Effect of Cooking Water ph on Commercial Sterility in the Production of Cooked Rice Packed under Semi-aseptic Condition

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1 , Vol. 9, No. 3, pp , Sep ph, Effect of Cooking Water ph on Commercial Sterility in the Production of Cooked Rice Packed under Semi-aseptic Condition Kinya SAKUMA,, Haruhiko KATODA, Tetsuya FUKAYA 2, Toshio JOH 3, Akira ITO 3 and Atsuo WATANABE 4 Nitto Aliment Corporation, Okada, Shibata, Niigata , Japan 2 Kagome Corporation Research Institute, 7 Nishitomiyama, Nasushiobara, Tochigi , Japan 3 Graduate School of Science and Technology, Niigata University, Ikarashi, Niigata, Niigata , Japan 4 Membrane 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. 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 8 minutes with 98 and that for the rice of ph 5.0 was 4 6 minutes with 05 or 9 minutes with 0. Keywords: semi-aseptic cooked rice, commercial sterility, cooking conditions, sensory test, F value, ph. cooked rice packed under semi-aseptic condition [] Fax: , kaihatsu-sakuma@nitto-aliment.co.jp [2] [3] F 2D i D i i 90 ph 2 []

2 F ph [] ph ph F p kg MR-D60 KEN MIX MAJOR [] 2..2 [] B. subtilis 2 B80 B ph ph 50 w/w 2..4 ph [4] ph 00 g 00 g TESCOM TM3 ph HORIBA F-2 ph ph ph [] [5] CFU/mL ml GA ph ph ph ph ph 4.6 ph L g ph g 6.8 g 48.7 g 23 mm 50 mm m ph ph ph cm mlindicon TRIDAK Division STEPPER 20 L cm 5 20 L D i z [5] [6] MPN /5M ph 4.6

3 ph 59 [7] /5M ph 5.0 ph 5.0 GA ph ph ph 5.0 :2 [8] Data Trace 2002 F 0 3 ph ph 4.6 Bacillus ph 5.0[9] [0] Fernandez[] ph Bacillus stearothermophilus D i ph 3. ph ph ph [4] Table ph B80 B802 2 ph B80 B802 ph ph 3.2 /5M ph [] 3.2. ph 4.6 D i MPN [6] D i D i U (log a-log b) ml ph 4.6 GA Table The effect of ph on the spoilage of cooked rice by Bacillus subtilis sp. Species Strain No. ph of cooked rice Number of test samples Number of spoiled samples Incubation time (day/30 ) B. subtilis B80 B NT ) NT NT NT NT NT ) NT: not tested when all sample were spoiled.

4 60 U a b CFU B80 98 D i 0 6 CFU/mL 5 a CFU/mL 6 b CFU/mL D 98 6/ log log 2.4 D i Tables 2 3 D i TDT Fig. Table 2 Effect of ph on heat resistance of strain B80 in /5M phosphate buffer (ph 4.6). Heating time (min) Heating temperature ( ) ) D value min ) : growth positive, : growth negative Table 3 Effect of ph on heat resistance of strain B802 in /5M phosphate buffer (ph 4.6). Heating time min Heating temperature ( ) ) D value min ) : growth positive, : growth negative

5 ph 6 00 z =8.5 z =0. 0 D value (min) z =0.3 z =0.9 Strain B80 in ph 5.0 Strain B802 in ph 5.0 Strain B80 in ph 4.6 Strain B802 in ph Heating temperature ( ) Fig. Thermal death time curve for Strain B80 and B802 spores in /5M phosphate buffer(ph 4.6 and 5.0). Strain B80 in ph 5.0, Strain B802 in ph 5.0, Strain B80 in ph 4.6, Strain B802 in ph 4.6 [] B80 B802 /5M ph 7.0 D D ph 4.6 D i ph 7.0 D i /30 / ph 5.0 D i D i /7 / ph 5.0 B80 B802 /5M ph 5.0 Fig. 2 D i D i TDT Fig. ph 5.0 D i [] ph 7.0 D i /4 /5 [2] Bacillus ph ph 7.0 B. subtilis D 05 ph ph F p [3] [4] ph F p D i B ph 4.6 F p ph 4.6 B80 D ph 4.6 F p 5 5 /2.4 D D 98 [] F 2D i ph 4.6 F 2D i ph 5.0 F p ph 5.0 B80 D ph 5.0 F p 5 5 /5.4 D D 98

6 Strain B D min 2 Log of survivors D min D min D min D 00.2 min Strain B D min 3 2 D min D min D min D 98.8 min Heating time(min) Fig. 2 Survivor curves for Strain B80 and B802 spores heated in /5M phosphate buffer (ph 5.0). ph 5.0 F 2D i ph F 2D ph ph ph 5.0 [5] [6] ph

7 ph :2 Table [] ph [7] ph 5.0 r D D r i D i D i D r 0 (r-i)/z 2 [8] ph 5.0 B80 2. D i D 2. D 06 0 (06-2.)/ [] B80 F 2D i 2. F F [] ph B80 F ph 5.0 F 0 /4 F 0 Table 4 ph 5.0 F ph F F ph 4.6 B.subtilis Table 4 Effect of heating factor on F 0 value or taste of cooked rice adjusted ph 5.0. Heating factors Temperature ( ) Time (min) F 0 value (min) Number of panelists Right answer Wrong answer Significance NS NS NS NS NS NS NS NS NS % significant difference

8 64 Clostridium [4] Clostridium Clostridium Clostridium Clostridium [9] 4 ph ph ph F F [] cooked rice packed under semi-aseptic condition [2] 996 pp. -2 [3] 2002 pp [4] A B ph [5] [6] [7] A B [8] 998 pp [9] 200 pp [0] 988 pp [] 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, 37-4 (994) [2] [3] 994 pp [4] 2000 pp [5] [6] 990 pp [7] [8] 996 pp [9] 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). cooked rice packed under semi-aseptic condition ph

9 ph 65 ph 4.6 ph 5.0 [] B. subtilis ph [] B. subtilis ph 4.6 D z 8.5 ph 5.0 D z 0. ph 4.6 F p D 98 ph 5.0 F p D 98 [] F F 2D i ph 4.6 ph 5.0 ph [] B. subtilis ph 5.0 D F 2D F ph F F ph 4.6