Xylitol

4-Nitrophenyl-α-D-glucopyranoside (p-NPG) and α-glucosidase were provided by Sigma-Aldrich Chemical Co., Ltd. (Shanghai, China). Organic solvents and the Folin–Ciocalteu reagent were purchased from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China). Arecoline hydrobromide, rutin trihydrate, and gallic acid were purchased from Aladdin Biochemical Technology Co., Ltd. (Shanghai, China). Choline chloride (98%), betaine (98%), L-proline (99%), glucose (99%), lactic acid (88%), xylitol (99%), malic acid (98%), urea (99%), citric acid (99.5%), glycerol (99%), 1,4-butanediol (98%), ethylene glycol (99.5%), and AB-8 macroporous adsorption resin were purchased from Macklin Biochemical Co., Ltd. (Shanghai, China). All these reagents were of analytical grade.

The Ginkgo biloba leaves picked on May were purchased from Chinese Herb Transaction Center (Bozhou, China). The leaves were dried at 40 °C to constant weight in vacuum oven, and then pulverized to 30–40 mesh by a disintegrator. The water content of the Ginkgo biloba leaves powder was 3.17% (w/w).
The standards of SA (≥99.0%), PA (≥99.0%), GAA (≥99.0%) and PHBA (≥99.0%) were purchased from Shanghai Yuanye Bio-Technology Co., Ltd (Shanghai, China). The 6-HKA (≥99.8%) was donated by Zhejiang Conba Pharmaceutical Co., Ltd (Hangzhou, China). Choline chloride (≥98.0%), citric acid (≥99.5%), d-sorbitol (BR) were purchased from Sinopharm Chemical Reagent Co., Ltd (Shanghai, China). Phosphorous acid (chromatographic grade, 85–90%), dl-malic acid (≥99.0%), malonic acid (≥99.0%), levulinic acid (≥99.0%) and 2-pyrrolidinecarboxylic acid (≥99.0%) were obtained from Aladdin Chemistry Co., Ltd (Shanghai, China). Glycolic acid (≥98.0%), xylitol (≥99.0%) and betaine (≥99.0%) were acquired from Shanghai Macklin Biochemical Co., Ltd (Shanghai, China). Acetonitrile (chromatographic grade) was purchased from Tedia Company, Inc. (Shanghai, China). Deionized water was obtained by a Milli-Q water purification system (Millipore, Billerica, MA, USA). All other reagents and chemicals used in this work were of analytical reagent grade.