10:30 〜 10:45
[4-1015-A-02] Application of the High Hydrostatic Pressure-Based Treatment as an Alternative for Food Retort Processing
キーワード：bacterial spores, heat resistance, hydrostatic pressure, shelf life
In order to extend the shelf-life of various foods, it is seriously essential to install some appropriate sterilizing technologies. In particular, various foods expecting to be stored for a long period are required to be in almost microbial-eliminated during processing. For satisfying such requirement, typical retort treatment with 121℃ for more than 5 min has been performed in the food industry. The main microbes targeted in retort processing are spores formed by some Gram positive bacteria. Bacterial spores are known to be extremely resistant to various stresses physically and chemically as compared to vegetative cells. Most of the spores are of soil origin, which means the fact that almost all agricultural products can be regarded as being contaminated with bacterial spores. Therefore, in order to preserve processed foods including agricultural commodities for a long period of time, it is required to introduce a technique capable of effectively inactivating bacterial spores. However, the current major problem is that no appropriate method other than retort treatment can be found. So far, we have investigated the effective treatment for the reduction of heat resistance of bacterial spores mainly based on high hydrostatic pressure(HHP). In particular, it has been shown that the reduction efficiency is accelerated by the combined use with alkaline electrolyzed water(AlEW), but, any experimental trials for actual processed foods has not been conducted yet. In this study, we investigated the application possibility of HHP-based treatment for extending shelf-life of some processed foods inoculated with typical bacterial spores. B. subtilis, B. cereus and C. sporogenes were used as test bacteria. After aerobically and anaerobically grown with appropriate media for Bacillus and Clostridium, respectively, spores were formed on the plate medium culture. After preparation of spore suspension with its spectrophotometric absorbance at 500 nm adjusted to 1 according to the conventional methodology, the same amount of each spore suspension was mixed to prepare a spore cocktail, then inoculated to material of the processed foods. In this experiment, hamburg and potato salad were used as test foods. The ingredients used in hamburg were minced pork, diced onion, and that in potato salad were potato and mayonnaise, respectively. No additional ingredients such as spices were used. All materials used were obtained from supermarket neighboring Kagoshima University. The material inoculated with spores was sealed in a plastic film bag with triplicate volume of sterile distilled water or AlEW, and subjected to HHP treatment. The treatment conditions were 80 MPa, 50℃ for 30 min, and the samples after treatment were prepared with hamburg and potato salad by a general cooking method. The cooked sample were heat-treated in water bath at 80℃ for 15 min, and then a storage test was conducted at 30℃. For both hamburg and potato salad, the increases in viable count of food samples treated by single HHP and HHP combined with AlEW were slower comparing with that of the untreated sample during storage. More than 2 days in storage, 4-5 logs differences were obtained between the treated and untreated sample. At the same time, gas production in sealed package of treated sample was not observed. Since the storage test was in an unaerobic state, bacterial growth was considered to be dominated by Clostridium, but it is considered that Bacillus could be also effectively inactivated considering our previous unpublished data. From the above, it was shown that the treatment based on HHP is as effective as the in vitro study in reducing the heat resistance of bacterial spore, and it may be possible to replace retort treatment.