Anthocyanin- and proanthocyanidin-rich extracts of berries in food supplements--analysis with problems

The fundamental nutritional benefit of fruit and vegetables in the prevention of degenerative diseases--especially in the light of the current "anti-aging wave"--has directed the attention of scientists and consumers to a variety of berry fruits and their constituents. Many of these fruits, e.g. blueberries, elderberries or cranberries, have a long tradition in European and North American folk medicine. Based on these experiences and due to the growing interest the number of food supplements on the market containing fruit powders, juice concentrates or extracts of these fruits has increased considerably. Advertising for these products mainly focusses on the phenolic compounds, especially the anthocyanins and proanthocyanidins and their preventive effects. Most of the preparations are combinations, e.g. of extracts of different fruits with vitamins and trace elements, etc. which are labelled in a way which does not allow a comparison of the products. Typically, information on the extraction solvent, the drug: extract ratio and the content of anthocyanins and proanthocyanidins is missing. Besides that, the analysis of these polyphenols causes additional problems. Whereas the quality control of herbal medicinal products is regulated in detail, no uniform requirements for food supplements are existing. A broad spectrum of methods is used for the assay of the constituents, leading to differing, incomparable results. In addition to that, the methods are quite interference-prone and consequently lead to over- or underestimation of the contents. This publication provides an overview of some selected berries (lingonberry, cranberry, black elderberry, black chokeberry, black currant, blueberry), their constituents and use. The analytical methods currently used for the identification and quantification of the polyphenols in these berries are described, including an evaluation of their advantages and disadvantages.