APPLICATION POSSIBILITIES OF BACTERIOCIN IN FOODS
LAB produced bacteriocin has been associated with fermented foods for a very long time as they increase shelf life and enhance the nutritional and organoleptic attributes. Bacteriocin-producing bacteria have been found in many fermented products such as Portuguese fermented meat, cheese, and yogurt (Yang et al., 2012; Todorov et al., 2014). Moreover, due to their bactericidal activity, they have gained importance as potential bio-preservatives in the food industry. They can be used as part of the hurdle concept in preservation (Perez et al., 2014). Examples of producer strains with potential in fermented food production, from generally recognized as safe (GRAS) LAB are Lactococcus, Streptococcus, Pediococcus, and Lactobacillus (Grosu- Tudor et al., 2014; Perez et al., 2014; Bali et al., 2016). These strains are found associated with cereals, fruits, vegetables, milk, and meat as normal microbiota or become associated with these foods during harvest, storage, slaughter, handling, and transport. These organisms play a vital role in their fermentation (Doyle et al., 2013). The current synthetic food preservatives have some major concerns regarding food quality and associated health hazards. Hence, bacteriocins offer a better alternative to food preservation. The class I bacteriocins called lantibiotics to have broad scope in food industry techniques (Ramu et al., 2015). The following features of LAB produced bacteriocins make them suitable food preservatives (Juodeikiene et al., 2012):
- • Inactivity against eukaryotic cells;
- • They are proteins in nature and so broken down by the mammalian digestive proteolytic enzymes of the gastrointestinal tract;
- • Activity against some gram-negative bacteria and most gram-positive bacteria;
- • They are thermostable and retain bactericidal activity even after sterilization and pasteurization;
- • They can be genetically engineered to design peptides with desired characteristics as the genetic determinants are located in the plasmids.
There are different ways of application of bacteriocins as biopreservatives in food. The purified bacteriocins can be added in food directly or the bacteriocin producer LAB strain can be used as starter culture which then produces bacteriocin in a food matrix (Figure 8.1) (O’Bryan et al., 2015).
FIGURE 8.1 Application potential of bacteriocin in food quality and safety.
The first bacteriocin used as a food preservative is Nisin from Lactococcus lactis. It has been used in cheese production for over 50 years (O’Connor et al., 2015). It was the most potent and only bacteriocin approved for food preservation by FDA (Ramu et al., 2015; O’Bryan et al., 2014). It has a bactericidal action against Staphylococci, Streptococci, Listeria, Bacilli, and Enterococci (О ’ Connor et al., 2015). It has been used to produce food products with enhanced shelf life (Ge et al., 2016). The Purist form of bacteriocins is expensive and partially purified Nisin is also commercially available for use (Ramu et al., 2015). Novel bacteriocins are now being reported from many different sources and places all over the world. Garviecin LG34 from Lactococcusgarrieae was isolated from Chinese fermented cucumber (Gao et al., 2015). Pediocin PA-1, from Pediococcus pentosaceus, when incorporated into packaging film on meat surfaces, reduces the initial load of Listeria monocytogenes (Perez et al., 2014). Acidocin В from bifidobacteria, in fermented products such as cheese and silage, helps to inhibit Clostridium sp. (Bali et al., 2016). Although these bacteriocins exhibit important bactericidal qualities, the outer membrane of gram-negative bacteria poses a challenge. They will be more effective when used in combination with other techniques of preservation. Nisin combined with high pressure used for homogenization in apples and carrot juices helps to control E. coJi. Encapsulated Nisin helps to control L. monocytogenes in milk at low temperature (O’Bryan et ah, 2014).
The application of LAB starter cultures in food is advantageous as they serve as a source of other antimicrobials like carbon dioxide, ethanol, organic acids, and hydrogen peroxide in addition to bacteriocins, acting in a synergistic way to eliminate the pathogenic microbes. LAB is thus desirable protective cultures in food (O’Bryan et al., 2014; Reis et al., 2012). When Pediococcus pentosaceus was used as a starter in Thai traditional fermented pork sausage from, the quality and organoleptic properties were the same and also L. monocytogenes was inhibited (Perez et al., 2014). Bacteriogenic Enterococci as co-culture or starter culture can effectively control the growth of microbial contamination. There are many strains of LAB that can function as starter cultures in fermented vegetables, legumes, fruits, and cereals such as olives, rniso, pickles, sourdough, and mung bean sprouts (Yang et al., 2014). Three strains of Leuconostoc mesenteroides applied as bio-preservative on golden apples and frozen lettuce leaf controlled E. coli and S. typhimurium while completely inhibiting contamination by L. monocytogenes without any sensoiy modifications in the food product (O’Biyan et al., 2014).
LAB with known antibacterial activity can be used in food systems or biofilm packagings. A combination of three LAB strains inoculated into frankfurters prevented the outgrowth ofZ. Monocytogenes (Koo et al., 2012). Another approach of applying the bacteriocins is in the form of probiotics. Probiotic strains namely, Lactobacillus casei and L. johnsonii produce bacteriocins that can be used commercially. These strains will lead to bacteriocin production, once inside the human body, in the large intestine (Duhan et al., 2013). Probiotic bacteria improve gut health and reduce gastrointestinal diseases (Yang et al., 2014). There are also veterinary applications of bacteriocins as described in Table 8.3. Thus, bacteriocins have great potential in the food industry as well as the medical sciences. Further studies can be focused on fully understanding the diversity, specific modes of action and also on cost-effective purification methods based on characteristics of each class of bacteriocins.