Atsushi Okiyama

Bacterial cellulose IV. Application to processed foods

Abstract A new form of cellulose, bacterial cellulose (BC), features smooth texture and high water-holding capacity. These properties function positively in food systems: BC functions as a heat-stable suspending agent as well as a filler to reinforce the body of fragile food hydrogels, improved the quality of pasty foods by reducing their stickiness, could be applied to meat products as a fat substitute and to jam as a noncaloric bulking agent. These results show that BC will be widely applicable to processed foods to improve their quality.

Bacterial cellulose II. Processing of the gelatinous cellulose for food materials

Abstract Gelatinous cellulose prepared by fermentation with Acetobacter aceti AJ 12368 consisted of cellulose fibrils (0.9%), bound water (0.3%) and free water (98.8%). The cellulose network absorbed water weakly in capillaries of about 0.5–1.0 microns. When stressed the gel released its water and deformed without fracture. The gel by itself was too tough to bite, but it became edible through processing either with sugar alcohol or with alginate and calcium chloride. The textures resemble fruit, such as grapes and molluscs such as squids, respectively. The mechanism is the immobilization of the water of gelatinous cellulose by viscous or gel-forming material, and accordingly the gel becomes easy to cut off with the teeth. These results show that gelatinous cellulose with its fibrous texture can be a new material for salads, low-calorie desserts, fabricated foods etc.

Bacterial cellulose I. Two-stage fermentation process for cellulose production by Acetobacter aceti

Abstract Production of cellulose by Acetobacter aceti AJ12368 was optimized in a two-stage fermentation process. A cell growth stage in an air-lift fermenter (agitated culture) was followed by a cellulose formation stage in production incubators (static culture). The optimal moment of process change was at day 3 of agitated culture when the cell density and intracellular Adenosin triphosphate content peaked; at this time culture broth in the air-lift fermenter could be subdivided to feed four production incubators equipped with nine trays. Surface aeration was effective in producing food-use gelatinous cellulose which is homogeneous and low in syneresis. This process was more economical than the conventional fermentation procedure in the Nata industry.

Taste dimensions of monosodium glutamate (MSG) in a food system: role of glutamate in young American subjects

Freshly cooked chicken broth was prepared with several concentrations (0.06-0.32 M) of added NaCl. In the first study, subjects were presented with pairs of samples, each having the same concentration of NaCl (salt) but one of which contained 0.01 M monosodium glutamate (MSG). The subjects preferred the sample with added MSG when the salt levels were low to moderate. The next two studies were designed to determine the relative role of the added sodium and glutamate in MSG in enhancing palatability. In the second study, NaCl was added in amounts equivalent to the sodium in 0.01 M MSG to one of the two samples. Subjects preferred the one with more salt at the low salt level indicating that the added sodium played a role in enhancing palatability. In the last study, the concentration of sodium was held constant in the soups but the glutamate was varied by adding 0.01 M MSG to one sample and 0.01 M NaCl to the other. Subjects preferred the sample with added glutamate to the one without, at the moderate salt concentrations, demonstrating a role for glutamate alone in enhancing palatability. These studies, in sum, demonstrate that MSG increases palatability of salted soups and that both the sodium and the glutamate independently contribute to this enhancement.

Gustatory sensation of l- and d-amino acids in humans

Amino acids are known to elicit complex taste, but most human psychophysical studies on the taste of amino acids have focused on a single basic taste, such as umami (savory) taste, sweetness, or bitterness. In this study, we addressed the potential relationship between the structure and the taste properties of amino acids by measuring the human gustatory intensity and quality in response to aqueous solutions of proteogenic amino acids in comparison to d-enantiomers. Trained subjects tasted aqueous solution of each amino acid and evaluated the intensities of total taste and each basic taste using a category-ratio scale. Each basic taste of amino acids showed the dependency on its hydrophobicity, size, charge, functional groups on the side chain, and chirality of the alpha carbon. In addition, the overall taste of amino acid was found to be the combination of basic tastes according to the partial structure. For example, hydrophilic non-charged middle-sized amino acids elicited sweetness, and l-enantiomeric hydrophilic middle-sized structure was necessary for umami taste. For example, l-serine had mainly sweet and minor umami taste, and d-serine was sweet. We further applied Stevens’ psychophysical function to relate the total-taste intensity and the concentration, and found that the slope values depended on the major quality of taste (e.g., bitter large, sour small).

Bacterial cellulose III. Development of a new form of cellulose

Abstract A new form of cellulose, bacterial cellulose (BC), was developed by disintegrating gelatinous cellulose which was produced by Acetobacter aceti AJ12368. BC is wet (97% water) and paste-like, and comprised of flocks of microfibrils. It swells in water and disperses homogeneously at a level of ≥0.3%. The suspension is a thixotropic fluid, and also shows dilatant flow at a low shear rate. The viscosity of a BC suspension is low compared to common thickeners. As a filler, BC has the highest water-holding capacity among commercial cellulose products. BC is considered as a stabilizer with low viscosity and a low-calorie material as a fat substitute.

Acute Effect of Poly-γ-Glutamic Acid on Calcium Absorption in Post-Menopausal Women

Objective: Poly-γ-glutamic acid (PGA) increases calcium (Ca) solubility in vitro and in vivo, and is associated with reduced bone loss in post-menopausal Japanese women. This study is the first to examine the effect of PGA on Ca absorption in humans. Methods: A single-blind, randomized, crossover study with a 3–4 week wash-out was performed to determine the effect of PGA (80.6% glutamic acids) on Ca absorption measured by the double stable isotope method. Twenty-four healthy, non-smoking, postmenopausal women (mean age: 56.4 ± SE 0.9) were given 200 g of orange juice containing 200 mg Ca as Ca-44 enriched CaCO3, with or without 60 mg of PGA, after an overnight fast. The two tests were separated by 3–4 weeks. An intravenous injection of Ca-42 (CaCl2 solution) was given 30 min after consuming the drink and a complete urine collection carried out from 24–48 h post-dosing. Ca absorption was calculated from the Ca isotope ratios measured by thermal ionization quadrupole mass spectrometry (TIQMS). Results: Mean Ca absorption with PGA was significantly higher (P < 0.01) than without PGA, 39.1 (SE 1.6) % and 34.6 (SE 1.9) %, respectively. The effect of PGA on increasing Ca absorption was more marked in a sub-group of subjects whose baseline Ca absorption (without PGA) was lower than the population mean value. Conclusion: Postmenopausal women who received a single dose of PGA increased their intestinal Ca absorption particularly those individuals with lower basal absorptive capacity.