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Characterization of polyphenol oxidase in coffee
1Departamento de Fisiologia Vegetal, Instituto de Biologia, Universidade Estadual de Campinas, SP, Brazil.
Phytochemistry
|December 16, 2000
Summary
Coffee polyphenol oxidase (PPO) activity is higher in early development and increases with wounding. This study characterized PPO enzymes from coffee leaves and fruit endosperm, revealing optimal conditions and inhibitors.
Area of Science:
- Biochemistry
- Plant Science
- Enzymology
Background:
- Polyphenol oxidase (PPO) plays a crucial role in plant defense and secondary metabolism.
- Understanding PPO characteristics in economically important crops like coffee (Coffea arabica L.) is vital for quality control and processing.
- PPO activity can be influenced by developmental stages, environmental factors, and tissue-specific expression.
Purpose of the Study:
- To characterize the partially purified polyphenol oxidase (PPO) from coffee leaves (PPO-L) and fruit endosperm (PPO-E).
- To investigate the kinetic properties, optimal conditions, and stability of coffee PPO.
- To identify potential inhibitors and understand the molecular form of PPO in different coffee tissues.
Main Methods:
- Partial purification of PPO from coffee leaves and fruit endosperm.
- Enzyme activity assays under varying pH, temperature, and substrate concentrations (chlorogenic acid).
- Analysis of PPO behavior with detergents (SDS), proteases (trypsin, proteinase K, pepsin), heat, and specific inhibitors (HTAB, PVP-40, cinnamic acid, SHAM).
- Determination of molecular weight (Mr) using gel filtration and SDS-PAGE, coupled with Western blotting.
Main Results:
- PPO activity was highest during early developmental stages of leaves and fruit endosperm and was induced by wounding and methyl jasmonate.
- Optimal activity for both PPO-L and PPO-E was observed at pH 6-7 and 30°C, with chlorogenic acid as the preferred substrate.
- The enzymes were inhibited by heat, certain chemicals, and proteases (except pepsin), with evidence suggesting a 67 kDa precursor cleaved to a 45 kDa active form.
Conclusions:
- Coffee PPO exhibits distinct characteristics in leaves and fruit endosperm, with higher activity in younger tissues and sensitivity to environmental triggers.
- The study provides insights into PPO's kinetic properties, stability, and molecular forms, crucial for understanding coffee processing and quality.
- Identified inhibitors and optimal conditions can inform strategies for managing PPO activity in coffee.