Pg. 31-37 Evaluation of fruit coatings to reduce dehydration, pericarp browning and post-harvest decay of litchi fruit

The aim of this project was to evaluate post-harvest treatments with different acids, fruit surface coatings and waxes in order to determine the effect on internal quality, dehydration, pericarp browning and post-harvest decay development on ‘HLH Mauritius’ and ‘McLean’s Red’ fruit. Two trials consisting of 20 and 28 treatments respectively, were conducted during January and February 2008. Fruit were incubated at 3±1 °C for 40 days to simulate export conditions and kept at 10±2° C for 14 days, simulating supermarket conditions. The effect of treatments on internal quality, weight loss, colour and post-harvest decay development was recorded over time.

Mauritius fruit treated with acidified prochloraz and ‘McLean’s Red’ fruit treated with acidified Semperfresh and citric acid had a slightly lower TSS than some of the other treatments evaluated in this trial. None of the treatments could improve on fruit appearance when compared to fruit treated with commercial sulphur dioxide (SO₂ ) fumigation. Fruit in most treatments had a poor appearance when evaluated after being kept for seven days at 10±2° C. Some of the products applied as 30 sec dip treatments or brush on treatments, showed improvement in fruit appearance compared to the untreated control, but efficacy will have to be improved dramatically in order to be an acceptable replacement for sulphur dioxide fumigation.

Summary:

• The study aimed to evaluate post-harvest treatments with various acids, fruit surface coatings, and waxes to reduce dehydration, pericarp browning, and decay in litchi fruit cultivars HLH Mauritius and McLeans Red.
• Trials involved 20 and 28 treatments applied as 30-second dips or brush-ons at ambient temperature, followed by simulated export storage at 31°C for 40 days and supermarket conditions at 10°C for 14 days.
• None of the tested treatments matched the commercial sulphur dioxide (SO₂) fumigation for preserving fruit appearance or preventing pericarp browning.
• Weight loss (dehydration) was not significantly prevented by most treatments; sulphur dioxide fumigation and certain waxes (hydrochloric acid, Carnauba wax) showed somewhat lower weight loss.
• Post-harvest decay control was best with sulphur dioxide fumigation, followed by prochloraz treatments.
• None of the tested coatings or acid dips effectively prevented pericarp browning, except for sulphur dioxide fumigation.
• Some coatings (Croplife, Hydrochloric acid) showed minor improvements but were not comparable to sulphur dioxide treatment.
• Fruit treated with Semperfresh (a commercial coating) and acidified prochloraz showed some color improvement, but prochloraz alone worsened pericarp browning.
• Carnauba wax treatments resulted in poor fruit quality.
• Literature indicates longer dipping times (10–15 minutes) with acids like oxalic acid may be more effective at reducing browning, suggesting 30 seconds may be too short.
• Oxalic acid is highlighted as a promising natural antioxidant for controlling post-harvest browning based on previous studies.
• Future research should explore longer exposure times, hot water treatments combined with acid dips, and advanced fruit coating technologies to find effective alternatives to sulphur dioxide fumigation.
• The study acknowledges challenges in controlling water loss, enzymatic browning, and fungal decay simultaneously in litchi fruit post-harvest management.
• The authors recommend further evaluation of coating coverage efficacy and development of new methods based on the latest hot water dip and rinse technologies.
• This work contributes valuable data on the limitations of current coating and acid treatments and guides directions for improving post-harvest quality retention in litchi fruit.