Evaluation of the Importance of Enzymatic and Non-enzymatic Softening in Low Salt Cucumber Fermentations
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Date
2006-03-13
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Abstract
Retention of a firm, crisp fruit texture is a major consideration for pickled vegetables including pickles made from fermented cucumbers. Cucumbers fermented in low salt (3% or less NaCl) without added calcium soften rapidly. However, it is not clear if softening of cucumbers in low salt occurs as a result of enzymatic or non-enzymatic mechanisms. The objective of this research was to assess the relative importance of non-enzymatic and enzymatic reactions in cucumbers in the softening that occurs when cucumbers are fermented and stored at a low salt concentration.
Fermentation of cucumbers in 6.0% NaCl plus 18 mM calcium maintained firmness better than any treatment with reduced salt. Heat treatment of cucumbers sufficient to inactivate cell wall degrading enzymes before fermentation helped reduce firmness loss during fermentation and storage. However, heat treatment of cucumbers after fermentation did not prevent firmness loss during storage at 30°C. This suggested that reactions that resulted in softening of the cucumber tissue during storage had occurred during the fermentation period and that heating after fermentation could not prevent those changes.
Polygalacturonase activity could not be detected in the cucumbers used in these experiments. α-D-galactopyranosidase and β-D-glucopyranosidase lost their activity completely in cucumbers blanched at 65°C. Other enzymes detected in the cucumbers that hydrolyzed p-nitrophenylglycosides lost ~60 to 80% of their activity at this blanch temperature. Pectinesterase retained over 70% of its activity in cucumbers blanched at 65°C. Pectinesterase along with all of the glycosidases detected in fresh cucumbers lost all detectable activity when cucumber slices were blanched at 85°C. At equal ionic strength, α-D-galactopyranosidase and β-D-galactopyranosidase were inhibited to a greater extent by calcium ions than sodium ions. However, for β-D-glucopyranosidase, the inhibition was dependent primarily on the ionic strength of the solution. During the first week of fermentation in 1.75% NaCl, there was a complete loss of activity of all the glycosidases assayed.
The fact that cucumbers heated sufficiently to inactivate all the enzymatic activities measured and fermented at a low salt concentration lost firmness compared to cucumbers fermented in 6% salt with 18 mM calcium chloride showed that non-enzymatic reactions were important in low salt softening. In three of four lots of cucumbers fermented there was additional softening if the cucumber tissue did not receive a heat treatment. This suggested that enzymatic reactions can also contribute to the softening that occurs during fermentation and storage of cucumbers at low salt levels. However, it was not possible to associate softening with specific enzymatic reactions.
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Keywords
Cucumber, Fermentation, Softening, Enzymes
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Degree
MS
Discipline
Food Science
