ARS | Publication request: Biochemical characteristics and thermal inhibition kinetics of polyphenol oxidase extracted from Thompson seedless grape

Submitted to: European Food Research and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 9, 2012
Publication Date: January 24, 2012
Repository URL: http://dx.doi.org/10.1007/S00217-012-1664-4
Citation: Shi, J., Zheng, Y., Pan, Z. 2012. Biochemical characteristics and thermal inhibition kinetics of polyphenol oxidase extracted from Thompson seedless grape. European Food Research and Technology. 234(4):607-616. DOI:10.1007/S00217-012-1664-4.

Interpretive Summary: Polyphenol oxidase (PPO) has been considered as one of major causes of discoloration of green raisins during processing. In this research the characteristics of isolated PPO were studied. It was found that the highest enzymatic activity of PPO occurred at pH 6.0 and temperature 25 degrees C. The inactivation kinetics of PPO was also determined and can be used for guiding the selection of optimum raisin production conditions. The results provided more basic understanding about the characteristics of PPO in grapes.

Technical Abstract: Polyphenol oxidase (PPO) was isolated from Thompson seedless grape (Vitis vinifera 'Thompson Seedless') and its biochemical characteristics were studied. Optimum pH and temperature for grape PPO activity were pH 6.0 and 25 degrees C with 10 mM catechol as substrate. The enzyme was heat-stable between 10 to 25 degrees C, but showed significant activity loss at temperatures higher than 40 degrees C and completely inactivation at 70 degrees C for 10 min. The PPO showed activity to catechol and D, L-DOPA, but not towards monophenol L-Tyrosine, diphenols guaiacol and caffeic acid, triphenols pyrogallic acid and Gallic acid. Apparent Michaelis-Menten constant (Km), maximum velocitiy of the reaction (Vmax) values were 45.0±0.05mM and 500.0±15.3 OD 400 nm/min for catechol, 34.6±0.03 mM and 384.6±11.7 OD 478 nm/min for D,L-DOPA, respectively. The obtained similar specificity values of ratio Vmax/Km of catechol and D,L-DOPA indicated their similar affinity to Thompson seedless PPO. The most effective inhibitor was L-cysteine, followed in decreasing order by sodium metabisulfite, ascorbic acid, sodium metabisulfite, EDTA, NaCl, citric acid. Metal ions of Mg2+ and Cu2+ increased, while Zn2+ and K+ reduced the PPO activity. Thermal inactivation of PPO showed a first-order kinetics with an activation energy (Ea) of 146.1±10.8 kJ/mol at pH6.0.