Source: Klaenhammer, 1988; Tagg, et al, 1976; Ward, 1995.

Source: Klaenhammer, 1988; Tagg, et al, 1976; Ward, 1995.

  1. Lactococci
  2. lactis subsp. lactis produces the bacteriocin nisin. Nisin was isolated by Mat-tick and Hirsch (1947) and is the only bacteriocin widely approved for use as a food additive. (Other bacteriocins can be present in foods as a natural part of the culturing process.) Nisin is a polypeptide containing 34 amino acids and usually occurs as a dimer with a molecular weight of 7000 D (Jarvis et al., 1968). It is the best known of the group of bacteriocins called lantibiotics, which contain the unusual amino acids, lanthionine, P-methyl lanthionine, and dehydroalanine (Vanenbergh, 1993). Nisin has a relatively broad spectrum of activity for a bacte-riocin, with activity against many lactic acid bacteria, spore-forming bacteria, and L. monocytogenes (Davidson and Hoover, 1993). Its ability to prevent outgrowth of bacterial endospores has led to its use in preventing the late gas defect in hard cheeses and as an inhibitor of C. botulinum and spoilage microorganisms in canned foods and processed cheese (Daeschel, 1989). Nisin is heat stable and has greatest activity under mildly acidic conditions. Like other bacteriocins, the site of action of nisin is the cytoplasmic membrane (Sahl, 1991).

Lacticin 481, produced by Lc. lactis subsp. lactis, has activity against lacto-cocci and some lactobacilli, leuconostocs, and clostridia. If produced by starter cultures used for cheese manufacture, lacticin 481 eliminates the sensitive microflora from the resulting cheese (Paird et al., 1991). Lc. lactis subsp. lactis DPC3147 produces lacticin 3147, a broad-host range, two-component bacteriocin. It inhibits a wide range of gram-positive bacteria, including Listeria, Clostridium, Staphylococcus, and Streptococcus species but is not active against gram-negative species (Ryan et al., 1996). Lc. lactis subsp. cremoris produces diplococcin, which, unlike nisin, has a narrow spectrum of activity (primarily against other lactococci) and lacks stability. Producers of diplococcin rapidly predominate in multiple-strain starter cultures. Also, Lc. lactis subsp. lactis var. diacetylactis produces lactococcin, a bacteriocin which has a bacteriolytic effect on other lactococci. This lytic action might be useful to accelerate cheese ripening (Morgan et al., 1995).

2. Lactobacilli

Lactobacilli used in starter cultures can produce many different bacteriocins, most with a limited range of activity. Lb. helveticus produces helveticin J and lacticin LP27. Helveticin J is an unusual bacteriocin, because it is coded for on chromosomal DNA and is active at neutral pH (Joerger and Klaenhammer, 1986). Lb. acidophilus produces numerous bacteriocins, including lacticins B and F and aci-docin J1229 (Muriana and Klaenhammer, 1991; Tahara and Kanatani, 1996); Lb. casei produces caseicin 80 (Rammelsberg and Radler, 1990); and Lb. delbrueckii subsp. lactis produces lacticins A and B (Toba et al., 1990). Bacteriocins produced by Lb. delbrueckii subsp. bulgaricus were recently isolated and character ized (Balasubramanyam et al., 1998; Miteva et al., 1998). In addition, Lb. plan-tarum, which grows well in cheese, produces pediocin AcH, a bacteriocin active against L. monocytogenes (Ennahar et al., 1996). Properties of these compounds have been described by Davidson and Hoover (1993).

3. Leuconostocs

Although Stiles (1994) concluded that bacteriocins of leuconostocs are active against L. monocytogenes but not necessarily against other lactic acid bacteria, three bacteriocins produced by Leu. mesenteroides TA 33 inhibited various strains of lactic acid bacteria as well (Papathanasopoulos et al., 1997). In addition, Leu. mesenteroides subsp. dextranicum J24 synthesizes a bacteriocin named dex-tranicin 24, which inhibited only other Leuconostoc strains (Revol-Junelles and Lefebvre, 1996). Leu. mesenteroides subsp. mesenteroides produces mesentero-cin 52A and mesenterocin 52B (Krier et al., 1998).

4. Propionibacteria

Propionicin PLG-1, a bacteriocin produced by Pr. thoenii, is unusual because of its broad range of activity, which includes some gram-negative bacteria, including Escherichia coli, Pseudomonas fluorescens, and Vibrio parahaemolyticus (Lyon and Glatz, 1991). It is also active against other propionibacteria, lactic acid bacteria, and some yeasts and molds. It is inactivated at temperatures above 80°C, unlike jenseniin G, which is produced by Pr. jensenii and is stable at 100°C. Jenseniin has a narrow range of activity but is active against microorganisms commonly found in Swiss cheese (Grinstead and Barefoot, 1992). Jenseniin G, which also inhibits yogurt starter, could be useful in preventing overacidification of yogurt (Weinbrenner et al., 1997).

5. Streptococci

Ward (1995) found that 13 of 41 strains of S. thermophilus produced bacteriocin-like substances that were active mainly against other S. thermophilus strains. He purified the bacteriocin, thermophilin A, which is heat stable and acid tolerant. Villani et al. (1995) isolated thermophilin 347 and determined it to be heat stable and inhibitory toward L. monocytogenes. Thermophilin T is also produced by S. thermophilus ACA-DC 0040 and is active against some food spoilage bacteria such as C. sporogenes and C. tyrobutyricum (Aktypis et al., 1998). A bacteriocin produced by S. thermophilus 81 was not effective against Lb. delbrueckii subsp. bulgaricus but inhibited various pathogens (Ivanova et al. 1998).

6. Applications and Commercial Preparations

The dairy industry can take advantage of the preservative properties of bacterio-cins either by using bacteriocin-producing cultures in the manufacturing process or by adding the bacteriocin-containing preparations directly to a product. Nisin can be purchased for use as a food additive under the brand name Nisaplin (Aplin and Barret, Ltd., Wilts, England). It is mainly used in dairy foods for its ability to inhibit bacterial spore germination.

Skim milk fermented with a bacteriocin-producing strain of P. freudenrei-chii subsp. shermanii, and when pasteurized, it can be purchased under the brand name Microgard (Wesman Food, Inc., Beaverton, OR). The presence of propionic acid, diacetyl, and acetic acid in Microgard enhances the preservative effect of the bacteriocin (Al-Zoreky, 1988). Microgard is used extensively in the United States as a preservative in cottage cheese (Daeschel, 1989). Other fermented milk and whey products containing bacteriocins are also commercially available. In addition, a novel method for accelerating cheese ripening utilizes bacteriocin-producing adjunct cultures. The use of a bacteriocin-producing strain of Lc. lactis subsp. lactis resulted in cheese with increased cell lysis, elevated concentration of free amino acids, and higher sensory evaluation scores (Morgan et al., 1997).

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