Modelling the effects of pH, storage temperature and redox potential (Eh) on the survival of bifidobacteria in fermented milk

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The effects of storage temperature, pH and Eh on the survival of Bifidobacterium longum and Bifidobacterium animalis ssp. lactis were modelled in a 3 × 4 × 3 factorial design using three storage temperatures (4, 8, 12 °C), four pH (4.0, 4.25, 4.5, 4.75) and three Eh (0, 200, 400 mV) values. Bifidobacterium animalis ssp. lactis showed significantly better survival than B. longum (P < 0.0001) in fermented milk under normal environmental conditions. Bifidobacterium longum was more susceptible to acidity and survival was log-linear at low pH values whereas at higher pH pronounced shouldering and tailing effects were apparent. Both individual environmental conditions (T, pH, Eh) and interactions between Eh and pH affected survival and death was always more rapid in B. longum. Bifidobacterium animalis ssp. lactis generally showed a simple log-linear reduction over time. Temperature, pH and Eh could be manipulated to enhance survival but Eh reduction appears to be the best way to enhance survival without adversely affecting other properties.

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