**3. Lactic acid bacteria (LAB) in food fermentation and new natural antimicrobial compounds**

LAB have traditionally been associated with food fermentation. LAB are generally considered beneficial microorganisms, with some strains even considered to promote good health (probiotic), and their extensive historical use contributes to their acceptance as being GRAS (generally recognised as safe) for human consumption [27]. LAB are used as natural or selected starters in food fermentation and exert health benefits through the antimicrobial effect produced from different metabolic processes (lactose metabolism, proteolytic enzymes, citrate uptake, bacteriophage resistance, bacteriocin production, polysaccharide biosynthesis, metalion resistance and antibiotic resistance) [28,29,9]. Spontaneous fermentation typically results from the competitive activity of a variety of autochthonous and contaminating microorgan‐ isms, which may lead to a high risk for failure. Both from a hygiene and safety perspective, the use of starter cultures is recommended, as it leads to rapid inhibition of spoilage and pathogenic bacteria while yielding processed fruit with consistent sensory and nutritional quality [30].

shelf-life properties of vegetables. Three technology options are usually considered for lactic acid fermentation of vegetable: spontaneous fermentation by autochthonous lactic acid bacteria, fermentation by starter cultures that are added into raw vegetables, and fermentation of mild heat-treated vegetables by starter cultures [18]. For thousands of years, microorganisms have been used to produce and preserve foods through the process of fermentation. Fermented foods have been adopted in various ways depending on the properties of the available raw materials and the desired features of the final products [8-10]. Food produced by traditional methods has become popular among consumers who know that their food is manufactured from high quality raw materials, without preservatives and other synthetic additives that are

Bourdichon et al. [12] describe the fermentation process as "a metabolic process of deriving energy from organic compounds without the involvement of an exogenous oxidising agent". Fermented foods are subjected to the actions of microorganisms or enzymes. Fermentation plays different roles in food processing, such that desirable biochemical changes have occurred [13]. The fermentation process is very important in the improvement of technological proper‐ ties of preservation, such as a relative cost-effectiveness and low energy requirements, which are essential for ensuring the shelf-life and microbiological safety of the product [8]. The major

**1.** preservation of food: the formation of inhibitory metabolites, such as organic acid (lactic acid, acetic acid, formic acid, propionic acid), ethanol, bacteriocins, etc., often in combi‐

**2.** improving food safety through the inhibition of pathogens [16,17] or the removal of toxic

**3.** improving nutritional value: biological enrichment of food substrates with proteins,

**4.** organoleptic food quality: enrichment of the diet through the development of a diversity

Interest in the biopreservation of food has created a demand for more natural and minimally processed food, with particular interest in naturally produced antimicrobial agents [26].

LAB have traditionally been associated with food fermentation. LAB are generally considered beneficial microorganisms, with some strains even considered to promote good health

**3. Lactic acid bacteria (LAB) in food fermentation and new natural**

nation with a decrease in water activity (by drying or the use of salt) [14-15].

essential amino acids, essential fatty acids and vitamins [19,20].

of flavours, aromas, and textures in food substrates [21-24].

**5.** decrease in cooking times and fuel requirements [25].

characterised by unique flavour values [11].

136 Biotechnology

**2. Fermentation from a biochemical point of view**

roles of fermentation are considered to be the following:

compounds [18].

**antimicrobial compounds**

Interest in the biopreservation of food has prompted the quest for novel antimicrobial compounds from different natural origins. The LAB of genera such as *lactobacilli* and *lactococ‐ cus* are amongst the most important known members that have probiotic activity [31]; these bacteria produce antimicrobial peptides most frequently referred to as bacteriocins [32,33]. Bacteriocins ensure the stability of fermented plant products, reduce microbial contamination during fermentation, inhibit the growth of moulds and delay microbiological spoilage of baked goods [34].

LAB have strong inhibitory effects on the growth and toxin production of other bacteria. This activity can occur due to the following factors: competition for available nutrients; decrease in redox potential; production of lactic acid and acetic acid and the resulting decrease in pH; production of other inhibitory primary metabolites, such as hydrogen peroxide, carbon dioxide or diacetyl; and production of special antimicrobial compounds, such as bacteriocins and antibiotics [35].

Each of these properties, particularly when combined, can be used to extend the shelf-life and safety of food products [36].

Amongst the various technologies, lactic acid fermentation may be thought of as a simple and valuable biotechnology for maintaining and/or improving the safety, nutritional, sensory and shelf-life properties of fruits and vegetables [37,38]. Overall, LAB are a small part (2–4 log10 CFU g−1) of the autochthonous microbiota of raw vegetables, and their cell density is mainly influenced by the vegetable species, temperature and harvesting conditions [37].

Interest in the use of LAB fermentation of vegetable products stems largely from the nutri‐ tional, physiological and hygienic aspects of the process and their corresponding implemen‐ tation and production costs [39].

LAB fermentation represents the easiest and most suitable way to increase the daily consump‐ tion of nearly fresh fruits and vegetables.
