Color formation in oils during frying is one of the most noticeable degradation reactions that occur in the frying oil. Degradation reactions cause formation of products that positively and negatively impact the nutritional and sensory qualities of both the food being fried and the frying oil. The origins of these pigment forming reactions in the oil and the factors affecting these reactions are not well understood. Assessments of the mechanisms, the components involved and external conditions affecting oil darkening were conducted. The effect of basic food ingredients, commercially sold and laboratory formulated breading and battering, preformed lipid hydroperoxides and phospholipids on color formation and oil degradation of the frying oil were investigated. Protein products, specifically whey protein, caused both the fastest darkening and thermo-oxidative deterioration of the frying oil. This breakdown was aided further through the addition of minor food materials such as glucose and amino acids as well as lipid hydroperoxides in concentrations greater than 5 % of the frying oil. Nonenzymatic browning is the main reaction causing color formation in the frying oil and utilizes carbonyls from the food product such as starches, sugars and lipid oxidation products as starting materials alongside amino groups from proteins and amino acids. Breading ingredients contributed to oil color formation due to particles from the food crust breaking off into the frying oil to further accelerate browning reactions. Increasing the temperature of the frying oil provided additional stimulus for color forming and thermo-oxidative reactions to progress at a faster rate. / xv, 184 leaves : ill. ; 29 cm