An improved analytical method for determination of trans‐resveratrol and related stilbenes in grape skin by QuEChERS coupled with HPLC‐PDA‐MS.

Summary: Grape is a popular fruit crop that generates about one‐fourth of total weight as pomace during winemaking and commercial juice production. However, a significant amount of resveratrol and related stilbenes is present in grape skin, and their effective isolation enables the production of functional foods. Herein, an improved analytical method for the determination of trans‐resveratrol and related stilbenes in grape skin waste by QuEChERS method coupled with a high‐performance liquid chromatograph‐photodiode array detector‐mass spectrometer was developed. By employing a Gemini C18 column and a mobile phase of acetic acid in water (pH 3.6) and acetonitrile, a total of five resveratrol and related stilbenes could be separated within 15 min with a flow rate of 0.8 mL min−1 and detection wavelength at 306 nm. The optimised QuEChERS conditions were 10 mL of acetonitrile, 1 mL of grape skin extract and 900 mg of magnesium sulphate plus 25 mg of primary secondary amine. Principal component analysis by two principal components (74.18%, 25.82%) could well describe the trans‐resveratrol recovery at different QuEChERS conditions. A mean recovery, as well as coefficient of variation (CV, %) of repeatability and intermediate precision, ranged from 96.6% to 104.4%, 1.96% to 3.10% and 1.68% to 4.27%, respectively, conforming to the regulation set by Taiwan Food and Drug Administration. Quantitation revealed cis‐piceid to be present in largest amount (2.616 μg mL−1), followed by trans‐piceid (1.027 μg mL−1), trans‐resveratrol (0.967 μg mL−1), ε‐viniferin (0.660 μg mL−1) and cis‐resveratrol (0.183 μg mL−1) in grape skin extract, with their corresponding contents in dried grape skin being 4.185, 1.643, 1.539, 1.056 and 0.293 μg g−1, respectively. [ABSTRACT FROM AUTHOR]