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Thermal pasteurization can achieve the U.S. Food and Drug Administration-required 5-log reduction of pathogenic Escherichia coli O157:H7 and Cryptosporidium parvum in apple juice and cider, but it can also negatively affect the nutritional and organoleptic properties of the treated products. In addition, thermal pasteurization is only marginally effective against the acidophilic, thermophilic, and spore-forming bacteria Alicyclohacillus spp., which is known to cause off-flavors in juice products. In this study, the efficiency of a combined microfiltration (MF) and UV process as a nonthermal treatment for the reduction of pathogenic and nonpathogenic E. coli, C. parvum, and Alicyclohacillus acidoterrestris from apple cider was investigated. MF was used to physically remove suspended solids and microorganisms from apple cider, thus enhancing the effectiveness of UV and allowing a lower UV dose to be used. MF, with ceramic membranes (pore sizes, 0.8 and 1.4 µm), was performed at a temperature of 10°C and a transmembrane pressure of 155 kPa. The subsequent UV treatment was conducted using at a low UV dose of 1.75 mj/cm². The combined MF and UV achieved more than a 5-log reduction of E. coli, C. parvum, and A. acidoterrestris. MF with the 0.8-² m pore size performed better than the 1.4-²m pore size on removal of E. coli and A. acidoterrestris. The developed nonthermal hurdle treatment has the potential to significantly reduce pathogens, as well as spores, yeasts, molds, and protozoa in apple cider, and thus help juice processors improve the safety and quality of their products. [ABSTRACT FROM AUTHOR]

Abstract: Pulsed light (PL) is a technology that uses short, high-energy pulses of UV-rich broad spectrum light to inactivate a range of pathogenic and spoilage microorganisms in foods and on food contact surfaces. Microbial inactivation is directly related to the energy dose (fluence) received by the target microbes. Since fluence decays away from the lamp source due to light absorption and scattering phenomena, it is necessary to accurately quantify the fluence received locally within a substrate in order to design uniform antimicrobial PL treatments. The main objective of this work was to quantify and map the spatial distribution of both total and UV fluence both in air and in liquid substrates with different optical properties. Butterfield’s phosphate buffer (BPB), trypticase soy broth (TSB), and apple juice (clarified apple cider) were used as substrates and Listeria innocua was used as the challenge microorganism. A pyroelectric head, and a UV–VIS–NIR spectrophotometer connected to a 1000μm optical fiber, were used to measure the fluence in air and the three liquid substrates. Fluence was measured at incremental distances from the lamp, along the x-, y- and z-axes. As expected, fluence decreased with increasing distance from the lamp, in all three directions. A 3-parameter Gaussian model described well the spatial distribution of fluence, both in air and in the liquid substrates. Overall, this study emphasizes the fact that substrate–light interactions affect the spatial distribution of fluence within a substrate, and these non-uniformities need to be taken into account when developing commercial applications of PL. [ABSTRACT FROM AUTHOR]

Pulsed light (PL) treatment has been proven effective for killing a wide variety of microorganisms on foods and food contact materials. However, there is concern regarding how shading may impact the effectiveness of PL when applied to imperfect surfaces. The main objective of this work was to examine how surface properties, particularly topography, influence the microbicidal effect of PL. Four types of stainless-steel surfaces were inoculated with Listeria innocua and treated with up to 12 pulses of light. The highest level of inactivation achieved was about a 4-log reduction. Initially, an increase in inactivation with increasing treatment intensity was observed, but the inactivation curves tailed off above 3 light pulses. The differences in inactivation levels among the 4 finishes at specific treatment levels were rather insignificant, but some interesting trends were observed. At low treatment levels, inactivation on the smoothest finish was slightly lower than for the other surfaces, due to clustering of the cells on the highly hydrophobic smooth surface and to its reflective nature. For the roughest surface, scanning electron microscopy (SEM) imaging confirmed the preferential location of the cells inside surface features, which also promoted a relatively uniform distribution of the cells across the surface. This counter balanced to some extent of the shading effects, and as a result inactivation on the roughest surface was comparable to inactivation on the smoother surfaces. These results demonstrate that PL can be effective on both smooth and rough surfaces, but also indicate a complex effect of various surface properties on inactivation. [ABSTRACT FROM AUTHOR]

Pulsed Light (PL) is effective for inactivation of bacteria in food and non-food systems, yet the mechanisms of inactivation are not fully understood. In this work, the response of Listeria monocytogenes to PL and continuous ultraviolet light (UV) was investigated using whole genome DNA microarray analysis. Suspensions of L. monocytogenes were treated with 3.20 J/cm 2 of PL and 33 mJ/cm 2 of UV, respectively, which yielded comparable levels of inactivation. In a separate experiment, cells were exposed to 3.20 J/cm 2 of full spectrum PL and UV-blocked PL. Whole genome microarray analysis of L. monocytogenes was performed to identify differential gene expression after the treatments, using a 1.5 fold change cutoff and adjusted P < 0.05. Compared to untreated cells, PL and UV treated cells had higher transcription levels for 80 and respectively 39 multiple stress related proteins, motility genes, and transcriptional regulators. Exposure to UV-blocked PL resulted in 131 motility related genes and cell membrane related genes with lower transcription levels, and no genes with higher transcription levels compared to untreated cells. The data suggests that the microbicidal effects of PL were primarily due to UV, and no significant differences in gene expression between PL and UV treated cells were found. [ABSTRACT FROM AUTHOR]