LACTIC ACID BACTERIA (LAB)

LAB constitute ecologically group of various bacteria that produce lactic acid as major metabolite of lactose metabolism. These are derived from different plant habitats, raw, and fermented products of milk, meat, and vegetables. Gram-positive, non-spore forming, facultative anaerobic, rod to spherical-shaped, possess genome size ranging from 1.8 to 3.2 Mb and DNA has low G+C content of (below 55 mol%). LAB is incapable of producing iron-containing porphyrin, such as catalase (CAT) and cytochrome oxidase and members are nutritionally fastidious; often require specific growth factors (viz., amino acids, nucleic acid derivatives, and vitamins).

Basically, the biochemical pathways of carbohydrate metabolism by LAB that influence fermentation can be classified as:

  • Homolactic Fermentation: It follows the route of Embden- Meyerhof-Parnas (EMP) pathway or glycolysis for glucose hydrolysis yield lactic acid (>85%) either D (-) or L (+) or both.
  • Heterolactic Fermentative: bacteria lack fructose 1,6-bisphosphate aldolase enzyme follows the route of pentose-phosphate (6-phospho- gluconate/phosphoketolase) pathway for glucose hydrolysis, therefore producing a mixture of lactic acid, acetate, ethanol, and CO,.

LAB AS PROTECTIVE CULTURES (PC)

Certain LAB can inhibit bacteria including foodborne pathogens; therefore it opened a new opportunity to exploit their use in food safety and preservation. Such applications were coined as “bioprotection” and the microbial preparations as “PC.” Therefore, many PC available for use are from the microorganisms grouped as starter cultures [42]. The benefits of using LAB as PC are: LAB is recognized as food-grade bacteria as many of them have the status of GRAS and QPS. Apart from this, LAB has been known for their vital ability to dominate the niches by the production of antimicrobials, thereby changing the microenvironment unfavorable to unwanted microorganisms. Some LAB can cause spoilage of food and may utilize some amount of food components, which could affect the sensory parameters. Therefore, the physicochemical changes caused by the culture should be considered.

Based on the available scientific reports, the antimicrobial producing LAB for applications in food biopreservation (Figure 14.1) can be grouped as below:

  • Bacteriocin-Producing (Bacteriocinogenie) LAB Cultures: These cultures mainly rely on bacteriocins to exhibit antagonism. Mode of action depends on the release of bacteriocins, which are peptides of low MW with a narrow mode of antibacterial action [3]. They may have narrow (taxonomically close bacteria) to broad-spectrum (wide variety of bacteria) of activity. For example, nisin, pediocin, entocin AS-48, and lactocin 3147 are often used in food biopreservation either single or in synergies with other preservation methods. Bacteriocinogenie LAB has gained tremendous research attention as a potential PC:
  • Antifungal LAB to Delay the Spoilages: Mode of action mainly depends on the production of different antifungal compounds, e.g., PLA, reuterin, fatty acids, etc. These cultures are mainly applied to safeguard the foods from decay and enhance the shelf-life.
Potential use of LAB as protective cultures

FIGURE 14.1 Potential use of LAB as protective cultures.

• LAB with Non-Proteinaceous Low Molecular Weight Compounds: This relies on the production of different metabolites other than bacteriocins, e.g., the protective effect of cultures on the metabolites of lactic acid, acetic acid, H,0„ and depletion of oxygen, etc.

AVAILABILITY OF PROTECTIVE CULTURES (PC) LAB

LAB plays a vital role in food fermentation and is exploited as a starter culture in the manufacturing of number of fermented products from dairy, meat, bakery, fruits, and vegetables. In mixed natural fermentations and other competitive niches, the incidence of fresh isolates with the potential to use as PC is greatest. The antimicrobial production by one bacterium is to strive against other bacteria. Bacteriocin productions appear to compete over non-producing bacteria, which are either closely-related or co-exist in the same ecological niche. The selected strains of antimicrobial producing LAB offer a selective advantage to be exploited as efficient alternatives to chemical preservatives. The bacteriocin producing strains LAB isolated from different sources is listed in Table 14.1.

TABLE 14.1 Species of LAB Producing Bacteriocin Isolated from Different Sources

Bacteriocin Producer Strains

Source

Bacteriocin

Enterococcus faecium CN-25

fermented fish

Enterocin A and В

Enterococcus faecium ST5Ha

Smoked salmon

Bacteriocin ST5Ha

Lactobacillus brevis UN

Dhulliachar

Bacteriocins UN

Lactobacillus gasseri KT7

Infant feces

Gassericin KT7

Lactobacillus helveticus G51

Whey

Helveticin J

Lactobacillus paracasei BGBUK2-16

white-pickled cheese,

Bacteriocin 217

Lactobacillus paraplantarum FT259

Cheese

Plantaricin NC8

Lactobacillus plantarum J23

Grape must

Plantaricin

Lactobacillus plantarum MBSa4

Brazilian salami

Plantaricin W

Lactobacillus plantarum ST16Pa

Papaya

Bacteriocin ST16Pa

Lactobacillus sakei ST154Ch

fermented meat

Curvacin A

Lactococcus lactis KU24

Kirnchi

Bacteriocin KU24

Lactococcus lactis ssp. lactis BGBM50

semi-hard cheese

Lactococcin G

Pediococcus acidilactici ITV 26

Fermented sausage

Pediocin

Streptococcus thermophilus SBT1277

Raw milk

Thermophilin 1277

Weissellaparames enteroides J1

Chicken gizzard

Bacteriocins BacJ 1

 
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