[Determination of total polyphenol content in food with the flow-injection method]

This paper describes an optimised flow-injection method for the determination of total polyphenol in food based on the Folin-Ciocalteau reaction in 0.5 mol L(-1) NaOH. The method allows different types of samples to be analysed automatically at a rate of 55 samples per hour by using gallic acid as standard. By applying the proposed method to real samples (white and red wines, green, Indian, lime-tree, mentha and chamomile teas, and blackberry and cherry juices), their total polyphenol indices were determined with a higher reproducibility than obtained by earlier methods, whatever the dilution used. This method is highly tolerant towards the most common interferences (SO2, reducing sugars, and ascorbic acid) associated with the batch method. The results obtained by the proposed method relatively agree with those obtained using the referent Folin-Ciocalteau method.