Ortho phthalaldehyde

General pro-analysis grade chemicals (hydrochloric acid, sodium acetate, sodium tetraborate, 2-mercaptoethanol) were purchased from Merck Biosciences (Darmstadt, Germany); ortho-phthalaldehyde, methanol and tetrahydrofuran, all HPLC-grade, were supplied by Sigma Aldrich (St. Louis, United States) and Milli Q water was HPLC-grade. The amino acids standards (aspartic acid, asparagine, glutamic acid, glutamine, serine, histidine, glycine, threonine, arginine, alanine, tyrosine, valine, methionine, tryptophan, phenylalanine, isoleucine, leucine and lysine) were supplied by Sigma Aldrich (St. Louis, United States).

L-arginine (>99%), N^G,N^G′-dimethyl-L-arginine di(p-hydroxyazobenzene-p′-sulfonate) (SDMA), perchloric acid (PCA), potassium tetraborate, ortho-phthalaldehyde (OPA), and 2-mercaptoethanol (ME) were obtained from Sigma-Aldrich (Steinheim, Germany). N^G,N^G-dimethyl-L-arginine hydrochloride (ADMA, >98%) was purchased from Cayman Chemical Company (Ann Arbor, MI, USA). Di-potassium hydrogen phosphate, potassium-dihydrogen phosphate, trichloroacetic acid (TCA), perchloric acid (PCA), hydrochloric acid (37%), ammonia (25%), ortho-phosphoric acid (85%), methanol, sodium hydroxide, and acetonitrile were purchased from Merck (Darmstadt, Germany). Oasis MCX mixed-mode SPE columns (30 mg, 1 ml) were kindly supplied by Waters Denmark.

GABA green tea and GABA oolong tea were purchased from an Italian specialist tea shop (La Teiera Eclettica, Milan, Italy). Gallic acid, epigallocatechin-gallate, epicatechin-gallate, theanine, glutamic acid and glutamine were obtained from PhytolabGmbH and Co., KG (Vestenbergsgreuth, Germany). Bovine serum albumin and a kit for protein determination were purchased from ZiestChem Company (Tehran, Iran). In addition, 5,5-dithiobis(2-nitrobenzoic acid), ethylenediaminetetraacetic acid, nitro blue tetrazolium chloride, potassium dihydrogen phosphate, reduced glutathione, sodium dihydrogen phosphate, trichloroacetic acid, thiobarbituric acid, hydrogen peroxide, sodium carbonate, hydroxylamine chloride, ketamine, lidocaine, xylazine, FolinCiocalteau’s reagent, LC/MS-grade methanol and acetonitrile, formic acid solution 1 M, caffeine, epicatechin, catechin, sodium acetate, trimethylamine, tetrahydrofuran, ortho-phthalaldehyde, fluorenylmethylchloroformate were purchased from Sigma-Aldrich Chemical Company (St. Louis, MO, USA). Other chemical reagents and solvents were purchased from Merck Chemical Company, Darmstadt, Germany.

All solvents and chemicals were of analytical grade. Nutrient Broth (NB), Nutrient Agar (NA), Mueller Hinton Broth (MHB), Mueller Hinton Agar (MHA), McFarland standard were purchased from Oxoid (Basingstone, UK). 6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid (Trolox), 2,2′-azobis (2-amidinopropane) dihydrochloride (AAPH), 2,7-dichlorodihydrofluorescein diacetate (DCFH-DA), dinitrophenylhydrazine (DNPH), trichloroacetic acid (TCA), perchloric acid (PCA), thiobarbituric acid (TBA), 1,1,3,3-tetramethoxypropane (TEP), guanidine hydrochloride, ortho-phthalaldehyde (OPA), reduced glutathione (GSH), phosphoric acid, potassium dihydrogen phosphate (KH₂PO₄), hydrochloric acid (HCl), streptozotocin (STZ), ethanol, ethyl acetate, and methanol from Sigma-Aldrich (St. Louis, MO, USA). All HPLC analytical standards, including protocatechuic acid, syringic acid, rutin, ellagic acid, cynaroside, daidzein, neochlorogenic acid, chlorogenic acid, vitexin, trans p-coumaric acid, trans-sinapic acid, trans ferulic acid, rosmarinic acid, resveratrol, apigenin, myricetin, quercetin, and kaempferol, were bought from Sigma-Aldrich (St. Louis, MO, USA). Phosphate buffer saline (PBS) was bought from VWR (Radnor, PA, USA).

Tea samples were purchased from an Italian specialist tea shop (La Teiera Eclettica, Milan, Italy). The selected teas differ in the degree of fermentation (green and oolong teas) and in the production process (GABA teas and non-GABA teas) (Table 1). Samples GT5, GT6, and GT7 were submitted to different light exposures: GT6 was unshaded, and GT5 and GT7 were shaded for 10 and 20 days, respectively.
EC, ECG, EGCG, and L-theanine were purchased from PhytoLab GmbH & Co. KG (Vestenbergsgreuth, Germany). GA, (±)-catechin, caffeine, glutamic acid, glutamine, GABA, sodium acetate, triethylamine, tetrahydrofurane, ortho-phthalaldehyde, fluorenylmethylchloroformate, Na₂CO₃, HPLC-MS-grade methanol, HPLC-grade acetonitrile, and formic acid solution 1 M were obtained from Sigma Aldrich Chemical Company (St. Louis, MO, USA). HPLC-grade water was obtained from an LC-PakTM Millex system (Millipore Coorporation, Billerica, MA). D₂O and TSP were purchased from Euriso-top (Saint-Aubin, France). D₂O phosphate buffer for NMR samples (400 mM, pH 7.00) was prepared using potassium phosphate monobasic and potassium phosphate dibasic from Sigma Aldrich.