Jill K. Winkler-Moser

Synthesis of steryl ferulates with various sterol structures and comparison of their antioxidant activity

Steryl ferulates synthesised from commercial sterols as well as commercial oryzanol were used to better understand how structural features affect antioxidant activity in vitro by the ABTS(+) radical decolorization assay, by oxidative stability index (OSI) of soybean oil, and by analysis of antioxidant activity during frying. Steryl ferulates inhibited the ABTS(+) radical by 6.5-56.6%, depending on their concentration, but were less effective, especially at lower concentrations, than ferulic acid. Ferulic acid and steryl ferulates had either no effect, or lowered the OSI of soybean oil by up to 25%, depending on the concentration. In their evaluation as frying oil antioxidants, steryl ferulates with a saturated sterol group had the best antioxidant activity, followed by sterols with one double bond in the C5 position. The results indicate that a dimethyl group at C4 as well as a C9,C19 cyclopropane group, as found in oryzanol, negatively affects antioxidant activity in frying oils.

Detection of Corn Adulteration in Brazilian Coffee (Coffea arabica) by Tocopherol Profiling and Near-Infrared (NIR) Spectroscopy

Coffee is a high-value commodity that is a target for adulteration, leading to loss of quality and causing significant loss to consumers. Therefore, there is significant interest in developing methods for detecting coffee adulteration and improving the sensitivity and accuracy of these methods. Corn and other lower value crops are potential adulterants, along with sticks and coffee husks. Fourteen pure Brazilian roasted, ground coffee bean samples were adulterated with 1-20% of roasted, ground corn and were analyzed for their tocopherol content and profile by HPLC. They were also analyzed by near-infrared (NIR) spectroscopy. Both proposed methods of detection of corn adulteration displayed a sensitivity of around 5%, thus representing simple and fast analytical methods for detecting adulteration at likely levels of contamination. Further studies should be conducted to verify the results with a much larger sample size and additional types of adulterants.

Antioxidant activity of amino acids in soybean oil at frying temperature: Structural effects and synergism with tocopherols

The purpose of this study was to evaluate amino acids as natural antioxidants for frying. Twenty amino acids were added to soybean oil heated to 180°C, and the effects of amino acid structure on the antioxidant activity were investigated. Amino acids containing a thiol, a thioether, or an extra amine group such as arginine, cysteine, lysine, methionine, and tryptophan had the strongest antioxidant activities. At 5.5mM, these amino acids had stronger antioxidant activities than 0.02% (1.1mM) tert-butylhydroquinone (TBHQ). A functional group such as an amide, carboxylic acid, imidazole, or phenol appeared to negatively affect amino acid antioxidant activity. Synergism between amino acids and tocopherols was demonstrated, and we found that this synergistic interaction may be mostly responsible for the antioxidant activity that was observed. In a frying study with potato cubes, 5.5mM l-methionine had significantly stronger antioxidant activity than 0.02% TBHQ.

Oxidative Stability and Shelf Life of Frying Oils and Fried Foods

Abstract Oxidative stability, antioxidants, and strategies to prevent oxidation of frying oils and fried foods are discussed in this chapter. Major challenges and problems of current antioxidant systems and the most recent advances in the researches to solve these problems are presented. Several promising natural antioxidants that may replace synthetic antioxidants and reduce the amount of saturated and trans -fats in frying oils are also discussed. At frying temperatures, one major problem of current antioxidants is their loss during frying by evaporation and thermal decomposition. Therefore, this book chapter focuses on possible solutions for this problem and on recently developed antioxidant systems technologies that improved activity of an antioxidant by an additive reducing volatility of the antioxidant. Accurate assessment of lipid oxidation in fried foods is very important for research efforts to develop effective new natural antioxidants, and this chapter includes discussions on proper testing methods, pros and cons of current methods used for the evaluation of frying oil stability, efficacy of antioxidants used for frying, and the evaluation of the oxidative stability of shelf-stable fried foods.