Antibacterial Mechanism of 3-Carene against the Meat Spoilage Bacterium Pseudomonas lundensis and Its Application in Pork during Refrigerated Storage

Pseudomonas lundensis is the main bacterium responsible for meat spoilage and its control is of great significance. 3-Carene, a natural monoterpene, has been proved to possess antimicrobial activities. This study aimed to investigate the antibacterial activity and mechanism of 3-carene against the meat spoilage bacterium P. lundensis, and explore its application on pork. After 3-carene treatment, cellular structural changes were observed. Cell walls and membranes were destroyed, resulting in the leakage of alkaline phosphatase and cellular contents. The decreased activity of Ca²⁺-Mg²⁺-ATPase and Na⁺-K⁺-ATPase showed the imbalance of intracellular ions. Subsequently, adenosine triphosphate (ATP) content and oxidative respiratory metabolism characteristics indicated that 3-carene inhibited the metabolism of the tricarboxylic acid cycle in P. lundensis. The results of binding 3-carene with the vital proteins (MurA, OmpW, and AtpD) related to the formation of the cell wall, the composition of the cell membrane, and the synthesis of ATP further suggested that 3-carene possibly affected the normal function of those proteins. In addition, the growth of P. lundensis and increase in pH were inhibited in pork during the 5 days of cold storage after the samples were pre-treated with 3-carene. These results show the anti-P. lundensis activity and mechanism of 3-carene, and its potential use in meat preservation under refrigerated conditions.

Effect of the homogenization technique on the enumeration of psychrotrophic bacteria in food absorbent pads

Four methods were tested for enumerating bacteria present in the absorbent pads (AP) used in packaging chicken and other meats. Viable counts were ascertained at day 0 and day 7 (d0 and d7, respectively). Sampling bacterial cells from AP were carried out using a countertop blender, Stomacher, sonication, and blender in combination to sonication. The release of bacterial cells by breaking down the AP with the blender resulted in the highest CFU counts. At d0, a bacterial recovery rate of 94% was obtained with the blender, while the recovery rates using Stomacher or sonication alone were 58% and 73%, respectively. At d7, the Stomacher treatment also gave the lowest colony forming unit (CFU) values in the AP incubated at 7 °C. Sonication of the AP prior to homogenization with the blender did not increase CFU counts. Results suggested that breaking down the AP with a blender gives higher CFU levels than the Stomacher, which is the most commonly used technique for this purpose.

Development of two specific multiplex qPCRs to determine amounts of Pseudomonas, Enterobacteriaceae, Brochothrix thermosphacta and Staphylococcus in meat and heat-treated meat products

Culturing methods are conventionally applied to investigate the contamination of food with several microorganisms after heat processing. However, with these methods, it is not possible to evaluate whether heat-treated meat products, such as cooked sausages, contained parts of spoiled meat. Therefore, two specific multiplex qPCRs were developed in this study in order to determine the microbiological quality of the raw materials used for these products. The PCR targets focused on four bacterial groups often found on meat (family Enterobacteriaceae, genus Pseudomonas, genus Staphylococcus and species Brochothrix thermosphacta). Specificity as well as sensitivity of the developed multiplex qPCRs, validated by using 68 microbial species, were 100%. The applicability of both multiplex qPCRs compared to culturing methods was performed using 96 meat samples (fresh and naturally spoiled) and 12 inhouse-made "Lyoner" sausages containing variable ratios of spoiled meat (0%, 5%, 12% and 25%; n = 3 for each group). Both methods showed similar results by evaluating the ∆log₁₀ cfu/g, the relative accuracy and the t-test analysis (p > 0.05). Comparing qPCR results of the different sausage groups, a significant difference between sausages containing fresh meat and sausages containing spoiled meat (12% and 25%) was found only for Pseudomonas and B. thermosphacta in both raw and cooked sausages. The statistical difference between 5% vs. 12% and 25% spoiled meat in cooked sausages, was also found only for these two bacterial groups. The developed multiplex qPCRs were further applied to 30 commercially available "Bologna-type" sausages. The results showed a total of 14 sausages considered to be suspicious for Food Fraud. While the role of Staphylococcus spp. in meat spoilage remains unclear, Pseudomonas, Enterobacteriaceae and B. thermosphacta could together be used as an indicator for "spoiled meat" used in sausages. The developed qPCR systems in this study allow the detection of four relevant bacterial groups in the heated Bologna-type sausages and provide information about the hygienic quality of raw materials used. This method could thus be helpful for screening food suspected of Food Fraud.

Purification and Characterization of a Novel Cold-Active Lipase from the Yeast Candida zeylanoides

Cold-active lipases have attracted attention in recent years due to their potential applications in reactions requiring lower temperatures. Both bacterial and fungal lipases have been investigated, each having distinct advantages for particular applications. Among yeasts, cold-active lipases from the genera Candida, Yarrowia, Rhodotorula, and Pichia have been reported. In this paper, biosynthesis and properties of a novel cold-active lipase from Candida zeylanoides isolated from refrigerated poultry meat are described. Heat-sterilized olive oil was found to be the best lipase biosynthesis inducer, while nonionic detergents were not effective. The enzyme was purified to homogeneity using hydrophobic chromatography and its enzymatic properties were tested. Pure enzyme activity at 7 °C was about 60% of the maximal activity at 27 °C. The enzyme had rather good activity at higher temperatures, as well. Optimal pH of pure lipase was between 7.3 and 8.2, while the enzyme from the crude extract had an optimum pH of about 9.0. The enzyme was sensitive to high ionic strength and lost most of its activity at high salt concentrations. Due to the described properties, cold-active C. zeylanoides lipase has comparative advantages to most similar enzymes with technological applications and may have potential to become an industrially important enzyme.

Microbial changes in vacuum-packed chilled pork during storage

Microbial composition in vacuum-packed chilled pork was investigated. The number of microbial counts increased during the period of 21 day storage with the deterioration of meat. A total of 28,216 bacterial sequences were obtained for the assessment of microbial diversity from vacuum packed pork during chilled storage. More than 200 bacterial genera belonging to eighteen phyla were observed, and most of them are likely to be associated with contamination via fecal, air and/or water during slaughtering and subsequent meat handling. Microbial populations changed greatly during storage, of which the seventh day was a critical time point for microbial diversity. Micrococcaceae, Flavobacteriaceae, Enterobacteriaceae, Lactobacillaceae and Carnobacteriaceae were the major components that may be associated with the spoilage of meat. Although the potential impact of detected microbes on meat hygiene and/or safety is unknown, effective decontamination of the whole chain is always important for meat industry to guarantee meat safety and to improve shelf-life of fresh meat.