In Vitro Evaluation of Bacteriocin-Like Inhibitory Substances Produced by Lactic Acid Bacteria Isolated During Traditional Sicilian Cheese Making.

Bacteriocins are antimicrobial proteins produced by bacteria that inhibit the growth of other bacteria with a bactericidal or bacteriostatic mode of action. Many lactic acid bacteria (LAB) produce a high diversity of different bacteriocins. Bacteriocinogenic LAB are generally recognised as safe (GRAS) and useful to control the frequent development of pathogens and spoilage microorganisms. For this reason they are commonly used as starter cultures in food fermentations. In this study, the authors describe the results of a screening on 699 LAB isolated from wooden vat surfaces, raw milk and traditional Sicilian cheeses, for the production of bacteriocin-like inhibitory substances, by comparing two alternative methods. The antagonistic activity of LAB and its proteinaceous nature were evaluated using the spot-on-the-lawn and the well-diffusion assay (WDA) and the sensitivity to proteolytic (proteinase K, protease B and trypsin), amylolytic (a-amylase) and lipolytic (lipase) enzymes. The indicator strains used were: Listeria monocytogenes, Staphylococcus aureus, Escherichia coli, Salmonella enteritidis. A total of 223 strains (belonging to the species Enterococcus spp., Lactobacillus spp., Pediococcus spp., Streptococcus spp., Leuconostoc spp. and Lactococcus lactis) were found to inhibit the growth of Listeria monocytogenes by using the spot-on-the-lawn method; only 37 of these were confirmed by using the WDA. The direct addition of bacteriocin-producing cultures into dairy products can be a more practical and economic option for the improvement of the safety and quality of the final product.

Characterisation of the Microflora Contaminating the Wooden Vats Used for Traditional Sicilian Cheese Production.

Traditional Sicilian cheese productions are carried out employing traditional wooden vats, called tina. Many studies have highlighted the beneficial role of wooden dairy equipment by contributing to enriching the milk microflora and improving the acidification processes. The present work was undertaken to evaluate the safety of the wooden vats used to coagulate milk. To this purpose, the different microbial populations hosted onto the internal surfaces of the vats used to produce two different stretched cheeses, namely Caciocavallo Palermitano and Vastedda della valle del Belìce DOP, were investigated for the presence of spoilage and pathogenic microorganisms as well as for bacteria with inhibitory effect in vitro against pathogenic microorganisms. A wide biodiversity of protechnological lactic acid bacteria (LAB), in terms of species, was revealed. Several LAB inhibited the growth of Listeria monocytogenes ATCC 7644. The wooden vats analysed resulted safe for three main findings: absence of the main pathogenic species, presence of high levels of LAB, anti-Listeria activity of many LAB.

Sensory and Microbiological Evaluation of Traditional Ovine Ricotta Cheese in Modified Atmosphere Packaging.

Ovine ricotta cheese is a traditional Sicilian dairy product characterised by high humidity and a short shelf life (2-4 days when refrigerated). The increasing demand for fresh food has prompted manufacturers to develop special packaging techniques, such as modified atmosphere packaging (MAP), that can extend the shelf life and maintain the organoleptic characteristics of ovine ricotta cheese. The aim of the present study was to evaluate the shelf life of fresh MAP-packed ovine ricotta cheese by monitoring the microbiological, chemical, physical and organoleptic characteristics of the product. Samples of a single batch were packed in MAP or vacuum packed and stored at 4°C for 24 and 7 days, respectively. Water activity, pH, physicochemical parameters and microbiological characteristics were examined. A sensory panel rated the product's main organoleptic characteristics (colour, odour, flavour and texture). Results showed that MAP controlled the development of any unwanted microflora, but did not affect the development of intrinsic lactic floras or chemical parameters. Sensory analysis revealed that overall the MAP-packed ricotta remained acceptable for up to 15 days of storage. The vacuum-packed ricotta cheese, however, showed a progressive deterioration in organoleptic characteristics from day 5 onward and therefore had a shorter shelf life. In conclusion, the ability of MAP to extend the shelf life of a traditional regional product (such as fresh ovine ricotta cheese) guarantees consumers a quality product and provides opportunities for manufacturers to expand their markets beyond national boundaries.