Abstract
The oxidative stability of food is defined as its capacity to resist changes during storage. It is an important aspect of food safety as oxidation is a key reaction in the food sector. It affects the shelf life of food which is mostly influenced by oxidation products that cause nutritional and quality deterioration such as rancidity, toxicity, and loss of nutritional value. Current trends promote the addition of beneficial ingredients such as antioxidants in order to increase their nutritional value as well as their shelf life. Therefore, understanding the antioxidant capacity and the oxidizability of food may be a major key to improving food quality. Antioxidants are compounds that can retard or inhibit oxidation while contributing to the nutritional value of food. Oxidizability is the ability of a food item to undergo oxidation. A great challenge encountered in the food sector is the assessment of intrinsic and exogenous antioxidants in food. Over the years, many rapid methods based on spectrophotometry and chromatography have been used for antioxidant assessment. However, some major drawbacks make the use of these techniques tedious and restricted to certain types of antioxidants. For instance, the sample preparation step preceding the proper analysis of antioxidants is revealed to be time consuming. Turbid antioxidant solutions cannot be analyzed by spectrophotometry due to the interference of colors. Consequently, the need to develop a method that can overcome the above-mentioned downsides is highly required. The aim of this thesis has been the assessment of the oxidative stability of food using a multi-sensor reactor isothermal calorimeter. The calorimetric reactor was used to measure the heat evolved by food and food ingredients during oxidation. Calorimetry measures the heat produced during physical and chemical reactions. The universal character of heat grants this method the possibility to be used in almost any type of reaction. In chapter one, a general description of lipid oxidation and the mechanisms involved are reviewed. Antioxidants are defined and explained in relation to their involvement in lipid oxidation. Furthermore, Calorimetric principles along with different types of calorimetry are reported. In chapter two, isothermal calorimetry was applied to the study of the oxidation of styrene, an oxidizable substrate. Kinetics and thermodynamics parameters were retrieved. Antioxidant activities of individual antioxidants and plant extracts were also investigated using this method. In the third chapter, isothermal calorimetry was used to study the oxidative stability of bulk oils. The oxidizability of olive seed oil, obtained from olive waste using different technologies, was calculated. Other commercially available oils were also analyzed and compared to olive seed oil based on their oxidizability, and antioxidant capacity. Overall, this project sustains the use of isothermal calorimetry for the study of food functionalities such as antioxidant activity and oxidizability.