4. Conclusion
Prior to the preparation of starch gels, gelatinization and pasting of starch suspensions is required. Heating and mixing are two unit operations which are commonly used together to obtain a uniform paste and gel. While previous studies suggested that increasing shear during heating–shearing processes increases starch degradation, there is limited detailed information on the effect of mixing conditions and heating time on starch pasting and subsequent final gels. Therefore, in this study the effect of pasting conditions, i.e. mixing speed and time, on final gel characteristics, was investigated. The results showed that textural and physicochemical properties of corn starch gels are affected by both mixing speed and heating time. With increasing mixing speed, gel hardness, cohesiveness and gumminess decreased, the air cells in the sponge-like structure of samples became larger, and the extent of molecular degradation increased as confirmed by intrinsic viscosity results. The effect of increasing mixing time at a constant mixing speed of 15 rpm had a minor but significant impact on gel parameters. This effect was greater when mixing speeds were increased. However, at 150 and 350 rpm the differences in gels in most cases were insignificant when mixing times were increased.
Taken together, it can be concluded that pasting conditions i.e. mixing speed and time, are determining factors in dictating the structural and mechanical properties of corn starch gels. Mixing speed was found to be more important than mixing time as judged by textural and physicochemical properties of starch gels. Therefore, controlling mixing condition during processing of starch based food gels is an important factor to produce final products of appropriate or consistent physical and textural properties. More investigations to study different shearing devices and mixer designs are suggested to develop a more in depth understanding of the starch pasting process.