The antioxidant activity of wheat kernel is very low. Kahkonen et al.110 found that wheat grain had minimal AOA while the bran fraction had low AOA. Ferulic acid and p-coumaric acid were predominant phenolic acids in hard red spring (HRS) wheat hulls while ferulic was the predominant phenolic acid in HRS wheat and flour.34 These authors reported that 50 and 500 ppm of ferulic acid was found in the flour and ground wholewheat, respectively. Durum wheat varieties protected oil oxidation equally well and were found to contain similar phenolic acid profiles.152 The wheat bran extract was composed of protocatechuic acid (226ppm), p-hydroxybenzoic acid (124ppm), gentisic acid (108 ppm), caffeic acid (116ppm), vanillic acid (637ppm), chlorogenic acid (84ppm), syringic acid (130ppm), p-coumaric acid (580ppm), and ferulic acid (764ppm). The individual phenolic acids were tested along with the durum wheat bran extract and a simulated extract made by mixing the identified phenolic acids in the proportion found in the original extract. The durum wheat extract was a significantly better antioxidant than the individual phenolic acids except protocatechuic acid and chlorogenic acid. The simulated extract had slightly less AOA than the durum wheat extract. The data supports the concept that synergistic activity occurs between the phenolic materials and therefore provides a better antioxidant than purified components.
Dolde et al.153 evaluated 18 wheat lines for tocopherol and found that the tocopherol content in wheat germ oil ranges from 1947 to 4082ppm. The range of individual tocopherols was 601-1396ppm a, 229-562ppm b, and 1135-2232ppm g. The 4a-methyl-sterols were found to protect against frying oils oxidation62 and the ethylidene group is believed to be responsible for the protective effect. It is not surprising that the sterols from wheat germ oil could protect against oxidation considering that D5-avenasterol and D7-avenasterol are present at 1600 and 900ppm, respectively.
To use plant sources as NAO their components must not affect the sensory quality of foods. Phenolic acids have long been associated with bitter and astringent perceptions,154 and as low as 5 ppm can contribute to these tastes. Sinapine, a choline ester of sinapic acid is an example of a product that can contribute a fishy odor.96 Cater et al. reported that chlorogenic acid contributes a brown and grey discoloration in products while caffeic acid can contribute a pink colour, which changes to grey.155
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