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1 Effect of Cooking Water ph on Commercial Sterility in the Production of Cooked Rice Packed under Semi-aseptic Condition Kinya SAKUMAl, Haruhiko KATODA1, Tetsuya FUKAYA2, Toshio JOH3, Akira IT03 and Atsuo WATANABE4 1Nitt o Aliment Corporation, Okada, Shibata, Niigata , Japan 2K agome Corporation Research Institute, 17 Nishitomiyama, Nasushiobara, Tochigi , Japan 3G raduate School of Science and Technology, Niigata University, Ikarashi, Niigata, Niigata , Japan 4M embrane and Separation Research Circle of Food (MRC), Kawaguchi, Kawaguchi, Saitama , Japan Many processing techniques have been developed to produce cooked rice packed under semiaseptic condition (here in after called semi-aseptic cooked rice) with less microbial spoilage, better taste and higher quality. In this study, effect of heat-resistant microorganisms in rice on commercial sterility of cooked rice was examined using ph-controlled rice. Improvement method of cooking process was investigated to upgrade the storage stability of cooked rice with microorganisms based on the concept of commercial sterility for the retort pouch foods. The growth of Bacillus subtilis isolated form brown rice was not inhibited on rice adjusted ph 4.6 and ph 5.0 at 30 Ž. To ensure the commercial sterility of semi-aseptic cooked rice, the isolated B. subtilis strain should be inactivated in heat cooking process. The conditions of heat cooking was investigated for semi-aseptic cooked rice adjusted ph 4.6 or ph 5.0 to ensure equivalent eating quality to conventional process and commercial sterility against B. subtilis. The optimum cooking condition for the rice of ph 4.6 was 18 minutes with 98 Ž and that for the rice of ph 5.0 was 14 `16 minutes with 105 Ž or 9 `11 minutes with 110 Ž. Keywords: semi-aseptic cooked rice, commercial sterility, cooking conditions, sensory test, F value, ph.

3 Table 1 The effect of ph on the spoilage of cooked rice by Bacillus subtilis sp. 1) NT: not tested when all sample were spoiled.

4 Table 2 Effect of ph on heat resistance of strain B801 in 1/15M phosphate buffer (ph 4.6). 1) +: growth positive, -: growth negative Table 3 Effect of ph on heat resistance of strain B802 in 1/15M phosphate buffer (ph 4.6). 1) +: growth positive, -: growth negative

5 Fig. 1 Thermal death time curve for Strain B801 and B802 spores in 1/15M phosphate buffer(ph 4.6 and 5.0). œstrain B801 in ph 5.0, Strain B802 in ph 5.0, Strain B801 in ph 4.6, Strain B802 in ph 4.6

6 Fig. 2 Survivor curves for Strain B801 and B802 spores heated in 1/15M phosphate buffer (ph 5.0).

7 Table 4 Effect of heating factor on Fo value or taste of cooked rice adjusted ph 5.0.

8 [11] P. S. Fernandez, M. J. Ocio, T. Sanchez, A. Martinez; Thermal resistance of Bacillus stearothermophilus spores heated in acidified mushroom extract, J. Food Prot., 57, (1994). [19] K. Yoshiaki, K. Bon, K. Susumu, F Tetsuya, S. Kinya, H. Tateo; Growth and toxin production by Clostridium botulinum in aseptic steamed rice packaged under modified atmospheres, J. Food Prot, 68, (2005).

1272 CHEMOTHERAPY MAR. 1975

1272 CHEMOTHERAPY MAR. 1975 VOL. 23 NO. 3 CHEMOTHERAPY 1273 Fig. 2 Minimal inhibitory concentration of aminoglycosides against 50 strains of Klebsiella Fig. 1 Minimal inhibitory concentration of aminoglycosides