Oven-dried table olives: textural properties as related to pectic composition

The effects of processing treatments on the microscopic structure, pectic fractions and firmness of ripe olives (Olea europaea L Cassanese variety), processed by the 'Ferrandina' method for oven-dried table olive production, were studied. The process included a first heating step, a salting step and a final oven-drying process. Scanning electron microscopic observations of olive tissue structure revealed that heat treatment was highly damaging, affecting the intercellular pectic substances and producing cell separation. Epicuticular waxes were barely affected and limited the shrivelling of the fruit during the oven dehydration process. The pectin content was higher in the oven-dried olives than in the fresh samples. The sodium hydroxide-soluble fraction was the main pectin fraction in the olive tissues. Its content decreased markedly after the heating step, while it increased after the oven dehydration step. The softening of the olive tissues increased after heat treatment, and a correlation was found between protopectin content and firmness. In oven-dried olives a firming of the olive tissues was observed due to the de-esterification of pectin and to its decreased solubility resulting from an increase in cell wall calcium bridging. © 2000 Society of Chemical Industry