Scientific aspects of tofuyo, low-salt fermented tofu, has yet to be fully clarified. The present study describes chemical characteristics of tofuyo and roles of fungus Monascus in food production.
Fermentation of tofuyo is unique with respect to its soybean proteins, which undergo limited hydrolysis by proteinases in the presence of ethyl alcohol originating from awamori (distilled liquor).The main components forming the body of tofuyo consist of basic subunit of glycinin and other polypeptides (Mr. 55kDa, 11-15kDa). The soybean proteins were digested into peptides and amino acids during maturation. The amount of free glutamic acid and aspartic acid was greatly related to good taste (umami-taste) of the product. Some of the liberated peptides (IFL and WL) inhibited angiotensin I-converting enzyme activity that produces the vasopressor peptide. As WL was completely preserved after treatment with gastrointestinal proteases, it was expected to have an antihypertensive effect.
Homogeneous preparation of proteinase from Monascus was characterized as an aspartic enzyme, a “key enzyme” for ripening, chemical and physical properties, and formation of bioactive peptides of the product. Carboxypeptidases of this fungus were characterized as serine peptidases, which contribute to the release of amino acids from soybean proteins and their related peptides and to the removal of bitterness during hydrolysis of soybean proteins.
We established a production method of a new type of tofu using an alkaline serine proteinase with high soybean-milk-coagulating activity isolated from Bacillus pumilus TYO-67. We prepared a new fermented foodstuff using soybean protein isolates. This method has the potential benefit for improving nutrition and adding physiologically functional properties to soybean foods.

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The applicability of microwave to the drying and blanching of tomatoes was examined. The changes of the drying rate and surface color were first measured and compared between drying by hot air (50°C) or microwave at three radiation powers. The drying rates using a microwave were higher than that using hot air. Both a constant-rate drying period and a falling-rate drying period were observed for each microwave radiation power. Compared to hot air drying, microwave drying resulted in an increase in lightness which is a preferable quality of tomatoes. Next, the changes in temperature, nutrients and surface color were measured and compared between blanching by microwave or boiling water. Microwave blanching required less time, resulted in higher retention of nutrients (ascorbic acid and lycopene) and caused less change in color in comparison with boiling water blanching. These results suggest that a microwave could be applied to drying and blanching tomatoes.

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Mollusks including cephalopods are one significant cause for food allergy due to their major allergen, tropomyosin. To determine cephalopods in food products, we developed a sandwich enzyme-linked immunosorbent assay (ELISA) using a cephalopod tropomyosin-specific monoclonal antibody which was obtained using Japanese flying squid Todarodes pacificus tropomyosin as an immunogen. Our ELISA showed 96.4% reactivity (based on the reactivity to T. pacificus tropomyosin) to tropomyosin from octopus, but no substantial reactivity (<0.1%) to those from other mollusks (shellfish) and crustaceans. No positive ELISA results were obtained for any cephalopod-free foods. The repeatability coefficients of variation were <10% and the detection limit based on cephalopod standard protein was 0.24ppm, sensitivity that meets the requirements of the current food labeling system in Japan. These results showed that the sandwich ELISA is highly specific to cephalopod tropomyosins, and may be useful as a detection method for cephalopods in food products.

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Astaxanthin is a red carotenoid pigment mostly distributed among marine organisms. Due to the multifunctional physiological benefits through its potent antioxidant activity, many products are supplemented with astaxanthin in the current market place. Although the demands for quantitative verification of astaxanthin have rapidly increased, the existence of its esterified forms in the products sometimes hampers accurate determination. In this study, high performance liquid chromatography was applied to examine their versatile quantification after enzyme-hydrolysis of esterified astaxanthin from Haematococcus sp. The activity among nine enzymes was compared using the chloroform extract of Haematococcus sp. A cholesterol esterase from Pseudomonas fluorescens gave the maximum activity at the optimized reaction condition of 37°C for 120min. In the validation study, an astaxanthin ester solution was added to three health food products to obtain an average recovery with a range of 97-101% and the residual standard deviation of<2% in the concentration range of 1.7-800mg/100g sample. A repeatability test using health food tablets containing Haematococcus extract was repeated seven times to determine precision of the method, giving a residual standard deviation of<2%. These results suggest that the proposed method was useful for analyzing total astaxanthin content in food supplemented with esterified astaxanthin from Haematococcus sp.

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FT-IR/ATR spectra of cotyledon, endosperm, and seed coat from raw ripened black sesame were analyzed to directly detect constituents contained in the seed. Lipids, proteins, and carbohydrates were easily identified by this method. Spectra of cotyledon and endosperm showed a few characteristic strong bands at 3000 (νC-H), 1746 (νC=O), and 1163 (νC-O) cm⁻¹ corresponding to lipids and prominent bands at 1652 (amide I) and 1546 (amide II) cm^-1 corresponding to proteins. The frequency of these amide bands suggests that the proteins in the seed have random coil structures. In contrast, the spectra of the seed coat showed hardly any lipid or protein bands. The bands corresponding to calcium oxalate were also very weak. Bands corresponding to carbohydrates were observed in the region of 1200-950cm⁻¹ for all parts of the seed.

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Astringency can be removed from astringent persimmon (Diospyros kaki Thunb.) fruit by various methods, including ethanol vapor treatment and carbon dioxide gas treatment. However following the removal of astringency by conventional methods, astringency may recur upon heating the fruits. In the case of astringent persimmon, such a phenomenon obstructs its food processing. Therefore, we developed a new method for removal of astringency of ‘Aizumishirazu’ persimmon fruit by adding a minimum amount of collagen peptide to the fruit, followed by mixing at room temperature. With this treatment, the taste of the fruit was undamaged. We also confirmed the inhibition of astringency recurrence due to heating. This technique shows promise for preparing astringent persimmon for use in food processing.

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[in Japanese]

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