Agriculture Reference
In-Depth Information
6.5.9 Humulones
Humulones and lupulones are the major constituents of the female fl owers of the
hop vine (
Lupulone humulus
) used in the brewing industry to impart desirable
bitter fl avour and aroma to beer, and also aid in beer preservation. Both Gram-
negative bacteria and Gram-positive bacteria (especially lactic acid bacteria) are
sensitive to the
α
and
β
analogues of these acids. The antimycotic effect of hops
against fungi is infl uenced by water activity, with increasing activity as the water
activity is lowered (Engelson
et al.
1980). Their use as with many other plant
antimicrobials will probably be restricted because of their bitter taste.
6.6 Enzyme-released antimicrobial agents
Two types of antimicrobial compounds activated by enzyme hydrolysis exist in
edible plants (Meyer
et al.
2002).
In the Allium family (garlic, onions, leek), sulfoxides are converted to pungent
smelling sulphides such as diallyl disulfi de upon tissue rupture (Walker 1994).
Most potent is garlic. It contains allinin (propenylcysteine sulfoxide), which is
hydrolysed by the enzyme alliinase to allicin (2-propenyl-2-propenethiol
sulfi nate). Various studies have shown these substances to be inhibitory to a wide
range of microorganisms, but only at high concentrations (Beuchat 1994). The
main hindrance to use is sensory effects.
In plants of the Cruciferae family (cabbage, mustard, horse radish, Brussels
sprout), glucosinolates are the substrates for hydrolytic enzymes. As an example,
sinigrin stored in mustard seeds is cleaved by myrosinase to yield allyl
isothiocyanate which is inhibitory against a wide range of bacteria and fungi
(Delaquis and Sholberg 1997). Applied through the gas phase, volatile allyl
isothiocyanate has proved effective in very low doses against food spoilage fungi
(Delaquis and Mazza 1995; Nielsen and Rios 2000). The gaseous form seems to
have higher antimicrobial potential than the liquid (Lin
et al.
2000). The
commercial product, Wasa Ouro® (Green Cross Corp., Osaka, Japan), is based on
volatile allyl isothiocyanate as the active ingredient. Wasa Ouro® has been
evaluated by the US Army for use in military rations and has been reported to
delay the growth of moulds on sandwiches from 10 to 100 days without undesirable
sensory effects on the food (Worfel
et al.
1995).
6.7 Other enzymes
Chitin (a polymer of
N
-acetylglucosamine), chitosan (a deacetylated derivative of
chitin) and mannan (a polymer of
β
-1,3,1,4 and 1, 6-linked mannose) are the
major components of the cell walls of fungi and yeasts (Roller and Board 2003).
Consequently, the use of chitinases has been proposed as antimicrobial agents
against fungi and yeasts involved in food spoilage (Roller and Lusengo 1997).
Various enzymes have been found to be effective, especially in buffers and
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