Rheological characterisation of food thickeners marketed in Australia in various media for the management of dysphagia. II. Milk as a dispersing medium

Abstract

The shear stress–shear rate relationship of six food thickeners from guar gum, modified starch and xanthan gum in homogenised and pasteurised full cream (HPFC), skim milk (SKIM) and ultra-high temperature or ultra-heat treated full cream (UHT) was investigated at 20 °C. For all the thickened fluids, shear stress increased as the rate of shear increased from 1 to 100 s⁻¹. An increase in solids content increased the viscosity, density and yield stress. The type of milk significantly influenced (p < 0.05) the density of the fluids and SKIM milk could yield the densest fluids. Irrespective of the type of milk, the guar gum-based thickened fluids (Guarcol^TM and Supercol^TM) were the most viscous, and they exhibited the highest yield stress. Among the three types of milk, the most viscous thickened fluids or thickened fluids with the highest yield stress were obtained when SKIM was the dispersing medium. The Herschel–Bulkley models were found to be the most suitable rheological models for the shear stress–shear rate data. The regression parameters obtained are valuable in calculating the weights of the thickener and dispersing medium for clinical uses.

Introduction

Dysphagia or swallowing impairment is a health concern that impacts on quality of life as it affects eating, drinking and, to a large extent, socialising. Although dysphagia affects all age groups, it is predominant in the elderly population due to, for example, increased longevity, chronic illness, multiple medications, and weakened reserves (Barczi et al., 2000, Germain et al., 2006, Langmore et al., 1998, Smith et al., 2004). As many as 15–30% of patients in hospital have swallowing difficulties or aspirate oral contents. Swallowing impairment can lead to complications such as malnutrition, dehydration, chest infection, aspiration pneumonia, and mortality (Ferraris et al., 2001, Groher and Bukatman, 1986, Lin et al., 2002).

In an earlier study (Sopade, Halley, Cichero, & Ward, 2007) and from reviewed papers (e.g. Dantas et al., 1989, Glassburn and Deem, 1998, Goulding and Bakheit, 2000, Mann and Wong, 1996, McCarthy and Seymour, 1994, Meng et al., 2005, Nicosia and Robbins, 2001, Paik et al., 2004, Smith et al., 1997, Steele et al., 2003), we identified the:

• Need for more studies on rheological characterisation of food thickeners in various media that are used in preparing them.

• Significance of objective assessment of flow properties of food thickeners.

• Importance of density and yield stress as additional physical properties of thickened fluids.

Thickened fluids are either pre-packaged ready-to-use or freshly-prepared from powder thickeners in various dispersing media such as water, cordial, fruit juices, and milk. Generally, food thickeners are manufactured from modified starch, guar gum or xanthan gum, and powder thickeners are becoming more popular because they are cheaper, more shelf-stable and can be packaged in sachets for ease of use. However, while variations in the characteristics of pre-packaged thickened fluids could be manufacturer-specific, freshly-prepared thickened fluids from powder thickeners can vary between preparations, clinicians and hospitals (Cichero et al., 2000a, Cichero et al., 2000b, Glassburn and Deem, 1998). Standardisation of procedures and accurate predictions of viscosity (e.g. to match videofluoroscopy fluids) are now recognised as essential in order to manage dysphagia properly. Milk is a dispersing medium that is used for thickened fluids to add variety and contribute to quality of life, but there are limited studies on the rheology of thickeners in different types of milk. Therefore, the present study investigated the relationships between shear stress and shear rate of some commercial powder food thickeners at various solids content in three types of milk. Rheological models were subsequently applied to the data with a view to obtaining predictive parameters for the development of a software that would serve clinicians involved in managing dysphagia.