Pesticide Residues and Berry Microbiome after Ozonated Water Washing in Table Grape Storage

Abstract

Nowadays, different systems for reducing pesticides in table grapes are being tested at different production stages either in the field or in postharvest. The present study tested ozonated water treatments at the beginning of the cold storage of the Princess® seedless table grape variety to reduce the residue contents of some pesticides and to evaluate their effect on gray mold and the berry microbiome. An ozone generator capable of producing an ozone concentration ranging from 18 to 65 Nm3 was utilized for obtaining three ozone concentration levels in water: 3, 5 and 10 mg/L. Ozonated water was placed in a 70 L plastic box where 500 g grape samples closed in perforated plastic clamshell containers were immersed utilizing two washing times (5 and 10 min). Overall, six ozonated water treatments were tested. After the ozonated water treatments, all samples were stored for 30 days at 2 °C and 95% relative humidity to simulate commercial practices. The pesticide residue contents were determined before the ozonated water treatments (T0) and 30 days after the cold storage (T1). The treatments with ozonated water washing reduced the pesticide residues up to 100%, while the SO2 control treatment reduced the pesticide residues ranging from 20.7 to 60.7%. Using 3 mg/L ozonated water to wash grapes for 5 min represented the optimal degradation conditions for all of the analyzed pesticides, except for fludioxonil, which degraded better with a washing time of 10 min. The ozone treatments did not significantly reduce the gray mold and the fungal and bacterial microbiome, while a relevant reduction was observed in the yeast population.