Optimization of the 4-Dimethylaminocinnamaldehyde Assay for Flavanols
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Date
2009-03-31T17:57:48Z
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Abstract
Flavanols and their polymeric condensation products, proanthocyanidins represent the most common flavonoids consumed in the diet and are powerful antioxidants. Because of large degrees of chemical variation, isolation and quantification are difficult. The optimal conditions of the 4-dimethylaminocinnamaldehyde (DMAC) spectrophotometric assay for flavanols was evaluated to increase the sensitivity of the reaction and accuracy of the assay. The effects of acid nature (HCl and H2SO4), concentration (2, 4, 6, 8, and 10N), temperature (5, 15, 20, 25, 35, and 45ºC), reaction time (1, 2, 5, 10, 15, 20, and 25 min), sample water content (1.0, 2.0, 3.0, 4.0, 5.0, and 10%), DMAC concentration (1.0, 1.5, 2.0, 2.5, and 3.0%), and presence of interfering substances, were examined in order to develop a robust method for accurate assessment of flavanols. The use of sulfuric acid as acidulant in the reaction significantly improved the results. A mixture of 2% DMAC (w/v) in 1:1 methanol and 6N H2SO4 (v/v) showed maximum sensitivity when allowed to react for 12-15 minutes prior to analysis, with no further improvement shown by extending the time to the usual 20 minutes. The reaction of DMAC was most precise when conducted at constant temperature between 20 – 25ºC, with a sample water content ≤3%. Excess water caused loss of color in the reaction resulting on underestimation of the values. Optimization of the DMAC assay allows maximal sensitivity and detection of small concentration changes, giving a more accurate estimation of the healthy natural plant flavanols present in foods.
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flavanol, dimethylaminocinnamaldehyde, proanthocyanidin