The objective of this study is the rheological characterization of photocrosslinked alginate hydrogels synthesized from methacrylated alginate macromonomers. We first optimized the rheological acquisition parameters for this hydrogels, that is, we studied the influence of the geometries diameter, distance between plates (gap), and solvent trap in the rheological response. Our results show important variations of shear storage modulus, G', and yield strain with the three parameters measured. Secondly, with the optimized experimental parameters, rheological tests were performed on hydrogels synthesized under different conditions. Three parameters were studied; UV exposure time (polymerization time), macromonomer concentration and photoinitiator concentration. Our data indicate that the polymerization time and the macromonomer concentration have an important effect on the viscoelastic properties of the hydrogel, significantly modifying the shear storage modulus, G', and the yield strain while the photoinitiator concentration did not influence the viscoelastic properties.

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Listeria monocytogenes is a major foodborne pathogen that can contaminate food products and colonize food-producing facilities. Foodservice operations (FSOp) are frequently responsible for foodborne outbreaks due to food safety practices failures. We investigated the presence of and characterized L. monocytogenes from two FSOp (cafeterias) distributing ready-to-eat meals and verified FSOp’s compliance with good manufacturing practices (GMP). Two facilities (FSOp-A and FSOp-B) were visited three times each over 5 months. We sampled foods, ingredients, and surfaces for microbiological analysis, and L. monocytogenes isolates were characterized by phylogenetic analyses and phenotypic characteristics. GMP audits were performed in the first and third visits. A ready-to-eat salad (FSOp-A) and a frozen ingredient (FSOp-B) were contaminated with L. monocytogenes, which was also detected on Zone 3 surfaces (floor, drains, and a boot cover). The phylogenetic analysis demonstrated that FSOp-B had persistent L. monocytogenes strains, but environmental isolates were not closely related to food or ingredient isolates. GMP audits showed that both operations worked under “fair” conditions, and “facilities and equipment” was the section with the least compliances. The presence of L. monocytogenes in the environment and GMP failures could promote food contamination with this pathogen, presenting a risk to consumers.

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