Degradation of potassium sorbate in vegetable spread by Trichoderma Harzianum rifai

摘要

Samples of a vegetable spread taken from a supermarket in Sao Paulo, Brazil, that had a strong off odor and altered appearance were examined to investigate the origin of the spoilage. Direct microscopic examination revealed the presence of mycelia. The product was inoculated into potato dextrose agar medium (PDA) with added antibiotics to isolate molds, and the concentration of the potassium sorbate used as a preservative was determined. The only species of mold isolated was inoculated onto simple PDA plates and onto PDA plates with added potassium sorbate at the following levels: 0.10%, 0.15%, 0.20%, and 0.25%; the plates were incubated at 25 deg C for 5 days. The mold was also inoculated into samples of unspoiled vegetable spread containing 0.1% potassium sorbate. Half of the samples were incubated at 25 deg C for 5 days and halfat 7 deg C for 14 days. Spoilage was very fast at 25 deg C but was prevented by refrigeration at 7 deg C. In spoiled vegetable spread samples, only traces of sorbate were detected, suggesting degradation of the preservative. The mold was identified in oat agar medium incubated at 25 deg C for 5 days. The mold that was isolated and assumed to be the source of the deterioration, which was identified as Trichoderma harzianum Rifai, was resistant to all concentrations of potassium sorbate tested. When samples of spoiled and unspoiled vegetable spread were examined by mass spectrometry to identify the compound responsible for the off odor, the compund was identified as 1,3 pentadiene originating from the decarboxylation of potassium sorbate.