The physical nature of stickiness in the spray drying of dairy products—a review

Abstract

This paper reviews developments in understanding the issue of stickiness in the spray drying of dairy products, with particular reference to the physical basis of stickiness. Investigation of stickiness in spray drying has followed two main directions: (1) approaches to measuring the phenomena of stickiness by empirical means and (2) understanding stickiness in the context of the science of soft matter (e.g. as being related to glass transition phenomena). The former approach has led to several techniques that have been used as empirical tools to study the influence of product formulation on stickiness. The latter approach underpins applied research in this area with a body of knowledge being developed in materials science. Empirical-type measurements can be used to validate mechanistic models which are emerging. Tools in the field of microscopy, such as X-ray photon spectroscopy, energy-dispersive X-ray spectroscopy and atomic force microscopy, are beginning to contribute to a better understanding of the underlying physical phenomena.