Factors that inhibit growth of Listeria monocytogenes in nature-ripened Gouda cheese: A major role for undissociated lactic acid
Wemmenhove, E. ; Valenberg, H.J.F. van; Hooijdonk, A.C.M. van; Wells-Bennik, M.H.J. ; Zwietering, M.H. - \ 2018
Food Control 84 (2018). - ISSN 0956-7135 - p. 413 - 418.
Acetic acid - Diacetyl - Free fatty acids - Gouda cheese - Growth inhibition - Growth limit - L. monocytogenes - Lactoferrin - Nisin - Nitrate - Nitrite - pH - Safety criteria - Temperature - Undissociated lactic acid - Water activity
In this study, factors relevant to nature-ripened Gouda cheese were evaluated for their potential to inhibit growth of Listeria monocytogenes. Factors included water activity, pH, undissociated acetic and lactic acid, diacetyl, free fatty acids, lactoferrin, nitrate, nitrite and nisin. In addition, the effect of temperature was evaluated. For each factor, the actual concentrations and values relevant to Gouda cheese were obtained and the inhibitory effect of these individual factors on growth of L. monocytogenes was assessed. This evaluation revealed that undissociated lactic acid is the most important factor for growth inhibition of L. monocytogenes in Gouda cheese and that, additionally, low water activity as present in the cheese rind and after prolonged ripening times can also cause full growth inhibition. Gouda cheeses have a typical total lactic acid content of 1.47% w/w. In a 2-week old Gouda cheese, with a pH value of 5.25 and a moisture content of 42% w/w, the concentration of undissociated lactic acid in the water phase is 10.9 mM. Growth of L. monocytogenes is not supported when the undissociated lactic acid concentration is > 6.35 mM. Concentrations of undissociated lactic acid in the water phase of Gouda cheese will be higher than this value when the total lactic acid content is > 0.86% w/w at a pH < 5.25 (relevant to young Gouda cheese), or > 1.26% w/w at a pH < 5.50 for mature Gouda cheese (moisture content of 35% w/w). This study underlines the importance of undissociated lactic acid as growth inhibitor for L. monocytogenes in Gouda cheese.
Minimal inhibitory concentrations of undissociated lactic, acetic, citric and propionic acid for Listeria monocytogenes under conditions relevant to cheese
Wemmenhove, Ellen ; Valenberg, Hein J.F. van; Zwietering, Marcel H. ; Hooijdonk, Toon C.M. van; Wells-Bennik, Marjon H.J. - \ 2016
Food Microbiology 58 (2016). - ISSN 0740-0020 - p. 63 - 67.
Growth inhibition - PH - Salt - Temperature - Undissociated organic acid
Minimal inhibitory concentrations (MICs) of undissociated lactic acid were determined for six different Listeria monocytogenes strains at 30 °C and in a pH range of 4.2-5.8. Small increments in pH and acid concentrations were used to accurately establish the growth/no growth limits of L. monocytogenes for these acids. The MICs of undissociated lactic acid in the pH range of 5.2-5.8 were generally higher than at pH 4.6 for the different L. monocytogenes strains. The average MIC of undissociated lactic acid was 5.0 (SD 1.5) mM in the pH range 5.2-5.6, which is relevant to Gouda cheese. Significant differences in MICs of undissociated lactic acid were found between strains of L. monocytogenes at a given pH, with a maximum observed level of 9.0 mM. Variations in MICs were mostly due to strain variation. In the pH range 5.2-5.6, the MICs of undissociated lactic acid were not significantly different at 12 °C and 30 °C. The average MICs of undissociated acetic acid, citric acid, and propionic acid were 19.0 (SD 6.5) mM, 3.8 (SD 0.9) mM, and 11.0 (SD 6.3) mM, respectively, for the six L. monocytogenes strains tested in the pH range 5.2-5.6. Variations in MICs of these organic acids for L. monocytogenes were also mostly due to strain variation. The generated data contribute to improved predictions of growth/no growth of L. monocytogenes in cheese and other foods containing these organic acids.