How is PPO activity measured?
Polyphenol oxidase (PPO) activity was determined by measuring the initial rate of quinone formation, as indicated by an increase in the absorbance units (AUs) at 420 nm. An increase in absorbance of 0.001 min−1 was taken as one unit of enzyme activity [20].
What is the substrate of PPO?
PPO may accept monophenols and/or o-diphenols as substrates. The enzyme works by catalyzing the o-hydroxylation of monophenol molecules in which the benzene ring contains a single hydroxyl substituent to o-diphenols (phenol molecules containing two hydroxyl substituents at the 1, 2 positions, with no carbon between).
What is the main function of polyphenol oxidase?
The enzyme polyphenol oxidase (PPO) catalyzes the oxidation of phenolic compounds into highly reactive quinones. Polymerization of PPO-derived quinones causes the postharvest browning of cut or bruised fruit, but the native physiological functions of PPOs in undamaged, intact plant cells are not well understood.
What is polyphenol oxidase and its properties?
Polyphenol oxidases (PPOs) are copper containing enzymes that are nearly ubiquitous among plants (Mayer, 2006). They have catechol oxidase activity (oxidation of o-diphenols to their corresponding o-quinones, EC 1.10. 3.1) and many also have the ability to hydroxylate monophenols to o-diphenols (tyrosinase, EC 1.14.
What is the optimum pH of PPO?
The assay of PPO activity in a pH range from 4.0 to 8.0, using catechol as a substrate, showed optimal conditions for total PPO activity in the pH range of 4.5–5.5.
How does pH affect polyphenol oxidase?
Polyphenoloxidase reached a plateau of maximal activity at pH 6.5 and 7.0, which decreased when the pH was reduced or elevated (Figure 5). A sharper decrease in the activity was observed when the pH was higher than 7.0 compared to a decrease to less than 6.5, and no activity was detected at pH 2.5 and 9.5 (Figure 5).
What pH does polyphenol oxidase work?
between 4.0 and 8.0
PPO activity depends on the pH, which affects the binding of substrates and the catalysis [18,19,20]. Generally, the optimal pH of PPOs ranges between 4.0 and 8.0.
What pH does PPO work best at?
4.5–5.5
The assay of PPO activity in a pH range from 4.0 to 8.0, using catechol as a substrate, showed optimal conditions for total PPO activity in the pH range of 4.5–5.5.
What is the optimum pH for polyphenol oxidase?
The optimum pH was at 6.5, and the enzyme activity was stable in the range of pH 5-11 at 5 degrees C for 48 h. The enzyme had an optimum temperature of 30 degrees C and was stable even after a heat treatment at 70 degrees C for 30 min.
What is PPO in food?
Polyphenol oxidase (PPO) is important in the beneficial coloration of some of our foods, such as prunes, dark raisins and teas. However, in most cases, PPO is the most damaging of enzymes in color deterioration (browning) of plant foods, with resulting losses of up to 50% for tropical fruits and others.
What factors affect PPO?
Polyphenol oxidases (PPOs) (EC 1.14. 18.1, EC 1.10. 3.1, or EC 1.10. 3.2) are widely distributed in the plant kingdom, and their level and activity are dependent on the age, species, variety, maturity, and stress status of plants [1,2].
At what temperature does polyphenol oxidase denature?
PPO activity slightly decreased at 60°C, while the relative enzyme activity remained 9.4% after 80°C for 10 min. The result of differential scanning calorimetry showed that the denatured temperature of PPO was 65°C.
What are polyphenol oxidase enzymes?
Introduction Polyphenol oxidases (PPOs) are a group of Cu-containing enzymes that catalyse the oxidation of several phenols to o-quinones [1,2].
Are polyphenol oxidases differentially expressed during vegetative and reproductive development?
Two polyphenol oxidases are differentially expressed during vegetative and reproductive development and in response to wounding in the Fuji apple. Plant Sci. 2001;161:1145–1152. doi: 10.1016/S0168-9452(01)00522-2.
Is polyphenol oxidase cDNA up-regulated in wounded tissues?
An apple polyphenol oxidase cDNA is up-regulated in wounded tissues. Plant Mol. Biol. 1995;27:429–433. doi: 10.1007/BF00020197. [PubMed] [CrossRef] [Google Scholar] 140. Kim J.Y., Seo Y.S., Kim J.E., Sung S.K., Song K.J., An G.H., Kim W.T.
How is tomato polyphenol oxidase B regulated during development?
Newman S.M., Tantasawat P., Steffens J.C. Tomato polyphenol oxidase B is spatially and temporally regulated during development and in response to ethylene. Molecules. 2011;16:493–517. doi: 10.3390/molecules16010493.