- SH Swart
- QMS Agri Science, PO Box 416, Letsitele 0885, South Africa
- 2009
In order to explore the possibilities of utilising hot water brushing technologies to reduce post-harvest decay and pericarp browning of litchi fruit, a trial was conducted using dip treatments in ambient or hot water, followed by dips in either hydrochloric, phosphorous or oxalic acids at different concentrations and for different exposure periods. Results, after fruit was stored for 40 days under simulated export conditions, showed that the best retention of the red pericarp pigment and control of post-harvest decay was obtained when fruit received a hot water dip treatment followed by dip treatments in either 3% hydrochloric acid or 10% oxalic acid. However, fruit of all treatments were totally decayed after 3 days incubation at 10°C, indicating that additional strategies will be necessary to ensure effective decay control after fruit have been removed from cold storage. It seems that postharvest decay and pericarp browning are influenced by several diverse factors and that several processes and different techniques will have to be employed in order to reduce these degrading factors to acceptable levels. The implementation of hot water and acid dip treatments, and therefore hot water brushing, certainly bring us closer to a solution but at this stage not without other technologies such as fungicides. The use of hot water brushing technology together with reduced, and possibly acidified fungicide concentrations and the application of fruit coatings to reduce dehydration effectively, must be explored further in order to set up a commercial acceptable protocol for the export of high quality litchi fruit.
Summary:
Post-harvest decay and pericarp browning significantly affect the export quality of litchi fruit, limiting marketability especially to Europe and other regions.
The study evaluated hot water dip treatments (55°C for 30 seconds) combined with acid dips (hydrochloric, phosphorous, or oxalic acid at different concentrations) to reduce decay and browning.
Best results for retaining red pericarp pigment and controlling decay were found with hot water dip followed by a 2-minute dip in 3% hydrochloric acid or 10% oxalic acid.
Acid dips alone were not effective in preventing decay, especially after removal from cold storage and subsequent warmer incubation (10°C for 3 days).
Hot water pretreatment enhances the efficacy of acid dips in disease control and color retention.
Hydrochloric acid was more effective than oxalic or phosphorous acids at comparable concentrations; higher concentrations of hydrochloric acid may be more effective but could be cost-prohibitive commercially.
Pericarp browning and decay are influenced by multiple factors, suggesting no single method can fully solve the problem.
A combination of treatments including hot water brushing, acid dips, fungicides (potentially at reduced and acidified concentrations), and fruit coatings to reduce dehydration is suggested for commercial protocol development.
Additional research is needed to establish optimal sequences and combinations of treatments for practical, cost-effective commercial application.
The study aligns with previous findings that acid stress inhibits fungal growth and strengthens the role of hot water treatment in quality retention.
Technologies like forced-air precooling, irradiation, and low-temperature storage have limitations or cost issues, highlighting the potential of hot water brushing technology currently in use in Israel.
Overall, integrating multiple approaches such as heat treatments, acid dips, fungicide treatment, and coating could improve shelf life, reduce decay, and retain fruit quality from orchard to table.