Polyphenol oxidase (PPO) shows two different enzyme activities in vitro. One is oxidase activity and the other is hydroxylase activity. PPO oxidizes various o-diphenols to o-quinones in the absence of an electron donor, while it hydroxylates various monophenols to diphenols in the presence of an electron donor such as L-ascorbic acid. This paper deals with hydroxylation of monophenols by PPO (tyrosinase from mushroom and mung bean, Vigna mungo) in a special reference to electron donor requirement. The enzyme and the substrates (monophenols) were incubated in an assay mixture either without or with an electron donor at 30°C for various times (until 10min.). After incubation, the reaction was stopped by adding HCl, and then the reaction mixture was subjected to HPLC. The amount of hydroxylated substrate was determined by the decrease of substrate on the chromatograms. PPO required an electron donor for hydroxylation of p-coumaric acid but not for hydroxylation of L-tyrosine. Hydroxylation of L-tyrosine was not stimulated by the addition of the electron donors tested. These results suggested that the amino group in L-tyrosine may function as an electron donor. This assumption was supported by the following two experimental results. First, hydroxylation of p-coumaric acid was stimulated by addition of amino group-containing compounds. Secondly, p-hydroxyphenylpyruvic acid which has a structure of amino group-eliminated L-tyrosine, behaved as p-coumaric acid in hydroxylation by tyrosinase.

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The oxidized tapioca starch, which was prepared by oxidizing with sodium hypochlorite at pH 10, exhibited the emulsificating ability. The mixture of the oxidized starch and sugar esters or casein also had a similar emulsificating ability. The addition of electrolytes such as salt or base, except acid, did not affect the ability. The ability depended on the degree of oxidization of starch concentration. The emulsificating ability was not considered to come from the high viscosity of the starch solution but to come from the electrostatic repulsion of carboxy groups formed on the oxidized starch chains.

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This study was undertaken to elucidate the biological properties and chemical structure of anthocyanins in the colored tuber flesh of potatoes that were derived from the cultivated diploids of Solanum phureja. These results may lead to a higher yield of functional pigments in potato breeding. The relative content of anthocyanin per one gram of fresh weight was determined by spectrophotometer at each maximal wavelength in Mcllvaine buffer (pH 3.0) after extraction by methanol containing 1% trifluoroacetic acid. The relative content in tubers declined with enlargement of tuber during a growth stage. The coefficients of variation of the relative contents in each plant ranged from 40 to 58%. However, there was no difference among plants in the average content of anthocyanins. The major anthocyanins from the red and the purple tubers were isolated and purified by column chromatography and TLC. The main anthocyanins in red and purple tuber were identified as 3-O-(6-O-[4-O-[(E)-p-coumaroyl]-α-L-rhamnopyranosyl]-β-D-glucopyranosyl)-5-O-(β-D-glucopyranosyl) pelargonidin and petunidin by proton NMR, FAB-MS and HPLC, respectively.

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It is known that the physical properties of whip cream vary with homogenization. However few investigators have referred to whipping properties. The effects of homogenization on the physical properties of imitation whip cream were investigated in this study. The whip cream consisted of 40% vegetable fat, 4% skim milk powder, 0.8% emulsifiers, 0.1% phosphate, and was homogenized at 0, 2, 5, 10, 20, 30 and 50MPa using a 3-piston 200l/h flat-valve homogenizer. The fat globule diameter and the free fat in the whip cream continuously decreased with an increase in homogenization pressures. Agglomeration of fat globules was observed at homogenization pressures higher than 20MPa. While the whipping time was a maximum at a homogenization pressure of 20MPa. The reason why the whipping time increased with an increase of homogenization pressures below 20MPa is that both of the fat globule diameter and the free fat, which is one of the main elements of the structure of typical whipped creams, decreased. The reason why the whipping time decreased at pressures higher than 20MPa is interpreted to be due to the fact that fat globules agglomerate to contribute to formation of whipped cream structure. Agglomeration of fat globules was not observed in whip creams to which sodium caseinate was added. Consequently, the whipping time increased with an increase of homogenization pressures, and the whip cream became unwhippable at the pressures higher than 20MPa.

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Distribution of water concentration in a bread under toasting by radiative heaters has been studied experimentally and the effects of the radiative characteristics on it has been discussed. A white bread was employed whose water content was 45.0%. Three kinds of electric heaters, whose radiative characteristics were different each other, were used. After toasting of predetermined period, the bread was divided by three parts; the crust layer, the upper half part of the crumb, and the lower half part of the crumb. The water content of these parts were measured by a constant pressure drying method. The experimental results show that as the toasting time is increased, the water content of upper and lower parts of crumb decreases, takes a minimum, increases, and then goes beyond the initial water content of the bread. In this process, the water content of the upper part changes faster and the extent of value change is larger than that of the lower part. The radiative characteristics of the heaters affects the water distribution history in the bread. If the bread is toasted by the heater with longer wave length, the water content both of crumb parts becomes higher, and the difference of these values are larger.

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Swelling phenomenon of packaged processed miso, which was called "Su-miso" and prepared by mixing miso, vinegar and sugar, was observed on its distribution process. Normal miso samples contained 5.2% NaCl and 17% total sugar. The pH value and acidity of the normal miso samples were 4.2±0.03 (mean±s.d.) and 8.3±0.02ml, respectively, while those of the swelled samples were 4.0±0.02 and 11.5±0.02ml, respectively. The swelled miso sample contained 106cfu/g of lactic acid bacteria, while the count of yeast was less than 10cfu/g. The strain L-1 isolated from the swelled miso sample produced carbon dioxide gas and ethanol from glucose by its heterofermentation, and was identified as Lactobacillus fructivorans. When the processed miso was inoculated with L-1 at 8×105cfu/g miso and sealed in a plastic bag, swelling phenomenon was observed after 2-day incubation at 30°C. Therefore, it is shown that L. fructivorans L-1 can cause swelling of packaged processed miso by its heterofermentation producing carbon dioxide gas and ethanol.

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To elucidate the mechanism of softening of combu fronds by seasonings during cooking processes, the effect of organic acids on the change in molecular weight of alginic acid was examined by means of gel permeation chromatography. Calcium alginate was immersed in model solutions of acetic acid, lactic acid, malic acid and citric acid, and the following results were obtained. Regardless of the kind of organic acids, the molecular weight of alginic acid decreased slightly until 50°C on immersion in each 1M solution. but above 70°C, the molecular weight rapidly decreased after immersion for 60min. In the range of 0.2-2M, the molecular weight decreased to about 1/10 of the initial molecular weight (1.1×10⁶) at 70°C and about 1/25 at 90°C regardless of organic acid concentrations. The effect of organic acids on the decrease in molecular weight was in the order of citric acid>malic acid>lactic acid>acetic acid. The smaller the molecular weight became, the narrower the molecular weight distribution (M_w/M_n) was. Although the initial M_w/M_n was 3.7, it became about 1.5 after immersion in 2M of each model solution at 90°C.

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The main purposes of smoking in manufacturing of dried bonito (Katsuo-bushi) were drying, flavoring and antioxidizing. We previously found that flavoring and antioxidizing were accomplished in the middle of smoking process. Drying was the most dominant in the last of smoking process. So, in the smoking, the drying by smoke could be substituted by hot dry air. Since heat pump drying system gave a energy saving with its high efficiency, we applied to the last of smoking process. Following results were obtained: (1) In a conventional smoking process, the process was repeated 9 times until the cut bonito meat (fillets) became harden. In the new method of smoking using a heat pump dryer, the fillets were continuously dried for 48 hours to harden after the 5 times repitition of conventional smoking. The conditions for the drying process were relative humidity (RH) of 80% at 50°C for 12 hours (at the start), RH of 75% for 12-24 hours (in the middle) and RH of 70% for 24-48 hours (in the last). The new method shortened the manufacturing period of 17 days to 9 days. (2) The browning of the Katuo-bushi flakes was suppressed by the heat pump process. The color of Katsuo-bushi was clearer than that of the conventional one. There was no difference in the flavor of Katsuo-bushi dried by the heat pump process and that of the conventional one. (3) By heat pump dryer, Katsuo-bushi were more effectively and uniformly dehydrated. The breakdown of the Katsuo-bushi flakes during the shaving process was reduced because the surface of the Katsuo-bushi was not excessively dried. The yield of the Katsuo-bushi flakes was improved by about 103% of that by the conventional method. It was unnecessary to take out the Katsuo-bushi from the smokehouse when it was smoked every one day and piled for 1 to 3 days for making the water content uniformly. So the manual labour was reduced. Further more, the fuel cost was reduced by reduction of an amounts of firewood by about 30%.

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Basic water obtained by electrolyzing of tap water was applied to improve a quality of cooked rice. In the measurement of the total volume swelling with polished rice and soaking water, basic water was more effective than natural water (tap water) and acidic water. The pH (of water) gave a favorable influence in this result. The texture of cooked rice, that is the adhesiveness/hardness ratio, was measured by the three grain method, and the size (two dimensions area) of cooked rice was measured by image processing system. The results indicated the same phenomenon. It showed that basic water was effective on the texture of cooked rice. We suggested that the increase of texture of cooked rice treated by basic water was caused by the increase of gelatinized starch on surface of cooked rice. An amount of starch liberated from the polished rice treated by basic water was the highest in three kinds of water. The fact was similar in cooked rice. It was suggested that these were caused by the influence of pH on washed rice and mineral density on cooked rice.

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In vitro studies on possibility of aluminium absorption into human body were carried out using green tea, black tea, oolong tea and instant coffee. Aluminium in green tea and black tea infusions and instant coffee solution were not found as ion form, but aluminium in oolong tea infusion was found as ion form in the range of 10-26% of total aluminium. In the case of simulated human gastric juice, aluminium in green tea and black tea did not ionize. About 50% of aluminium in instant coffee was found in ion form and ionized ratio of oolong tea increased 5-10% compared with the former experiment. These results suggest that daily intake of teas may not give any adverse effect to human health.

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The rupture and damage of cell particles in the dry mashed potatoes, which were three products on the market, were studied by observing microscopically and measuring the starch solubilized with an α-amylase treatment. Microscopic examination of the mashed potatoes showed that the proportion of ruptured particles was estimated to be less than 2% on the basis of the numbers of starch granules in a cell particle. The proportions of starch solubilized for three samples were 8-16% by single treatment with 0.01 unit of amylase, 58-82% with 1 unit, and 70-98% by double treatment with 1 unit. The proportions of the solubilized starch were assumed to reflect mainly the proportion of damaged particles and the susceptibility of starches in particles to the enzyme. The starch solubilization by the double treatment suggested that the proportions of damaged particles for three samples were 70-98% and those of intact particles were 2-30%. From these results it was concluded that the cell particles in mashed potatoes were largely made up of the damaged particles in which the amylase and solubilized starch could easily pass through the cracks on the cell walls.

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The gelatinization of starches in cells was studied using separated cells and starches isolated from potatoes. The loss of birefringence of starches against temperatures and DSC characteristics of potato cells were almost the same as those of isolated starches. The solubilities of starches in cells heated at temperatures between 50 and 90°C were almost the same as those of isolated starches, while those of cells heated for 20min were lower than those of isolated starches. The swelling powers of potato cells heated for 20 and 60min were low, compared with those of isolated starches. These results indicate that water required for the rupture of ordered structure of starches during gelatinization is fully supplied in cells, though the solubilization and swelling of starches in cells are suppressed possibly by the physical strength of cell walls which surround starches.

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The contents of 5'-inosinic acid (5'IMP) in dried and toasted nori, sheet-like products of Porphyra yezoensis (a red alga), were measured with HPLC from the stand point of an enzymatic increase in them, and the following facts were observed. 1) 5'IMP was not determined by HPLC in the case of directly extracting the sample with 80% ethanol, while 5'-adenylic acid (5'AMP) and 5'-guanylic acid were. However, a considerable amount of 5'IMP could be determined when soaking the sample in a small volume of water for a short time prior to the ethanol-extraction, and it was, moreover demonstrated that an increase in the 5'IMP content was followed by a decrease in the 5'AMP content. 2) The maximum production of 5'IMP was attained by soaking for 180 or 120sec for dried or toasted nori, respectively. 3) In both samples of nori, the 5'IMP content reached the maximum at 30-40°C in the soaking temperature, but could not be determined above 75°C. In commercial toasted nori, considerable amounts (201-304mg/100g dry matter) of 5'IMP could be determined with pre-soaking at 30°C for 120sec. 4) The extract of dried nori with 50mM tris-acetate buffer at pH 6.5 containing 3mM 2-mercaptoethanol and 10mM CaCl₂ showed high activities of 5'AMP deaminase. These results strongly suggest that 5'AMP deaminase in dried nori takes part in the increase of 5'IMP content.

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This study was pursued to elucidate the food chemical properties of anthocyanins in the colored tuber flesh of 5 varieties. Freeze-dried anthocyanins were prepared and dissolved into a buffer solution by the following procedures. Anthocyanins were extracted from the sliced tubers with methanol containing 1% TFA. After removal of lipid, the crude liquid was washed and purified by a Diaion HP-20 resin. The anthocyanin fraction was eluted from the resin by adding methanol to the column, followed by condensation and lyophilization. Heat treatment faded the anthocyanin color and its degree was more intense in purple pigmented varieties than in red ones. Radiation of light also weakened the pigment intensity, and its effect was slightly mild to purple colored varieties compared to red ones. Addition of fer rous ion decomposed the anthocyanin pigments, but its effect differed among the varieties tested. Influence of pH on the color depended on the acidity in a buffer solution, namely, the lower pH, the more intensity. Antioxidative activity was assayed by a ferric thiocyanate method. The extract of anthocyanins showed more effective antioxidative activity than that of α-tocopherol against the oxidation of linoleic acid in a potassium phosphate buffer (pH 7.0), and exhibited a strong activity as the same as BHA and BHT.

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The short chain peptides derived from sardines were incubated for 120min with an extract of porcine small intestinal mucosa. Digestionresistant dipeptides found in the digest, Val-Tyr, Val-Trp, Ile-Tyr and Ile-Trp, inhibited angiotensin I converting enzyme (ACE). Amounts of the four dipeptides isolated from the digest using a Sep-pak C-18 cartridge column and three steps of high-performance liquid chromatography, were 85.88, 21.87, 10.69 and 6.51mg/100g peptides, respectively, and the contribution of four peptides to total ACE inhibitory activity was 10.5%. It was confirmed that ACE inhibitory dipeptides were present in the digest of the short chain peptides.

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A vertically placed test tube (ID: 22mm, L: 200mm) contained 25 grams of gelatinized starch sample was tilted to angle of -20° from horizontal line, and the flowing time of leading edge of the sample solution from initial position to the test tube mouth was measured. The values of the flowing time, t, were correlated with the power law flow parameters of the samples measured by using a capillary viscometer. The log t values increased linearly with the increase of starch concentration. The values of log K and log μ_a correlated linearly with log t irrespective of origin, level of substitution, cross-linking level, and concentration of the modified starches, where K is consistency factor and μ_a is apparent viscosity. The values of flow behavior index, n, were also correlated with the t values as one regression curve.

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