Materials
SBO (Crisco®, refined), olive (Bertolli®, cooking oil), canola oil (Crisco®), avocado oil (Spectrum Culinary®, refined), and corn oil (Mazola®) were purchased from a grocery store in Peoria, IL, USA. High oleic soybean oil (HO SBO, Plenish®) was provided by DuPont (Johnston, IA, USA). Aluminum oxide, amino acids, food grade mixed tocopherols, and monosodium L-glutamate were obtained from Sigma-Aldrich (St. Louis, Missouri, USA). According to the certificate of analysis from the manufacture, the mixed tocopherols contains 13.2% α-, 0.16% β-, 42.9% γ-, and 16.3% δ-tocopherols in weight (74.0% total). Considering the purity (74.0%), the factor 1.35 was used to obtain an accurate concentration of mixed tocopherols in oil. L-Proline sodium salt was purchased from Combi-Blocks (San Diego, CA, USA). TBHQ, sodium hydroxide (NaOH), and potassium hydroxide (KOH) were purchased from Fluka (Deisenhofen, Germany). Tetrahydrofuran (THF), dichloromethane, ethanol, and hexane were obtained from Fisher Scientific (Fair Lawn, NJ, USA).