The influence of the pre-drying treatment on the hydration properties of dried cell wall materials from apples

Abstract

Wet cell wall materials from apples containing high or low methoxylated pectin components were treated with aqueous solutions of natural components, such as potassium (K) as potassium acetate, malic acid (A), fructose (F) as well as mixtures of these substances. These pre-drying treatments were followed by a water-ethanol exchange and vacuum drying. The structure, state and properties of the dried preparations were investigated. An experimental design (2-level factorial design with the four factors being de-methoxylation, K, A and F) was created for the examination of the influence of the pre-drying treatments on structure and properties of the materials, and the data were analysed by analysis of variances (ANOVA). It was found that the hydration properties of the dried low methoxylated (LM) materials and the rheological properties of the rehydrated samples were particularly influenced by these soluble components. Especially, LM materials charged with potassium ions are characterised by outstanding hydration properties while LM materials treated with A or F had strongly reduced water retention capacities. Interactions between the influencing factors played an important role for the properties of high methoxylated materials. The results were interpreted regarding the pre-formation of structure and state during pre-drying treatment as well as the structural changes and state transitions occurring during pre-drying, drying and rehydration.