Effect of ozone application for low-input postharvest dehydration of wine grapes

Abstract

The postharvest dehydration of grapes is a traditional practice to obtain wines with unique traits (e.g., sweet, dry/reinforced). The modern dehydrating rooms are equipped with systems for artificially controlling the inside environment parameters to obtain the desired dehydration kinetic and preserve the grapes from grey mold infection. However, the conditioning systems are extremely energy-demanding and the identification of practical solutions effectively controlling/reducing the postharvest decay would lower the operational costs. To this end, we explored the potential of ozone-based treatments on harvested grapes and preliminarily tested if the treatment could impact the normal behavior and metabolism/composition of grapes during the traditional dehydration practice. Harvested cv. Corvina and Sangiovese grapes were treated with ozone (ozonated water or gas at different concentrations) and partially dehydrated in a dedicated room under controlled temperature and humidity conditions. Technological, metabolomic, and transcriptomic analyses were performed on berry samples collected at different times during the post-treatment dehydration.

Weak differences regarding the dehydration kinetics and the main technological parameter dynamics were detected between treated and untreated grapes. Analyses of phenolic compound content of the cv. Sangiovese berries revealed that the treatment with the gas resulted in higher levels of phenolic acids, flavanols, flavonols and flavanones after 7 days of dehydration. Phenolic acids and stilbenes were higher in ozonated berries at the final stages (40 and 54 days) of the process. The ozone treatment induced only limited changes in the phenol compound profiles of the cv. Corvina berries. In both cultivars, the treatment modified the amino-acid pool of the berries. The transcriptomic analysis revealed that stress-response genes, including those coding for peroxidases, phytosulfokines, and pathogenesis-related proteins, were slightly upregulated shortly after exposure to the higher ozone concentration. Subsequently, modulation of transcripts related to secondary metabolism was weakly detectable.

Overall, the results will shed light on grape physiological response to ozone during the postharvest dehydration process. Sanitizing grapes using ozone will significantly increase their capacity to withstand higher temperature and humidity conditions, reducing spoilage and production losses.