Improving the Nutritional Properties and Reducing the Oil Absorption of Donut Using Saponinized Quinoa Flour

IntroductionDonut is a type of sweet fried snack which is usually produced from leavened and deep fried dough. The deliciousness and high energy of donut has made it very popular among sweet products made from wheat flour. The sensitivity of wheat flour to weather conditions as well as bad economic conditions in recent years led to perfomingt research to replacewheat flour with other grains. Quinoa is a rich source of protein (the essential amino acids lysine, methionine, cysteine, and threonine), magnesium, fiber, vitamin B, potassium, and other minerals such as iron. Quinoa seeds have less starch than other grains (wheat, barley, corn, and rice). The value of dietary fiber in quinoa is much more in comparison to other grains, it had about 31% insoluble fiber. Also, as a source of phytoestrogens, it prevents cancer, cardiovascular diseases, and osteoporosis. The main problem with quinoa to be used for human diet is the presence of saponin in the outer shell of the seed. Saponins are considered anti-nutritional agents due to their hemolytic activity on red blood cells, bitterness, foaming ability, and inhibition of enzymes. Therefore, the most important step for using quinoa in food products is to remove saponin. The other problem with using saponin its too bitterness hence causing bloating and heartburn. This study aimed to choose the best saponinization method from quinoa and the possibility of using the saponinization quinoa instead of wheat in donut formulation and investigation the quality, texture, and sensory properties of the donuts. Materials of Methods The methods for saponin removal include (maceration, microwave, ultrasound, wet method, and a combination of wet and dry methods) were compared. Donuts were produced with quinoa flour at two levels of 20 and 40% substitution. The Fiber, ash, and protein values of wheat flour, saponinized quinoa flour, and donuts with different levels of saponinized quinoa flour were measured. The effect of replacement wheat flour with saponinized quinoa flour on oil absorption, texture, SEM, and sensory properties of donuts was evaluated. Results and Discussion A comparison between different methods of saponinization indicated that the ultrasound method had the minimum efficiency in saponin removal and the highest amount of saponin removal was in the combined wet and dry methods, followed by the maceration method. The difference between the combined method and maceration was not significant and had the most influence in extracting saponin from quinoa flour. Of course, the maceration method is economically important due to the long time of the process and production of a lot of waste water leading to loss of nutrients from quinoa. The highest amount of protein, fiber, and ash was obtained in saponinized quinoa flour and a donut containing 40% quinoa flour. The amount of firmness, elasticity, SEM, and sensory properties in the sample with 20% quinoa flour had similar characteristics to the control sample, but increasing the amount of quinoa flour reduced these factors. The oil absorption percentage in donuts containing 40% quinoa flour was higher than in other samples. The results of using saponinized quinoa flour on the sensory characteristics (color crust and crumbs, taste, smell, texture and overall acceptance) of donuts showed that donut with 20% quinoa was similar to the control sample and was acceptable for panelists but increased the concentration up to 40% wasn’t  pleasant.  Conclusion In this study, the saponinized quinoa flour used in donut formulation to increase the nutritional value and reduced the calories of donuts also overcame the challenges of wheat shortage. The saponinization methods were compared to choose the method with the highest saponin removal. Then donut with saponinized quinoa flour was prepared. The use of saponinized quinoa flour as a replacement of wheat flour increased the nutritional value of donuts.  Adding saponinized quinoa flour to the donuts formulation significantly declined the oil absorptions.  Generally, the donuts containing saponinized quinoa flour had relatively similar sensory properties to the donuts with wheat flour (commercial donuts). Therefore, it seems that saponinized quinoa flour could be used successfully to improve the nutritional value of donuts and also consumers' acceptance.