5 methylquinoxaline 5 mq

Dragon fruit peels were sourced from Ramathibodi Hospital in Bangkok, Thailand. The cookie ingredients used were commercially available from a supermarket. The following reagents and chemicals were purchased from Sigma-Aldrich Chemical Co. Ltd. (St. Louis, MO, USA): Folin–Ciocalteu reagent, betanin (betanidin 5-β-D-glucopyranoside), TPTZ (2,4,6-tripyridyl-s-triazine), 2,6-di-tert-butyl-4-methylphenol (BHT), 2-thiobarbituric acid (TBA), malondialdehyde tetrabutylammonium salt (MDA), pepsin from porcine gastric mucosa powder (250 U/mg), α-amylase type VI-B from porcine pancreas (15.8 U/mg), pancreatin from porcine pancreas, methylglyoxal (40% aqueous solution), 5-methylquinoxaline (5-MQ), and o-phenylenediamine (OPD). Amyloglucosidase from Aspergillus niger was purchased from Roche Diagnostics in Indianapolis, IN, USA.

HMF, [U-¹³C₆]-HMF, 3-DG, quinoxaline, 2-methylquinoxaline, o-phenylenediamine (OPD), 5-methylquinoxaline (5-MQ) and formic acid were obtained from Sigma-Aldrich (St. Louis, MO, USA). CML and CEL standards as well as d₄-N^ε-(carboxymethyl)lysine (d₄-CML) and d₄-N^ε-(carboxyethyl)lysine (d₄-CEL) standards were purchased from Toronto Research Chemicals Inc. (North York, ON, Canada). Ammonia solution (≥25% in H₂O), monobasic and dibasic potassium phosphate were of HPLC grade and obtained from Shanghai Aladdin Biochemical Technology Co. (Shanghai, China). Analytical grade chloroform, sodium borohydride, sodium borate, boric acid, sodium hydroxide and hydrochloric acid were purchased from Sinopharm Chemical Reagent Co., Ltd. (Beijing, China). Methanol (MS grade) was acquired from Merck (Darmstadt, Germany). Dietary curcumin (≥90%), pectin (≥80%) and chitosan (≥90%) were purchased from Xingmu Biological Engineering Co., Ltd. (Shenzhen, China). Dietary catechins was purchased from Hongda Tea Co., Ltd. (Wuyuan, China), and the composition of catechins is summarized in Supplementary Materials (Table S1). Oasis HLB or MCX solid phase extraction cartridges (6 cc, 200 mg) were supplied by Waters (Milford, MA, USA). Deionized water was provided by the Watson Group Ltd. (Hongkong, China).