Material properties of processed fruit and vegetables. II. Water hydration properties of cell wall materials from apples

Apple cell wall material was exposed to different processing steps, commonly used in the fruit and vegetable industry, such as heat and enzymatic treatment (maceration, liquefaction) as well as extraction with diluted acid. The influence of these procedures was investigated with respect to chemical composition and structural features and their effect on the material and functional properties. Besides water binding determinations commonly used, kinetic methods were introduced. In this way it was shown that the treatments influence not only the water retention capacity but also the velocities of swelling and water release under pressure, respectively. Heat treated materials with softened cell walls released water slower than cold water extracted materials. Furthermore, it was found that a high pectin content or a remaining natural grown cell structure are no prerequisites for a good water binding ability. The relationships are rather very complex and multivariate and all factors influence mutually.