- D. Lemmer, F.J. Kruger, T.R. Malumane, and Y. Nunxdu
- ARC-Institute for Tropical and Subtropical Crops, Private Bag X 11208, Nelspruit 1200
- 2003
During the 2000-2001 season, a semi-wet quaternary ammonium compound (QAC) treatment packed in modified atmosphere packaging (MAP) and stored at 1°C, showed promise in terms of the inhibition of funal growth as well as the retention of skin colour. During the 2001-2002 season, three QA C’s (Prasin®, Desogerme® and Sporekill®) were applied to McLean’s Red fruit for different time and concentrations before being packed and stored in Everfresh® MAP bags. Effective inhibition of fungal growth and retention of colour was obtained at a Prasin® and Desogerme® concentration of 1ml/l and an application time of 1 minute. All treatments exhibited signs of phytotoxic damage when dipped for longer than 1 minute. Further trials involved the addition of a range of food additives, fungicides, food coatings and S02 pads. Theses methods gave mixed results. The QAC/MAP application described above show considerable potential, especially for the problematic McLean’s Red cultivar.
Summary:
- Semi-wet quaternary ammonium compound (QAC) treatments packed in modified atmosphere packaging (MAP) at 1∘C effectively inhibited fungal growth and retained skin colour in litchis during trials.
- The most effective results were achieved with Desogerme and Prasin QACs at a concentration of 1 ml/l for a one-minute dip, as longer dips caused phytotoxic damage.
- Everfresh MAP bags performed best in reducing mass loss and retaining fruit colour, compared to PVC bags with various perforation sizes.
- Slow-release SO2 pads at 10 ppm in unperforated PVC bags improved colour retention but risked yellow SO-bleached areas in fruit near the pads.
- Fungal infections were best controlled by wet Desogerme treatments, with no infection during cold storage and three days of shelf life; however, infections developed by day seven and Acid B treatments proved ineffective.
- Higher concentrations or longer exposure to QACs or fungicides like Sporekill led to phytotoxic fruit damage; rinsing with distilled water did not prevent this damage.
- Supplementary additives and coatings, such as potassium sorbate, sodium-acid-pyro-phosphate, and N-benzyladenine, gave mixed or negative results (off-tastes, white crystals, or phytotoxicity), and did not improve fungal resistance over the wet Desogerme protocol.
- Recommendations for packhouses include: timely harvest (before 10 am), careful fruit sorting, using QACs at proper concentration/duration, packing fruit in a semi-wet state, using suitable MAP materials (Everfresh preferred), and pre-cooling fruit to 1∘C before transport.
- Though promising for local market and air-freighted export, the method is not yet recommended for sea freight; future trials will explore further fungicide combinations.