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.

Identification of key sensory attributes for consumer acceptance and instrumental quality of aseptic‐packaged cooked rice

“…() proposed the inclusion of more than 10% oxygen in the package to prevent the growth of Clostridium botulinum . For microbial growth, various levels of pH (4.6–6.8) were applied in production and no Clostridium botulinum below pH 4.9 during a 24‐week shelf life study was present (Kimura et al ., ). Kwak et al .…”

“…Kasai et al (2005) proposed the inclusion of more than 10% oxygen in the package to prevent the growth of Clostridium botulinum. For microbial growth, various levels of pH (4.6-6.8) were applied in production and no Clostridium botulinum below pH 4.9 during a 24-week shelf life study was present (Kimura et al, 2008). Kwak et al (2013) compared the descriptive attributes and consumer acceptance of two aseptic-packaged cooked rice samples with steamed rice and frozen-cooked rice.…”

Regional Variations in Home Canning Practices and the Risk of Foodborne Botulism in the Republic of Georgia, 2003

“…The prevalence of keeping unopened home-canned vegetables for ≥6 months was higher in households of eastern ROG than in households in western ROG. Long incubation times (2 to 3 months) are required for C. botulinum toxin production (6). Initially low pH levels of highly acidic products may increase over time due to the activity of mold and other organisms in jars, creating favorable conditions for C. botulinum spore germination and toxin production (4, 10).…”