Effect of superfine grinding on physicochemical properties of mulberry leaf powder

Abstract: Superfine grinding technology is a type of food processing that used to produce powders with outstanding properties such as high solubility, dispersion, adsorption, chemical reactivity and fluidity. In order to expand the application of the superfine grinding technology in food additive and pharmaceutical industries, the physicochemical properties of mulberry leaf micro-powders were investigated. Four types of mulberry leaf micronized powders were prepared by pulverizing its coarse through superfine grinding for different periods of time (2, 4, 6 and 8 h). The physicochemical properties of the micronized powders and the coarse powder were then compared and investigated. The results showed that superfine grinding could effectively pulverize coarse powder to different micro-sizes. With increased superfine grinding time, the particle size significantly decreased (P<0.05). Furthermore, with narrowed particle size distribution, the specific surface area and bulk density significantly increased (P<0.05); the angle of repose and slide and swelling capacity significantly decreased (P<0.05); and water and oil holding capacity, protein and polysaccharide solubility and water solubility index improved to different extents. These indexes were tightly dependent on particle size with absolute coefficients beyond 0.6156. However, no significant difference was observed in flavonoid content among mulberry leaf particles (P>0.05). Scanning electron micrography observations revealed the shape morphology of the fragmented mulberry granules. The physicochemical properties of micro-powder D milled at 8 h were more satisfying than micro-powders A, B, and C (milled at 2, 4 and 6 h, respectively). These results suggested that superfine grinding could improve some physicochemical properties of mulberry leaf powder, thereby enabling its applications as a functional food additive and food product, as well as a material for the pharmaceutical industry.