Natural methods (biocontrol) for the preservation of harvested fruits and vegetables were investigated.This was in order to potentially help the industry overcome the environmental problems and pathogen resistance
being encountered with the use of synthetic fungicides.
The main focus of research was the use of volatile compounds found in citrus fruit. These were utilised in in vivo studies with citrus fruit artificially inoculated with Penicillium digitatum and P. italicum, as well as strawberries
inoculated with Botrytis cinerea. The extent of pathogen growth was measured after exposure to the volatiles for a number of days (7 for citrus fruit and 3 for strawberries) in environmentally-controlled containers.
The ‘freshness’ of the fruit was also ascertained via measurements of water/weight loss. The essential oil of orange itself was highly effective
at reducing Penicillium growth (> 30% inhibition) and water/weight loss in the fruit (>20% reduction), as were some of its individual components-(E)-2-hexenal, neryl acetate and linalool. The aldehyde (E)-2-hexenal also had high efficacy against B. cinerea and reduced water/weight loss in strawberries, although in these investigations the ketone, (R)-carvone was the most
effective overall (> 30% mean pathogen inhibition and > 35% mean reduction in water/weight loss).
Organic and non-organic fruit wereutilised in the in vivo experiments and discrepancies were observed in the results for each type. In vitro studies were
therefore conducted with the volatiles, both alone and in combination with commercial fungicides (imazalil, thiabendazole and fludioxonil) in amended
-agar investigations. Aldehydes (including (E)-2-hexenal) displayed the highest efficacy against Penicillium species and B. cinerea (> 90% inhibition), followed by carvone and methyl salicylate (> 40% inhibition). These
observations were repeated in the fungicide-amended-agar work, where it was shown that these volatiles could be utilised to supplement the activity of synthetic fungicides and therefore reduce their overall use with in the industry.
Chitosan was also investigated as a biological coating for harvested fruit. At 2% concentrations it reduced water/weight loss in oranges compared to uncoated fruit, whilst at 0.1% it reduced Penicilliuminfection in inoculated fruit by almost 50%. Acid and enzyme hydrolysis techniques were
performed to obtain chitooligosaccharides with a degree of polymerisation (DP) of 3-10, reported to possess superior antifungal properties than commercially-available chitosan. The hydrolysates were analysed via MALDI-TOF
-MS. Chitooligosaccharides produced by one of the acid hydrolysis methods and one obtained using the enzyme Laminarinase were found to be of the desired DP.
Overall, the work revealed the potential of some alternative methods for maintaining the freshness and extending the storage-life of fresh fruits. A number of citrus volatiles were found to be effective at reducing pathogen
growth as well as protecting the fruit from water/weight loss. They
were also found to operate in parallel with synthetic fungicides, thus implying that the domination of these chemicals in the post-harvest industry could be
diminished by combined applications. Chitosan as an edible coating for fresh produce has also been shown to have potential, although additional work is required to elucidate this further.