BACKGROUND: The performances of four autochthonous isolates of Lactobacillus plantarum were assessed to study the most important variables acting on acidification and to propose a possible step-by-step approach for the validation at laboratory scale. This main topic was addressed through three intermediate steps: (1) evaluation of acidification in liquid and solid media, as a function of salt, nitrites, nitrates, lactose, pepper and temperature; (2) assessing acidification in a pork-meat preparation; and (3) designing a protocol to improve the performances at sub-optimal temperatures. The concentration of the ingredients and the temperature were combined through a 3k-p Fractional Factorial Design. Acidification and viable count were assessed and modelled through a multi-factorial ANOVA. RESULTS: In model systems acidification was affected by lactose and was maximum (ΔpH of ca. 2.8-3.0) in the combinations containing 0.4% lactose, 250 mg kg-1 nitrates or 150 mg kg-1 nitrites, 5% salt, and at 30 °C. Solid media caused a higher acidification. In the pork meat preparation, the effect of salt and nitrites was significant. At 10 °C the strains could not reduce pH, but this ability could be induced using an adaptation step. CONCLUSION: Acidification was affected by lactose in the model system, whereas in meat preparation the other variables were significant. In addition, a protocol to improve acidification at 10 °C was optimised.
BACKGROUND: The performances of four autochthonous isolates of Lactobacillus plantarum were assessed to study the most important variables acting on acidification and to propose a possible step-by-step approach for the validation at laboratory scale. This main topic was addressed through three intermediate steps: (1) evaluation of acidification in liquid and solid media, as a function of salt, nitrites, nitrates, lactose, pepper and temperature; (2) assessing acidification in a pork-meat preparation; and (3) designing a protocol to improve the performances at sub-optimal temperatures. The concentration of the ingredients and the temperature were combined through a 3k-p Fractional Factorial Design. Acidification and viable count were assessed and modelled through a multi-factorial ANOVA. RESULTS: In model systems acidification was affected by lactose and was maximum (ΔpH of ca. 2.8-3.0) in the combinations containing 0.4% lactose, 250 mg kg-1 nitrates or 150 mg kg-1 nitrites, 5% salt, and at 30 °C. Solid media caused a higher acidification. In the pork meat preparation, the effect of salt and nitrites was significant. At 10 °C the strains could not reduce pH, but this ability could be induced using an adaptation step. CONCLUSION: Acidification was affected by lactose in the model system, whereas in meat preparation the other variables were significant. In addition, a protocol to improve acidification at 10 °C was optimised.