Effect of microfluidization on microstructure, protein profile and physicochemical properties of whole cowpea flours

Whole cowpea flours from three cultivars were microfluidized through a 200 μm “Z” type interaction chamber at room temperature for two passes. The confocal micrographs showed the microfluidization process could effectively disintegrate the structure of both cotyledon and seed coat, two major components of a cowpea seed. Disruption of cotyledon released the embedded starch granules and proteins, whereas disruption of seed coat generated large amounts of fiber fragments with amorphous and fluffy microstructure. Depending on the cultivars of cowpea, these effects significantly decreased mean particle size by up to 92.3% and bulk density by up to 68.7%, and increased specific surface area by up to 286.4%, swelling capacity by up to 107.7%, water-holding capacity by up to 16.1%, oil-holding capacity by up to 162.1%, and total water extractable proteins of whole cowpea by up to 39.7%. Reduced intensity of protein bands in SDS-PAGE was also observed. This indicated high pressure and high shear stress during microfluidization induced fundamental structural changes of cowpea proteins. Under the present experimental conditions, the microfluidization process had no apparent effects on both particle size and structure of cowpea starch granules present in the flours.