Constituents

A. Raemy , P. Lambelet and Ph. Rousset

Nestle Research Centre, Nestec LTD, Vers-chez-les-Blanc, CH-1000 Lausanne 26, Switzerland

Introduction

Thermal analysis and calorimetric techniques, which include principally differential scanning calorimetry (DSC), differential thermal analysis (DTA), thermo-gravimetry (TG), thermomanometry and adiabatic calorimetry have been widely used to investigate physico-chemical properties of foods and food ingredients as well as to determine optimal and safe food processing parameters.

In food science and technology, thermal analysis and calorimetric techniques have been extensively applied to determine specific heat values, transition enthalpies, glass transition temperatures (Tg), induction periods for oxidation phenomena or crystallization and to determine safe process conditions by detecting exothermic phenomena and determining self-ignition temperatures. They have also been used to predict thermal and structural behaviour of lipids (polymorphism) during phase transition and to control parameters (gelatinisation or retrogradation of polysaccharides, denaturation of proteins) which are essential to maintain product quality. As foods are multicomponent systems, these techniques have also helped to elucidate interactions between food constituents (macro-nutrients), i.e. lipid-polysaccharide, protein-polysaccharide or lipid-pro-tein interactions.

In addition to improvement of product quality and process safety, new reasons to perform calorimetric studies of food, as well as physico-chemical studies of food in general, have appeared recently, namely:

• food aspect (surfaces, foams, etc.) has acquired more importance due to increased visual sensitivity of the consumer and to improvements in packaging,

• processing technologies have often to be adapted to entrap gases or active ingredients; in this context the glass transition phenomenon is today so important that it is sometimes called glass transition technology,

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D. Lorinczy (ed.), The Nature of Biological Systems as Revealed by Thermal Methods, 69-98. © 2004 Kluwer Academic Publishers. Printed in the Netherlands.

• new issues have appeared such as the presence of acrylamide in food products.

There is a renewed interest in the Maillard reaction from which acrylamide may arise.

The present chapter systematically analyses applications of thermal analysis and calorimetry in the field of food science and technology. It summarizes and completes preceding papers with the purpose of giving the state of the art (Raemy and Lambelet, 1991; Raemy et al., 2000; Schenz, 2003).

The thermal behaviour of foods strongly depends on their composition. Therefore, we first present thermal characteristics of food constituents: carbohydrates, lipids, proteins, water, air, minor constituents and ingredients, and then we consider raw and reconstituted foods.

Both endothermic and exothermic phenomena occur in foods. Some exothermic reactions present a hazard in industrial operations or during storage. They can lead either to self-ignition and to fire or even to dust explosions in open systems such as spray-dryers, or to pressure increase and bursting of closed vessels such as extraction cells. Accordingly, use of thermal analysis and calorimetry in process safety is also briefly discussed.

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