## 3 Results and Discussion
The pastes made from extruded and roasted starch (E) or from starch extruded with apple distillery wastewater and roasted (EW) at various temperatures exhibited the properties of shear-thinned non-Newtonian fluids (Tables 2 and 3). In the case of the starch extruded with apple distillery wastewater at all the temperatures tested and roasted at 140 \({}^{\circ}\)C, it was impossible to determine the values of the rheological coefficients described according to [PERSON]'s model because of the drastically decreased viscosity of the pastes in the entire course of the flow curves. The viscosity of the pastes made of extruded and roasted starch depended on both the extrusion and roasting temperatures. In all the roasting variants, the highest viscosity in the whole course of the flow curves was demonstrated for the paste prepared from the starch extruded at the lowest temperature tested (80 \({}^{\circ}\)C), followed by the starch extruded at 100 \({}^{\circ}\)C. In contrast, the pastes prepared from the starch extruded at 120 or 140 \({}^{\circ}\)C had the lowest and similar viscosities. An analogous tendency of changes was noted for the rheological coefficients, including those describing the viscosity at the beginning of the shearing, K and \(\tau_{\rm o}\), as well as \(\eta_{\rm c}\) describing viscosity at the end of the shearing [17; 37]. One of the major causes of the decreased viscosity of starch pastes is a decrease in the molecular weight of  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Extrusion and Roasting Temperature (\({}^{\circ}\)C)**} & \multicolumn{2}{c}{**Initial Pasting Temperature (\({}^{\circ}\)C)**} & \multirow{2}{*}{**LSD**} & \multicolumn{2}{c}{**Final Pasting Temperature (\({}^{\circ}\)C)**} & \multirow{2}{*}{**LSD**} & \multicolumn{2}{c}{**Heat of Phase Transition (J/g)**} \\ \cline{2-3} \cline{5-7}  & **Preparation Type** & & & & **Preparation Type** & & **Preparation Type** & \\ \cline{2-3} \cline{5-7}  & **E** & **EW** & & **E** & **EW** & **E** & **EW** \\ \hline
80/80 & 42.72 & 45.45 & 75.65 & 74.40 & 4.14 & 5.04 \\ \hline
100/80 & 44.71 & 46.17 & 74.05 & 74.74 & 5.20 & 1.41 \\ \  
starch under the influence of enzymes or physical interactions [38]. The unbeneficial effect of starch extrusion temperature on the viscosity of pastes made of it was reported by many authors [39; 40]. As mentioned earlier, the production process of starch esters was, probably, accompanied by processes of both thermal-acidic hydrolysis and crosslinking induced by esterification. Both these processes, having an opposite effect on the molecular weight of the starch, caused changes in the viscosity of the pastes. Therefore, paste viscosity was an outcome of both of these processes. All of the starch esters produced at the highest roasting temperature (140 \({}^{\circ}\)C) formed the least viscous pastes despite the highest degree of esterification, which is indicative of very advanced hydrolytic processes of starch. The lower roasting temperatures resulted in the increased viscosity of the pastes made of the starch extruded at the highest temperatures (120 and 140 \({}^{\circ}\)C) and in the decreased viscosity (in the entire course of the flow curves) of those prepared from the starch extruded at lower temperatures (80 and 120 \({}^{\circ}\)C). An exception was observed for the EW100/100 preparation, whose viscosity increased noticeably. The color difference (darkening) \(\Delta\)E of the starch extruded with apple distillery wastewater and roasted (EW) compared to the reference sample (E) increased with increasing roasting temperature, on average from about 9 to 27 (Figure 4). Such a significant color change may result from the caramelization reaction proceeding under these conditions [41] and the Maillard reaction [42].