Natural antimicrobials as additives and ingredients for the preservation of foods and beverages - Natural Food Additives, Ingredients and Flavourings - page 128

legislation and can be labelled as 'fermented dextrose powder' or 'fermented milk
powder'. Finally there is the use of live protective cultures available as freeze-
dried powders, frozen pellets or in liquid forms. These require to be able to grow
in the food and are less powerful than defi ned antimicrobials, but still can provide
good protection against spoilage in fermented foods such as yoghurt, soft cheeses,
sour cream and fermented sausages.

6.2.1 Nisin
Nisin is an example of a bacteriocin. Bacteriocins are ribosomally synthesised
antimicrobial peptides produced by bacteria that show action against other
bacteria that are usually closely related to the producer strain. Nisin was fi rst
discovered in 1928. Since its discovery, numerous other bacteriocins predominantly
produced by lactic acid bacteria have been identifi ed and characterised but nisin
remains the only bacteriocin in a purifi ed form that is commercially used as a food
preservative. It is arguably the fi rst natural preservative produced by biotechnology.
Nisin is produced by the lactic acid bacteria, Lactococcus lactis subsp. lactis .
It is active against many Gram-positive bacteria and especially those that produce
heat-resistant spores but have no or little activity against Gram-negative bacteria,
yeasts and mould. Nisin was fi rst introduced as a food preservative in 1953 with
the brand name, Nisaplin® (Danisco) and has the EU food additive number E234.
The Nisaplin® product is based on nisin A (Fig. 6.1). In the past 20 years Chinese
manufactured nisin preparations based predominantly on nisin Z have been
introduced. Nisin Z differs from nisin A in the substitution of His 27 for Asn 27
(Mulders et al. 1991).
More recently two other nisin variants namely nisin F (de Kwaadstenient et al.
2008) and nisin Q (Zendo et al. 2003) have been discovered, although these are
not used in commercial preparations. Nisin preparations are made by pH controlled
fermentations of Lc. lactis in either milk- or sugar-based media, followed by
concentration by either foam extraction or membrane fi ltration technology. The
concentrated nisin is precipitated by the addition of salt and then spray-dried, and
by addition of further salt standardised to a potency of one million international
units per g. In 1969, the Joint Food and Agricultural Organization (FAO) and
World Health Organization (WHO) Expert Committee on Food Additives
(JEFCA) concluded that nisin A was safe to be used as a food additive (JEFCA
1969) and in 1988 it was declared GRAS (Generally Recognised As Safe) (FDA
1988). The no or low toxicity of nisin A preparation has recently been confi rmed
by a new feeding study using rats in Japan (Hagiwara et al. 2010). This resulted
in the approval in 2009 of nisin A preparation as a food preservative in Japan.
For a bacteriocin, nisin has an unusually broad spectrum of activity against
Gram-positive bacteria. Nisin acts against vegetative cells by absorbing to the cell
wall precursor lipid II, inserting into the cytoplasmic membrane and producing
transient pores allowing effl ux of cell material (Breukink et al. 1999; Wiedemann
et al. 2001). The effect can be either bactericidal or bacteriostatic depending on
the physiological status of the target bacteria or the nisin concentration. Nisin has

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