We investigated the structural and functional properties of polysaccharides that constitute the cell walls of plant foods (including dietary fiber). We established methods to determine the fine structure and quantity of xyloglucans (XGs) and compared the structures of XGs from commonly consumed vegetables, fruits, and grains. The results demonstrated that XGs had different structures depending on the type, variety, and ripeness of the products. Glucuronoarabinoxylan (GAX) isolated from the primary cell walls of grasses contained ferulic acid esterified to its arabinose side-chains. Oligosaccharides originating from XGs and GAXs were found to have physiological functions. Water-insoluble cell walls (dietary fiber) had molecular sieving properties and delayed the diffusion rate of glucose in vitro.

Moreover, we explored potential added value of local agricultural, forestry, and fishery products, including unused resources, by analyzing their components, mainly polysaccharides. The following are the major findings of our research. (a) We developed a method to brew vinegar from apple pomace. This method involved treatment of the material with commercial bacterial enzymes to generate health-promoting oligosaccharides that remained in the final product, unutilized by yeast or acetic acid bacteria. (b) Using purple-black rice bran containing antioxidant anthocyanin pigments, we developed processed food that could serve as a rich source of health-promoting oligosaccharides, in addition to having high polyphenol (anthocyanin) and GABA contents. (c) We determined seasonal changes in the amounts of nutrients and health-promoting ingredients in Ecklonia stolonifera growing off the coast of Oma town, Aomori Prefecture. (d) We characterized the structure of proteoglycan (PG) present in salmon nasal cartilage. For the mass production of inexpensive PG-containing dietary ingredients, we established methods to defat (with water) and powder salmon nasal cartilage and to extract its PG fraction with hot water. We confirmed the safety of the resulting PG-containing product, demonstrated its skin anti-aging effects after oral administration, and developed a food item from the hot-water extract.

We investigated the effects of γ-aminobutyric acid (GABA) on facial skin conditions in humans. A placebo-controlled, double-blind 8-week study of GABA (100 mg/day) was conducted on 36 women with dry skin, fatigue and sleep disorder. After 8 weeks, skin elasticity of the cheek was significantly higher in the GABA group than in the placebo group. Although improvement in sleep quality was observed in both groups, there was no significant difference between groups. These results suggest that ingestion of GABA increases skin elasticity.

An analytical method for the determination of O-methylated catechin in ‘benifuuki’ green tea (Camellia sinensis L.) was investigated and evaluated by an interlaboratory study. Epigallocatechin-3-O-(3-O-methyl) gallate (EGCG3"Me) was well separated within ten minutes by high performance liquid chromatography (HPLC). The detection limit (S/N=3) of EGCG3"Me in this method was 0.005% (w/w). Ten participating laboratories independently analyzed five test materials (five pairs of blind duplicates) in an interlaboratory study. The repeatability (RSD_r) and reproducibility (RSD_R) of the evaluated methods were 1.4∼2.0% and 1.6∼5.7%, respectively, in a concentration range from 1.1 to 1.9% (w/w). The HorRat values of the EGCG3"Me concentration were 0.39 to 1.4. The present study showed that this method has acceptable precision.

We evaluated the plasma cholesterol lowering effect of Reishi (Ganoderma lucidum) extracts. Reishi hot-water and ethanol extracts lowered plasma cholesterol and promoted fecal cholesterol excretion in rats fed a high cholesterol diet. We also assessed the influence of Reishi extracts on micellar solubility of cholesterol. Reishi hot-water and ethanol extracts both decreased micellar solubility of cholesterol, and the ethanol extract exhibited the greatest effect. These results suggest that Reishi extracts lower plasma cholesterol in part because of the decreased micellar solubility of cholesterol.

Persimmon (Diospyros kaki Thunb.) is a hexaploid (2n=6x=90) that originated in southern China through polyploidization from a diploid ancestor. The exact ancestor of persimmon has not been clarified yet though much research has been conducted to elucidate it. Recent studies showed that D. glandulosa and D. oleifera have a close relationship with the diploid ancestor. Many persimmon cultivars have been developed through the long history of cultivation. Based on the nature of loss of astringency of the fruit, persimmon cultivars are classified into four types. There are two non-astringent types, PVNA and PCNA, and the mechanism of astringency loss is different between them. Furthermore, Chinese PCNA cultivar (C-PCNA) was proven to have a different physiological nature from Japanese PCNA cultivars. Though the gene conferring the PCNA or C-PCNA trait has not been identified yet, the nature of astringency loss has been gradually elucidated at the molecular level.

Persimmon is well known to be a polyphenol-rich fruit. The polyphenol fraction (PPfr) was obtained from persimmon fruits using a novel method, and its effect on postprandial blood glucose levels in rats and humans was examined. PPfr contained 20% carbohydrate and 70% polyphenol which consisted of epicatechin : epicatechin gallate : epigallocatechin : epigallocatechin gallate at a ratio of 1 : 1 : 3 : 2. In vitro studies revealed that lowering effect of PPfr on blood glucose after carbohydrate ingestion was attributable to the inhibition of digestive enzymes, such as alpha-amylase and maltase, as well as the inhibition of glucose absorption through the digestive tract. Following the administration of 3 g PPfr to 10 healthy human volunteers with 150 kcal maltose, postprandial blood glucose was significantly lowered compared with placebo. These results suggest that PPfr from persimmon fruits was useful for blood glucose control and the primary prevention of diabetes.