- T J C Regnier, D Sivakumar, B T Demo.z and L Korsten
- Department of Microbiology and Plant Pathology University of Pretoria, Pretoria 0001, South Africa
- 2004
Litchi fruit cv. Mauritius were subjected to post-harvest dip treatments in potassium metabisulphite (250 ppm), Vapogard® (0.1%), Chitosan (0.1%), combined potassium metabisulphite (250 ppm) and Vapogard® (0.1%), combined Chitosan (0.1%) and potassium metabisulphite (250 ppm), combined Anolyte® (2%) Triton X-100 and chitosan, combined ammonia solution (0.5%) and Carnauba wax (1%). The fruit were held for 21 days in cold storage at 1°C and 95% relative humidity (RH) to simulate refrigerated sea shipment conditions; thereafter at simulated retail shelf conditions at 18°C and 80% RH for 2 days. Fruit were evaluated for decay, marketability, desiccation and browning.
The combined potassium metabisulphite and Vapogard® treatment retained the marketability of the fruit most effectively by reducing browning severity, post-harvest diseases and fruit firmness compared to commercial sulphur dioxide fumigated fruit. This treatment also revealed superior taste compared to the commercial sulphur dioxide fumigation with 19. 5% soluble solid concentration and 0.2% titratable acidity. The red colour retention was highest in fruit dipped in potassium metabisulphite and Vapogard®, and a decline in anthocyanin concentration was also evident in this treatment. This combined treatment provided an effective alternative for commercial sulphur dioxide fumigation.
Summary:
- The study investigated the effect of various post-harvest dip treatments on the retention of quality and shelf life of litchi fruit (cv. Mauritius) during low temperature storage and simulated retail conditions.
- Treatments included potassium metabisulphite (PM) 250 ppm, Vapogard (an antitranspirant) 0.1%, chitosan 0.1%, and combinations of these with other chemicals such as Anolyte, Triton X-100, ammonia solution with Carnauba wax, and commercial sulfur dioxide (SO2) fumigation.
- Fruit were stored at 1°C and 95% relative humidity for 21 days and then held at 18°C and 80% RH for 2 days to simulate post-storage retail display.
- The combined potassium metabisulphite and Vapogard treatment most effectively maintained fruit marketability by reducing browning severity, post-harvest diseases, and maintaining fruit firmness compared to commercial SO2 fumigated fruit.
- This combined treatment also preserved the red color and anthocyanin concentration better than most other treatments, indicating effective color retention.
- It achieved superior taste as indicated by higher soluble solid concentration (19.5%) and favorable titratable acidity (0.2%), closer to freshly harvested fruit levels.
- SO2 fumigation, although effective, leaves undesirable residues and alters natural fruit taste, posing health hazards and economic challenges due to strict residue limits in export markets.
- Chitosan coatings showed some benefits but also intensified browning and reduced anthocyanin content in this study.
- Potassium metabisulphite is considered safe, with low sulfur residue in fruit and showed antifungal and antioxidant properties.
- The study recommends the potassium metabisulphite and Vapogard combined dip as a promising alternative to SO2 fumigation for maintaining overall fruit quality during export storage for up to 21 days.
- The research highlights the need for environmentally friendly and economically feasible alternatives to SO2 fumigation, given regulatory and health concerns with the latter.
- Detailed physico-chemical parameters such as weight loss, fruit firmness, soluble solids, titratable acidity, anthocyanin, phenolic, and flavonoid contents were assessed to support these findings.
- The study was conducted with support from the South African Litchi Growers Association and provides insights for better post-harvest handling of litchi fruit to maintain export quality.