Evaluate edible coatings on plums and nectarines currently used worldwide.

It was deemed important to source locally and internationally available edible coatings with potential for postharvest application to control shrivel on sea freight export nectarines and plums, to gain an understanding of the commercial potential of each product.

In the 2024/25 season, research was conducted on three nectarine and three plum cultivars.

Fruit packed for export was sourced and the treatments applied in a Two-Way Factorial:

Factor A – Edible coating: (1) no edible coating, (2) edible coating 1 (TBC), (3) edible coating 2 (Vegetable oils and coformulants, emulsion of oil in water – EW), (4) edible coating 3 (E473 – sucrose esters of fatty acids), (5) edible coating 4 (E473 – sucrose esters of fatty acids) or edible coating 5 (E471 – mono- and diglycerides of fatty acids).

Factor B – Internal packaging: Each of the edible coating types was packed with the following: (a) no liner, (b) polyethylene (PE) perforated bag / shrivel sheet (as per commercial recommendation) and (c) paper liner.

2023 – Mass loss data indicated that the perforated shrivel sheet or perforated PE bag is still the best way to reduce mass loss and shrivel in general. In the case of coatings, both coating 1 and 2 have potential as an alternative. The combination of paper liner together with coating 1 showed potential.

2024 – Results indicated that the perforated PE shrivel sheet or perforated bag is still the best way to reduce mass loss and shrivel in general. In the case of edible fruit coatings, both coating 1 and 5 showed potential. If petroleum-based plastics must be replaced, the combination of paper liner together with coating 1 (for nectarines) and coatings 5 and 1 (for plums) showed the best potential.

2025 – Perforated PE shrivel sheets or perforated bags provided the best reduction in mass loss and shrivel in general. In the case of edible fruit coatings, coatings 1 and 5 in combination with 35 gsm paper liners showed potential as alternatives to limit mass loss and shrivel. If overseas markets ban the use of petroleum-based plastics, these combinations should be more comprehensively tested.

Research needs to be expanded on the use of edible coatings to incorporate more cultivars, different fruit maturities, and methods of application. It is important to understand the way coatings work and how the different nectarine and plum cultivars react to combinations of edible coatings and internal packaging formats. Good results were generated thus far, with the recommendations given below. Cost analysis to establish feasibility should be conducted.

This project indicates that it is difficult to replace petroleum-based plastics for use on sea export nectarines and plums, and identifies next best alternatives in the form of fruit coatings combined with paper liners. With companies developing new coatings it is important to continue research on this subject. Coating 1 is currently not actively marketed by the supplier, but these results may change the situation. In the case of coating 5, the supplier would need to register the product on stone fruit in South Africa. New registered products should be tested as they become available.