Powdered rooibos tea extract (RTE), which is rich in polyphenols, is made from rooibos tea by freeze-drying. "Rooibos" is Afrikaans for "red bush," and the scientific name is "Aspalathus linearis." It is a broom-like member of the legume family of plants and is used to make an herbal tea which has been popular in South Africa for generations and is now consumed in many countries. In the present work, the anti-oxidative effect of RTE on oils and fats in autoxidation or thermal oxidation was studied, and it was confirmed that RTE has a very strong anti-oxidative effect on emulsifying oils owing to the water-soluble polyphenols such as rutin and quercetin contained in RTE. RTE was found to have a strong ability to quench radicals generated in the water phase, and to confer higher thermal stability against deep fat frying than tocopherol. But RTE showed little anti-oxidative effect on frying oil because of its lower oil-solubility.

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Triacylglycerols TAGs containing conjugated linolenic acid CLN lack oxidative stability. In general, the oxidative stability of oils and fats depends on their fatty acid composition, and when the fatty acid composition is equal, the TAG molecular species has a decisive influence on oxidative stability. In the present study, structured oils containing 24% or 45% CLN were prepared by introducing CLN into oleic acid-rich TAG by enzymatic transacylation, and mixed oils containing 24% or 45% CLN were prepared by mixing oleic acid-rich TAG and Tung oil. The influence of TAG molecular species on the oxidative stability of the TAGs containing CLN was evaluated by comparing the oxidation stabilities of the TAGs. The molecular species of the TAGs containing CLN were analyzed by HPLC, and this revealed that TAG consisting of three molecules of CLN 3CLN-TAG , was present in the mixed oils, while TAG consisting of one or two molecules of CLN was present in the structured oils. In addition, the results of autoxidation and heating oxidation tests indicated no difference in the oxidative behavior of TAG between the structured oil and the mixed oil containing 24% CLN. However, the structured oil containing about 45% CLN showed an obviously high oxidative stability in comparison with mixed oil containing about 45% CLN. These results indicate that structured oils lacking 3CLN-TAG are more stable against oxidation.