine). This knowledge is related to fundamental studies aimed at maintenance of health, and is expected to lead to the development of new physiologically functional foods.

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The present study was performed to aquire data on factors affecting the palatability of meat, such as texture, taste and odor. A decrease in the structural rigidity of the actin-myosin complex, regarded as a cause of postmortem meat tenderization, was observed as an enhancement of the KCl concentration dependency and the maximum value of myofibrillar Mg-ATPase activity. The enhancement of both factors was ascribed to cooperative action of muscle cathepsins B, D, H and L, and irreversible adhesion of glyceraldehyde-3-phosphate dehydrogenase to myofibrils, respectively. We also developed new methods for preparing highly purified muscle cathepsins B, D and H. An unknown proteinase was isolated from muscle by the author and from liver by other researcher at almost the same time, and this was named cathepsin L on the basis of the high similarity between their respective properties. The postmortem increase in free amino acids that helps to improve the taste and odor of meat was found to be caused by a group of muscle neutral aminopeptidases. From these aminopeptidases, two new enzymes were isolated and named aminopeptidases C and H. Both enzymes readily hydrolyze oligopeptides larger than tetrapeptides cooperatively. The main factor responsible for the superior palatability of Japanese Black (Wagyu) cattle meat was found to be an odor named Wagyu beef aroma, which was generated by heating of the marbled meat conditioned in the presence of oxygen. The compounds responsible for the aroma were also demonstrated. Moreover, aroma was shown to be the most important sensory factor contributing to the individual palatability of meat from each animal species, the contribution of taste being much smaller.

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