Phenylalanine

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).

Methanol HPLC grade was purchased from Sigma-Aldrich (St. Louis, MO, United States). Melphalan (compound 1) and phenylalanine (compound 2) were purchased from J&K Scientific Ltd (Shanghai, China) with a purity>99%. 3,4-Dimethoxyphenylalanine (compound 3), 4-chlorophenylalanine (compound 4), 4-methoxyphenylalanine (compound 5), 4-methylphenylalanine (compound 6), tyrosine (compound 7), 4-bromophenylalanine (compound 8) and 2-hydroxylbenzylamine were purchased from Sinopharm Chemical Reagent Co., Ltd. Their structures of them are listed in Scheme 1. Experimental ultrapure water produced by Millipore ultrapure water system.