Lactic acid fermentation: a traditional process for new applications

Fruit and vegetable harbour different microbial species and among them lactic acid bacteria were ranged from 2 and 4 Log CFU/g. Leuconostoc, Lactobacillus, Weissella, Enterococcus and Pediococcus genera can be found, however Lactobacillus plantarum as versatile species, is often encountered and employed for fruit and vegetable fermentations. Lactic acid fermentation can be applied using microorganisms as cell factories, for the production of interesting compounds as enzymes, flavouring agents, metabolites, etc. Moreover, can leads to the transformation of raw materials into final products (fermented food) contributing to shelf life extension, microbial safety and to the implementation of organoleptic, technological and nutritional properties. Some chemicals and physical parameters, such as pH, the concentration of sugars and organic acids, make, especially fruits, an hostile environment for microorganisms. Generally lactic acid bacteria has great biodiversity at species and strain level, derived from their ability to adapt in different environment. In adverse conditions, microorganisms shift towards specific metabolic pathways, using non-conventional carbon source, exploiting alternative substrates to improve stress tolerance. This attempt to adapt can resulted in flavours formation, phenolic compounds metabolism and molecules production. Based on these assumptions the aim of the present thesis was to exploit lactic acid bacteria in order to valorise different plant matrices, from fruit juices to food by-products. An overview on the metabolism of LAB strains, of plant but especially dairy origin, during fermentation, was reported. Two types of fruit juices, elderberry and cherry, and one by-product, orange peels, were used for fermentations in order to study the metabolism of the different strains applied, to modulate/improve the organoleptic and nutritional properties of juices and to produce lactic acid, a valuable chemical compound, from orange by-products.