Rheological, thermal, micro structural and functional properties of freeze dried onion powders as affected by sprouting

The effect of sprouting on rheological, functional, thermal and micro structural properties of freeze dried onion powders obtained from four Indian onion cultivars (Punjab White, Punjab Naroya, PRO-6 and Commercial) were studied to assess the feasibility of using sprouting as a tool to imparting desirable thermal, functional and rheological properties in various food products. Sprouting showed an increase in protein, ash and fibre content with decrease in fat and carbohydrate content of onion powders. Functional properties (water solubility index, hygoscopicity, dispersibility and wettability) improved in sprouted powders as compared to the unsprouted powders. Sprouted onion powders showed lower elastic modulus (G′) and viscous modulus (G") in the linear viscoelastic region as compared to unsprouted powders. Sprouted powders recorded significantly (P < 0.05) higher glass transition temperature than the unsprouted powders. The morphological pattern which differed in both types of powders was determined by scanning electron microscopy. The increased protein content accounted for increase in particle size and solubility index thereby decreasing the viscosity as reflected by lower elastic (G′) modulus in sprouted onion powders. The improvements in composition and quality parameters were seen in all the cultivars tested showing that sprouting could be beneficial for product development across cultivars.