Pg. 44-47 A Comparison of Different Postharvest Treatments and Packing Materials for McLean’s Red Litchi Fruit

Fumigation with sulphur dioxide (SO₂) is the standard postharvest treatment of export litchi fruit from South Africa, but fruit sulphur residue limits in France, the major importer of South African litchis, are strict and have recently been reduced. Alternative postharvest treatments, viz SO₂ + 1 N HCI dip, 2 s steam (95°G) + 1 N HCI, and 2 s steam + 1 N HCI + Vapor Gard® (an anti-transpirant), were compared to untreated controls and standard SO₂ treated fruit of the cultivar McLean’s Red. Fruit from these five postharvest treatments were packed in standard ventilated cartons, pun nets wrapped in Vitafilm^®, or P-Plus® polypropylene bags, and stored for 28 days at 1°C to simulate sea export. Ventilated cartons resulted in excessive moisture loss (13.5%) during storage, compared to Vitafilm^® (1.33%) and P-Plus^® (0.25%). Untreated control fruit had severe skin browning but were firm and tasted good. SO₂ treated fruit (industry standard treatment) were also firm and had good taste, but colour was an unattractive dull pink. A four minute dip in 1 N HCI following SO₂ fumigation resulted in an attractive red colour, but fruit were slightly less firm than fruit treated with SO₂ fumigation alone. Two seconds of steam followed by 1 N HCI dip resulted in attractive red fruit, but some steam (or HCI) scalding was evident and fruit were soft with poor flavour, when compared to untreated control and SO₂ treated fruit. Vapor Gard^® had little positive effect on steam and HCI treated fruit. Further research is required to improve the postharvest treatment of McLean’s Red litchi fruit.

Summary:

• Sulphur dioxide (SO₂) fumigation is the standard postharvest treatment for export litchi fruit from South Africa, but strict residue limits in major markets like France have prompted the search for alternative treatments.
• The study compared SO₂ fumigation, SO₂ followed by 1N HCl dip, 2 seconds steam at 95°C followed by 1N HCl dip, and steam+HCl followed by Vapor Gard (an anti-transpirant) against untreated control fruit.
• Fruit were packed in ventilated cartons, punnets wrapped in Vitafilm plastic, or P-Plus polypropylene bags and stored for 28 days at 1°C to simulate shipping conditions.
• Ventilated cartons caused excessive moisture loss (13.5%), while Vitafilm (1.33%) and P-Plus bags (0.25%) significantly reduced dehydration.
• Untreated fruit showed severe skin browning but remained firm with good taste; SO₂ treated fruit were firm with good taste but had unattractive dull pink coloring.
• SO₂ + HCl dip produced attractive red fruit with slightly less firmness than SO₂ alone.
• Steam + HCl treatments produced red fruit but caused some skin or HCl scalding, softness, and poor flavor compared to controls and SO₂-treated fruit.
• Vapor Gard had little positive effect on firmness or other qualities in steam+HCl treated fruit.
• Postharvest treatment had no significant effect on moisture loss; packing material had a much larger impact.
• Fruit in ventilated cartons had higher sugar concentration due to dehydration but this did not improve taste.
• Steam treatments caused more flesh shriveling and browning; McLeans Red cultivar has delicate skin and did not tolerate harsh steam or chemical treatments well.
• Alternative, less harsh treatments should be investigated for McLeans Red to preserve fruit quality without high SO₂ residues.
• Vitafilm and P-Plus polypropylene packaging effectively reduced moisture loss and preserved quality, warranting further economic viability assessment.
• The study concludes that while SO₂ remains effective, its discoloration effect and residue concerns push the need for improved methods in postharvest treatment and packaging for McLeans Red litchi fruit.