title: The role of various amino acids in enzymatic browning process in potato tubers, and identifying the browning products.
abstract: The effects of five structurally variant amino acids, glycine, valine, methionine, phenylalanine and cysteine were examined as inhibitors and/or stimulators of fresh-cut potato browning. The first four amino acids showed conflict effects; high concentrations (⩾ 100mM for glycine and ⩾ 1.0M for the other three amino acids) induced potato browning while lower concentrations reduced the browning process. Alternatively, increasing cysteine concentration consistently reduced the browning process due to reaction with quinone to give colorless adduct. In PPO assay, high concentrations (⩾ 1.11 mM) of the four amino acids developed more color than that of control samples. Visible spectra indicated a continuous condensation of quinone and glycine to give colored adducts absorbed at 610-630 nm which were separated and identified by LC-ESI-MS as catechol-diglycine adduct that undergoes polymerization with other glycine molecules to form peptide side chains. In lower concentrations, the less concentration the less developed color was observed.
authors: Agricultural Biochemistry Department, Faculty of Agriculture, Ain Shams University, Shoubra El-Kheima Cairo, Egypt. Electronic address: hussein_galaleldeen@agr.asu.edu.eg.
authors: Hussein M
authors: HM
authors: Ali
authors: Horticulture Department, Faculty of Agriculture, Ain Shams University, Shoubra El-Kheima Cairo, Egypt.
authors: Ahmed M
authors: AM
authors: El-Gizawy
authors: Vegetable Handling Department, Horticulture Research Institute, Agricultural Research Center, Giza, Egypt.
authors: Rawia E I
authors: RE
authors: El-Bassiouny
authors: Vegetable Handling Department, Horticulture Research Institute, Agricultural Research Center, Giza, Egypt.
authors: Mahmoud A
authors: MA
authors: Saleh
mesh_terms: D000596:Amino Acids / Q000737:chemistry*; D004156:Catechol Oxidase / Q000737:chemistry*; D003116:Color; D005998:Glycine / Q000737:chemistry; D035281:Plant Tubers / Q000737:chemistry*; D011198:Solanum tuberosum / Q000737:chemistry*
chemical_list: D000596:Amino Acids; D004156:Catechol Oxidase; D005998:Glycine
keywords: Amino acids; Browning process; Browning products; Glycine; LC–ESI–MS; Polyphenoloxidase