Properties of lactose and its caking behaviour

Caking of lactose creates problems for the manufacturers and users since it leads to the disruption of efficient materials handling, and poor product stability and quality. Caking of lactose-rich powders is of concern to Australian manufacturers because a high proportion of Australian production is destined for use under tropical and semi-tropical conditions. While caking of lactose and related products is addressed often enough in commercial circles, scientific studies are dispersed across many fields. There is a need to collect and critique these studies with a dairy focus. Notwithstanding the limited publications and data, some methods to overcome caking have been published, such as storage at low moisture and the addition of desiccant. However, caking is still a problem. Caking is commonly indicated by stickiness and the formation of lumps. This paper reviews the difficulties in studying and eliminating the problem of caking. The problem of caking begins with an inadequate understanding and definition of the degree of caking. There are methods for the characterisation of the degree of caking of powders, such as flow measurement, tablet hardness and microscopic examination, but none is universally accepted. Study of the caking of lactose is also complicated by the existence of lactose in different solid forms (polymorphism). Amorphous lactose is the most hygroscopic form of lactose and is usually the cause of caking. The crystalline forms of lactose - α-lactose monohydrate, α-lactose anhydrous stable, α-lactose anhydrous unstable and β-lactose anhydrous - have different physical characteristics and may contribute to caking but this has not been mentioned in earlier papers. The formation and stability of lactose polymorphs are reviewed here. There is a lack of information in the literature regarding the factors that may contribute to caking of lactose such as: particle size and the cohesiveness of powder, particle shape and density, and high pressures or compression. Control of caking in lactose powders might be improved by the availability of detailed composition of the products including the polymorphic composition, free moisture, and water of crystallisation contents