Abstract
As one of the emerging non-thermal technologies, pulsed light (PL) facilitates rapid, mild and residue-free microbial surface decontamination of food and food contact materials. While notable progress has been made in the characterization of the inactivation potential of PL, experimental data available on the tolerance development to the same (homologous) stress or to different (heterologous) stresses commonly applied in food manufacturing (e.g., acid, heat, salt) is rather controversial. The findings of the present study clearly indicate that both the homologous tolerance development against PL as well as the heterologous tolerance development from heat to PL can be triggered in Listeria monocytogenes. Further, conducted kinetic analysis confirmed that the conventionally applied log-linear model is not well suited to describe the inactivation of L. monocytogenes, when exposed to PL. Instead, the Weibull model as well as the log-linear + tail model were identified as suitable models. Transmission electron microscopic (TEM) approaches allow suggestions on the morphological alterations in L. monocytogenes cells after being subjected to PL.
Highlights
Research and development have increasingly focused on the substitution of conventionally used heat treatments like sterilization and pasteurization with novel and mild decontamination techniques in order to meet consumer expectations and microbiological safety criteria of foods (Aymerich et al, 2008; Sofos, 2008; Havelaar et al, 2010; Rajkovic et al, 2010; Weiss et al, 2010; Knorr et al, 2011)
The present results show that homologous tolerance development to pulsed light (PL) is possible in L. monocytogenes and that repeatedly treated microorganisms are approximately 1 log colony forming units (CFU) cm−2 less susceptible to subsequent PL treatments
The present study showed that L. monocytogenes Li-P492 exhibited a significant (p < 0.05) higher cross-tolerance behavior following PL treatment of 0.46 J cm−2 after previous heat stress (45◦C) of approximately 1 log CFU cm−2
Summary
Research and development have increasingly focused on the substitution of conventionally used heat treatments like sterilization and pasteurization with novel and mild decontamination techniques in order to meet consumer expectations and microbiological safety criteria of foods (Aymerich et al, 2008; Sofos, 2008; Havelaar et al, 2010; Rajkovic et al, 2010; Weiss et al, 2010; Knorr et al, 2011). Technologies like mild heat treatments, high pressure processing, pulsed electric field, weak organic acids and aqueous chlorine dioxide. S. Food and Drug Administration (FDA) making progress to broad industrial application, is of highest interest for food business operators since it allows for a fast, mild and residue-free decontamination. When applying PL, it must be considered that the efficiency of the treatment is strongly influenced by the three main factors, namely the nature of the treated matrix (transparency or opacity, surface characteristics, and composition), microbial contamination (microorganism, physiological state, population density, and growth characteristics) and the process parameters (spectrum, geometry, and set up) chosen (Dunn et al, 1989; Food and Drug Administration [FDA], 1996; Palmieri and Cacace, 2005; Wang et al, 2005; Heinrich et al, 2016)
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