6 - Formation and Analysis of Oxidized Monomeric, Dimeric, and Higher Oligomeric Triglycerides

Abstract

During frying, it is well-known that a wide variety of chemical reactions results in the formation of new compounds that differ in molecular weight and polarity. This chapter provides a summary of the main groups of alteration compounds formed during frying, resulting from the oil or fat being exposed to high temperatures in the presence of air and moisture. Hydrolysis occurs due to the presence of moisture in the food. This involves breaking ester bonds and releasing free fatty acids, monoglycerides, and diglycerides. These compounds have higher polarity and lower molecular weight than the original Triglycerides (TG). While diglycerides, monoglycerides, and fatty acids likewise originate in the stage before intestinal absorption and hence have no relevance from a nutritional point of view, non-volatile alteration products do modify the nutritional properties of oils and fats. Therefore, the evaluation of the complex mixture of non-volatile compounds, ingested as a part of fried food, and the understanding of its dependence on the main variables of the frying process are a subject of great interest not only for processors and food technologists, but also for nutritionists and consumers. The chapter addresses the major non-volatile alteration compounds in used frying oils and fats, oxidized monomeric, dimeric, and higher oligomeric TG, also named oxidized monomers, dimers, and polymers. It discusses their formation and the analytical techniques used for their quantitation, as well as their occurrence in used frying fats.