Improved Lactose Powder Properties by In-situ Coating with Additives during Spray Drying

Abstract

 Abstract—The ability of different additives to enrich on the droplet surface during spray drying of aqueous lactose solutions was investigated. The goal of this study was to find an additive coating that increases spray-dryer yield, improves powder flow and prevents caking due to lactose crystallization during storage. The additives tested were Nacaseinate (NaCas), gelatin, lecithin, anhydrous milk fat (AMF) and hydroxylpropyl methylcellulose (HPMC). The aqueous lactose solutions had 10 weight% solids content with a lactose-to-additive dry weight ratio of 9:1. All additives enrich significantly on the droplet surface at the expense of lactose during spray drying. Every additive except AMF enhances the glass transition temperature at the particulate surface and therefore reduces particle stickiness, as demonstrated by improved powder flow and/or product yield compared with the pure lactose powder. Low product yield for HPMC-containing lactose powder can be explained by its low bulk density, which reduces the separation efficiency of the cyclone. Poor powder flow for lecithin-containing lactose powder can be explained by its agglomerated nature. AMF is not suitable as an additive due to a low product yield and poor powder flow, a result of stickiness due to the low melting point of fat. None of the additives improve the wetting time of lactose powder, since lactose is already highly hydrophilic, and most of the additives tend to make the particle surface more hydrophobic. NaCas and HPMC are the most promising additives with regards to improving powder flow. NaCas results in a higher product yield than HPMC, but HPMC is the only additive that provides a protective coating for lactose capable of preventing the formation of a hard brittle cake upon lactose crystallization during storage at ambient room conditions.