Effect of sprouting on the physical properties, morphology and flowability of onion powder

Abstract

Onion (Allium cepa L.) important as spice and vegetable in daily Indian cuisine undergoes a natural biological process of sprouting. This is the first study to examine the effect of sprouting on the physical properties, flowability, particle size and microstructure of freeze dried onion powder from four Indian onion varieties (Punjab White, Punjab Naroya, PRO-6 and Commercial). Two-way analyses of data revealed significant (p < 0.05) effect of sprouting as well as variety on flowability and other physical parameters of freeze dried onion powders. The effect of sprouting on the flowability of freeze dried onion powders was evaluated using flow indicators viz., bulk density, true density, angle of repose, frictional coefficient, Carr’s index, and Hausner’s ratio and instrumentally by powder flow analyser viz., cohesive index, caking strength, mean cake strength and powder flow stability. Both, flow indicators and powder flow analysis showed that the powders from raw onion varieties were more cohesive while the free flowing nature was found in powders from sprouted onion varieties. Moreover, the particle size distribution and microstructural analysis also revealed a significant effect of sprouting on onion powders. In all the powder samples, the significant (p < 0.05) increase in mean particle diameter and a decrease in powder flow parameters (cake strength, cohesion index) resulted in improved powder flowability with sprouting. The results implied the beneficial effect of sprouting on physical properties, particle size, microstructure and powder flowability that will be useful in the analysis and design of handling systems for powders developed from sprouted onions. The present study suggests the potential application of the process of sprouting as a tool to improve properties of the products developed from onions.