Alois Raemy

Oxidation of lipios studied by isothermal heat flux calorimetry

Abstract The exothermic reaction of the autoxidation of lipids has been studied by isothermal heat flux calorimetry at temperatures between 80°C and 160°C. A number of lipid samples have been kept in the calorimeter under excess of oxygen for 1 or 2 hours. The capabilities of the method are illustrated by examples exhibiting different thermal behaviour, where the influence of temperature and the role of unsaturation and of antioxidants are presented for selected lipids.

THERMAL BEHAVIOUR OF MILK POWDERS STUDIED BY DIFFERENTIAL THERMAL ANALYSIS AND HEAT FLOW CALORIMETRY

The technique of heat flow calorimetry was used to study the thermal behaviour of different milk powders above 20°C. Exothermic reactions of different types occurred when measurements were made with the samples in sealed cells. According to our interpretation of the calorimetric curves, these reactions correspond to: crystallization of amorphous lactose, Maillard reaction between milk proteins and lactose, oxidation of milk fat and decomposition of lactose. Their relative importance is discussed. In addition, the technique of high-pressure differential thermal analysis was used for studying spontaneous ignition and combustion of milk powders, under a large oxygen excess. The role of fat, carbohydrate and protein decomposition is underlined. Some self-ignition temperature values are given.

DIFFERENTIAL THERMAL ANALYSIS AND HEAT FLOW CALORIMETRY OF COFFEE AND CHICORY PRODUCTS

The techniques of differential thermal analysis (DTA) and heat flow calorimetry were used to study the thermal behaviour of coffee and chicory products above 20°C. Intensive exothermic reactions were particularly evident when measurements were made under pressure, which prevents vaporization of the water contained in the products, in the temperature domain of interest.

Selfignition of powders studied by high pressure differential thermal analysis

Abstract The technique of differential thermal analysis was used, in an original way, for studying spontaneous ignition and combustion of powders. The measurements were performed with a high-pressure differential thermal analysis instrument. Selfignition temperatures of powders were determined by analysing the samples under a high pressure of oxygen (25 bar). Self ignition temperature values are given for powders which are of interest in the food industry.

Thermal analysis and safety in relation to food processing

Abstract The adaptation of thermal analysis techniques to study exothermic phenomena and self-ignition of foodstuffs, and the use of special tools to simulate and analyze dust explosions are described. The examples shown should provide a better understanding of the mechanisms involved in phenomena which can lead to the bursting of an autoclave, to fires or to dust explosions during food processing operations.