Assessment and effects of starch properties in food materials

Abstract

Starch is an important food carbohydrate, and accounts for many of the properties of popular starchy foods such as noodles. Generally noodles can be divided into two types: wheat-based noodles (containing gluten) and starch-based noodles (gluten free). Physical properties of wheat noodles blended with buckwheat or millet flour, and mung bean starch noodles blended with other starches were investigated in this study. Commercial buckwheat and millet flour were added to wheat flour at different mixing ratios ranging from 0–100 %, and their pasting, thermal, gelling and rheological properties were investigated. Two endotherms were observed during DSC measurement of millet-wheat blends at high mixing ratio, as individual starch tended to gelatinize separately in excess water. Large and mostly non-additive changes were observed in pasting and rheological properties, indicating interactions existed between components. However, within a complex flour-water system, with many variables altered at the same time (protein, lipid, gluten content), it is difficult to accurately model these changes.

Mung bean is widely considered as the best material to make starch noodles. Potato, sweet potato, rice and sorghum were added to mung bean starch and their impact on pasting, thermal, swelling, rheological, and gelling properties were studied. Non-additive effects were found in most attributes, and were partially explained by amylose content and particle size distribution.

After studies on flour and starch blends, corresponding noodle qualities were investigated. Higher level of buckwheat and millet addition led to a weaker texture in wheat noodles but no big variation in cooking properties. A similar situation was found in most noodles made from starch blends. A 10 % addition of buckwheat and millet to wheat noodles can lower in vitro digestion, while addition of other starches all led to worse qualities.

A wire cutting and peeling test model was established, using seven kinds of noodle sheets for texture evaluation, but was not fully consistent with oral sensations on corresponding noodle strands, possibly due to impact of humidity variation on the sample surface and on the effect of saliva lubrication in the mouth. Further, an indentation test for elasticity evaluation was performed on nine types of noodle sheets, in combination with AFM imaging, pasting and texture study. Results indicated that relaxation ratio of noodle sheets may relate to final viscosity of flour and starches, but a larger sample size is needed for further confirmation.