Effect of drying treatment on nutritional, functional and sensory properties of three varieties of onion powders

Onion powder is a worldwide food ingredient with great commercial value due to its culinary and medicinal properties in Nutraceuticals, which has not been investigated. This study aimed at evaluating the effect of drying treatment on the nutritional, functional and sensory properties of onion powder from three varieties (Violet of Galmi, Goudami and White of Galmi). The fresh harvested onions were dried by two drying methods (solar drying and air electric drying) and milled into fine particle. The proximate composition, the functional properties, the bioactive molecules total phenolics, flavonoids, tanins and vitamin C contents were evaluated. The 1,1-diphenyl-2-picrilhydrazyl (DPPH) radical scavenging activity and the Ferric-reducing power (FRP) were equally determined. Descriptive sensory analysis and the general acceptability of powders alone and sprinkled on grilled meat were also determined. The results showed that the variety Violet of Galmi was rich in carbohydrate and proteins, variables highly positively correlated to the ability to absorb water, to solubilise and to form gel. In contrast, the variety White of Galmi was higher in fat content, variable correlated to the high ability to absorb oil, and the odor and taste of onion. Based on its violet/red colour characteristic of high phenol content, flavonoid and tannin, Violet of Galmi exhibited the highest DPPH scavenging activity and ferrous reducing power. However, not only the phenol (60-85%, loss) was lost during powder production, but also the antioxidant activity (78-85%, loss). Nevertheless the powder offered high level of phenols and antioxidant activity and was well accepted by the panel.