Effect of shear rates on egg white proteins: V. Lechevalier et al. XI th European Symposium on the Quality of Eggs and Egg Products Doorwerth, The Netherlands, 23-26 May 2005 6 Effects of shear rates on rheology, foaming properties and protein structure of egg white: structure-function relationships V. LECHEVALIER 1 *, A. ARHALIASS 2 , J. LEGRAND 2 and F. NAU 1 1 UMR Agrocampus Rennes-INRA Science et technologie du lait et de l’œuf, 65 rue de Saint Brieuc, CS 84215, 35042 Rennes cedex, France 2 UMR CNRS 6144 Laboratoire de Génie des Procédés, Environnement, Agroalimentaire (GEPEA), CRTT, BP 406, Boulevard de l’université, 44602 Saint Nazaire, France *lecheval@agrocampus-rennes.fr Keywords: egg white; shear rates; protein structure; foaming properties; rheology The transformation of shell eggs into safe liquid, frozen or spray-dried egg white with extended shelf life requires many technological operations that result in modifications to the egg white’s functional properties. During these processes, shear rates underwent by egg white may be responsible for part of the loss of its functional properties. The present study was aimed at measuring the effects of a wide range of shear rates (from 0.1s-1 to 36000s-1 during 10 minutes) on egg white’s rheology, foaming properties and protein structure. Results highlighted three ranges of shear rates leading to different behaviour of egg white: very low shear rates (0.1s-1), low to medium shear rates (from 1 to 1000s-1) and high shear rates (over 1000s-1). At very low shear rates, egg white viscosity increased during the first few seconds. This led to a better foam stability, which was put down to protein unfolding. Medium- sheared egg white did not show any significant variation of its rheological properties and foaming capacity, compared to non-sheared egg white. Nevertheless, compared to low-sheared egg white, its viscosity, consistency and thixotropic behaviour decreased as well as protein surface hydrophobicity and foaming capacity whereas foam stability increased. These results were put down to the disruption of ovomucin-lysozyme complex as well as protein aggregation. High-sheared egg white (over 1000s- 1) tended to a Newtonian behaviour. It showed a strong increase of its foaming capacity and of its protein surface hydrophobicity. A multivariate factorial analysis highlighted correlations between rheological measurements, foaming properties and protein structure. Introduction The transformation of shell eggs into safe liquid, frozen or spray-dried egg white with extended shelf life requires many technological operations that result in modifications to the egg white’s functional properties. During these processes, shear rates underwent by egg white may be responsible for part of the loss of its functional properties (Lechevalier et al., in press). Few literatures are dedicated to shear rates effects on foodstuff liquids and especially egg white. However, Forsythe and Bergquist, 1951, suggested that high shear rates broke ovomucin chain and Thapon, 1981, explained foam stability variations by ovomucin structure changes. More recently, Hagolle, 1997, followed the viscosity of ovalbumin and lysozyme solutions at low shear rates and highlighted orthokinetic aggregation phenomena. But shear rates effects on egg white mainly stay unexplained. This is probably due to the complexity of egg white but also to the difficulty to quantify and qualify shear rates that occur in industrial processes. The present study aimed at measuring the effects of a wide range of shear rates (from 0.1s -1 to 36000s -1 during 10 minutes) on egg white’s rheology, foaming properties and protein structure. Material and methods MATERIAL Shell eggs were collected from a local factory “l’oeuf du Breil” (Melesse, France) and stored at 10°C during 8 days. The egg whites were manually separated from the yolks and filtered on a grille (holes