Analysing the antioxidant activity of food products: processing and matrix effects

The intake of several bioactive components in food products has been associated 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 natural antioxidants that are present in many food products of plant origin. It is important to know what the effects of processing steps are on the level and activity of these compounds in processed foods. With this information, more accurate figures can be given for epidemiological work. Also product development can be directed to consumer foods with an optimal content and activity of natural antioxidants. Results from studies on the effects of processing on the level and activity of antioxidants in apple and tea are presented as examples of such an approach. A combination of using analytical techniques for the determination of the level of bioactive compounds and in vitro techniques for the determination of the biological activity of the final food product and the intermediate products has been applied. Both decreases as well as increases in the level and activity of antioxidants have been observed depending on the processing conditions. A comparison is made between the measured antioxidant activity of a food product and the predicted activity based on a model taking into account the level and activity of the individual components as determined in the analytical assays. The correlation 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.