Effect of Operational Parameters on Determination of Oxidative Stability Measured by Rancimat Method

Approaches of lipid oxidation mechanisms in oil matrices using association colloids and analysis methods for the lipid oxidation

Lipid oxidation is one of the key chemical reactions in foods containing fats and oils during production and storage. For several decades, many researchers have tried to understand the mechanisms of lipid oxidation and ways to control the rates of lipid oxidation. Theories of autoxidation or free radical chain reaction have been developed to successfully explain the phenomenon observed in oxidized lipids. Many studies have been conducted to explain the other factors that can affect the lipid oxidation such as food matrix, oxidation time and temperature, transition metal ions, pigments with sensitizing abilities, and surface-active compounds such as phospholipids, free fatty acids, monoacylglycerols, and diacylglycerols. Several strategies were developed to evaluate the degree of oxidation and oxidative stability. This review provides crucial information on the mechanism of lipid oxidation affected amphiphilic compounds and association colloids. This review article will extensively discuss about the methods for determining the oxidative stability.

Optimization and Validation of Rancimat Operational Parameters to Determine Walnut Oil Oxidative Stability

This study was performed to optimize and validate Rancimat (Metrohm Ltd., Herisau, Switzerland) operational parameters including temperature, air-flow, and sample weight to minimize Induction-Time (IT) and IT-Coefficient-of-Variation (CV), using Response Surface Methodology (RSM). According to a Box–Behnken experimental design, walnut oil equivalent to 3-, 6-, or 9-g was added to each reaction vessel and heated to 100, 110, or 120 °C, while an air-flow equal to 10-, 15-, or 20-L·h−1 was forced through the reaction vessels. A stationary point was found per response variable (IT and CV), and optimal parameters were defined considering the determined stationary points for both response variables at 100 °C, 25 L·h−1, and 3.9 g. Optimal parameters provided an IT of 5.42 ± 0.02 h with a CV of 1.25 ± 0.83%. RSM proved to be a useful methodology to find Rancimat operational parameters that translate to accurate and efficient values of walnut oil IT.

Prediction of Walnut Deterioration Using Kernel Oxidative Stability

Monitoring walnut oxidation is essential to control walnut quality during storage. An accelerated oxidation method for differentiating the oxidative stability index (OSI) of walnut kernels was examined and the effects of instrument operational parameters such as temperature and airflow were evaluated. Four cultivars, Chandler, Solano, Durham, and Howard were analyzed at 110, 120, and 130 °C with 15, 20, and 25 L h⁻¹ airflow. Analysis using 110 °C with 25 L h⁻¹ yielded the lowest coefficients of variance (4.4) than other operational parameters; analysis using the same temperature at lower airflow, 15 L h⁻¹, yield the highest coefficient of variance (10.5). Kernel OSI values were independent of airflow, however, dependence of temperature coefficient and Q₁₀ were demonstrated. The results from selected parameters were correlated with fat and moisture content, peroxide value, UV absorbances, oil oxidative stability, hexanal, and rancidity to establish the relationships between OSI values and quality changes during storage. Using 0.5 g of ground kernels, at 110 °C with 25 L h⁻¹ airflow gave a lower coefficient of variance and higher correlation with kernel quality and oxidative markers comparing to other combinations of operating parameters.

Comparison of the oxidative stability of linseed (Linum usitatissimum L.) oil by pressure differential scanning calorimetry and Rancimat measurements

The aim of this study was to compare the oxidative stability of linseed oil using the pressure differential scanning calorimetry (PDSC) and Rancimat methods, and to determine the kinetic parameters of linseed oil oxidation. Five cold pressed linseed oils were oxidized at different temperatures under PDSC (90-140 °C) and Rancimat (70-140 °C) test conditions. The oxidative stability of the linseed oils was calculated based on induction times (PDSCτ_max, Rancimat τ_on), the Arrhenius equation and activated complex theory, frequency factors (Z), the reaction rate coefficient (k) for all temperatures, activation energies (Ea), Q₁₀ numbers, activation enthalpies (∆H⁺⁺), and activation entropies (∆S⁺⁺). The PDSC method was more convenient for the determination of the induction time of linseed oils than the Rancimat method. During oxidation measurement by Rancimat method, the linseed oil polymerized, which affected the measurements. The reaction rate coefficient increased with rising temperature during measurement by both methods. The activation energy values of linseed oil oxidation using the PDSC and Rancimat methods ranged from 93.14 to 94.53 and 74.03 to 77.76 kJ mol^-1, respectively. The Q₁₀ , ∆H⁺⁺, and ∆S⁺⁺ values for the analyzed linseed oils were between 2.11-2.13, 90.54-91.30 kJ mol^-1, -33.20 to -30.90 J mol K^-1 calculated by PDSC measurements, and 2.23-2.32, 71.03-74.76, -59.42 to -49.08 J mol K^-1 by Rancimat measurements, respectively.