The main function of hydrocolloids in food systems is to control and modify texture via changes in physical and geometrical properties. Texture is important in terms of both food palatability and eating safety, and hydrocolloids play a dominant role in controlling food texture. Hydrocolloids are thus the base ingredients for the development of food products. Research activities on food hydrocolloids have increased recently in terms of texture modifiers for nursing-care foods and also dietary fiber with physiological effects for an aged society, where the number of people with mastication and swallowing difficulties as well as patients with lifestyle-related disease are increasing. The author has aimed to analyze the fundamental properties of various food polysaccharides in terms of colloidal science and to obtain practical knowledge regarding food applications. Target materials for studies on gelling polysaccharides include gellan gum, carrageenan, curdlan, and methylcellulose, while pectin from sugar beet, gum arabic, and soybean soluble polysaccharide are targeted for those on emulsifying polysaccharides. Polysaccharides that control the gelatinization and retrogradation behaviors of starch have also been investigated, including galactomannan, soybean soluble polysaccharide, and gum arabic. This article reviews a part of these studies.

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Since collagen-peptide (CP) is composed of peptide chains and fragments with different molecular weights, the rheological and thermal properties of CP must depend on not only amino acid composition but also molecular weight (M_w). Therefore, in the present study, we investigated the effects of the molecular weight of added CP on agar gels using four kinds of CP from porcine skin with M_w=1.1×10³, 1.9×10³, 5.4×103 and 1.0×10⁴ (CP1000, CP2000, CP5000 and CP10000, respectively). Measurement methods included gel permeation chromatography [GPC], dynamic viscoelastic measurement, rupture properties, syneresis, liquid chromatography mass spectrometry [LC/MS] and differential scanning calorimetry [DSC]. Results showed that for CP1000, rupture stress and Young's modulus increased slightly, and syneresis was inhibited at high density. Since the results of CP2000 differed from CP1000 for rupture properties, it was suggested that ingredients with higher molecular weight influenced rheological and thermal properties of agar gels. On the other hand, it was suggested that ingredients with low molecular weight influenced syneresis, since the results of CP2000 were similar to CP1000. Because the results for CP5000 and CP10000 significantly differed from those for CP1000 and CP2000, it was suggested that ingredients with higher molecular weight influenced agar gels and their ingredients hindered the cross-linking formation.

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The effect of oral administration of elastin peptide (hydrolysate of elastin from porcine aorta) on human skin elasticity was studied. First, five healthy volunteers were administered elastin peptide after fasting for 12h. A significant increase in total amino acid concentration in blood was observed. The composition of increased amino acids in blood was similar to the amino acid composition of the elastin peptide. In addition, the concentrations of peptide forms of hydroxyproline and arginine significantly increased in blood. These results suggest that a portion of the administered elastin peptide migrates into blood in peptide form. Second, thirty-nine middle-aged volunteers were divided into three groups and administered 0, 100, or 200mg/day of elastin peptide for 8 weeks. Significant increases in skin elasticity were observed in the 100and 200-mg groups after 8 weeks. Increase in skin elasticity of the 200-mg group was significantly higher than that in the 0-mg group. These results suggest that ingestion of elastin peptide increases skin elasticity.

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Diabetes mellitus is considered to be one of the main life style diseases. As one of the treatment methods for postprandial hyperglycemia in patients with diabetes, several α-glucosidase inhibitors that inhibit the absorption of glucose have been used clinically, with some mild and severe side effects. We prepared a Shiso (Perilla frutescens)-extract fraction containing a large quantity (>5% in weight) of the flavonoid rosmarinic acid. We studied the effects of this fraction in vitro and in vivo, in enzymological and physiological experiments, using rats with or without diabetes mellitus. Results indicated two different hypoglycemic activities, an α-glucosidase inhibitor and a glucose transport inhibitor, which are present at safe levels and which act at the level of the small intestine. This discovery will facilitate the use of Shiso-extract for the control of postprandial hyperglycemia in diabetes mellitus.

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Lutonarin was isolated from young barley (Hordeum vulgare L. var. nudum Hook) leaves. It has been suggested that lutonarin found in plants, especially in leaves, plays a role in removing reactive oxygen species⁶⁾. In this study, we examined the antioxidative effects of lutonarin and related flavones against the free radical DPPH and Fenton's reaction in vitro. The DPPH radical-scavenging activity was higher in the flavones with a catechol structure in the B-ring of the flavone compared to those in which the B-ring contained only a single hydroxyl molecule. Furthermore, the higher DPPH radical scavenging activity of saponarin compared to apigenin suggests that the 6-C-and/or 7-O-glucosyl moiety in saponarin stimulates its radical scavenging activity. In a comparison of lutonarin with luteolin, the inhibitory action against the oxidation of ethyl linoleate by Fenton's reaction appeared to be weakened by the 6-C-and/or 7-O-glucosyl moiety.

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The conversion of soy isoflavone glucosides to aglycones by intestinal bacteria is necessary for efficient absorption. In this study, 137 strains of lactic acid bacteria were isolated from 58 kinds of plant food materials, and the ability to ferment soymilk and convert soy isoflavone glucosides to aglycones were examined. Thirty-seven strains fully coagulated soymilk during the fermentation for 48 hours. Among them, 17 strains showed high conversion of isoflavone glucosides to aglycones, and many of them were from fruits and vegetables. Bacterial identification showed that conversion ability is related to the strain characteristics, not the species or genus of bacteria.

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Meyer lemon is considered a hybrid of lemon and mandarin. The characteristics of flavonoids and coumarins in Meyer lemon were examined by comparison with Eureka lemon and mandarins (Satsuma mandarin and navel orange). The contents of eriocitrin, hesperidin, and nobiletin in Meyer lemon were comparable to mandarins, while narirutin, 6,8-C-diglucosylapigenin, 6,8-C-diglucosyldiosmetin, and diosmin were comparable to Eureka lemon. Meyer lemon held an intermediate position between Eureka lemon and mandarins on a scatter diagram generated from principal component analysis. 5-Geranyloxy-7-methoxycoumarin, 8-geranyloxypsoralen, and 5-geranyloxypsoralen were detected only in Eureka lemon. 5,7-Dimethoxycoumarin was abundantly contained in green Meyer lemon.

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This study investigated γ-amino butyric acid (GABA) barley seeds for its potential uses such as in foodstuffs. A simple method was designed to produce “mochi” barley containing a high concentration of GABA. Scaled seeds of “mochi” barley (Hordeum vulgare) were soaked in a glutamic acid solution. After draining off the solution, the processed seeds were allowed to stand at room temperature overnight. During this process, glutamate decarboxylase in the mochi barley converted glutamic acid to GABA. For optimal conversion, seeds were scaled before soaking in a solution containing 0.3-1% glutamic acid at pH 4 to 8.

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[in Japanese]

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