Studying the effect of wheat flour fortification with soy protein isolate on quality characteristics of doughnut during storage time

Doughnut is a special fermented and fried snack. There are a few studies about wheat flour fortification with soy protein isolate to produce doughnut. The present research was done to study the effect on quality features of doughnut during preservation. Partial substitution of wheat flour with soy protein isolate at the levels of 0, 1, 2 and 5 g/100 g was carried out to determine its influence on quality characteristics of doughnuts. The water absorption and protein content of the samples were measured by Farinograph and kjeldahl method respectively. Quality characteristics of doughnut such as porosity and color were determined with Image J software. Sensory evaluation of doughnuts was carried out on 9-point hedonic scale by a panel of 12 judges.The protein content and water absorption of the fortified samples were higher, but their Volume, porosity and lightness were lower than the control. Control sample had the highest overall acceptability rating although the difference between samples were not significant (P>0.05). So it is possible to produce a doughnut fortified with 1-5% soy protein isolate with higher protein content without having significant negative effect on its acceptability.