A Study on Commercial Sterility of Cooked Rice Packed Under Semi-aseptic Condition from the Viewpoint of Cooking Condition

微生物的変質がなく, 食味がよい, より高品質な準無菌包装米飯 (cooked rice packed under semi-aseptic condition) の製造を目的に多くの技術開発が進められてきた.今回, レトルト食品の商業的無菌性の考え方に基づき, 準無菌包装米飯において, 微生物に関わる保蔵安定性をより向上させることを目的に, 準無菌米飯の商業的無菌性に及ぼす米由来の耐熱性生菌の影響を調べ, 製造方法の改良を検討した.本研究で玄米よりB.subtilis菌株が分離された.その耐熱性はD_<100℃>=41.4分で, これより従来の炊飯加熱による殺菌加熱時間はF=0.43D_<100℃>と推算された.Diは任意の温度i (℃) のとき耐熱性生菌が90%死滅する加熱時間を表す.また商業的無菌性を達成するための必要殺菌加熱時間F (分) はF=2D_iであることが推算され, 従来の製造工程の炊飯加熱において, 上記の商業的無菌性を達成するための必要殺菌加熱時間を満たしていなかった.そこで, 商業的無菌性を達成するための炊飯加熱操作を検討した.その結果, 105℃で18～28分間, 110℃で13～14分間の炊飯では米飯の食味において問題が生じないことがわかった.また, 玄米より分離したB.subtilis菌株の耐熱性はD_<121.1℃>=0.32分で, これより商業的無菌性を達成するための必要殺菌加熱時間はF_0=2D_<121.1℃>=0.64分相当以上と推算され, F_0=0.7分を達成するには, 105℃で38分間以上, 110℃で14分間以上の加熱炊飯が必要であることがわかった.本研究の結果より, 準無菌包装米飯において従来と同等の食味で, より保蔵安定性を有した高品質の製造工程として, 110℃で14分間 (F_0=0.7) の炊飯加熱操作を提案する.Many techniques of production have been developed to produce cooked rice packed under semiaseptic condition (here in after called semi-aseptic cooked rice) with less spoilage by organism, better taste and higher quality. Effect of heat-resistant organisms from rice on commercial sterility of semiaseptic cooked rice were researched and the improvement of production process were investigated in order to upgrade the stored stability involved organisms for semi-aseptic cooked rice based on philosophy of commercial sterility of retort pouch foods in this study. The necessary time for heat sterilization were estimated at 2D_i to ensure commercial sterility in a production process of semiaseptic cooked rice in this study. D_i means the heating time that 90 % of heat-resistant organisms will be dead at any temperature, i. The Time of heat sterilization for present process of production were estimated at 0.43D_<100℃> against B.subtilis strain from brown rice, and it didn't reached necessary time of heat sterilization "F= 2D_i" to ensure commercial sterility. The Conditions of heat cooking was investigated to ensure commercial sterility on method of production for semi-aseptic cooked rice. We suggest that the conditions of heat cooking are 14 minutes and a temperature of 110℃ as new production process to ensure equivalent eating quality to present process and commercial sterility against B.subtilis strain from brown rice for semi-aseptic cooked rice in this study