Measurement of total phenolic content in wine using an automatic Folin–Ciocalteu assay method



Measuring the total phenolic content in wine is important in estimating the taste and health benefits of wine. We developed an automatic Folin–Ciocalteu (F-C) method to reduce processing times (3 min), human errors and waste volume as compared it to the manual method. The gallic acid standard responded linearly up to 5000 μg mL−1, and the wine dilution series responded linearly between four- and sixteenfold dilutions. Anthocyanins showed slower reaction rate compared with wine, gallic acid and quercetin, while ascorbic acid showed the fastest rate. Fructose and glucose at the 10% level showed approximately 8% interference in port wines, and the interference was thought to be negligible in most dry wines containing <1% sugar. Total phenolic contents ranged between 1600 and 3300 μg mL−1 by the automatic method and were approximately 20% less than those by the manual method, except in pink wines which was nearly identical. The regression analysis of the phenolic contents showed a very linear relationship between the methods (r2 = 0.97***). This automatic method was thought to be efficiently adopted in wine testing laboratories as a fast and reproducible assay.