Color Formation in Dehydrated Modified Whey Powder Systems As Affected by Compression and T g Leila Burin,* ,† Kirsi Jouppila, ‡ Yrjo ¨ Roos, § Jarno Kansikas, # and Marı ´a del Pilar Buera †,⊥ Department of Food Technology, P.O. Box 27, University of Helsinki, Latokartanonkaari 7, FIN-00014 Helsinki, Finland; Department of Food Science and Technology, University College, Cork, Ireland; and Department of Chemistry, P.O. Box 55, University of Helsinki, FIN-00014 Helsinki, Finland Whey powders have attracted attention for use in the food industry. The Maillard reaction is a major deteriorative factor in the storage of these and other dairy food products.The objective of the present work was to further study the Maillard reaction as related to the physical structure of the matrix, either porous or mechanically compressed, or to storage above the T g of anhydrous whey systems. Sweet whey (W), reduced minerals whey (WRM), whey protein isolate (WPI), and whey protein concentrate (WPC) were stored in ovens at selected temperatures. Colorimetric measurements were performed with a spectrocolorimeter, thermal analyses (TGA) by means of a thermobalance, and glass transition temperature studies by DSC. The browning order in the vials and in the compressed systems followed the order W > WRM> WPC > WPI. k w2 , the slope of the second linear segment of the TGA curve, was related to the loss of water due to nonenzymatic browning (NEB). Browning development was in good relationship with this loss of weight. In the glassy state, the compressed systems developed higher rates of browning and weight loss (assigned to NEB reactions) than the porous systems. Reaction rates in both (porous and compressed) systems became similar as (T - T g ) increased. Keywords: Browning; whey powder; glass transition; compression INTRODUCTION Dried whey powders, a major byproduct of cheese manufacturing, have attracted attention for use in the food industry due to their low price, versatility with respect to functionality, and nutritive value as a food ingredient (Kim et al., 1981). Whey proteins are well- known for their high nutritional value and versatile functional properties in food products. During recent decades, interest has grown in the nutritional efficacy of whey proteins in infant formula and in dietetic and health foods (de Wit, 1998). At the 1997 International Whey Conference, the presentations highlighted the multitude of valuable components present in whey, methods for their commercial isolation, approaches to maximizing their various functionalities, and their wide application in the food, medical, biotechnology, veteri- nary, chemical, and plastics industries. Particulary, the 1997 conference reflected the growing interest of the food industry in functional foodssthose that promote health beyond providing basic nutrition (Smithers and Copeland, 1998). Both nutritional value and functional properties of whey proteins are governed by the com- position and structure of the protein and influenced by the prevailing environmental conditions, prior treat- ments, and processing conditions. With increasing uses, there has arisen a practical need to predict the shelf life of whey powders. It is well recognized that nonenzymatic browning (NEB) through the Maillard reaction is a major dete- riorative factor in the storage of dehydrated dairy food products (Choi et al., 1949; Labuza and Saltmarch, 1981; Roos, 1996). Molecular mobility in the amorphous region of the solid is important in determining its physical stability (Hancock et al., 1995), and the nature of the amorphous solid will change depending upon the difference between the temperature (T) and the glass transition tempera- ture (T g ). In glassy systems, molecular mobility and diffusion are claimed to be virtually nonexistent (Levine and Slade, 1986; Slade, 1989). There has been consid- eration of the great significance of changes in physical state of the solid having an impact on the diffusion and access of water into products (Parker and Ring, 1995). The presentation of the product (pellets or powders) during storage can thus be very important from the standpoint of quality loss and could result in the acceleration of deteriorative reactions in hygroscopic whey products (Kim et al., 1981), limiting its shelf life and the food products into which they are incorporated as a principal ingredient. The objective of the present work was to further study the Maillard reaction as related to the physical structure of the matrix, either porous or mechanically compressed, or to storage above the T g of anhydrous whey systems. MATERIALS AND METHODS Preparation of Model Systems. Amorphous matrices were obtained by freeze-drying solutions containing 20% (w/ * Address correspondence to this author at the Departa- mento de Industrias, Facultad de Ciencias Exactas y Natu- rales, Universidad de Buenos Aires, (1428) Buenos Aires, Argentina [telephone (5411) 4576-3397; fax (5411) 4576-3366; e-mail leis@di.fcen.uba.ar]. † Universidad de Buenos Aires. ‡ Department of Food Technology, University of Helsinki. § University College, Cork. # Department of Chemistry, University of Helsinki. ⊥ Member of Consejo Nacional de Investigaciones Cientı´ficas y Te ´cnicas de la Repu ´ blica Argentina. 5263 J. Agric. Food Chem. 2000, 48, 5263-5268 10.1021/jf000240y CCC: $19.00 © 2000 American Chemical Society Published on Web 10/27/2000