Hydroxypropyl Methylcellulose Reduces Particle Adhesion and Improves Recovery of Herbal Extracts During Spray Drying of Chinese Herbal Medicines

Abstract

The effectiveness of hydroxypropyl methylcellulose (HPMC) as an anti-adherent during spray drying of traditional Chinese herbal extracts was explored. A small amount of HPMC (minimum concentration 8%) was sufficient to overcome problematic particle adhesion, whereas a large amount of maltodextrin (50%) was required for the same effect. HPMC exerted a strong anti-adhesive effect that was independent of the type of HPMC, raw materials used, and the process used to synthesize HPMC. The anti-adhesion mechanism was studied through an analysis of the surface tension of the prepared solutions before spray drying, the glass transition temperature (T g ), and X-ray photoelectron spectroscopy (XPS) of spray-dried powders. The T g of powders containing more than 8% HPMC was approximately 40°C and did not increase linearly with the HPMC concentration. The surface tension of Crataegi fructus extract was 54.1 ± 0.2 mN/m and further decreased to 46.6 ± 0.2 mN/m upon addition of HPMC to 24%. When the concentration of HPMC increased to 8%, potassium could not be detected on the surface of dried powders by XPS. These results suggest that modification of the surface properties of sprayed droplets/particles by HPMC increased the HPMC surface coverage of the particles and reduced adhesion during spray drying.