Suppression of the growth of psychrotrophs by inactivating an enzyme essential for their growth was studied by analyzing the lability of thermolabile alanine racemase from a typical psychrotroph, Pseudomonas fluorescens, in comparison with the thermostable enzyme from Bacillus stearothermophilus. The thermolabile enzyme lost about 50 % of its initial activity after being incubated at 30°C for 5 min with sodium lauryl sulfate (0.08 %), guanidine hydrochloride (1M), urea (4 M), ethanol (45 %), and dimethyl sulfoxide (50 %), respectively, whereas the thermostable enzyme was resistant to these reagents at the same concentrations. Thus, the thermolabile enzyme was markedly less resistant to denaturation by denaturants and organic solvents than the thermostable type. The denaturation process for the thermolabile enzyme with urea was analyzed by circular dichroism, K_m value for L-alanine, and the content of pyridoxal 5'-phosphate (PLP). The thermolabile enzyme was denatured in one transition phase occurring at a concentration of 3.5M urea, whereas the thermostable type was denatured in two transition phases (dissociation of PLP with 4.0M urea; unfolding with 5.5 M urea).

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Observations of fresh and salted ume fruit brined with calcium hydroxide were performed by conventional scanning electron microscopy (SEM) and by low-vacuum scanning electron microscopy (low-vacuum SEM). An energy dispersive spectrometric (EDS) microanalysis was also carried out during the low-vacuum SEM observation.
The cell-wall structure of the high-Ca sample (calcium hydroxide at 0.6 % of the fruit weight was added) was almost the same as that of fresh ume fruit. However, the cell walls of the low-Ca sample (0.15%) were wrinkled and the cells had collapsed. These same results were observed by both conventional SEM and low-vacuum SEM.
Crystalline deposits were observed on the surface of the skin only by low-vacuum SEM. These deposits are presumed to have been dissolved in the fixation fluid during the fixation procedure required with conventional SEM observation. The appearance of crystalline deposits in the cells was different between the conventional SEM and low-vacuum SEM observations of the high-Ca sample. The crystalline deposits were of ellipsoid form by conventional SEM, whereas they appeared as thin layers sticking to the inner side of the cell walls by low-vacuum SEM.
The EDS microanalysis indicated that Ca was distributed throughout the tissue from the skin to the innermost part of the flesh in the high-Ca sample. In the case of the low-Ca sample, the Ca content of the innermost part of the flesh was 40% of that of the skin.
Although methods for avoiding damage to samples need to be devised, low-vacuum SEM was sufficiently effective to observe the tissues of ume fruit and of crystalline deposits both inside the cells and on the surface of the skin, and to carry out an EDS microanalysis.

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A sensory study was conducted to evaluate the degree of grittiness when samples (an aqueous suspension, low- and high-viscosity suspensions, and soft and hard gels) dispersed in ten kinds of microcrystalline cellulose of 11-78μm average particle size were placed in the mouth. The effects of the average particle size, concentration of the microcrystalline cellulose, and dispersion medium were each examined. With the aqueous suspension, the degree of grittiness increased with increasing concentration and increasing average particle size of the microcrystalline cellulose, so the degree of grittiness depended on both these factors. A regression analysis of the relationship between the degree of grittiness and the logarithm of (average particle size×concentration) indicated high correlation, and a regression equation expressing this relationship was obtained. When (average particle size×concentration) was used as the stimulus strength, the degree of grittiness followed Fechner's rule, which is generally known to provide the relationship between the strength of sensation and the strength of stimulus. With the viscous suspensions and gels, it was also recognized that Fechner's rule helds true between the degree of grittiness and (average particle size×concentration). A multiple regression analysis indicated that the degree of grittiness was most influenced by the average particle size, less by the concentration of microcrystalline cellulose, and least by the dispersion medium.

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The cause of sauce separation in cream stew was investigated when a mixture of 16.6 g of white sauce, 40 g of chicken thigh meat, and 33.4 g of bouillon soup was cooked under a vacuum. The sauce in the cream stew separated irrespective of the evacuation procedure during 60 min of cooking at 90°C, but this separation did not occur in a cream stew without the chicken thigh meat. The amount of protein eluted from the chicken thigh meat during cooking increased with increasing cooking time, reaching about 300 mg after cooking. The addition of 200 mg or more of bovine serum albumin or ovalbumin instead of chicken thigh meat also caused the sauce in the cream stew to separate.
These results suggest the sauce separation in the cream stew during vacuum cooking depended not on the evacuation procedure but on the sarcoplasmic protein eluted from the meat during cooking.

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[in Japanese]

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