Nisin was first introduced commercially as a food preservative in the UK approximately 30 years ago. First established use was as a preservative in processed cheese products and since then numerous other applications in foods and beverages have been identified. It is currently recognised as a safe food preservative in approximately 50 countries. The established uses of nisin as a preservative in processed cheese, various pasteurised dairy products, and canned vegetables will be briefly reviewed. More recent applications of nisin include its use as a preservative in high moisture, hot baked flour products (crumpets) and pasteurised liquid egg. Renewed interest is evident in the use of nisin in natural cheese production. Considerable research has been carried out on the antilisterial properties of nisin in foods and a number of applications have been proposed. Uses of nisin to control spoilage lactic acid bacteria have been identified in beer, wine, alcohol production and low pH foods such as salad dressings. Further developments of nisin are likely to include synergistic action of nisin with chelators and other bacteriocins, and its use as an adjunct in novel food processing technology such as higher pressure sterilisation and electroporation. Production of highly purified nisin preparations and enhancement by chelators has led to interest in the use of nisin for human ulcer therapy, and mastitis control in cattle.

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This study describes the genetic analysis of the riboflavin (vitamin B 2 ) biosynthetic (rib) operon in the lactic acid bacterium Lactococcus lactis subsp. cremoris strain NZ9000. Functional analysis of the genes of the L. lactis rib operon was performed by using complementation studies, as well as by deletion analysis. In addition, gene-specific genetic engineering was used to examine which genes of the rib operon need to be overexpressed in order to effect riboflavin overproduction. Transcriptional regulation of the L. lactis riboflavin biosynthetic process was investigated by using Northern hybridization and primer extension, as well as the analysis of roseoflavin-induced riboflavin-overproducing L. lactis isolates. The latter analysis revealed the presence of both nucleotide replacements and deletions in the regulatory region of the rib operon. The results presented here are an important step toward the development of fermented foods containing increased levels of riboflavin, produced in situ, thus negating the need for vitamin fortification.Riboflavin (vitamin B 2 ) is an essential component of basic cellular metabolism since it is the precursor of the coenzymes flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD). The latter two biomolecules play a central role in metabolism acting as hydrogen carriers in biological redox reactions involving enzymes such as NADH dehydrogenase (for a review of this topic, see reference 32). Many microorganisms, plants, and fungi possess the biosynthetic ability to produce riboflavin. However, vertebrates, including humans, lack this ability and must therefore obtain this vitamin from their diet.Dietary riboflavin is present in liver, egg yolk, milk, and meat, whereas the vitamin is commercially synthesized for nutritional use in the fortification of various food products such as bread and breakfast cereals. Because of its intense yellow color it is also used in small amounts as a coloring agent in foods such as ice cream and sauces, and as a medical identification aid. The recommended daily requirement of riboflavin is set at 1.3 mg (14) and sufficient amounts of riboflavin need to be ingested regularly since the body is unable to store the vitamin. Symptoms of riboflavin deficiency (ariboflavinosis) in humans, which still occurs in both developing and developed countries (6, 34), include sore throat, hyperemia, edema of oral and mucous membranes, cheilosis, and glossitis (48). Furthermore, riboflavin is used as a treatment for nucleoside analogue-induced type B lactic acidosis, which can occur as a result of AIDS treatment (9), for migraine (23), and for malaria (1). Commercially available riboflavin has traditionally been produced by chemical processes, but in recent times this has been replaced by biotechnological and more economical processes with Ashbya gossypii, Candida famata, or Bacillus subtilis (43).Riboflavin biosynthesis has been studied in both gram-positive and gram-negative bacteria, in most detail in B. subtilis (36) and Escherichia coli (4). Th...