Chemical Changes in Deep-Fat Frying: Reaction Mechanisms, Oil Degradation, and Health Implications

Deep-fat frying remains a prevalent culinary technique due to its ability to enhance sensory properties; however, it also initiates complex physicochemical transformations that compromise oil integrity and food safety. This review critically evaluates the current understanding of thermal degradation pathways in frying oils, including oxidation, hydrolysis, and polymerization, highlighting the underlying reaction mechanisms and their interdependence. The influence of intrinsic oil properties (e.g., fatty acid composition, minor components) and extrinsic factors (e.g., temperature, food matrix, fryer design, metal contaminants) on oxidative stability is assessed with particular attention to inconsistencies in reported degradation kinetics. Comparative analysis of conventional versus advanced analytical methods (e.g., titration vs. GC, HPLC, BBCEAS) underscores the limitations of legacy approaches and advocates for the adoption of more sensitive, specific techniques. Furthermore, the review contrasts the efficacy and thermal stability of synthetic and natural antioxidants, while examining conflicting findings on replenishment practices and the impact of emerging technologies such as air and vacuum frying. The health implications of degradation products are critically appraised, including evidence linking frying by-products to chronic diseases. Finally, gaps in the literature are identified, including the need for mechanistic studies under real frying conditions and standardized assessment protocols. Future research should prioritize oil formulation, frying system design, and regulation to ensure food safety and public health.