Biopreserve products with nisin.The objective of this research is to improve the efficiency of the natural preservative nisin nisin an antibiotic substance isolated from cultures of lactic acid producing streptococci and reputed to have antibacterial activity against gram-positive bacteria. , which is approved in most European countries for use in several foods. As you know, nisin is a bacteriocin bacteriocin /bac·te·rio·cin/ (bac-ter´e-o?-sin) any of a group of substances, e.g., colicin, released by certain bacteria that kill other strains of bacteria by inducing metabolic block. produced by the lactic acid bacterium L. lactis, which may kill Gram-positive bacteria by forming pores in the bacterium's cytoplasmic membrane. However, nisin leaves Gram-negative bacteria unaffected because the bacterium's extra outer membrane is impermeable to nisin. This limitation means that nisin does not inhibit such important pathogens as E. coli, Salmonella, Campylobacter Campylobacter Genus of gram-negative spiral-shaped bacteria infecting mammals. Many species, especially C. fetus, cause miscarriage in sheep and cattle. C. jejuni is a common cause of food poisoning. Sources include meats (particularly chicken) and unpasteurized milk. and Yersinia. But it does inactivate Bacillus, Clostridium and Listeria. In order to improve the efficiency of nisin as well as its activity against Gram-negative bacteria, European scientists screened for food compounds synergistic to nisin. They found an improved preservative effect by nisin on Gram-positive bacteria when the product was treated with nisin and essential oils--carvacrol, thymol thy·mol n. A white crystalline aromatic compound derived from thyme oil and other oils or made synthetically and used as an antiseptic, a fungicide, and a preservative. and carvone from oregano; thyme; and caraway caraway, biennial Old World plant (Carum carvi) of the family Umbelliferae (parsley family), cultivated in Europe and North America for its aromatic seeds. seeds. The addition of lysozyme lysozyme: see immunity. Lysozyme An enyme that was first identified and named by Alexander Fleming, who recognized its bacteriolytic properties. enhanced the effect of nisin and carvone (from caraway and dill) against L. monocytogenes. Sucrose fatty acid esters (emulsifiers) enhanced the effect of nisin on Gram-positive bacteria. Another bacteriocin, a pediocin-like antimicrobial, enhanced the effect of nisin. Nisin treatment combined with modified atmosphere packaging extended the shelf life of marinated beef and fresh fish. Researchers gained an improved effect by combining nisin with protective cultures in certain products tested--tofu, fruit juice and coleslaw. Nisin combined with pulsed electric fields has a synergistic effect on the inactivation of B. cereus. In addition, permeabilization of the outer membrane of Gram-negative bacteria with EDTA EDTA: see chelating agents. and possibly sodium hexametaphosphate (NaHMP) sensitizes these bacteria to nisin. Further information. E. J. Smid, Agrotechnical Research Institute (ATO), Wageningen Univiersity Center, PO Box 17, NL-6700 AA Wageningen, The Netherlands; phone: +31 317 475000; fax: +31 317 475347; email: m.h.j.bennik@ato.dlo.nl. |
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