Influence of sulfur dioxide-emitting polyethylene packaging on blueberry decay and quality during long-term storage

Authors: Saito, Seiya; Obenland, David - Dave; Xiao, Chang-Lin

Submitted to: Postharvest Biology and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/13/2019
Publication Date: 2/1/2020
Citation: Saito, S., Obenland, D.M., Xiao, C. 2020. Influence of sulfur dioxide-emitting polyethylene packaging on blueberry decay and quality during long-term storage. Postharvest Biology and Technology. 160. Article 111045. https://doi.org/10.1016/j.postharvbio.2019.111045.
DOI: https://doi.org/10.1016/j.postharvbio.2019.111045

Interpretive Summary: Blueberries are highly susceptible to decay after harvest and application of sulfur dioxide has been shown in prior work to be effective in lessening decay during storage. Typically, long-term application of sulfur dioxide to packaged fruit during storage is achieved by placing pads or sheets that emit sulfur dioxide inside of a polyethylene liner that surrounds the fruit. This method is effective but introduces extra labor into the packaging process as the sulfur dioxide-emitting materials must be placed separately into the final package. In this study a polyethylene liner that itself emits sulfur dioxide, and negates the use of extra pads or sheets, was evaluated. Research conducted over two years, utilizing five varieties, evaluated the performance of sulfur dioxide emitting liners with various degrees of venting, including a product with no venting designed to develop altered oxygen and carbon dioxide gas concentrations. Comparisons were made to similar packaging without sulfur dioxide. Results from both years indicated that the sulfur dioxide-emitting liners were effective in reducing the occurrence and spread of decay. Liners with no venting were the most effective in decay reduction and improved blueberry quality by reducing weight loss and shriveling. This study demonstrated that sulfur dioxide-emitting liners are an effective means of preserving blueberry quality during long-term storage. The potentially greater ease in assembling the final packaging could be of benefit to blueberry packers.

Technical Abstract: Blueberries are highly susceptible to decay after harvest and application of sulfur dioxide (SO2) has been shown in prior work to be effective in lessening decay during long-term storage. This study examined a means of SO2 application during storage in which box liners, which are already sometimes used with other commodities to reduce water loss, have sodium metabisulfite incorporated into the liner film and emit SO2. In 2017 three varieties, ‘Emerald’, Jewel’ and ‘Misty’, were obtained from commercial packing houses. For each variety the fruit were contained in plastic clamshells with 12 clamshells per box. Sulfur dioxide-emitting liners surrounding the clamshells, within each box, with either 0.9%, 0.3% or no vent area were evaluated, the product with no venting designed to achieve a modified atmosphere (MA) during storage. Treatments utilizing SO2-emitting sheets with no liner, modified atmosphere with no SO2 and no liner or treatment were included as comparisons. After packaging the fruit were placed into storage for either 3 or 6 weeks and then evaluated for decay and fruit quality. The effect on decay was determined both by assessing natural decay and by determining the spread of decay from berries inoculated with mycelium. In 2018 two varieties, ‘Draper’ and ‘Duke’ were tested in a similar manner, except a 0.1% vented liner replaced the 0.9% liner and the SO2-emitting sheets were not included as a treatment. Also, in 2018 concentrations of SO2 and atmospheric gases were monitored within the appropriate packaging. Results from both years indicated that the SO2-emitting liners were effective in reducing the rate of natural decay and reducing the spread of mycelial growth from inoculated berries in comparison to treatments that that not have SO2. Treatments with SO2 and MA (SO2/MA) were the most effective, while MA only was not consistent in decay control. The high effectiveness of the SO2/MA treatment in controlling decay seems likely due to higher humidity levels within the packaging that help enhance SO2 activity, as SO2 concentrations did not differ among the liner types and concentrations of CO2 in the MA packaging were too low to have had much effect. Weight loss was significantly less in packaging with lesser vent area, with the least being in the MA packaging, regardless of the presence of SO2. This was associated with lower shrivel, although firmness was not always greater. Sulfur dioxide concentrations measured in 2018 indicated that the gas concentration did not exceed 10 µL L-1 and bleaching of the berries was not an issue in either year. This study demonstrated that sulfur dioxide-emitting liners are an effective means of preserving blueberry quality during long-term storage, particularly when combined with MA. The potentially greater ease in assembling the packaging versus that using a conventional SO2-emitting material plus a conventional liner could be of benefit to blueberry packers.