Abstract
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.
Highlights
Operational Parameters to DetermineOxidative deterioration, commonly known as lipid oxidation or rancidity, causes offflavors, discoloration, unpleasant odors, and decreases edible oil nutritional value
Walnuts are susceptible to oxidation-induced rancidity because of their high oil content (60 to 70%) and elevated content (~70%) of polyunsaturated fatty acids (PUFA), such as linoleic (56.5–57.5%) and linolenic (11.6–13.2%) fatty acids, and monounsaturated
The quantification of free fatty acids (FFA) and peroxides or peroxide value (PV), p-Anisidine, and test of thiobarbituric acid (TBA) are important measurements that have been used for decades to evaluate oil oxidative stability [1]
Summary
Operational Parameters to DetermineOxidative deterioration, commonly known as lipid oxidation or rancidity, causes offflavors, discoloration, unpleasant odors, and decreases edible oil nutritional value. In order to evaluate rancidity in walnut oil, extracted from fresh walnut kernels, it is necessary to determine the oil oxidative stability. The quantification of free fatty acids (FFA) and peroxides or peroxide value (PV), p-Anisidine, and test of thiobarbituric acid (TBA) are important measurements that have been used for decades to evaluate oil oxidative stability [1]. These tests provide information regarding a temporal fat oxidative state, and rely on the use of toxic solvents [7] and manual titration that may lead to erroneous results [8,9]. The Rancimat equipment is widely used by the edible and pharmaceutical oils industries, as it does not require the use of hazardous materials and intensive labor in comparison to other accelerated oxidation methods, such as the Active Oxygen Method
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