Abstract:

Based on the principle of Folin-Ciocalteu (F-C) assay for determining total polyphenol in grape and grape wine, a new method was developed by optimizing reactive conditions with the aid of micropipette and microwave irradiation. The optimalconditions were 0.1 mL of sample, 0.1 mL of 1 mol/L F-C reagent and 0.8 mL of 60 g/L Na2CO3, microwave treatment for 20 s at the middle power level, determination wavelength of 765 nm. The standard curve exhibited a good linear relationship between absorbance and gallic acid concentration from 1 to 50 mg/L (R2 = 0.9996). When several gallic acid solutions were added to grape and grape wine samples, the average recovery rates of spiked gallic acid in grape and grape wine samples were 98.1% and 97.2%, respectively, with a relative standard deviation (RSD) ranging from 1.40% to 1.01%. This new method is characteristic of simple operation, fast determination, excellent precision, prefect reproducibility and significant reduction in the consumption of samples, reagents as well as time. Therefore, this new method is a promising method for determining total polyphenol in grape and grape wine.

Key words: grape, grape wine, total polyphenol, determination, Folin-Ciocalteu assay