Journal
FOOD CHEMISTRY
Volume 140, Issue 1-2, Pages 289-295Publisher
ELSEVIER SCI LTD
DOI: 10.1016/j.foodchem.2013.02.028
Keywords
Polyphenoloxidase (PPO); Citric acid; Activity; Thermodynamic parameters; Conformation
Funding
- National Natural Science Foundation of China [31060209]
- Research Program of State Key Laboratory of Food Science and Technology, Nanchang University [SKLF-QN-201101]
- Young Scientist Training Objects Program of Jiangxi Province [20112BCB23003]
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Few reports have focused on the effect of citric acid on thermodynamics and conformation of polyphenoloxidase (PPO). In this study, variations on activity, thermodynamics and conformation of mushroom PPO induced by citric acid (1-60 mM) and relationships among these were investigated. It showed that with the increasing concentration of citric acid, the activity of PPO decreased gradually to an inactivity condition; inactivation rate constant (k) of PPO increased and the activation energy (E-a) as well as thermodynamic parameters (Delta G, Delta H, Delta S) decreased, which indicated that the thermosensitivity, stability and number of non-covalent bonds of PPO decreased. The conformation was gradually unfolded, which was reflected in the decrease of alpha-helix contents, increase of beta-sheet and exposure of aromatic amino acid residuals. Moreover, two linear relationships of relative activities, enthalpies (Delta H) against alpha-helix contents were obtained. It indicated that changes of activity and thermodynamics might correlate to the unfolding of conformation. (C) 2013 Elsevier Ltd. All rights reserved.
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