Submitted to: Proceedings of Florida State Horticultural Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/6/2006
Publication Date: 4/11/2007
Citation: Plotto, A., Narciso, J., Baldwin, E.A., Rattanapanone, N. 2006. Edible coatings and other surface treatments to maintain color of lychee fruit in storage. Proceedings of Florida State Horticultural Society. 119:323-331. Interpretive Summary: Lychee is a tropical fruit with a very attractive red skin (pericarp), but the pericarp turns brown quickly after harvest, reducing the fruit attractiveness. The browning is mostly due to cell dehydration and membrane leakage, allowing oxidative enzymes to get into the vacuole and oxidize the red pigments (anthocyanins). Surface coatings that would prevent, or delay skin dehydration were tested. Additionally, treatments must be acidic, as the red pigment turns brown if the pH is around 5.0. Treatments were performed in Florida and Thailand, as dip treatments of the fruit, which were then stored for 2 or 3 weeks at 2 or 5 °C. Acidic treatments that included antioxidants worked better than acids or antioxidants alone. Polysaccharide coatings increased decay development. Some hydrophobic coatings such as sucrose fatty acids, and a carnauba wax had a favorable effect on decay reduction, but not so much on browning reduction, probably due to higher pH. Decay was mostly due to the pathogen, anthracnose, and future effort will be directed towards reducing decay in the field.
Technical Abstract: The bright red pericarp of lychee (Litchi chinensis Sonn.) fruit quickly turns brown after harvest due to peel dehydration, anthocyanin degradation, and fungal growth on the fruit surface. Lychee fruit, cv. ‘Brewster’ and ‘Mauritius’ in Florida, and ‘Juckapat’ in Thailand, were dipped in acidic treatments (2-2.5% citric acid, 2% ascorbic acid, 2% acetic acid, 1% isoascorbic acid), antioxidants (0.5% acetylcysteine, 0.02% hexylresorcinol), antimicrobial treatments (peroxyacetic acid [Storox], 5 or 20% ethanol) and various coatings (carrageenan, hydroxypropylcelulose [HPC], sucrose fatty acid esters [Semperfresh], pectin oligomers, carnauba wax [Rainox]), alone or in combination. Combinations of acid solutions with antioxidants gave better results than acid solutions alone. In particular, the mixture of isoascorbic acid with acetylcysteine and hexylresorcinol gave higher chroma readings with the L*a*b* color measuring system, indicating higher color intensity. This treatment also had better decay control and reduced browning. Ascorbic acid, isoascorbic acid, and acetylcysteine alone resulted in higher chroma in one experiment. Visual quality was higher for these treatments after 15 and 21 days storage at 5 °C, as well as for the sucrose fatty acid ester. Ascorbic and citric acid gave the best results in the Thai experiments. HPC performed well on the Thai fruit, but not on the Floridian fruit. Finally, among the antimocrobial treatments, ethanol at 5% had lower browning and better decay control, and resulted in higher visual quality of ‘Mauritius’ lychee after 2 weeks. Future efforts will also aim at reducing pathogen pressure in the field, as well as after harvest.