BIOTECHNOLOGICAL AND SPECTROSCOPICAL EVALUATION OF SELECTED LACTOBACILLUS PLANTARUM STRAINS WITH PROBIOTIC AND NUTRACEUTICAL POTENTIALITIES

Probiotics are non-pathogenic microorganisms that, when ingested in adequate amounts, exert a positive influence on their host’s health. A variety of microorganisms, typically food grade lactic acid bacteria (LAB), have been evaluated for their probiotic potential and are applied as adjunct cultures in various types of food products or in therapeutic preparations. Within the genus Lactobacillus, Lactobacillus plantarum is a member of the facultatively heterofermentative group of lactobacilli. It is a heterogeneous and versatile species that is encountered in a variety of environmental niches, including dairy, meat, fish, and many vegetable or plant fermentations. L. plantarum strains have also been found in many cheese varieties. Moreover, strains of L. plantarum have proven ability to survive gastric transit and colonize the intestinal tract of humans and other mammals. Thus, the aim of this Ph.D. thesis was to select and characterize strains belonging to Lactobacillus plantarum species for their probiotic and nutraceutical potentialities which could be added to other foods for exploitation as carrier of functional supplements. Eighty Lactobacillus plantarum strains isolated from different matrixes were evaluated for their probiotic and nutraceutical potential. After a preliminary subtractive screening based on the presence of msa and bsh genes, the strains which showed the presence of these two genes, were characterized for their nutraceutical features dealing with their ability to produce riboflavin and to remove cholesterol from growth medium. At the same time, a spectroscopical characterization of these bacteria was carried out. Strains were tested for their ability to grow in milk whey and the fermentation parameters, such as microbial growth, lactose decrease and lactic acid increase, were monitored by a NIR optic probe. Results obtained show how this non-destructive technique could be a viable alternative to traditional methods. In fact, the NIR proposed regression models were very satisfactory for all of the three considered analytes showing an high correlation coefficient coupled with low errors both in calibration and prediction. Thanks to this technique, it was verified whether strains with different ability to remove cholesterol can show changes in the cell wall. Preliminary data obtained by PCA analysis showed the suitability of these techniques for the study of the bacterial cell walls: changes in the spectra seemed to highlight the possibility to distinguish not only different strains but also different effects produced by the addiction of cholesterol in the medium. The potential of NIR coupled with Aquaphotomics and multivariate techniques to identify species has been investigated for evaluating its feasibility in microbiology. Spectral data analysis revealed very promising results for discrimination and classification of samples, demonstrating how this technique successfully distinguished between different bacteria. The research of lactic acid bacteria with probiotic and nutraceutical potentialities offer the opportunity to improve the nutritional quality of many fermented foods by increasing their added value. The development of new functional foods by fermentation may contribute to a further expansion of the market for this class of products. These new functional foods could help people with illnesses from vitamin deficiency, but could also pave the way for the development of food products "functional" for specific consumer groups with special needs such as the elderly, adolescents, pregnant women, children, athletes and vegetarians.