Lactic acid bacteria (LAB) play a critical role in food production and health maintenance. There is an increasing interest in these species to reveal the many possible health benefits associated with them. The actions of LAB are species and strain specific, and depend on the amount of bacteria available in the gastrointestinal tract. Consumers are very concerned of chemical preservatives and processed foods. However, products with or processed with LAB are accepted as a natural way to preserve

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... ood and promote health. This paper aimed to review the recent data in regard to the role of probiotic LAB in the preservation of foods, in the immunomodulation in the gastrointestinal tract, and in its health benefits. The hypothetical first niche of the ancestral LAB is considered soil and plants and, subsequently, the gut of herbivorous animals [6] . The mammalian intestine is colonized by 100 trillions of microorganisms (called "microbiota") that are essential for health [7] [8]. The transition from soil and plants to the animal gut has three areas of genomic adaptation [9]: resistance to host barriers, adhesion to intestinal cells, and fermentation of some substrates in the gut. The membrane lipid composition is affected by low pH and bile salts. Microarray analysis has shown the expression of a glycerophosphatase in Lactobacillus reuteri after an acid shock, and an increase in the sensitivity to acid in Lactobacillus acidophilus [10] . Extracelullar lipopolysaccharides (LPS) also play a role in the resistance, but it is unclear [6] . The adhesion of LAB to intestinal cells is associated with the peristaltic flow, a good adherence capacity and the presence of mucins to protect and lubricate the epithelial surfaces [11] . Resident intestinal bacteria are able to inhibit the adherence of pathogenic bacteria to intestinal epithelial cells as a result of their ability to increase the production of intestinal mucins [12] . Lactobacillus plantarum increases the levels of expression of the mRNA of some mucins, inhibiting the cell attachment of enteropathogenic Escherichia coli [13] [14] . LAB have access to simple sugars and complex carbohydrates, so bacteria with genes involved in its degradation are probably in better condition to multiply in the gut [6] . The resident gastrointestinal microbiota provide a microbial barrier against microbial pathogens [12] . Lactobacillus and Bifidobacterium spp. of human intestinal origin produce antimicrobial substances that are active in vitro and in vivo against enteropathogenic microorganisms involved in diarrhea [15]; both genera have the capacity for interfering with or block the pathogenic process of enteric bacterial pathogens [12]. Strains of Lactobacillus acidophilus, L. johnsonii, L. rhamnosus, L. casei, L. acidophilus, and L. rhamnosus interfere with a wide range of pathogens, such as enteropathogenic Escherichia coli, enterohemorrhagic E. coli, Listeria monocytogenes, Salmonella enterica serovar Typhimurium, and S. flexneri [16]-[22]. Blocking the process of pathogenicity of enteric pathogens is carried out without affecting their viability, such as the inhibition of Salmonella spp, S. flexneri, and L. monocytogenes by E. coli strain Nissle 1917 [23], and the blocking of E. coli LF82 adherent-invasion in the Crohn's disease [24]. Biopreservation of Food Consumers are very concerned of chemical preservatives and processed foods, but they accept easily LAB as a natural way to preserve food and promote their health [25] . Bacteriocins are ribosomally synthesized small proteins produced by LAB that inhibit the growth of spoilage and pathogen bacteria in foods; moreover, bacteriocinogenic LAB are linked and are used as starter cultures in food processing [26] . Bacteriocins have been classified into four major groups [27] . Group I, also known as lantibiotics, has nisin as the first and best known bacteriocin. Group II is a large group of small heat-stable proteins subdivided into three groups [25]: i) subgroup IIa, bacteriocins active against Listeria monocytogenes, and pediocin PA-1, sakacins A and P, leucocin A, bavaricin MN, and curvacin A are members of this group; ii) subgroup IIb require two different peptides for activity, and lactococcins G and M, and lactacin F are members of it; and iii) subgroup IIc, such as lactacin B, require reduced cysteines for activity. Into group III are classified the larger heat-labile proteins, such as helveticins J and V, and lactacins A and B. Leuconocin S, lactocin 27, and pediocin SJ-1 have lipid or carbohydrate moieties and are classified into group I.V. Yang et al. [28] classified the gram-positive bacteriocins into three classes: Class I (modified peptides, lantibiotics), Class II (unmodified peptides, non-lanthionine), and Class III (large proteins, heat unstable). Cotter et al. [29] subdivided Class II into five sub-classes. Only the bacteriocin nisin is commercially available for addition in pure form. It is added to milk, cheese, and dairy products, canned foods, mayonnaise, and baby foods [30] . Bacteriocinogenic cultures can also be added to the non-fermented foods or to fermented foods as starter cultures. Due to the sensitivity of bacteriocins to some proteases, harmless bacteriocins are possibly digested [31] [32]. Thus, bacteriocins are considered as basically safe food additives after intake by the gastrointestinal system [28]. Immunity Stimulation External microorganisms can penetrate the gut wall by translocation through the epithelial layer or through Peyer's patches. Indigenous intestinal bacteria including lactobacilli are able to cross the intestinal mucous layer