The influence of pressure and temperature, in the presence (in glucose broth, GB) or absence (in phosphate bu#er, PB) of nutrients, on hydrostatic pressure (HP) induced-germination and inactivation of Bacillus subtilis, B. cereus, and B. polymyxa spores was investigated for a relatively low range of ,*ῌ+** MPa (low HP). Low HP-induced germination was more potent in GB than in PB at ,*ῌ0* MPa, and the di#erence in germination ratio between the growth media (GB and PB) tended to decrease with increasing pressure. For B. subtilis and B. cereus, the optimal temperature for the low HP-induced germination in PB tended to be higher than in GB, whereas temperature dependence on low HP-induced germination of B. polymyxa was di#erent considerably from those of B. subtilis and B. cereus. After -*ῌ0* min incubation at .*ῌC and 0* MPa, the three types of bacterial spores germinated / log-cycles in the presence of nutrients and ,ῌ-log-cycles in the absence of nutrients. These results indicate that the low HP-induced germination of Bacillus spores has potential as a method of reducing bacterial spores in foods and foodstu#s, especially those containing large amounts of nutrients.
The combined e#ect of mild heating and pressurization on germination and inactivation of Bacillus subtilis spores was investigated. The spore count decreased remarkably at 0*῍ῌ2* MPa in glucose broth as opposed to phosphate bu#er. These results suggested that the spores germinated due to pressure and germination-inducing components in the glucose broth, and that the germinated spores were then inactivated by mild heating. The induction of germination started at +* MPa at .*῍ or ,* MPa at 0*῍ with the number of spores decreasing by two log-cycles in one hour. The relationship between the logarithm of spore number and pressure became linear in the pressure range of /*ῌ-** MPa. The germination ratio was
The pressure range that prevents growth of microorganisms (two yeast, three lactic acid bacteria, E. coli, three bacilli and one clostridium) was investigated in order to apply it to food processing. The growth of the microorganisms could be restrained in a pressure range of 40-70 MPa depending on the species of microorganism. Growth of Lactobacillus plantarum was inhibited at 70 MPa, and two kinds of yeast at 40 MPa. The pressurization treatment is presumed to induce the germination of the spores of Bacillus and Clostridium, and the germination of B. subtilis and B. stearothermophilus were especially remarkable. Most of the germinated spores were killed at the optimum growth temperature of each microorganism under pressurized conditions. Practical usefulness of these results was verified in the autolysis process of fish meat without decomposition. Growth inhibition and inactivation of spores by pressurization treatment at less than 100 MPa can be utilized as a new technique for killing microorganisms and for producing food.Keywords: pressurization, growth inhibition, microorganisms, autolysis.Many researchers have investigated the effect of high hydrostatic pressure (HHP) on inactivation of microorganisms since the HHP treatment for milk preservation was first reported more than 100 years ago by Hite (1899). Hayashi (1989) suggested the availability of HHP in food processing, though he proposed the exclusive utilization of pressure ranges higher than 200 MPa. On the other hand, Okami (1990) also suggested utilization of relatively low pressure of less than 100 MPa for food-preservation and storage of food materials.ZoBell and Johnson ( 1 949) studied the effect of pressure on the growth of many kinds of microorganisms, and showed that hydrostatic pressure from 50 MPa to 60 MPa retarded their growth. Clouston and Wills (1969) showed that germination of Bacillus pumilus spores was accelerated at 500 atm (c.a. 50 MPa). Recently, Furukawa and Hayakawa (2001) reported that B. stearothermophilus spores can be sterilized at 95'C, 60 MPa. However, such relatively low pressures have not yet been applied in practice. Recently, Okazaki et al. (2003) applied the growth inhibition behavior of microorganisms under pressurized conditions to autolysis of fish meat. The report showed that the fish meat could be autolyzed in an extremely short period without decomposition at 60 MPa. This result also indicates the growth inhibition of microorganisms by pressurization treatment can be applied to other enzymatic processings without decomposition. To apply the HHP to food processing, it is necessary to clarify the growth behavior of microorganisms under pressurized conditions. The purpose of this study was to determine the pressure range capable of inhibiting growth of microorganisms, and growth inhibition by pressurization treatment was also confirmed in autolysis of fresh fish meat as a viable applica- Pressurizing apparatus The pressurizing apparatus (Hikarikouatsu-kiki Co. , Ltd. , Hiroshima), capable of pressurizing up to 400 ...
For the purpose of producing fish sauce without any addition of salt, an autolytic technique under pressurization combined with warming was investigated. While rancidity caused by the autolysis could be inhibited by pressurization at higher than 50 MPa combined with warming at 50∞C, the effect of pressurization on the autolysis was not observed in the range of 50-250 MPa. The optimum temperature and treatment time for the autolysis under pressurization were 50∞C and 48 h, respectively. The extract of anchovy produced under the autolysis conditions under 60 MPa at 50∞C for 48 h contained 2.6% total nitrogen, 1.4% formol nitrogen, and 11.6% free amino acids by weight. These contents were higher than those of commercially available fish sauce and soy sauce. The sensory test revealed that saltiness was hardly perceived, and odors like 'cheesy' and 'rancid' were not as strong as in fish sauce. Thus, this autolytic technique under pressurization combined with warming could be a new method for producing a good-quality autolytic extract similar to fish sauce without any addition of salt in an extremely short period of time.
Bacillus subtilis spores were pressurized at 0* MPa at .*ῌ for *ῌ,. hours in phosphate bu#er or GAM broth. After ,. hours, viable counts and spore counts decreased by about / log cycles in the broth and by only +.0 log cycles in the phosphate bu#er. Most of the spores in the broth changed from bright to dark after . hours, after which some of them began to bud, as observed by phase contrast microscopy. These results show that the spores germinated due to pressure and the presence of germination-inducing components in the broth, and that the germinated spores were then inactivated before changing into vegetative cells. We conclude that it is possible to inactivate B. subtilis spores by pressure-holding in non-thermal conditions. The same phenomenon was observed for B. licheniformis, B. cereus and B. coagulans, but the viable counts for these bacilli did not decrease as much as that of B. subtilis.
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