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D Values of Bacillus stearothermophilus Spores as a Function of pH and Recovery Medium Acidulant

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The effect of the pH and the type of acidulant (citric acid or glucono-δ-lactone) of the recovery medium on the thermal resistance of Bacillus stearothermophilus ATCC 12980 was studied. The spores were heated in bidistilled water as a reference substrate and in acidified mushroom extract using citric acid or glucono-δ-lactone as acidulants (pH 6.2) and subcultured in reference (pH 7) and acidified (pH 6.2) media. A period of treatment-dependent pH sensitization was observed in heat-treated spores. In all cases, D values were lower in the acidified recovery medium than those obtained in the reference medium, but the type of acidulant used in the recovery medium had no influence on the D values. No influence on z values was observed as a consequence of the different recovery media, but they changed within a range of 7 to 10°C as a function of the different heating substrates. Glucono-δ-lactone proved to be as effective as citric acid in controlling the microbiological spoilage of foods. The pH has a great influence on decreasing the D values, mainly when acidification of the substrate and acidification of the recovery medium are combined. Consequently, it would be appropriate to take this effect into account in process calculations or validation.


Document Type: Research Article

Affiliations: 1: Centro de Edafologia y Biologia Aplicada del Segura (C. S. I. C.), Apartado de Correos 4195, 30080 Murcia, Spain 2: Instituto de Agroquimica y Tecnologia de Alimentos (C. S. I. C.), Jaime Roig 11, Valencia, Spain

Publication date: June 1, 1995

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