Inhibitor‐Assisted High‐Pressure Inactivation of Bacteria in Skim Milk

Abstract

The combined inactivation effects of high hydrostatic pressure (HHP) and antimicrobial compounds (potassium sorbate and ε-polylysine [ε-PL]) on 4 different bacterial strains present in skim milk and the effect of these treatments on milk quality were investigated in this study. HHP treatment at 500 MPa for 5 min reduced the populations of Escherichia coli, Salmonella enterica Typhimurium, Listeria monocytogenes, and Staphylococcus aureus from 6.5 log colony-forming units (CFUs) or higher to less than 1 log CFU/mL. Compared to HHP alone, HHP with potassium or ε-PL resulted in significantly higher reductions in the bacterial counts. After 5 min of treatment with HHP (500 MPa) and ε-PL (2 mg/mL), no growth of E. coli, S. enterica Typhimurium, or L. monocytogenes in skim milk was observed during 15 d of refrigerated storage (4 ± 1 °C). Scanning electron microscopy analysis revealed that the synergistic treatments caused more serious damage to the bacterial cell walls. Quality assessments of the treated samples indicated that the combined treatments did not influence the color, the turbidity, the concentrations of -SH group of the proteins, or the in vitro digestion patterns of the milk. This study demonstrates that HHP with potassium or ε-PL may be useful in the processing of milk or milk-containing foods.

Synergistic effect of high‐intensity ultrasound, UV‐A light, and natural preservatives on microbial inactivation in milk

“…A significant change ( p < .05) in pH was also shown for the combination of 30 s US, 15 min UVA, and 2 mg/ml ε‐poly(lysine) when compared to the control UHT milk while there was no significant change ( p > .05) in the UHT milk subjected to the combination of 30 s US, 15 min UVA, and 0.5 mg/ml Nisin. These results are in agreement with what has been observed with the addition of ε‐poly(lysine) in milk in previous works (Kozak et al, 2018; Liu et al, 2017).…”

“…For the case of the factor antimicrobial concentration, ε‐poly(lysine) (labeled as EPL) had the levels of 0 and 2 mg/ml while Nisin (labeled as N) had the levels of 0 and 0.5 mg/ml. The EPL concentration was chosen based on a previous study that used a concentration of 2.0 mg/ml in skim milk (Liu et al, 2017). The concentration for Nisin was also chosen based on various other works (Alves et al, 2016; Dong & Yang, 2015; Pokhrel et al, 2019).…”

“…Changes in color were measured from the treatments with the combinations of the highest and lowest levels of the factors in the 2 k design (Tables 1 and 2), based on previous studies (Kozak et al, 2018; Liu et al, 2017). The samples were treated as stated above, with the exception that the samples were divided into six sterile glass test tubes with a volume of 1 ml per test tube for the UV‐A treatment.…”

Plant nutraceuticals as antimicrobial agents in food preservation: terpenoids, polyphenols and thiols

“…On the other hand, nonthermal technologies for food preservation, such as pulsed electric fields (PEFs) and high hydrostatic pressure (HHP), are really interesting since they do not affect food organoleptic properties. Nevertheless, under certain circumstances, these techniques are not able to ensure food safety, since some experiments have demonstrated that these physical treatments can lead only to sub-lethal damages in the bacterial cell walls [8] [9,10].…”

Hazard of Staphylococcal Enterotoxins in Food and Promising Strategies for Natural Products against Virulence

“…Furthermore, multiple chemical preservatives and antimicrobial physiotherapy are used in the food industry to extend the shelf life of food, but this approach may cause serious hazards . Synthetic chemical preservatives can cause many negative effects after long-term ingestion, such as toxicity and drug resistance. , Additionally, some heat treatment methods may cause undesirable changes in the sensory and nutritional properties of certain foods, while some non-thermal technologies, such as high hydrostatic pressure (HHP), may lead to incomplete sterilization because they can only cause sublethal damage to bacteria. ,− …”