Polyphenols versus vitamins as antioxidants

Polyphenols have much better antioxidant properties than vitamins, and have been the object of growing interest on the part of nutritionists, epidemiologists, agrifood firms and consumers over the past decade or so.

Their main advantage is that they protect against numerous diseases such as cancer or cardiovascular disease. In particular, they help fight the formation of free radicals in the human body and thus slow cell ageing. They are found in many common consumer products, primarily in fruit and vegetables but also in processed products such as chocolate, tea or wine.

Nobody knew until now the precise total polyphenol content of different foods or the level of consumption in France. A composition table compiled by CIRAD and its partners now goes some way towards providing an answer to those questions. The table was produced under the French Research Ministry's Nutrialis programme. Researchers studied 162 samples from 24 vegetables and 71 samples from 28 fruits. The total polyphenol content of 85 tea samples was also analysed.

It is not always the fruits and vegetables with the highest polyphenol contents that are the most consumed

It is strawberries, lychees and grapes that have the highest polyphenol contents, but vegetables are not far behind, particularly artichokes, parsley and brussels sprouts. Moreover, the total amount consumed plays a considerable role. As Pierre Brat, a CIRAD biochemist, points out: "If we look at total polyphenol content in apples, they rank fifth compared to other fruits, but the extent of their consumption places them first!". Likewise, in terms of vegetables, potatoes rank just 19th, but their massive consumption means that they account for almost 60% of the polyphenols obtained from vegetables.

This was the aim of the table compiled by CIRAD and its partners: to set product composition against consumption. The working method used to do this is in itself a tangible result of the study. In effect, the researchers had to select a range of fresh fruits and vegetables that was representative of consumption in France. To this end, they took account of the different varieties eaten, the different production sites and countries and where those fruits and vegetables are purchased. Total polyphenol content was then analysed using a technique adapted from a chemical colorimetric assay method: the Folin Ciocalteu method. The researchers then established a relation between the result obtained and consumption levels. In this last stage, the team's links with the Agence française de sécurité sanitaire des aliments (AFSSA) proved crucial, since the researchers were able to use two AFSSA databases: one on food consumption - Suvimax - and the other - Secodip - on fresh fruit and vegetable purchases. Moreover, AFSSA will be making the table available to researchers and the general public on its website shortly.

Researchers are preparing to analyse the polyphenol content of processed products

This research is now continuing under a new project, Phenobase, coordinated by the Centre technique de la conservation des produits agricoles in Avignon, in which CIRAD is also involved. The aim is to supplement the composition table, this time by looking at the so-called "processed" products included in the daily diet in France.

Both these products have called upon CIRAD researchers' expertise, notably in terms of citrus fruit treatments. The method developed under the Nutrialis programme, for its part, is currently being disseminated to CIRAD's partners in developing countries.