Technology testing for the ability to control shrivel in cold-stored plums and nectarines

The control of shrivel on fruit is rapidly becoming a serious challenge, with pressure from consumers and governments to limit the use of single-use petroleum-based plastics and including a plastic tax. These are currently used as liners to prevent moisture loss from fruit packed in boxes, and hence, alternatives are required. The objective of this study is to scan available technologies and/or technologies under development, to gain an understanding of the potential of each and subsequently identify individual or combination treatments to achieve commercial success.

The plum and nectarine cultivars were sourced from commercial pack-houses and repacked with the required packaging treatments. Some of the fruit received a fruit coating that was applied via an atomizer as stated in the work plan. Fruit were weighed at intake and after cold storage and shelf life to determine the mass loss from the fruit of each treatment per cultivar and fruit type. Fruit quality assessments were conducted after single- or dual temperature cold storage plus shelf life.

In the three seasons of research, all the fruit cultivars packed in 36 x 4 mm polyethylene (PE) perforated bags exhibited significantly lower mass loss and shrivels levels, followed closely by fruit packed in the standard 48 x 6 mm PE perforated wrappers or standard PE 54 x 2 mm perforated bags for the African Delight plums and August Red nectarines. The 35 gsm paper liner that replaced the 19 gsm and 55 gsm paper liner tested in the first year, was the best alternative to PE perforated bags or wrappers in terms of packaging. Fruit coating 2 that showed some positive results on certain cultivars in previous years, exhibited some skin pitting when used as a combination with paper liners on Ruby Sun and African Delight plums, but worked well on Tiffany, August Red nectarines and Laetitia plums. It is postulated that the skin pitting was a side effect of this specific fruit coating. This implies the type of fruit coating to be used may be cultivar specific.

This research clearly showed that at present, the best liner packaging to lower mass loss and shrivel in stone fruit is the 36 x 4 mm PE perforated bags that were identified in previous work done on plums and nectarines (PL 03-17 & N 01-17) and confirmed in all three seasons, followed by the 48 x 6 mm standard PE perforated wrappers. In most cases the 35 gsm paper liner was the best alternative to the PE plastic bag and wrappers, and this could be of immense value if single-use plastics are banned. More research on edible coatings is recommended as a matter of urgency to test their efficacy without any negative effects on fruit quality and each coating should be tested on its own and in combination with the 35 gsm paper liner.

This project has identified the best in-carton packaging for sea-export storage of plums and nectarines, and the current best alternatives. More emphasis needs to be placed on edible coatings and use thereof in combination with paper liners, as well as relative humidity control from time of harvest until stuffing of the shipping containers.