Tryptophan

HPLC-grade formic acid was obtained from Sigma-Aldrich (USA). HPLC/MS-grade formic acid, ammonium formate, and acetonitrile were acquired from Fisher Scientific (USA). The internal standards Labeled Carnitine Standards (L-carnitine (N-trimethyl-D₉), L-acetylcarnitine (N-methyl-D₃), L-propionylcarnitine (Nimethyl-D₃), L-butyrylcarnitine (N-methyl-D₃), L-isovalerylcarnitine (N-trimethyl-D₉), L-octanoylcarnitine (N-methyl-D₃), L-myristoylcarnitine (N-trimethyl-D₉), L-palmitoylcarnitine (N-methyl-D₃)) were attained from Cambridge Isotope Laboratories. Seventeen amino acid standards (alanine, valine, leucine, isoleucine, phenylalanine, methionine, proline, glycine, serine, threonine, cysteine, tyrosine, histidine, lysine, arginine, aspartic acid, glutamic acid) were purchased from Sigma-Aldrich. Eight amino acid standards (tryptophan, asparaginate, glutamine, ornithine, taurine, citrulline, cysteine, γ-aminobutyric acid) were gained from J&K Scientific. Ultrahigh purity water was prepared by Millipore-Q Water Purification System (Millipore, Germany).

Beef was obtained from a local market in Changsha, China. Hydrocolloids including alginic acid, chitosan, carrageenan, xanthan gum, konjac glucomannan (KGM), pectin and gellan gum were purchased from Aladdin (Shanghai, China). Chemical standards of HAs: PhIP, IQ, MeIQ, MeIQx, 4,8-DiMeIQx, IQx, Harmane and NorHarmane were supplied by Santa Cruz Biotechnology, Inc. (Santa Cruz, CA, USA). Chemical standards of AGEs, N^ε-(carboxymethyl)lysine (CML), d₄-CML, N^ε-(carboxyethyl)lysine (CEL) and d₄-CEL, were obtained by Santa Cruz Biotechnology Co. (Paso Robles, CA, USA). The standards of lysine, phenylalanine, creatinine, glucose, threonine, tryptophan, phenylacetaldehyde, 2,5-dimethylpyrazine, glyoxal, methylglyoxal, O-phenylendiamine, 2,3-hexanedione and nonafluoropentanoic acid (NFPA) were purchased from J&K Scientific Co, Ltd. (Beijing, China). Mass spectral grade methanol and acetonitrile were purchased from Merck KGaA (Darmstadt, Germany). Oasis MCX (3 cc/60 mg) cartridges were purchased from Waters (Milford, MA, USA). The chemicals were all analytical grade and purchased from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China).

Beef was obtained from a local market in Changsha, China. Hydrocolloids including alginic acid, chitosan, carrageenan, xanthan gum, konjac glucomannan (KGM), pectin and gellan gum were purchased from Aladdin (Shanghai, China). Chemical standards of HAs: PhIP, IQ, MeIQ, MeIQx, 4,8-DiMeIQx, IQx, Harmane and NorHarmane were supplied by Santa Cruz Biotechnology, Inc. (Santa Cruz, CA, USA). Chemical standards of AGEs, N^ε-(carboxymethyl)lysine (CML), d₄-CML, N^ε-(carboxyethyl)lysine (CEL) and d₄-CEL, were obtained by Santa Cruz Biotechnology Co. (Paso Robles, CA, USA). The standards of lysine, phenylalanine, creatinine, glucose, threonine, tryptophan, phenylacetaldehyde, 2,5-dimethylpyrazine, glyoxal, methylglyoxal, O-phenylendiamine, 2,3-hexanedione and nonafluoropentanoic acid (NFPA) were purchased from J&K Scientific Co, Ltd. (Beijing, China). Mass spectral grade methanol and acetonitrile were purchased from Merck KGaA (Darmstadt, Germany). Oasis MCX (3 cc/60 mg) cartridges were purchased from Waters (Milford, MA, USA). The chemicals were all analytical grade and purchased from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China).