Biopreservation and Antimicrobial Peptides
Biopreservation processes and application of antimicrobial compounds were part of the preparation of fermented meat products, including various types of salami over the past few centuries. However, only after the scientific discovery of antibiotics produced from various fungi by Fleming in beginning of 20th century, and the detection of nisin a few years later, various antimicrobial peptides have been the subject of intensive research and scientific interest in biopreservation of fermented food products. Nowadays, we have sufficient scientific knowledge to state that antimicrobial peptides can be detected in all life forms, including not only microorganisms, but also animals, insects, fishes, birds and plants. The most frequent antimicrobial peptides produced by microorganisms are referred to as “bacteriocins” and enormous research was focused on those produced by lactic acid bacteria (LAB) (Cotter et al. 2005). According to Cotter et al. (2005), bacteriocins can be produced by almost all bacterial species as a part of the defending molecules. Several research groups have been focused on the inhibitory effect of bacteriocins from LAB against food- borne pathogens and spoilage bacteria (De Vuyst and Vandamme 1994; Garrna et al. 2010). Several studies on the application of bacteriocins have been involved with their potential application in the treatment of food-borne contaminations, improving food quality and safety and the fight against antibiotic resistance problems.
LAB can produce various antimicrobial compounds, including organic acids (lactic, acetic, formic, propionic acids), however, their principal antibacterial action is related to the reduction of the pH of the media. Other methabolites like fatty acids, acetoin, hydrogen peroxide, diacetyl, antifungal compounds (propionate, phenyl- lactate, hydroxyphenyl-lactate, cyclic dipeptides and 3-hydroxy fatty acids), bac- teriocins (nisin, reuterin, reutericyclin, pediocin, lacticin, enterocin and others) and bacteriocin-like inhibitory substances (BLIS) (Reis et al. 2012) can be actively involved in the antimicrobial action. Other antimicrobials entourage of LAB may include different biopolymers, sugars, sweeteners, nutraceuticals, aromatic compounds and various enzymes, and in this manner indicate that LAB have higher flexibility and a wider application than just as starter cultures. Study of the new antimicrobial compounds is very intensive in order to provide an alternative to the chemical additives, and to offer the market more natural food products. In addition a specific spectrum of activity of bacteriocins against certain emerging food-borne pathogens and spoilage microorganisms, their resistance to thermal processing and low pH, combined with their sensitivity to human proteolytic enzymes are important positive characteristics in the application of these compounds in food preservation (Masuda et al. 2011).
By definition, bacteriocins are ribosomally synthesized antimicrobial proteins (polypeptide or small proteins), usually active against genetically related species (Cotter et al. 2005). Based on the intensive research in area of bacteriocins since the discovery of nisin, we have sufficient examples of bacteriocins that may have applications in controlling Gram-negative bacteria, some yeast, Mycobacterium spp. and even viruses (Todorov et al. 2010; Schirru et al. 2012). However, amino-acid sequences of only a few of these unusual bacteriocins are provided (Todorov et al. 2010; Todorov et al. 2012). These reports need to be carefully screened, since only a few pieces of work explain the mechanisms of modes of action for this “unusual” bacteriocinogenic activity.
Many classifications have already been proposed (Cotter et al. 2005), but according to the most recent (Heng et al. 2007), bacteriocins of Gram-positive bacteria are grouped into four classes, based on their structure and function. Class I: lantibiotic peptides, class II: small non-modified peptides with < 10 kDa, class III, large proteins with > 10 kDa and class IV: cyclic proteins.