The Effect of Spray-Drying Feed Temperature and Subsequent Crystallization Conditions on the Physical Form of Lactose

Abstract

Lactose solutions (20 g/100 mL) in distilled water were prepared and equilibrated at 25, 30, 40, and 50°C, then spray-dried using a Buchi 190 spray drier. The spraydrying variables were kept constant and were as described by Chidavaenzi et al, except for the feed rate, which was varied for each feed temperature to minimize fluctuations in the outlet temperature. The materials were collected and immediately desiccated over silica gel. Spray-drying is known to produce predominantly amorphous material because of rapid solidification. The detection and control of the amorphous portion of powdered material is of utmost importance, as different physical forms of materials have different physicochemical properties that give rise to significant differences in functionality when used in dosage forms. The influence of spray-drier feed concentration on the degree of crystallinity and the crystal form of lactose (β-lactose, anhydrous α-lactose, α-lactose monohydrate) has been described previously. It is known that the spray-drying process can be made to produce completely amorphous lactose particles. Furthermore, it is clear that the amorphous form is unstable and that it will revert to the crystalline form. In this work, the impact of feed temperature variation and the conditions used to induce crystallization have been investigated, with respect to the physical form that is produced. Crystallization of amorphous samples