Optimising postharvest packaging to prolong storage and maintain quality of table grapes

PROJECT TITLE:    Optimising postharvest packaging to prolong storage and maintain quality of table grapes

Project leader:       Pieter Louw (ExperiCo)

Contact:                     pieter@experico.co.za

Duration:                   1 November 2022 – 31 December 2024

Problem identification and project objectives:

Postharvest pathogens like Botrytis cinerea, Penicillium expansum, Alternaria alternata, Cladosporium spp. and Aspergillus spp. occur more readily on table grapes, especially under changing weather conditions which favour decay. Logistical problems experienced in the supply chain the past season resulted in prolonged shipment / storage of grapes, extending beyond eight weeks before reaching retail shelfs in some cases. The loss in quality and development of decay became evident during cold storage and shipment, more so if grapes were stored for extended periods. SO2 is used fairly successfully to limit decay development during storage, however, it may have limitations to control decay if not applied in the correct combination with a liner bag, moisture absorbing material (MAMs) and cooling conditions. Other factors like cultivar type (differ in susceptibility), preharvest quality and postharvest conditions (packaging, cooling and logistics) further complicate grape quality and the efficacy of in-box treatments with SO2. It has become unclear to producers what concentration of SO2 and delivery system (type of SO2 sheet) in combination with different liner bags and MAMs are more effective to maintain the quality of specific table grape cultivars. Furthermore, the composition and manufacturing of SO2 sheets have changed, bringing along uncertainty of efficacy related to release patterns and levels maintained in the changed grape packaging used at present. This study aims to determine the release and efficacy of SO2 in combination with different packaging options to limit decay and maintain quality of table grapes subjected to long term storage. An optimised guide-line will be suggested.