Determination of tocopherol isomers and fatty acids in cottonseed oil and oil blends during accelerated storage

The purpose of this study was to evaluate and determine the oxidative stability and the amount of tocopherol isomers in cottonseed, corn, canola, peanut and pecan oils and 50% cottonseed oil blends and also commercially available cottonseed oil containing TBHQ. The oil samples were stored at 65°C for a total of 120 days. The α and γ-tocopherol concentration of each sample were determined using a Waters, model 717 HPLC.

The results showed that the initial α-tocopherol concentrations range from 450 ppm in cottonseed oil to 110 ppm in pecan oil. The initial α-tocopherol concentrations followed the order of cottonseed oil>corn oil>canola oil>peanut oil>pecan oil. The higher the α-tocopherol concentration in the oil, the longer period before α-tocopherol was completely depleted in the oil. The same trend also were observed in cottonseed oil blends. Cottonseed oil enhanced the levels of α-tocopherol of the oils, which were low in α-tocopherol. Addition of cottonseed oil to oils lower in α-tocopherol increased both the initial tocopherol concentration, and the length of time before it was depleted during the storage study.

Gamma tocopherol concentrations in the pure oils ranged from 430 ppm for corn oil to 90 ppm for peanut oil. The order of γ-tocopherol concentrations were in order of corn oil>pecan oil>cottonseed oil>canola oil>peanut oil. The γ-tocopherol concentrations were observed to decrease in oils similarly to the reduction in α-tocopherol levels. There was a significant difference in the γ-tocopherol concentrations of corn oil and most of the other oils and oil blends.

The peroxide value of cottonseed oil containing TBHQ did not change for the first 17 days, but increased dramatically after 17 days. This was the only oil that observed induction period. This was probably due to prevention of oxidation of cottonseed oil by TBHQ. The tocopherols were also protected against oxidation by this antioxidant. No significant changes in color as measured by Hunter Lab Scan L, a, b values of any oil or oil blend during the storage study. There were little changes in the fatty acid profiles of oils during 120 days of the study as measured by Tracor 540 gas chromatograph.