Pre- and Post-Harvest Infection of Pasteurized Pickles with Fungi and Their Pectinolytic Potential to Soften the Product

Abstract

Fungi and their enzymes have long been thought to cause the softening of pasteurized gherkins; however, the exact fungal species and timing of contamination are unknown. Ready-to-sell pickle jars and blossoms of growing gherkins were inoculated with DNA-sequenced fungi isolated from rotting gherkins to cause softening at various stages of production. Ready-to-sell gherkins inoculated with Fusarium oxysporum, Fusarium equiseti, Galactomyces geotrichum, Mucor circinelloides, Mucor hiemalis, Mucor fragilis, Plectosphaerella cucumerina, Alternaria sp., and Cladosporium sp. indicated a measurable texture reduction after pasteurization and 6 months of storage at room temperature. No texture changes were observed in gherkins infected during the growth phase. The fungi M. hiemalis, M. fragilis, and G. geotrichum tolerated the acidic-saline (approx. pH 4) environment in the jar for several days, thus the pectinolytic enzymes of these candidates were tested for heat and pH resistance. Although the measured endo-Polygalacturonase (PG) of M. fragilis had its optimum activity at pH < 4, all fungal enzymes were inactivated within 3 min at 80 °C corresponding to the pasteurization heat. Our study shows that conventionally occurring fungi and their enzymes have the potential to induce softening in pickles. Softening by these fungi is unlikely due to post- or pre-harvest contamination without any other influences.