Effects of chemical modification on the physicochemical and baking properties of cereal dietary fibers

Abstract

Dietary fibers (DF) extracted from whole grains (rice, barley, wheat, buckwheat) were chemically modified by cross linking (CL), carboxymethylation (CM), hydroxypropylation (HP) and their physicochemical properties in a food system were evaluated. CM contributed to the increase in soluble dietary fiber (SDF) contents and water solubility. CL and HP contributed to the decrease in water solubility as contents increased. These results were confirmed by Pearson correlation analysis. That is, high insoluble dietary fiber (IDF) contents were negatively correlated with water solubility (r = -0.869, p < 0.01) whereas high SDF contents were positively correlated with water solubility (r = 0.741, p < 0.01). Among four DFs, rice DF had the highest total dietary fiber (TDF) by cross linking and hydroxypropylation, while wheat DF had the highest SDF contents by carboxymethylation. In the interaction with wheat starch, substitution of DFs increased the solubility of wheat starch and the starch hydrolysis was low in the samples with high TDF contents (CL ≈ HP > CM ≈ Native). In case of the viscoelasticity and pasting property, wheat starch-DF mixtures had lower G’, G” and viscosity than wheat starch itself. The G’, G” and viscosity values of native and modified DFs decreased in this order: CM ≈ HP > CL > Native. Especially, CM- and HP-DFs had a similar pasting behavior to wheat starch. As a result, it was explained that the characteristics of DFs and starch mixture were more affected by the functional group than IDF/SDF ratio in modified DFs. Also, in the cake properties, wheat DFs were substituted into wheat flour cake. CL-1% cake had lower volume and higher hardness than the control cake. The CM- and HP-cakes were produced in both 1% and 3% substitution concentration and they had improved-cake qualities such as appearance, high volume and low hardness compared to CL 1%-cakes. Consequently, this study suggested that: the chemical modifications (CL, CM, and HP) of cereal DFs can effectively regulate the IDF/SDF ratio and TDF contents, resulting in the change of physicochemical properties of them. When applied to starch-based foods, modified DFs diversified the physicochemical properties of wheat starch and final quality of product by introduction of a functional group.