Role of yeast in the persistence of pesticides during the fermentation of vegetable products

The effect was studied of several yeast strains of the genera Saccharomyces, Pichia, and Kluyveromyces on the persistence of four pesticides (pyraclostrobin, dimethoate, oxamyl, and pymetrozine) in brine during the fermentation process of vegetable products. The growth of yeast strains in a synthetic brine in the presence of the pesticides was recorded with a Bioscreen C kinetic growth reader and compared with their growth in a control brine without pesticides. After incubation for 7 days with the yeast strains, the concentration of pesticides in the synthetic brine was determined. Prior to this pesticide assay, the brines were centrifuged to removing the yeast pellets. The pesticides were determined in both yeast-free brine and yeast pellets and compared with the control consisting of sterile brine with pesticides. A modified QuEChERS (quick, easy, cheap, effective, rugged, and safe) method was used to extract the pesticides, which were assayed by LC-MS. The effect of the yeasts on the concentration of the four pesticides in synthetic brine depended on the yeast strain, and was clearest on pymetrozine and pyraclostrobin.