Abstract: In this study, the effect of NaOH concentration, liquid-to-solid ratio, extraction time and number of extraction cycles on the recovery of phenolic acid from wheat grains using ethyl acetate as the extraction solvent were investigated. The extraction conditions were optimized by response surface methodology. High performance liquid chromatography-mass spectrometry (HPLC-MS) was used to quantify phenolic acid in wheat grains from different varieties grown in different areas of China. The results showed that all the conditions had significant effects on extraction efficiency. Using response surface methodology, the optimum conditions were obtained as follows: NaOH concentration 1.56 mol/L, liquid-to-solid ratio 15.53:1 (mL/g), extraction time 17.33 min, and two extract cycles. Under these conditions, the yield of phenolic acids was 1 055.99 mg/kg. In total, 9 phenolic acids were detected in wheat grains, including gallic acid, protocatechuic acid, 4-hydroxybenzoic acid, vanillic acid, caffeic acid, eugenoic acid, p-coumaric acid, sinapic acid and ferulic acid. Ferulic acid was the main phenolic acid, accounting for 73.07%–89.10% of the total phenolic acids. The Ningmai 14 cultivar contained the highest total phenolic acid content (1 001.12 mg/kg) of the various cultivars grown in Yangtze–Huaihe River region, showing significant differences from Baomai 6 and Huaimai 33. The total phenolic acid content of Xinmai 26 was the highest (1 016.03 mg/kg) in the Yellow-Huaihe River region, which was significantly different from that of Aikang 58 and Bainong 207, grown in this area. It can be concluded that phenolic acid content varies greatly among different wheat varieties.

Key words: wheat, phenolic acid, high performance liquid chromatography-mass spectrometry, optimization