Properties of Low Moisture Composite Materials Consisting of Oil Droplets Dispersed in a Protein-Carbohydrate-Glycerol Matrix: Effect of Continuous Phase Composition YEUN SUK GU, † MARIA G. CORRADINI, † D. JULIAN MCCLEMENTS, † AND JULIA DESROCHERS* ,‡ Biopolymer and Colloids Research Laboratory, Department of Food Science, University of Massachusetts, Amherst, Massachusetts 01003, and Kraft Foods Global, Inc., Glenview, Illinois 60025 The influence of continuous phase composition on the properties of low moisture (<3% water) composite materials consisting of oil droplets dispersed in a protein-carbohydrate-glycerol matrix was investigated. These composites were produced by blending canola oil (62.3%), whey protein concentrate (1.7%, WPC), and corn syrup and glycerol together (36.0% combined) using a high speed mixer equipped with a whisk. The polyol composition was varied by changing the ratio of corn syrup to glycerol in the system while keeping the total concentration of these two polyol components constant. Some composites were analyzed directly after preparation (“unbaked”), while others were analyzed after heating at 176 °C for 10 min to simulate baking of a food product (“baked”). The “lightness” of the composites was greater before baking (higher L value), but the color intensity of the composites was greater after baking (higher b value), which was attributed to Maillard browning reactions. The brownness of the baked composites increased with increasing corn syrup concentration, which was attributed to Maillard browning reactions. Squeezing flow viscometry indicated that the consistency and yield stress of the composites increased with baking, which was attributed to whey protein unfolding and aggregation. These rheological parameters also increased with increasing corn syrup concentration, which was attributed to its influence on the continuous phase rheology and on the interactions between the whey proteins. This study shows that the continuous phase composition and thermal history of low moisture composite materials have a large impact on their final physicochemical properties. KEYWORDS: Emulsion; whey protein concentrate; flocculation; squeezing flow viscometry INTRODUCTION Normally, the oil-in-water emulsions used in the food industry consist of oil droplets dispersed in a continuous phase that is predominantly water (1, 2). These microphase separated systems form because of the thermodynamic incompatibility of the polar water molecules and the nonpolar oil molecules. The physico- chemical properties of oil-in-water emulsions depend on their composition, microstructure, processing, and history (2). Recent studies have shown that low moisture (<5% water; a w < 0.2) composite materials can be produced by blending oil, protein, corn syrup, and glycerol together (3, 4). These composite materials consist of nonpolar oil droplets dispersed in a polar continuous phase consisting of whey protein, corn syrup, and glycerol (4) and are therefore analogous to traditional oil-in- water emulsions that also consist of nonpolar oil droplets dispersed in a polar continuous phase (water). The oil droplets are stabilized by whey protein molecules adsorbed to their surfaces during the blending procedure. These composite ma- terials are optically opaque, have good water holding capacity, and exhibit viscoplastic rheological behavior. In addition, they can be baked in an oven, which increases their apparent yield stress, consistency, and opacity. This type of composite material could be used in food applications where low moisture content is needed, for example, as a filling in dried food products that provides a desirable texture and flavor. At present, there is a poor understanding of the major factors that determine the overall physicochemical properties of the low moisture composite materials described above. The purpose of the present study was therefore to examine the influence of continuous phase composition on the properties of unbaked and baked composite materials produced by blending canola oil, whey protein, corn syrup, and glycerol together. This informa- tion is practically important because it will indicate how composite materials with different physicochemical properties can be produced by systematically manipulating product com- position. * To whom correspondence should be addressed. E-mail: julia.desrochers@kraft.com. † University of Massachusetts. ‡ Kraft Foods Global, Inc.. J. Agric. Food Chem. 2006, 54, 417-424 417 10.1021/jf0514221 CCC: $33.50 © 2006 American Chemical Society Published on Web 12/22/2005