A comparative study of polyphenoloxidases from taro ( Colocasia esculenta) and potato ( Solanum tuberosum var. Romano)

• Published in: Food chemistry 1999-02, Vol.64 (3), p.351-359
• Main Authors: Duangmal, Kiattisak, Owusu Apenten, Richard K.
• Format: Article
• Language: English
• Subjects: Biological and medical sciences; Food industries; Fruit and vegetable industries; Fundamental and applied biological sciences. Psychology
• ISSN: 0308-8146; 1873-7072
• DOI: 10.1016/S0308-8146(98)00127-7

Taro ( C. esculenta) is a staple food in many tropical regions. A comparative study of crude polyphenoloxidases from taro (tPPO) and potatoes (pPPO) was carried out to provide information useful for guiding food processing operations. Crude PPO was prepared by cold acetone precipitation using ascorbic acid as antioxidant. The PPO content of taro acetone powder was 770±17 units (mg protein) −1 as compared with 3848±180 units (mg protein) −1 in potato acetone powder. The pH-activity optimum was pH 4.6 for tPPO and pH 6.8 for pPPO. Both enzymes retained >80% activity after incubation at pH 4.5–8 but there was rapid activity loss at pH chlorogenic acid> dl-dopa>catechol>pyrogallol> dopamine>>caffeic acid for tPPO. There was no detectable activity towards caffeic acid. The substrate specificity for pPPO was: 4-methylcatechol>caffeic acid>pyrogallol>catechol>chlorogenic acid > dl-dopa>dopamine. According to the order of inhibitor effectiveness (sodium metabisulphite>ascorbic acid>NaCl≈ (EDTA), there was a significant lag-phase before increases occurred in the absorbance at 420 nm. Preincubation of PPO with inhibitors increased the extent of inhibition, indicating a direct effect on the structure of the enzyme.