Changes In Aw Research Articles

細菌細胞中のＡＴＰ量に及ぼす水分活性の影響

ATP levels of bacteria in Tryptic Soy Broth with 0.5 to 8.7% (w/w) NaCl (water activity, aw 0.997-0.945) were studied during 3-day incubation period at 25°C by the luciferin-luciferase bioluminescence reaction method. The amount of intracellular ATP per cell of Staphylococcus epidermidis, Escherichia coli and Vibrio parahaemolyticus ranged from 1.3 to 6.1×10-18 mol/cell in the stationary phase. ATP content of bacterial cells varied greatly with age. The changes in aw had little effect upon the amount of ATP.

CAROTENE OXIDIZING FACTORS IN RED PEPPER FRUITS (Capsicum annuum L.): EFFECT OF ASCORBIC ACID AND COPPER IN A β‐CAROTENE‐LINOLEIC ACID SOLID MODEL

ABSTRACTThe carotene‐bleaching activities of ascorbic acid and copper were investigated in a solid model consisting of carotene and linoleic acid adsorbed on powdered cellulose. The effects depended on the water activity (aw) of the system. Ascorbic acid in the presence of Cu++ had very little activity in the dry model but displayed increasing bleaching effects as the aw value of the system was raised. However this bleaching activity in the moist model reached a maximum as the ascorbic acid concentration rose to about 1 μmol/g cellulose, or 1.4 μmol ascorbic acid/mmol linoleic acid. At higher concentrations of ascorbic acid, the bleaching activity decreased and was eventually converted into an antioxidant effect. A peroxidase‐like protein extracted from pepper was also tested in the present model and found to exhibit prooxidant activity, which was little affected by changes in aw. The antioxidant system composed of copper and ascorbic acid at high concentrations was able to overcome the pro‐oxidant effect of peroxidase.

Combined effects of water activity, pH and temperature on the growth and spoilage potential of fungi.

Summary. An arbitrary parameter ‘rejection time’, i.e. the time required for a fungal inoculum to form a 2 mm diam. colony, was used to express the shelf life of jam after unsealing and exposure of the contents to airborne contamination. Individual and combined effects of water activity (aw), pH value and temperature on rejection time of low sugar jam were estimated from the radial growth on agar of colonies of 9 fungi. The decreases in aw (0·94–0·90) and temperature (25–15°) practicable for low sugar jam were more effective in increasing rejection time than the feasible decrease in pH value (3·7–2·9). The interaction between aw and temperature was significant. The effect of the changes in aw, temperature and pH on rejection time was broadly similar for media adjusted by either sucrose or glycerol. At a given aw, moulds were slightly more tolerant of glycerol than sucrose but yeasts, except for the osmophile Saccharomyces rouxii, were markedly more tolerant of glycerol than sucrose.