Analysis of pectolytic enzymes and Alternaria spp. in fresh dill, mustard seeds, onions, and vinegar, and their influence on the softening of pickled cucumbers

Abstract

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.

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

“…Sample preparation and the preparation of all required solutions for the individual measurements of pectinolytic enzyme activities were performed according to the methods described in Scharf et al (2022) [31]. Chemicals were purchased from Carl Roth (Carl Roth GmbH & Co.KG, Karlsruhe, Germany) and Sigma-Aldrich (Sigma-Aldrich, Corp., St. Louis, MO, USA).…”

“…The preparation of all buffers, pectin substrates, sample solutions, and procedures for enzyme activity measurements and calculations were performed with minor deviations according to Scharf et al (2022) [31]. In this section, only the minor deviations were described, and the equipment used was listed.…”