Texture softening of pickled cucumbers does not meet consumers’ quality expectations and leads to economic losses. The factor(s) triggering this phenomenon is still unknown. We investigated the importance of plant viruses such as Cucumber green mottle mosaic tobamovirus (CGMMV) and Zucchini yellow mosaic potyvirus (ZYMV) in the context of softening of pickles. Cucumber plants (Cucumis sativus) were infected by mechanical inoculation, grown under greenhouse conditions and tested positive for the viral infection by ELISA. The severity of virus infection was reflected in yield and symptom expression. Histological and morphological alterations were observed. All fruits were pasteurized, separately stored in jars and subjected to texture measurements after four, six and 12 months. CGMMV-infections were asymptomatic or caused mild symptoms on leaves and fruit, and texture quality was comparable to control. At the same time, fruits of ZYMV-infected plants showed severe symptoms like deformations and discoloration, as well as a reduction in firmness and crunchiness after pasteurization. In addition, histological alterations were detected in such fruits, possibly causing textural changes. We conclude that plant viruses could have a considerable influence on the firmness and crunchiness of pickled cucumbers after pasteurization. It is possible that the severity of symptom expression has an influence on texture properties.

Proteolytic enzymes or fungi have long been identified as causing softening of pickled cucumbers. As the softening of cucumbers occurs mainly in the pasteurized state, this study considers the hypothesis that vinegar and the added spices could be responsible for this softening by studying polygalacturonase (endo-/exo-PG), pectinesterase (PE), and pectin lyase, as well as Alternaria spp. found in the spices. Because of the high endo-PG activity found in dill, this spice emerged as a possible factor causing spoilage. Compared to dill, the enzyme activity in mustard seeds is eight times lower, and only low levels of enzymes or Alternaria spp. are present in onions or vinegar. Different harvest times and the associated degree of freshness of dill also played a crucial role regarding the endo-PG activity of up to 25.11 U/g (30 • C, mature and very woody dill in late July) but of less than 9.00 U/g in fresh and soft green dill harvested in late June. A temperature of 80 • C, held for 3 min, reduced the enzyme activity to less than 1.0 U/g. A final examination of cucumbers with a fixed quantity of mustard seeds, vinegar, and onions but with different variants of dill showed that the quantity of dill and the other ingredients added to the jars is not a potential factor leading to cucumber softening, which conflicts with the hypothesis of cucumber spoilage by vinegar and spices.

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.

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