Physicochemical and Toxicological Changes in Foods and Frying Oils during Deep-Frying

Deep frying is one of the most common processes used in food preparation to improve aroma, taste, crispness, and flavor characteristics. However, the simultaneous Maillard reactions, caramelization, and thermal decomposition of sugars occurring in the food and oil phases during frying, along with oxidation, hydrolysis, and polymerization processes in the oil, may trigger the formation of certain heat treatment contaminants, primarily acrylamide, nutritional losses in heat-sensitive components, increased energy density due to oil intake, and sensory quality defects (burnt/stale taste/odor, irregularities in texture and crispness). In addition, the gradual accumulation of total polar compounds (TPC/TPM) in frying oil, the increase in volatile oxidation products, and physical quality shifts such as increased viscosity, darkening of color, and a decrease in foaming and smoke points, limit the shelf life of the oil; make process control more difficult through fluctuations in heat transfer and cooking kinetics; weaken product standardization; and ultimately create a more negative risk profile in terms of food safety. Toxic compounds such as acrylamide and acrolein, which are formed as a result of polymerization, especially during frying, cause diseases such as cardiovascular disease, Alzheimer’s disease, diabetes, and tumors. In this review, the physical, chemical, and nutritional changes occurring in the food-oil system during deep frying and their effects on human health were evaluated with the guidance of studies in the literature. The focus of the study was to consider all parameters (oil-food and other factors) together in the frying system. In addition, application suggestions were presented that could preserve food quality and pose the least risk in terms of health and nutrition during the frying process. Furthermore, it was aimed to increase consumer awareness about the possible health risks arising from excessive consumption of fried foods.