| Popis: |
Starches and food gums are combined very often in commercial foodstuffs like sauces, dressings and dairy desserts. The central aim of this PhD research was to better understand waxy starch/xanthan functionality in order to improve their performance in industrial applications. More specifically, the influence of varying processing conditions was investigated. General principles were presented that can assist in tuning the final properties of these systems. The flow behavior of the mixed pastes during pasting, but also after cooling, strongly depended on the specific type of waxy starch that was combined with the gum. These differences were attributed to variations in swelling power and more importantly, variations in degradation behavior of the granules. It was concluded that granule integrity is a prerequisite for optimal xanthan functionality. However, when fragile native waxy starches are pasted at temperatures just above the gelatinization onset temperature, granule disruption can be limited and a higher shear rate is even beneficial towards complete viscosity development. Furthermore, these mild heating steps yield starch pastes with an acceptable physicochemical stability. Nevertheless, the correct choice of processing temperature appears of utmost importance considering that an increase in breakdown renders the pastes highly unstable and a strong gelation is observed during longer storage periods. Xanthan gum has the ability to inhibit granule disruption during pasting, whereas guar gum appeared not to have this property. It was suggested that xanthan gum reduces the impact between the granules by the formation of a shear-induced anisotropic organization in the continuous phase. This strong molecular alignment, which is typical for extended molecules like xanthan gum, may guide the granules and induce a smooth flow, thus protecting them from breaking down. Hence, the rheological properties of native waxy starch systems can be tuned directly and indirectly (granule protection) by the incorporation of xanthan gum. |
