Heat Shock Conditions

There are two purposes for using a heat shock during recovery protocols. First, it eliminates vegetative cells (including vegetative alicyclobacillus) to allow germination of spores without competition from other organisms. Second, it activates spores to germinate and outgrow although the actual increase in spore recovery is not well established. Unpublished results by Parish show as much as a 400% increase in recovery of alicyclobacillus from orange juice by use of a mild heat shock. However, heat shock may not be necessary in finished, shelf-stable, low pH products that do not contain competitive microflora. Further research is warranted to determine the effect of heat shocks on spore viability.

Heat shock regimes should be of appropriate duration to eliminate competing microflora but not so stringent as to inactivate spores. Baumgart et al. [43] suggest 20 minutes at 70° C as an effective heat shock regime. Parish and Goodrich [58] investigated various times and temperatures from 60° C for 30 minutes to 90°C for 5 minutes, but ultimately recommended 75°C for 10 minutes to recover alicyclobacilli from diluted orange juice. They reported optimal recovery over a range of times at specific temperatures: 10 to 30 minutes at 60 and 65°C; 5 to 25 minutes at 70 and 75°C; and up to 5 minutes at 80 and 85° C. Recovery at 90° C was inadequate compared to results at the other temperatures. Additionally, the heating menstruum may affect recovery. Several studies show that percent recovery increases as samples are diluted to lower sugar content.

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