The influence of predrying treatment and of suspension solution conditions on the rehydration of apple cell wall materials

Abstract

The aim of this work was to investigate the influence of structure variations, predrying treatment and the suspension solution conditions on the hydration properties of cell wall materials from apples. For this purpose, materials with high methoxylated (HM) as well as with low methoxylated (LM) pectin components were treated in the wet state (predrying treatment) and as dried preparations (rehydration) with water (W, reference) or with potassium acetate (K) and malic acid (A) solutions, respectively. It was found that the results were determined by interactions of the examined influencing factors to a great extent. The best hydration properties of all the samples investigated were achieved by a combined demethoxylation and a charging with potassium ions during predrying treatment. In this way, mean values for the maximum W-retention capacities from 73–82 g W/g dried sample were obtained. In contrast, all other LM samples were characterised by reduced hydration properties, independent of the conditions applied (W-retention capacities 30–46 g/g). In the case of HM materials, predrying treatment with K or A decreased the hydration properties compared with the reference material (treatment with W, W-retention capacities 53–57 g/g). In comparison with the rehydration of HM preparations with W, the use of A solution affected the hydration properties negatively, but the application of K solution enhanced the velocity of rehydration. The results of the hydration properties and of the rheological properties of the rehydrated samples were interpreted regarding the preformation of the structure/state during predrying treatment as well as the changes occurring during drying and rehydration.