Fast determination of procyanidins and other phenolic compounds in food samples by micellar electrokinetic chromatography using acidic buffers

Procyanidins are phenolic oligomers, mainly composed of (+)-catechin and (- )-epicatechin units that exhibit certain sensorial and physiological proper ties of interest (e.g., astringency and bitterness of food, antioxidant act ivity, etc.). This paper shows the development of a micellar electrokinetic chromatography (MEKC) method for the separation of three procyanidin dimer s (B1, B2, and B3), their monomers ((+)-catechin and (-)-epicatechin), and the cis- and trans-forms of p-coumaric acid. Separation conditions are opti mized in terms of buffer pH, SDS concentration, and washing routine between injections. The best results in terms of peak resolution and reproducibili ty between separations were obtained with a MEKC running buffer at pH 5 wit h 100 mM SDS and a washing routine that includes a rinse step with 0.1 M so dium hydroxide. Using this new MEKC method it is possible to separate in le ss than 5 min the seven substances. More interestingly, it is demonstrated that the low pH used in this MEKC method allows one to obtain clean electro pherograms when samples are injected. The method is shown to be reproducibl e between different days with relative standard deviation (RSD) values lowe r than 1% for migration times and lower than 7% for peak areas (3 days, 24 injections). The usefulness of this procedure to determine these compounds in effluents from food processing (i.e., soaking water from lentils, white beans and black beans) and in food by-products (i.e., almond peels) conside red as potential procyanidin sources is demonstrated. To our knowledge, thi s is the first report of separation and determination of procyanidins in fo od samples done by capillary electrophoresis.