Effect of wheat protein isolate addition on the quality of grape powder added wheat flour extrudates

Addition of bioactive ingredients into cereal products is reported to have some detrimental effects on the product quality. However, sometimes those negative effects are known to be compensated by protein sources. In this study, the single and combined effects of both Concord grape extract powder (CGEP) and wheat protein isolate (WPI) on quality parameters of hard wheat flour extrudates were investigated. Beside the physical quality and colour parameters of extrudates, their pasting and thermal properties were also evaluated at three different die temperatures. Results revealed that CGEP substitution (7%), even with WPI (6.5 and 13%), was not so much effective on quality of extrudates extruded at 90 and 120 °C die temperatures. The only parameter effective on quality was the die temperature; especially at 150 °C, differences between formulations were more distinct for (diametric expansion, bulk density) when compared to lower die temperatures (90 and 120 °C). However, pasting properties were detrimentally affected by the single addition of CGEP (about 55.4% loss in final viscosity) with respect to single WPI substitution (about 66.7% loss in final viscosity). Presence of both CGEP and WPI made the pastes even weaker (34.1 to 61.1% decrease in peak viscosity), on the other hand, decreased the extent of delay (in gelatinisation (about 2 to 9 °C) provided by the sole use of CGEP. Besides no distinct effect on retrogradation was observed neither by CGEP nor with WPI. Therefore, in extrudates, CGEP substitution and related decrease in protein content did not exert a significant quality loss and even by increasing the protein level no improvement in quality parameters was obtained.