Research Papers – Raw Milk Cheese Microbiology, Salmonella PCR, Hydrogen Peroxide – Listeria

Science Direct – Microbiology of Raw Milk Cheese

Cheese may be manufactured in the United States using raw milk, provided the cheese is aged for at least 60 days at temperatures not less than 35 °F (1.7 °C). There is now increased concern among regulators regarding the safety of raw milk cheese due to the potential ability of foodborne pathogens to survive the manufacturing and aging processes. In this study, 41 raw milk cheeses were obtained from retail specialty shops, farmers’ markets, and on-line sources. The cheeses were then analysed for the presence of Listeria monocytogenes, Salmonella, Escherichia coli O157:H7, Staphylococcus aureus, and Campylobacter. Aerobic plate counts (APC), coliform and yeast/mould counts were also performed. The results revealed that none of the enteric pathogens were detected in any of the samples tested. Five samples contained coliforms; two of those contained E. coli at less than 102 cfu/g. Three other cheese samples contained S. aureus. The APC and yeast-mould counts were within expected ranges. Based on the results obtained from these 41 raw milk cheeses, the 60-day aging rule for unpasteurized milk cheeses appears adequate for producing microbiologically safe products.

Science Direct – Salmonella Serotyping PCR

The most commonly used method for serotyping Salmonella spp. is based on the Kaufmann–White scheme, and is composed of serological reactions using antibodies to LPS agglutinins. The multiplex PCR used in this investigation was established by Kim et al. to serotype the 30 most common clinical Salmonella serotypes, as determined by CDC. The PCR assay consists of two five-plex reactions and a single two-plex PCR reaction, based on six genetic loci from Salmonella enterica serotype Typhimurium and four loci from S. enterica serotype Typhi. In this investigation, we further evaluated the method for serotyping Salmonella spp. using a reference collection, environmental samples collected from a Mid-Atlantic region tomato farm study, four food matrices spiked with different Salmonella serotypes and a proficiency test. The PCR assay was first evaluated using DNA isolated from pure cultures of isolates obtained from various clinical and environmental samples, and then DNA isolated from broth cultures of food matrices of “Red round” and Roma tomatoes, Romaine lettuce, green onions and Serrano peppers spiked with serotypes Newport, Typhimurium, Javiana and Saintpaul, respectively. The results showed that the PCR assay correctly serotyped Salmonella spp. from the clinical, environmental, spiked food matrices, and proficiency test samples. These findings are significant because the PCR assay was successful in the identification of Salmonella in the spiked samples in a broth culture containing other non-salmonella organism. This method may be a useful resource for the food safety community.

Science Direct – Hydrogen Peroxide – Listeria

The impact of sodium hypochlorite and hydrogen peroxide (H2O2 at 1 and 5%) solutions on Listeria innocua in red bell peppers, total mesophiles in strawberries and total coliforms in watercress was studied. Quality attributes such as colour, firmness and pH were studied for all products; total anthocyanins content was determined for strawberries. Sensorial analyses were also carried out for all products. Results showed that H2O2 (5%) provided the highest reductions of microbial loads. Besides H2O2 (1%) had a lower impact, it was more effective than water-washings. Sodium hypochlorite solutions lead to microbial reductions comparable to water risings. In terms of quality, H2O2 (5%) was the solution with higher negative impact on products’ colour. For strawberries, such colour alterations were also detected by sensorial analyses. The anthocyanins content decreased significantly. Overall it was found that H2O2 (1%) was a good sanitizer solution, since microbial reduction was attained while quality factors did not suffer considerable alterations.