Pg. 44-46 Effect of Heat-Acid Treatment on Quality of Lychee Fruit

Brown marking on the thin membranous layer a few cells thick, on the surface of the aril is the main problem encountered with the heat-acid treatment. The degree and intensity of browning vary greatly with treatments. Cultivar differences also play a great role. Another serious problem is pinking and subsequent browning of the fruit aril, which is likely due to stain from the dissolved anthocyanins in the rind under the strong acidic conditions used in the treatment. The present study was an attempt to clarify and identify factors associated with these problems.

Summary:

• The study investigates the effects of heat and acid treatments on lychee fruit quality, focusing on common problems like brown marking and pinking of the aril caused by heat-acid treatment.
• Several lychee varieties were tested: Mauritius, McLeans Red of Madras from South Africa, and Hong Huai, Kim Cheng, and Kom from Thailand.
• Heat treatment involved steaming at 98°C or hot water baths at various temperatures (75°C, 85°C, 95°C) for short durations (2 to 5 seconds), followed by acid dipping in hydrochloric acid (pH 0) for several minutes.
• Electrolyte leakage of the rind was used as an indicator of heat injury; Mauritius was found to be more susceptible to heat damage compared to other varieties.
• Browning of the aril after treatment varied greatly with cultivar and treatment specifics, with extensive browning noted in Madras variety under heat-acid treatments.
• Browning was associated with the combination of heat and acid treatments but not with either treatment alone; lower heat temperatures (75°C and 85°C) reduced browning and rind injury compared to 95°C.
• Delaying acid dipping for 30 minutes to 1 hour after heat treatment significantly reduced browning and increased fruit acceptability.
• Acid dipping improved rind coloration, particularly for lighter-colored varieties like Mauritius, but some irreversible pigment-enzyme complexes formed during heat injury reduced color intensity one hour post-treatment.
• Color stability varied among varieties, with Madras showing more fading over days post-treatment despite fixed coloration initially.
• The study concludes heat-acid treatment effects on lychee quality are strongly variety-dependent, and more focused research is needed to optimize treatment parameters and mitigate browning issues for commercial viability.
• The research was supported by the Thai Research Fund and South African Litchi Growers Association, with experiments conducted mainly at TISTR in Thailand and Merensky Technical Services in South Africa.​
• This summary encapsulates key findings and insights from the detailed study on lychee fruit post-harvest treatment quality.