- P C Fourie
- Navorsingsinstituut vir Vrugte en Vrugtetegnologie, ·Privaatsak XS0B, Stellenbosch 7600
- 1990
Swaweldioksiedgasberoking word ook as ‘n na-oesbehandeling by lietsjies toegepas. Swaweldioksiedberoking is egter ‘n proses wat moeilik beheerbaar is. Die sukses van hierdie tegniek word deur verkskeie faktore soos konsentrasies, temperatuur, tyd, relatiewe humiditeit, swawelkamergrootte, hoeveelheid vrugte, berokingshouers, rypheidsgraad en toelaatbare vlakke beinvloed: Kennis van die berokingstegniek, deeglike beplanning en gekontroleerde toediening is noodsaaklik om beter kwaliteit vars lietsjies te verseker.
Summary:
Sulphur dioxide fumigation is used as a post-harvest treatment on litchis but is a difficult process to control.
The success depends on multiple factors including concentrations, temperature, time, relative humidity, size of the sulphur chamber, quantity of fruit, type of fumigation containers, fruit maturity, and permissible residue levels.
Sulphur dioxide has been used historically as a preservative and disinfectant, accepted worldwide despite growing concerns since the 1980s about its health effects, especially in causing asthma attacks.
In South Africa, its use on litchis is approved with restrictions ensuring consumer information and residue limits (maximum 20 mg/kg pulp).
Sulphur dioxide gas is produced by burning sulphur in the presence of oxygen, forming a colorless gas with accompanying water vapor mist.
It is a heavy gas that moves by convection within the fumigation chamber.
Functions of sulphur dioxide include inhibiting enzymatic browning, acting as an antioxidant and reducing agent, and controlling microorganisms responsible for postharvest decay in litchis.
It bleaches the natural red color in litchis to an attractive, stable pink by reacting with natural pigments (anthocyanins).
Controlling the fumigation process is challenging due to variability in sulphur dioxide concentrations caused by burning rate, airflow, chamber size, fruit load, container placement, and temperature differences.
Over-or under-concentration may occur, and incorrect absorption by containers can lead to uneven treatment.
The degree of fruit ripeness affects how much sulphur dioxide is absorbed, with greener fruit absorbing less and thus having uneven pink coloration.
Recommendations include careful research to determine desired sulphur dioxide concentration within allowed limits and controlled application.
Using fruit of uniform maturity placed in containers that do not absorb sulphur dioxide and allowing gas circulation can improve uniformity.
Treatment should be done in a sealed fumigation chamber using pre-calculated amounts of sulphur dioxide gas from cylinders.
Fans can be used to evenly distribute the gas throughout the chamber.
Producers need to accept the process as complex and take responsibility for designing programs suited to their needs to achieve high-quality litchis.