Agriculture Reference
In-Depth Information
species require higher concentrations. Yeasts are generally inhibited at 1.0-5.0
μg/ml. It is believed that natamycin acts by binding to ergosterol in fungal cell
membranes, which results in loss of enzyme function and inhibition of cell
division. Originally it was thought that natamycin's interaction with ergosterol
caused pore formation but recent research has shown this not to be the case
(te Welsher et al. 2008; van Leeuwen et al. 2009). Ergosterol is not present in the
cell membranes of bacteria and protozoa.
6.2.5 Reuterin
Reuterin is sometimes mistakenly considered to be a bacteriocin but is in fact an
organic chemical, β -hydroxypropionialdehyde. It has a broad antimicrobial
spectrum against Gram-positive and Gram-negative bacteria, yeasts and moulds
(Chung et al. 1989). Reuterin was fi rst isolated by Lerche and Reuter (1962) and
is produced as an intermediate during anaerobic metabolism of glycerol by Lb.
reuterii (El-Ziney et al. 1998). Lb. reuterii is a species of heterofermentative
lactobacilli present in the gastrointestinal tract of man and animals. It is also found
in a range of foods particularly dairy products, meats and sour dough (Dellagio
et al. 1981; Kandler and Weiss 1986; Vogel et al. 1994).The fact that Lb. reuterii
strains are natural inhabitants of the intestine, have a brood antimicrobial spectrum,
are resistant to heat and proteolytic and lipolytic enzymes, are stable over a wide
pH range, and have high solubility in water and lipid, makes reuterin an ideal
candidate for use as biological preservative (El-Ziney et al. 1999). However,
reuterin as a food additive has yet to be approved. Various researchers have
demonstrated its potential. Lindgren and Dobrogosz (1990) extended the shelf life
of herring by dipping the fi llets in a suspension of Lb. reuterii (10 9 /ml) and 250
nmol glycerol. The bactericidal action of reuterin against E. coli 0157:H7 and L.
monocyogenes in minced meat (El-Ziney et al. 1999) and against L. monocyotogenes
in milk and cottage cheese has been demonstrated (El-Ziney and Deberve 1998).
￿ ￿ ￿ ￿ ￿
6.2.6 ε -Poly- L -lysine
ε -Poly- L -lysine is a naturally occurring homo-polymer of L -lysine with a degree
of polymerisation of 25-35, molecular weight of approximately 5000, and
characterised by the peptide bonds between the carboxyl and ε -amino groups of
L -lysine (Hiraki et al. 2003). The compound was fi rst isolated from Streptomyces
albulus sp. Lysinopolymerus strain 346 (Shima and Sakai 1977, 1981). It is
produced in Japan using a mutant strain of the above microorganism and has been
used as a food preservative predominantly in that country.
The antimicrobial activity of ε -poly- L -lysine has been reported as being
effective against a wide spectrum of microorganisms including Gram-positive
and Gram-negative bacteria, yeasts, and fungi (Shima et al. 1984; Yoshida
and Nagasawa 2003). The mode of action is its electrostatic adsorption on to
the cell surface of microorganisms due to its cationic properties, which results
in disruption of the outer membrane and abnormal distribution of cytoplasm
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