Agriculture Reference
In-Depth Information
Rhodotorula glutinis
and rhodotorulic acid for control of
Botrytis cinerea
on apple
wounds and found
R. glutinis
reduced disease severity by 54% alone, and by 75% in
combination with rhodotorulic acid. In both instances, it is thought that the siderophore
inhibited conidial germination because large amounts of iron are required for this to
occur. The combined use of siderophores and yeasts on fresh-cut produce may facili-
tate a more rapid colonization of available niches and reduce the probability of patho-
gen colonization at these sites.
Lysozyme
Lysozyme is an enzyme that degrades bacterial cell walls and leads to cell lysis. These
enzymes are produced by a wide range of prokaryotes and eukaryotes and form a
passive defense against bacterial colonization. Some of these enzymes also have
antifungal activity (Wang and others 2005). Activity is optimal against Gram-positive
bacteria, but under high barometric pressure Gram-negative bacteria can also become
sensitive to lysozymes (Nakimbugwe and others 2006b). This has been demonstrated
with phage lambda lysozyme in banana juice (Nakimbugwe and others 2006a). The
use of lysozyme, possibly in enzyme cocktails, has been suggested for pathogen
control.
Polylysine
Culture fi ltrates of a
Streptomyces
sp. contain the antimicrobial compound
- Polylysine,
a linear polymer of 25-30 L-lysine residues. A commercially available preparation of
this compound reduced the numbers of
E. coli
O157:H7,
Salmonella
Typhimurium
and
L. monocytogenes
in a blended mixture of caulifl ower and broccoli, although the
vegetables had been autoclaved prior to use (Geornaras and others 2007). In all three
cases pathogens were able to grow on the substrate, but in the presence of
ε
- Polylysine
their numbers declined to become nondetectable after 2 to 4 days of incubation at
12 °C. This compound is considered GRAS for use in rice.
ε
Conclusions
The information presented here illustrates the wide diversity of potential biocontrol
approaches that are available. They represent a toolbox of controls that can be applied
across the farm-to-fork spectrum. Examples have been provided whereby these con-
trols have been used in combination, an approach which would seem likely to present
the best possibility for success. The application of multiple controls as hurdles means
that each individual control need not infl ict a huge reduction in pathogen numbers,
comparable to the 12D “bot cook” for low-acid canned foods, but the combined effect
is satisfactory control of the pathogen. In addition the use of multiple controls using
different mechanisms reduces the likelihood of resistant pathogens emerging.
None of these controls will be of use unless they are approved by the regulators.
However, when provided with adequate information, regulatory approval has been
readily forthcoming, at least in the area of phage biocontrol. The advantage of these
controls is that they are by defi nition derived from nature, which should be appealing
to the consumer, given the dislike for synthetic “chemical” controls, and should make
the prospect of obtaining regulatory approval more likely.
