Pg. 59-69 Effect of the addition of prochloraz to PolymerCoat on weight loss and mould colonization during and after extended cold storage of sulphured and non-sulphured Madras litchi fruits

Late harvested Madras litchi fruits were coated with PolymerCoat at full-strength (100%), 50% or 10% strength, to which Chronos (prochloraz) at 18 or 36 ml per 10 f PolymerCoat was added. Treatments were individually applied to all of the fruits in 2 kg cartons shortly after harvesting. After treatment, the fruits were held at 3°C for 38 days and subsequently at 20°C for a further nine days (47 days of storage). Two identical experiments were carried out, one on sulphured and the other on non-sulphured litchis. Each experiment comprised the six treatment combinations (factorial arrangement) and an untreated control. There were 10 single-carton replicates in a Randomized Complete Blocks experiment design. Weight loss, mould incidence, and skin browning were monitored and quantified during the storage period. Taste and indentation incidence were quantified on termination, nine days after cold storage.

In the sulphured fruits, weight loss bore no apparent relation to treatment, and was of the order of 18.5% during the storage period. PolymerCoat application at full-strength was highly effective in preventing mould colonization and fruit indentation. Efficacy was reduced where PolymerCoat was diluted. Differences in colonization relating to prochloraz application rate were not apparent. Taste was positively affected by coating. Fruit browning or darkening did not occur. The fruits treated with 100% PolymerCoat were acceptable for consumption after the storage period. In the non-sulphured fruits, weight loss in the untreated fruits was greatest during storage, being of the order of 21%. In the coated fruits, differences in weight loss relating to treatment were not clearly apparent. In the coated fruits, average weight loss was in the order of 17.3%. Skin browning occurred during cold storage. It was slightly delayed in the coated fruits treated with prochloraz at the lower rate. PolymerCoat application at full-strength was effective in suppressing mould colonization during cold storage, and preventing fruit indentation during the storage period. Efficacy was reduced when PolymerCoat was diluted. Differences in mould colonization relating to prochloraz application rate were not apparent. Taste was positively affected by treatment, but was generally unappealing.

PolymerCoat application at full-strength to sulphured Madras litchi fruits during packing was recommended for commercial evaluation or adoption.

Summary:

• The study evaluated the effects of adding prochloraz (Chronos) at two rates to PolymerCoat applied at full strength, 50%, or 10% dilution on Madras litchi fruits.
• Treatments were applied to sulphured and non-sulphured litchi fruits, which were then stored at 3°C for 38 days followed by 9 days at 20°C.
• Weight loss, mould incidence, skin browning, fruit indentation, and taste were monitored during and after storage in a randomized complete block design with 10 carton replicates per treatment.
• In sulphured fruits:
  • Weight loss (~18.5%) was not clearly affected by treatment.
  • Full-strength PolymerCoat effectively prevented mould colonization and fruit indentation; diluted coatings were less effective.
  • Prochloraz concentration did not significantly affect mould control.
  • Fruit taste was positively affected by coating; browning did not occur.
  • Full-strength PolymerCoat coated sulphured fruits remained acceptable for consumption after storage.
• In non-sulphured fruits:
  • Untreated fruits lost about 21% weight; coated fruits lost about 17.3%.
  • Skin browning occurred during cold storage, slightly delayed by lower prochloraz rates with coating.
  • Full-strength PolymerCoat suppressed mould colonization and fruit indentation effectively; dilution reduced efficacy.
  • Prochloraz concentration did not significantly change mould incidence.
  • Taste was generally unappealing despite positive effects from coating.
• Visual differences after dipping suggest greater PolymerCoat absorption in sulphured fruits compared to non-sulphured.
• Mould colonization was delayed in coated sulphured fruits but advanced in non-sulphured fruits by the end of storage.
• PolymerCoat at full strength on sulphured fruits is recommended for commercial use without necessarily requiring prochloraz.
• For non-sulphured fruits, the coating reduces weight loss and delays mould but does not prevent browning or improve taste to an acceptable level.
• The study suggests exploring combined treatments with colour-loss preventing acids for non-sulphured fruits for better quality preservation.
• The study involved late-season harvested fruits more prone to deterioration.
• The research confirms previous findings on the benefits of PolymerCoat and adds evaluation of prochloraz inclusion as a possible enhancer.
• This work involved detailed quantitative assessments, with statistically significant effects mostly linked to PolymerCoat concentration rather than prochloraz rate.