Abstract
Oxidative stability and antioxidant activity play a crucial role in determining the quality, shelf-life, and nutritional content of food products. However, current methods for analyzing lipid oxidation and antioxidant effectiveness have several limitations, including a lack of real-time monitoring, challenges in handling complex food matrices, and insufficient sensitivity and mechanistic understanding. These issues are compounded by invasive sample preparation techniques and reliance on simplified model systems. Addressing these challenges is vital for advancing food preservation technologies and product development. Herein, we detail our work on developing kinetic-based methods for evaluating lipid oxidation and antioxidant activity. We successfully implemented an isothermal calorimetric approach to monitor the heat flow generated during lipid autoxidation. This heat data was then converted into oxygen consumption measurements over time and validated against the oxygen uptake method. Additionally, a lipid oxidation kinetic model was employed to assess the antioxidant efficiency and oxidizability of mayonnaise samples made from five different vegetable oils, including sunflower, corn, apple seed, grape seed, and extra virgin olive oil. Results showed that mayonnaise made with extra virgin olive oil had the lowest oxidizability, while sunflower oil demonstrated the highest antioxidant efficiency. One key advantage of this isothermal calorimetry method is its ability to analyze up to 24 samples at once with minimal effort. Additionally, existing methods for photostability testing often separate the irradiation of samples from the analysis phase, making sample preparation a crucial step in the overall process. Differential photocalorimetry (DPC) presents an alternative that overcomes many of the limitations associated with traditional photostability tests. The DPC setup, which combines a differential scanning calorimeter (DSC) with a light source, ensures uniform and reproducible exposure of light to the sample, while the DSC continuously measures heat throughout the photo-oxidation process. The experiments used stripped linseed oil (SLSO), which lacks natural antioxidants, no induction time (τ) was observed. However, when SLSO was spiked with increasing amounts of trans-ferulic acid, the induction time (τ) increased in direct proportion to the antioxidant concentration (R² = 0.99). A comparison across various vegetable oils showed that rice bran oil had the greatest resistance to photo-oxidation, followed by corn, soybean, and sunflower oils. These findings were analyzed in terms of oxidizability and antioxidant efficiency, and validated using high-performance liquid chromatography with diode array detection (HPLC-DAD). The method also allowed for easy adjustment of light intensity, providing considerable potential for routine oil stability screening. Finally, we present an inhibited autoxidation method that employs a standard microplate reader along with a food-derived oxidizable substrate, specifically stripped sunflower oil (SSO), to accurately study the kinetics of antioxidant reactions with peroxyl radicals. This approach utilizes styrene-conjugated BODIPY (STY-BODIPY) chromophores as co-oxidants, providing a simple way to monitor the reaction progress. The method was calibrated using the synthetic α-tocopherol analogue 2,2,5,7,8- pentamethyl-6-chromanol (PMC) as a reference antioxidant and was effectively used to assess its synergistic effects with γ-terpinene, quercetin, and caffeic acid. The validity of this approach was further corroborated through isothermal calorimetry, highlighting its potential as a reliable and practical tool for evaluating antioxidants in food systems.