Dichloromethane

All chemicals and solvents were analytical grade. Standard catechin was purchased from Sigma^® (Sigma‐Aldrich, USA). Stock solutions of Standard catechin were freshly prepared for daily use. Stationary phase was TLC plates precoated with silica gel 60 F₂₅₄ (20x10 cm) and thickness of 0.2 mm purchased from Merck (USA). Ethanol, hexane, dichloromethane, ethyl acetate, and mEthanol were purchased from Labscan (Dublin, Ireland). 2,20‐azino‐bis‐3‐ethylbenzothiazoline‐6‐sulfonic acid (ABTS), 2,4,6 tripyridyl‐s‐triazine (TPTZ), 6‐hydroxy‐2,5,7,8‐tetramethylchroman‐2‐carboxylic acid (Trolox), and linoleic acid were purchased from Sigma‐Aldrich (St. Louis, MO, USA). Tris base was purchased from Fisher Chem Alert (Fair Lawn, NJ, USA). Potassium persulfate, ferric chloride, ferrous sulfate, and sodium acetate were purchased from Fisher Chemicals (Loughborough, UK). Hydrochloric acid, acetic acid, trichloroacetic acid, thiobarbituric acid, and ascorbic acid were purchased from Merck (Darmstadt, Germany).

Hydroxyl ammonium chloride, pyridine, methyl tertiary‐butyl ether, and sodium methylate for the extraction and derivatization were HPLC grade. N‐trimethylsilylimidazole and N‐Methyl‐N‐(trimethylsilyl) trifluoroacetamide were GC derivatization grade. Undecane, hexadecane, Tetracosane, triacontane, and octatriacontane were retention time standards; Tetracosane, 5α‐cholestan‐3ß‐ol, phenyl‐ß‐D‐glucopyranoside, and p‐chloro‐L‐phenylalanine were internal standards; and all reference standards were obtained from Sigma Aldrich Co. (St.Louis, MO, USA). Acetonitrile, hexane, methanol, and dichloromethane were analytical grade purchased from RCI Labscan Ltd. (Pathumwan, Bangkok, Thailand).

All rice grains harvested during July–September 2016 were used. The glacial acetic acid, sodium hydroxide, monochloroacetic acid, and polysorbate 80 from Sigma Chemical Co. (St. Louis, MO, USA), dichloromethane and methanol from RCI Labscan Co., Ltd. (Bangkok, Thailand) were used for preparing the modified rice. A chemical modification method of the powder of rice grains was previously documented [12 (link)]. Briefly, the milled rice powder was subjected to etherification in a mixture of methanol–water medium. The proper amount of monochloroacetic acid was gently added. The dispersion was unceasingly stirred at 60 °C for 3 h and the solid phase obtained was then washed with 95% ethanol. The dried coarse sample was crushed into a fine powder by pulverizing machine and passed through an 80-mesh sieve. The modified rice powder was subjected to a hot air oven at 65 °C for 24 h to ensure the complete removal of alcohols, confirmed by GC analysis, before using for hydrogel base preparation.

Commercial grade ethyl acetate (≥98%), hexanes (≥98%), dichloromethane (≥99%) and ethanol (≥96%) were obtained from RCI Labscan (Bangkok, Thailand) and used as received from commercial suppliers without further purification. Boron oxide (≥98%), acetyl acetone (≥99%), vanillin (99%), tributyl borate (≥99%), 4-(N,N-dimethylamino)pyridine (DMAP) and succinic acid monoethyl ester chloride (95%) were purchased from Sigma-Aldrich (St. Louis, MO, USA). n-Butylamine (99.5%) was procured from ACROS Organics (Geel, Belgium ). n-Octanol was obtained from Merck (Darmstadt, Germany). Water was produced in-house using a Milli-Q water purification system (Millipore S.A.S, Molsheim, France)