Journal of Nutrition & Food Sciences
Open Access
ISSN: 2155-9600
+32 25889658
ISSN: 2155-9600
+32 25889658
Hussein M Ali, Ahmed M El-Gizawy, Rawia E I El-Bassiouny and Mahmoud A Saleh
Ain Shams University, Egypt
Agricultural Research Center, Egypt
Scientific Tracks Abstracts: J Nutr Food Sci
Ascorbic, citric and various amino acids i.e. cysteine, glycine, valine, metaionine and phenylalanine were examined as antibrowning
agents and/or browning promoters. Mechanisms of the effects of each compound on the browning process were investigated and
discussed. Ascorbic acid, citric acid and cysteine reduced significantly both the browning process and PPO activity. Browning index
gave strong correlation with PPO activity (r2=0.96, n=19) indicating that the browning process is mainly enzymatic. Ascorbic acid could
reduce the formed quinone instantly to the original substrate (catechol) at high concentration (>1.5%) while at lower concentrations
acted as competitive inhibitor (KI=0.256 �±0.067 mM). Cysteine, at higher concentrations (â�¥1.0%), reacted with the resulted quinone
to give a colorless products while at the low concentrations, cysteine worked as competitive inhibitor (KI=1.113�±0.176 mM). Citric
acid acted only as PPO non-competitive inhibitor with KI=2.074�±0.363 mM. The products of PPO-catechol-cysteine reaction could
be separated and identified by LC-ESI-MS. Results indicated that quinone undergoes two successive nucleophilic attacks by cysteine
thiol group. Cysteine was condensed with the resulted mono and dithiocatechols to form peptide side chains.
The examined amino acids, except for cysteine, showed conflict effects. High concentrations (�100 mM for glycine and �1.0
M for valine, metaionine and phenylalanine) induced potato browning while lower concentrations reduced the browning process.
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.
Hussein M Ali obtained his Master’s degree in Biochemistry from Agricultural Biochemistry Department, Ain Shams University, Egypt in 1982. He has obtained PhD in Organic Chemistry from Michigan State University, USA in 1990. He is the Professor of Chemistry in Agricultural Biochemistry Department, Ain Shams University, Egypt (2000-present), and Head of the Department (2007-2010). He is the member of the Permanent Scientific Committee of Promoting Professors and Associate Professors Egypt (2008-2010) and Visiting Professor at Umm Al-Qura (1994-2000) and Dammam Universites (2010-2015) SA. He is the regular referee of some reputed journals (IF 2.0-4.0). His research experience includes Agricultural & Food Chemistry, Enzyme Kinetics & Inhibition, Computational Chemistry, QSAR and Spectroscopy. He has published >40 papers, most of them in international journals with IF 1.0-4.5.