title: Growth and toxin production of proteolytic Clostridium botulinum in aseptically steamed rice products at pH 4.6 to 6.8, packed under modified atmosphere, using a deoxidant pack.
abstract: Demand for aseptically steamed rice products has been increasing rapidly in Japan over the past 10 years. In our previous study, we showed that proteolytic Clostridium botulinum produce toxins in steamed rice products packaged under a modified atmosphere of < or =0.3% oxygen. In the present study, we examined the effect of pH to control botulism risk in steamed rice products packaged under modified atmosphere (5% CO2 and 95% N2 as the balance) with the inclusion of a deoxidant pack to produce an oxygen concentration of < or =0.3%. A mixture of 10 strains of proteolytic C. botulinum (5 type A strains and 5 type B strains) was inoculated into steamed rice products at pH values between 4.6 and 6.8 prior to packaging. All samples were stored at 30 degrees C for 24 weeks. Samples at higher pH showed earlier starts of neurotoxin production. Neurotoxin was detected after 2 weeks of incubation in samples at pH 5.4 or above, whereas it took 4 weeks for the toxin to be detected in samples at pH 5.2 to 5.3 and 12 weeks in samples at pH 5.0 to 5.1. In samples at pH 4.9 or below, no toxin was detected during the experimental period. Apparent sample spoilage did not occur before C. botulinum produced neurotoxin in most of the samples. Based on these results, we conclude that aseptically steamed rice products must be packaged at pH 4.9 or below under modified atmosphere containing < or =0.3% oxygen, with the inclusion of a deoxidant pack.
authors.affiliation: Department of Food Science and Technology, Faculty of Marine Science, Tokyo University of Marine Science and Technology, 4-5-7 Konan, Minato, Tokyo 108-8477, Japan. kimubo@kaiyodai.ac.jp
authors.forename: Bon
authors.initials: B
authors.lastname: Kimura
authors.forename: Ryusuke
authors.initials: R
authors.lastname: Kimura
authors.forename: Tetsuya
authors.initials: T
authors.lastname: Fukaya
authors.forename: Kinya
authors.initials: K
authors.lastname: Sakuma
authors.forename: Satoko
authors.initials: S
authors.lastname: Miya
authors.forename: Tateo
authors.initials: T
authors.lastname: Fujii
mesh_terms: D001905:Botulinum Toxins / Q000096:biosynthesis*; D003014:Clostridium botulinum / Q000254:growth & development* / Q000378:metabolism*; D015169:Colony Count, Microbial; D003257:Consumer Product Safety; D005506:Food Contamination / Q000032:analysis / Q000517:prevention & control; D005511:Food Handling / Q000379:methods; D005516:Food Microbiology; D018857:Food Packaging / Q000379:methods*; D006863:Hydrogen-Ion Concentration; D012275:Oryza / Q000737:chemistry / Q000382:microbiology*; D010100:Oxygen / Q000378:metabolism; D013171:Spores, Bacterial / Q000254:growth & development; D013696:Temperature; D013997:Time Factors
chemical_list: D001905:Botulinum Toxins; D010100:Oxygen