Salt-induced gelation of partially heat-denatured whey protein isolate (WPI) solution and the rheological properties of the resultant gels were investigated. A 10% WPI solution, pH 7.0, was heated at 80°C for 30min, and then cooled to 5°C for obtaining the partially heat-denatured WPI solution. The solution was incubated at 20°C in the presence of salts such as NaCl and CaCl₂. During incubation, the solution turned to homogeneous gel with increasing viscosity. Gel strength was dependent on heating temperature of the WPI solution and salt concentration. Electron microscopy showed the presence of short-chained soluble aggregates in the partially heat-denatured WPI solution, and the gelation of the aggregates initiated by the addition of NaCl at 20°C. The network structure of salt-induced gel was to some extent coarser than that of acid-induced gel. It was indicated that the formation of the soluble aggregates by heating and the interaction between the soluble aggregates by salt were related to salt-induced gelation.

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Changes in hydrophobicity and SH content related to salt-induced gelation of partially heat-denatured whey protein isolate (WPI) at neutral pHs have been investigated. Soluble aggregates were formed when a 10% WPI solution was heated at 70°C or more for 10min. During heat treatment, the hydrophobicity of WPI solution increased considerably with increasing temperature while the SH content decreased. In the first stage of salt-induced gelling process, the hydrophobicity increased immediately after the addition of NaCl, while the SH content decreased gradually. Salt-induced gelation was strongly inhibited by the addition of N-ethylmaleimide to the WPI solution preliminarily heated at 80°C for 30min. Major forces for the formation of soluble aggregates and salt-induced gel network were indicated to be non-covalent bonds, such as hydrophobic interaction and intermolecular disulfide bonding. (Received Feb. 7, 1994)

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Cotyledon tissues of adzuki bean (Vigna angularis) were prepared by soaking cotyledons in water at 20°C for 22h and then cutting into about 1.5mm cubes. Heating the tissues up to 95°C in excess water resulted in nearly complete loss of birefringence of starches inside tissues. The heating, however, caused neither the softening of tissues nor the separation of cotyledon cells. These results indicated that the structure of tissues remained almost intact after heating up to 95°C. The gelatinization of starches inside tissues was studied by differential scanning calorimetry (DSC). DSC thermogram of tissues showed an endothermic transition with peak temperature at about 74°C which trailed a shoulder up to about 100°C. While the DSC curve of tissues was similar to that of cotyledon cells, the onset (To), peak (Tp) and conclusion (Tc) temperatures of endotherm were higher than those for cells by 2-4°C. The transition enthalpy (cal/g starch) obtained for the tissues was almost the same as those for isolated starches and starches inside cotyledon cells. To, Tp and Tc for ground beans were higher than those for isolated starches by about 2-3°C. The temperatures for isolated starches and cotyledon cells were shifted to higher temperatures by about 1-4°C by adding water extracts of adzuki beans. From these results, it was concluded that the gelatinization of tissues was suppressed compared with those of isolated starches and starches inside cells. It was assumed that the higher temperature transition for the tissues might reflect the gelatinization, melting of crystallites, of starches in limited supply of water. The suppression of gelatinization might be attributed to not only the physical strength of cell walls but also the structure of tissues and water-soluble substances.

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Effect various amino acids on the formation of 2, 3-dihydro-3, 5-dihydroxy-6-methyl-4 (H)-pyran-4-one (DDMP) and 5-hydroxymethylfurfural (HMF) have been investigated using a model system of cookie baking. A mixture of fructose and each amino acid was heated at 150°C for 10min in a test tube. Each reaction mixture was extracted with 1ml of water, and the extracts were analyzed by HPLC. DDMP was the major product in this reaction. The position of amino group affected on the formation of DDMP, and the amount of DDMP from fructose and β-amino acids was much more than that from fructose and other amino acids such as α- and γ-amino acids. The carbon chain length of α-amino acids also affected on the formation of DDMP, and DDMP was generated most remarkably in the reaction between fructose and α-alanine. When the carbon chain length was longer than that of α-alanine, DDMP formation decreased gradually. N-substituted arginine and lysine formed a large quantity of DDMP in the reaction with fructose than their N-unsubstituted amino acids. Basic amino acids reacted strongly and quickly with the sugar, and arginine also generated DDMP in the earlier stage of the reaction with fructose than β-alanine.

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Effects of thymus extracts on growth of mouse hybridoma and its production of monoclonal antibody (Mab) against human serum albumin were investigated. Water extracts of calf thymus were fractionated into high- and low-molecular weight fractions (HM and LM, respectively) by ultrafiltration through a Millipore membrane filter with nominal molecular weight limit of 5000. The Mab production was increased about 10 times by supplementation of serum-free basal medium with HM at a concentration equivalent to 0.5% calf thymus. The increases of Mab titers paralleled with those of cell counts. Trypsin-digested HM showed least capacities in promoting the hybridoma growth and its Mab production. DEAE-HM, a fraction made free of basic proteins from HM by DEAE-cellulose chromatography, showed capacities similar to those observed with HM. Electrophoretic analysis revealed that DEAE-HM was composed of a number of proteinaceous components with molecular sizes of 25 to 30 kDa and pIs ranging from neutral to acid.

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Four kinds of tropical starches, i.e., edible canna, arrowroot, cassava and sago were used to study the molecular structure of amylopectins. Potato and corn amylopectins were used as controls. The changes in the weight average molecular weight M_W, radius of gyration R_G which is a function of the molecular size and intrinsic viscocity [η] were determined to establish differences in the debranching reaction induced by isoamylase. The weight average molecular weight M_W and radius of gyration R_G were monitored by the light scattering method. It was shown that R_G per M_W was different among six kinds of amylopectins as a function of decreasing M_W (10⁸-10⁷), i.e., cassava and corn were the highest, potato, edible canna, and arrowroot were intermediate and sago was the smallest. An addition, the velocity of the isoamylase α-1·6 debranching reaction varied a little among the six kinds of amylopectins. However, the decreasing ratio of R_G: M_W was almost similar for six kinds of amylopections from observation of almost identical slopes in a log-log plot of R_G vs M_W. As the debranching reaction proceeded, the plots became non-linear and showed individual specificities. Accordingly, it was postulated that the debranching mechanism was the same in relation to M_W and R_G among all six amylopectins.

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Tofuyo is a unique fermented soybean food in Okinawa Prefecture, Japan. In this study, evaluation of tofuyo prepared by red koji which grew genus Monascus on steamed rice, and/or yellow koji which grew Aspergillus oryzae on it, was investigated. The product obtained by using the combination of red and yellow kojis was preferred rather than that one used individually. The most desirable product was obtained by the mixed koji composed of 25% of red koji and 75% of yellow koji. Furthermore, chemical and physical changes of the tofuyo during fermentation were also investigated. Crude protein content decreased during a ripening period. Digestion of soybean protein during fermentation was examined by slab polyacrylamide gel electrophoresis. Some polypeptide bands of soybean globulin such as α'-, α-, and β-subunits in β-conglycinin, and acidic subunit in glycinin in the water-insoluble fraction of tofuyo disappeared after 3 month ripening, but that of basic subunit in glycinin still remained. The main components which formed the body of tofuyo consisted of basic subunit in glycinin and other polypeptides (Mr. 40-32, 15-10, and smaller than 10kDa). The ratio of water-soluble nitrogen, 4%-trichloroacetic acid-soluble nitrogen or 75% ethyl alcohol-soluble nitrogen to the total nitrogen reached to 39.0, 36.8 or 23.9% after 3 month ripening, respectively. Hardness and cohesiveness of the product decreased during a ripening period.

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Sterilization methods for a reverse osmosis (RO) equipment were investigated from the standpoint of heat resistance of microorganisms and that of membrane used for concentration of tomatojuice. The heat resistance of microorganisms was 15 seconds of D₆₀ value and 6.6°C of Z value. The permeation flux and the salt rejection of membrane did not change after hot water (≤60°C) treatment. However, the permeation flux decreased about 30% and the salt rejection increased about 8% during 20min in hot water (80°C) treatment, because of heat shrinkage and compaction of membrane. The effects of hot water (80°C) treatment and a sterilizer on the sterilization of RO membrane were evaluated in a commercial scale RO process. In consequence, the number of microorganisms in RO concentrate was 1010²cells/ml at the start of concentration in the case of sterilizer and 10⁰cells/ml in the case of hot water (80°C). And also, the time to reach the number of microorganisms up to 10⁵cells/ml, which causes deterioration odor, was 12h in the case of sterilizer and 36h in the case of hot water. It was suggested that the hot water treatment is applicable sufficiently for the sterilization of RO membrane in the commercial scale RO process.

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Vacuum cooking was compared with ordinary cooking in some dishes. Decrease of the total ascorbic acid content in some vegetables during vacuum cooking was slower than that during boiled cooking. The green color of kiwi fruit sauce was maintained. The weight loss, hardness, springness, gumminess and chewiness in cooked chicken and pork by vacuum cooking were lower than those by ordinary cooking. Sensory evaluation scores of takikomigohan, which is rice cooked with some other materials and tasted by soy sauce, and saba-nituke, which is boiled mackerel with soy sauce, cooked by vacuum cooking were lower than those by ordinary cooking. On the other hand, such scores of nikujyaga, which is boiled potato and meat with soy sauce, and fruit compote cooked by vacuum cooking were higher than those by ordinary cooking. From these results, it was concluded that the well boiled and soaked type dishes were suitable for vacuum cooking.

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Commercially available processed meat products are generally pasteurized under more excessive conditions (70°C for 30min) than those required by the Japan Food Sanitation Law which demands pasteurization by keeping the core part of meat at 63°C for 30min. However, pasteurization at higher temperature inevitably leads to reduction of the sensory and nutritional quality as meat products. The present study was undertaken to look for alternative pasteurization conditions below 63°C which could secure food safety and minimize demotion of food quality. Microbial population and microflora in a mimetic pork sausage pasteurized at 55°C for various periods were examined. Micrococcus sp. of Z=6.9°C indicating thermotolerant bacteria and Streptococcus sp. of Z=6.3°C were found to be the dominant species in the mimetic. sausage. Pasteurization conditions required to decrease the initial microbial populations of Micrococcus sp. by 1/10000 were at 55°C for 304min or at 60°C for 92min. Pasteurization at 55°C for 304min gave the best results showing sufficient pasteurization effect without any reduction of sensory quality, and improved the sensory quality compared with the conventional pasteurization.

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The effects of non-dialyzable extracts of several vegetables such as eggplant, green pepper, cabbage, Garland chrysanthemum, kidney beans, cucumber and Welsh onion on the differentiation of U-937 human myeloid leukemia cells were examined. Among the vegetables, the extract of eggplant induced the adhesion of U-937 cells on the culture plate and the morphological change of U-937 cells. A few adhesive and elongated cells was detected in the presence of Garland chrysanthemum. The extracts of cucumber and kidney bean induced only the morphological change of U-937 cells. The evident expression of cell surface antigens of CD11b and CD36 of U-937 cells, which is a marker of differentiation of U-937 cells into monocytes/macrophages, was induced by the extracts of eggplant, kidney bean, cucumber and Welsh onion. These results suggested that the factors which induce the differentiation of U-937 cells into monocytes/macrophages may exist in the non-dialyzable extracts of these vegetables.

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