Analysing the antioxidant activity of food products: Processing and matrixeffects

The intake of several bioactive components in food products has been associ ated with lower incidence in various ageing diseases. A group of compounds that is receiving a lot of attention in this respect is the group of natura l antioxidants thar are present in many food products of plant origin. It i s important to know what the effects of processing steps are on the level a nd activity of these compounds in processed foods. With this information. m ore accurate figures can be given for epidemiological work. Also product de velopment can be directed to consumer foods with an optimal content and act ivity of natural antioxidants. Results From studies on the effects of proce ssing on the level and activity of antioxidants in apple and tea are presen ted as examples of such an approach. A combination of using analytical tech niques for the determination of the level of bioactive compounds and in vit ro techniques for the determination of the biological activity of the final food product and the intermediate products has been applied. Both decrease s as well as increases in the level and activity of antioxidants have been observed depending on the processing conditions. A comparison is made betwe en the measured antioxidant activity of a food product and the predicted ac tivity based on a model taking into account the level and activity of the i ndividual components as determined in the analytical assays. The correlatio n between these figures is quite good For tea, but for apple juice about 80 % of the activity cannot be explained by the measured antioxidants. Matrix effects or the presence of yet unidentified antioxidants in the product can be responsible for this discrepancy. (C) 1999 Elsevier Science Ltd. All ri ghts reserved.