In a study published in a recent issue of BioFactors, researchers from Plant Research International, Wageningen, The Netherlands, discuss specific compounds found in the berry, some appropriate methods for assaying the antioxidant concentration, and the biochemistry of antioxidant uptake in humans.
“Raspberries contain vitamin C and anthocanines,” says Jules Beekwilder, “but these can also be found in other products. However, approximately 50% of the antioxidant effect of raspberries is caused by ellagitannins. These you find in small doses in strawberries and practically nowhere else.” Some Chinese herbs may also be a source of these compounds.
The authors describe a special testing method for analyzing the antioxidant activity of raspberries. They point out that any beneficial effects will likely come from rapid chemical reactions between the antioxidant and the target molecule in the body. In a standard testing procedure, these rapid reactions may be missed, leading to confusing or conflicting results. By measuring these reactions in a 30-second window, a clearer picture of antioxidant capacity can be developed.
Because raspberries spoil rapidly, the study discusses the effect of storage and processing on the antioxidant content of the fruit. While flash freezing in liquid nitrogen and storage at -20°C destroys much of the vitamin C, the antioxidant capacity remains. Processing the berry into jams may alter some of the antioxidants, however most of the valuable compounds remain.
There is also some evidence that certain raspberry cultivars or varieties are higher in antioxidant capacity than others. The authors suggest that selective plant breeding could result in “extra healthy” raspberries, but that consumers tend to favor a better tasting and cheaper berry. According to Beekwilder and his colleagues, "It is clear that raspberry, like several other fruits and vegetables such as tomato, strawberry, kiwi and broccoli, represents a valuable contrasting source of potentially healthy compounds and can represent an important component of a balanced diet."