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Pressure-assisted thermal food processing offers enhanced lethality using antimicrobial compounds.

Thermal sterilization has traditionally been used to inactivate bacterial spores in low-acid foods. However, the use of conventional heating at more than 100 C can adversely affect a product's quality attributes. Pressure-assisted thermal processing (PATP), which involves the use of pressures from 500 to 700 MPa at from 90 C to 121 C, offers new opportunities to overcome this limitation.

Scientists at The Ohio State University set out to enhance the lethality of PATP against pressure- and heat-resistant spores of B. amyloliquefaciens by sensitizing the spores with selected antimicrobial compounds. Their research revealed that PATP-induced inactivation of bacterial spores could be enhanced in this manner, and this approach could be one way to process low-acid foods using less severe heat and pressure conditions. This would preserve quality attributes to an extent greater than is possible with traditional thermal retorting.

The researchers prepared a spore crop of B. amyloliquefaciens TMW 2.479 Fad 82 on nutrient agar, which also contained 0.6% yeast extract and 10 ppm of manganese sulphate and water. The mix was incubated at 32 C for three days.

The spores were suspended in 50 mM of 4-(2-hydroxyethyl)-1piperazineethanesulfonic acid (HEPES) buffer or a buffer containing selected antimicrobial compounds, including chelating agents, surfactants, natural polymers and enzymes, at an inoculum level of about 4.7 X [10.sup.8] CFU per ml. The spore suspensions were treated at 600 MPa and 105 C for two minutes in a high- pressure microbial kinetic tester. The scientists determined the viable counts after the PATP treatment.

Among the 20 different compounds tested, lysozyme, sodium dodecyl sulfate (SDS) and chitosan were most effective at increasing the lethality of PATP. Spore inactivation of the bacteria was enhanced by at least 1.0 log using 2 g per of lysozyme or SDS at pH 7.0, and by 2.0 logs using 2 g per L of chitosan at pH 6.0. A synergistic effect resulted from combining chitosan with SDS. This enhanced the PATP lethality by 3.0 logs. Pre-process temperature history also influenced spore inactivation. No significant germination of spores was detected by the scientists.

Further information. Ahmed E. Yousef, Department of Food Science and Technology, The Ohio State University, 2015 Fyffe Rd., Parker Building, Columbus, OH 43210; phone: 614-292-7814; fax: 614-292-0218; email:
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Publication:Microbial Update International
Date:Dec 1, 2011
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