The fate of Listeria monocytogenes (IID 581, serotype 4b) was studied in various Japanese fishery products. Numbers of L.monocytogenes were reduced in all samples (“nishinhirikomi”, “ ika-shiohara” and “sake-izushi”) during maintenance at 5°C, 12°C and 25°C. In “nishin-kirikomi”, numbers of L. monocytogenes were gradually reduced at 5 and 12°C (reduction of 1.6log cfu/ml and 2.8 log cfu/ml, respectively), but were reduced only slightly for 7 days at 25°C. However, numbers of L. monocytogenes rapidly reduced to undetectable levels in “ika-shiokara” at all temperatures examined (5, 12 and 25°C). In“sake-izushi”, numbers of L.monocytogenes were reduced at all temperatures, but it survived 2.2 log cfu/ml after 28 days at 5°C. The fate of L. monocytogenes was also evaluated in three kinds of “izushi”. It was shown that numbers of L. monocytogenes rapidly reduced in all samples examined, as the number of lactic acid bacteria (LAB) increased. Most of the LAB isolated from the three kinds of izushi were cocci. These results showed that inclusion of LAB in izushi resulted in the reduction of numbers of L. monocytogenes.
Extracellular xylan-degrading enzymes (xylanase I, xylanase II and β-xylosidase) were purified as electrophoretically and isoelectrophoretically homogeneous proteins from the culture broth of Penicillium expansum O-385-10 concerning the spoilage of apple fruit. The molecular weights of xylanase I, xylanase II and β-xylosidase were 21.0, 40.0 and 91.0 kDa, respectively. The pIs of xylanase I, xylanase II and β-xylosidase were 9.20, 4.30 and 4.20, respectively. Xylanase I produced xylose and several xylooligosaccharides from xylan. On the other hand, xylanase II mainly produced xylose and xylobiose from an early stage of the reaction, and oligosaccharides over xylotriose were almost absent. In the presence of K+ ion, the activity of xylanase I increased almost two-fold, while the activity of xylanase II decreased to about 80%. When xylanase I and II were simultaneously incubated with apple fruit, reducing sugar was hardly liberated from the fruit tissue, but the tissue was significantly affected by adding β-xylosidase to this incubation mixture, and a large amount of the sugar was liberated.
The purpose of this study was to clarify the bacterial contamination in fresh-cut fruits. Total viable aerobes, coliforms and fecal Escherichia coli in fresh-cut fruits were investigated. We prepared samples of fresh-cut melon, pineapple, watermelon, grapefruit, orange and kiwi. The incidence of total viable aerobes was the order of 2-6 log10 cfu/g depending on the fruits tested. Fecal E. coli was detected in fresh-cut melon, pineapple and watermelon, and the numbers were 8, 1 and 2 of 10 samples each, respectively. The ability of E. coli O157: H7 and Salmonella Enteritidis to survive and grow on cubes of melon, watermelon, pineapple and grapefruit was investigated. After being inoculated withE. coli O157: H7 and S. Enteritidis, the samples were kept at 4, 10 and 20°C, and their bacterial counts were examined after 0, 12, 24 and 48 hr of incubation . In the samples of melon and watermelon, E. coli O 157: H7 and S. Enteritidis proliferated during stor. age at 20°C, but showed no change during storage at 4 and 10°C. However, E. coli O157: H7 and S.Enteritidis inoculated onto fresh-cut cubes of pineapple and grapefruit did not grow during 48 hr of storage at 4, 10 and 20°C. This result indicates that E. coli O157: H7 and S. Enteritidis were capable of growth and rapid proliferation on fresh-cut melon and watermelon at higher temperatures than those of a refrigerator.
A food-borne outbreak of Escherichia coli 0157 occurred at a day nursery in Fukuoka city in June 2002. The causative food was asazuke (salted cucumber). The cause of O157 contamination of asazuke was not clarified by epidemiological investigations . Therefore, laboratory inoculation test using the causative 0157 strain on asazuke during the production process were performed. Additionally, inoculation test with 0157 strains into marketed asazuke products, marketed nukazuke products and homemade shiomomi were undertaken. Results were as follows; (1) O157 organisms rapidly increased when they were inoculated during the initial or early (less than 12 hr) production process of asazuke. No increase, however, was observed following a later (more than 24 hr) inoculation process. (2) O157 organisms inoculated on marketed asazuke and nukazuke did not increase, probably because of large populations of other bacteria. From the above results, the cause of the outbreak was suspected to be O157 contamination and increase which occurred during the initial or early production process of asazuke when other bacteria were low in number.
Total plate counts, coliform counts and E. coli in food samples determined by a rapid measurement kit “ SimPlate” were compared with those determined by conventional methods: the pour plate methods using plate count agar, desoxycholate agar and 3M Petrifilm EC plate. The results are shown below. 1. The correlation coefficient between the total counts in 154 food samples determined using “SimPlate” and the standard agar plate method was 0.95, showing a very high correlation. 2. Of 258 food samples, 131 and 112 samples were coliform positive on plates using “Sim-Plate” and desoxycholate agar. The correlation coefficient of the coliform counts on the two media was 0.79, showing a good correlation. 3. Of 65 pork meats, E. coli was detected, using “SimPlate” and 3M Petrifilm EC plate 54 and 52 samples, respectively, and the correlation of E. coli counts obtained by the two methods was 0.86. 4. 96 strains isolated from fluorescent wells of “SimPlate” were E. coli 95 strains and K. cryocrescens 1 strain. The above findings clarified that “SimPlate” obtained results comparable to those obtained by the conventional total count, coliform counts and E. coli count methods in food samples and thus, the rapid measurement kit “SimPlate” is useful for rapid on-site testing of food samples.