Effects of Wheat Gluten and Ethyl Cellulose on Hygroscopicity of Freeze-Dried Apple Powder

Abstract

In order to enhance the inhibitory effect of wheat gluten (WG) on the hygroscopicity of freeze-dried apple powder and to improve its storage quality, ethyl cellulose (EC), with low hygroscopicity, was selected to substitute for WG in different proportions in the production of freeze-dried apple powder. The effects of WG and EC on the hygroscopic behavior, macromorphology and moisture migration of freeze-dried apple powder were studied. The results showed that at 75% relative humidity, the equilibrium moisture content of freeze-dried apple powder decreased by about 2.26% for every 10% increase in EC addition. The Peleg model had the best fitting effect on moisture adsorption isotherms of freeze-dried apple powder, which belonged to type III. In addition, macroscopical photographs and low field-nuclear magnetic resonance analysis of freeze-dried apple powder showed that the optimal ratio of apple pulp to WG to EC was 7:2:1. This ratio not only had a certain inhibitory effect on the hygroscopicity of freeze-dried apple powder, but also avoided an increase in the proportion of free water caused by excessive addition of EC, which was conducive to keeping freeze-dried apple powder in a good powder state.

Keywords

• apple powder; wheat gluten; ethyl cellulose; freeze-dried; moisture adsorption; moisture migration