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 25.11U/g (30°C, mature and very woody dill in late July) but of less than 9.00U/g in fresh and soft green dill harvested in late June. A temperature of 80°C, held for 3min, 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. PRACTICAL APPLICATION: This work provides insights into the activity of various pectolytic enzymes and the load of Alternaria spp. in different ingredients used for pickle production. Based on these data and additional pasteurization experiments, this paper evaluates the influence of dill, onions, mustard seeds, and vinegar on cucumber softening.