A monolithic device for in-package SO2 generation for the control of postharvest Botrytis decay of table grapes

The occurrence of Botrytis cinerea and sulphur dioxide (SO2) bleaching on table grapes are the main causes for the deterioration of fruit quality during postharvest storage. Efficacy tests were conducted with novel monolithic type devices which release SO2 at a constant rate over an extended period. The devices comprise a polymer matrix, with sodium metabisulphite (Na2S2O5) particles dispersed evenly throughout the matrix. Treatment combinations consisting of various Na2S2O5 concentrations (10% to 50%) and number of devices (2 and 4) placed amongst the grapes, were tested along with the inclusion or exclusion of paper liners, acting as barrier between the grapes and the SO2 device. The efficacy of the new SO2 device was compared with the dual release SO2 system. The new device reduced SO2 bleaching as result of lower initial SO2 levels and the emission of lower levels of SO2 over an extended period. Storage decay was also reduced with the use of the new devices. The number of discs used within the carton, the concentration Na2S2O5 incorporated in the discs, and the use of corrugated paper liners, affected the proficiency of the devices. Decay control was more effective iri absence of a liner than in its presence, while SO2 damage increased when the liners were omitted. Reduced control was associated with the packaging treatments where only two discs were included, or when devices of low Na2S2O5 concentrations were used. Decay control was dramatically improved by increasing the Na2S2O5 concentration incorporated in the new polymer SO2 devices.