THE USE AND CONTROL OF MICROORGANISMS TO IMPROVE THE QUALITY OF FOOD

In this present PhD thesis were examined and evaluated different methods for improving the quality of various food products. The first work involved the study of antibacterial properties of the extract of the leaves of the plant Cocculus orbiculatus, against several serotypes of Listeria monocytogenes. The study of the composition of the extract showed the presence of 26 different compounds, thirteen of which have been extracted by hydro distillation and thirteen compounds by extraction with ethanol. Preliminary, also, the identification of the plant was carried out using molecular techniques. The results showed a bacteriostatic effect of the extract against the target organism under examination. The work presented in the second chapter, is part of a research project on “Qualification of pig genetic resources aimed at enhancement of production for the Protected Designation of Origin of the dry-cured ham San Daniele Friuli (D.O.P. Prosciutto di San Daniele Friuli), the Protected Designation of Origin of the Gran Padano pig (D.O.P. Gran Suino Padano), and to the Protected Geographical Indication (I.G.P. Sauris) of fresh meat and sausages obtained and recognized with the brand AQUA of Friuli Venezia Giulia”. It follows the chain of the pig from birth to slaughter. In particular, it was evaluated the impact of different pig breed on the final quality of the meat, using the same system of breeding and feeding. The breeds tested were Goland and Duroc per Large White mother. The evaluation was made by taking into account both, the meat (M. longissimus dorsi muscle) and San Daniele dry-cured ham, which is one of the transformed products. The results showed that there are no differences in the chemical-physical and microbiological characteristics of the meat as such, nor significant differences of physico-chemical characteristics of the dry-cured ham. The third work involved the use of starter cultures of L. curvatus and L. sakei to improve the shelf-life of cooked ham, sliced and packaged under modified atmosphere packaging (MAP). The use of bioprotective cultures influenced the flavour, odour and colour stability of the sliced cooked ham. In addition, the growth of indigenous lactic acid bacteria was inhibited, preventing the formation of the white superficial slime and consequently extending the shelf-life of the product up to 30 days. The fourth part of this thesis deals with the use of ozone for the decontamination of the equipment and tools used in food chain. Results obtained showed a great variability, depending on both, the type of the tested microorganisms (more or less-resistant, vegetative cells or spores) and the method used to deliver the ozone (wet and dry). As a result, an ozone concentration of 2 or 4 ppm allowed to obtain a reduction from 1 to 5 logs of the target microorganisms. The last part of this work involved a mix of bioprotective cultures, which were Lactobacillus carnosus/Lactobacillus sakei + Staphylococcus xylosus, Lactococcus lactis subsp. lactis/Lactobacillus sakei + Staphylococcus xylosus, also in different ratio, for the improvement of the shelf-life of hamburger packed under modified atmosphere (MAP) and stored at 4 ± 2 °C. Data showed that inoculated cultures extended the hamburgers shelf-life by limiting the ammoniacal molecules production, the development of spoilage and pathogenic microorganisms, in particular Brochothrix thermosphacta, and avoiding the formation of the white slime on the surface of the hamburgers.