Effect of salt concentration on acid‐ and salt‐adaptedEscherichia coliO157:H7 andListeria monocytogenesin recombined nonfat cast cheese

Abstract

In Turkey, legislation reduced the salt content in fresh cheeses from 10% to 6.5% in dry matter (DM). This study investigated the effect of salt reduction on the fate of acid‐ and salt‐adapted Escherichia coli O157:H7 and Listeria monocytogenes, as well as the textural quality of recombined nonfat cheese. The cheese was manufactured using milk protein concentrate (85% protein) and skim milk powder (35% protein). After pasteurization and addition of starter culture (0.1%), cheese milk was inoculated with acid‐ or salt‐adapted pathogens (1 × 103 cfu/g). Following salting (4%, 6%, 8%, or 10% in DM) and fermenting (24 hr/30 °C), the microbiological and textural properties of the cheese were analyzed during 8 weeks of storage at 4 °C. Salt concentration did not affect E. coli survival during storage (p > .05). Acid‐adapted L. monocytogenes and E. coli survived 1 week longer than the unadapted control. Cheese hardness was unaffected (p > .05) by the salt concentration. Practical applications The results of the present study can be used to assess the risk of survival of acid‐ and salt‐adapted Listeria monocytogenes or Escherichia coli O157:H7 in nonfat cheese (with different salt concentration) produced from unpasteurized milk.

Protective culture: Is it a solution to improve the quality of culture‐free white cheese?

“…Obtaining higher yield and dry matter (31.74 ± 0.13%) values in the LC cheese and a lower rate of dry matter passing into the whey is thought to be related to faster acidity development throughout the process. This can be explained by the decrease in electrostatic repulsion forces and the increase in hydrophobic interaction as the cheese pH value approaches the isoelectric point of casein (Wusimanjiang et al, 2019). The acidity development has a positive effect on the separation of whey from curd and also reduces the loss of nondry matter in whey.…”

“…These results may be associated with the penetration of brine salt into the cheese over time and are consistent with Soltani et al (2015). Wusimanjiang et al (2019) pointed out that the increasing salt concentration decreased the growth and survival of LAB. As presented in Figure 3e,f, where the salt change in cheese is shown during the ripening period, it is seen that the salt movement increases in cheese after 15 days and then tends to decrease.…”

“…Also, the manufacturer stated that the culture has low acidifying and fermenting activities. Several studies have reported that L. plantarum produced weak acidity after inoculation into sterile milk (Ma et al, 2016;Xanthopoulos et al, 2000). Similarly, with the addition of L. plantarum to sterile donkey milk, it was stated that a pH change of 1.78 ± 0.66 units was measured at the end of 24 hr at 37°C incubation, whereas S. thermophilus produced almost twice as much acidity (Turchi et al, 2017)…”

“…Soltani et al (2015) Wusimanjiang et al (2019). pointed out that the increasing salt concentration decreased the growth and survival of LAB.…”

From Cheese-Making to Consumption: Exploring the Microbial Safety of Cheeses through Predictive Microbiology Models

“…Microbial stress responses can lead to adaptation or cross-protection mechanisms, which can increase the survival/growth capacity of cells or enable the recovery of injured cells back to their healthy status [ 79 ]. Although no differences between the survival rates of non-acid and acid-adapted cells were revealed when accessing the survival of L. monocytogenes in a traditional Greek cheese in the study by Mataragas et al [ 79 ], higher survival capacity of acid-adapted L. monocytogenes and E. coli O157:H7 compared with non-acid adapted strains was observed on fresh cheeses [ 98 ].…”