Inactivation of Heat-Resistant Pectinmethylesterase from Orange by Manothermosonication

• Published in: Journal of agricultural and food chemistry 1999-02, Vol.47 (2), p.432-437
• Main Authors: Vercet, Antonio, Lopez, Pascual, Burgos, Justino
• Format: Article
• Language: English
• Subjects: Biological and medical sciences; Carboxylic Ester Hydrolases - chemistry; Citrus - enzymology; enyzme inactivation; Food industries; Food Preservation; Fruit and vegetable industries; Fundamental and applied biological sciences. Psychology; heat resistance; heat treatment; Hot Temperature; inactivation; kinetics; orange juice; oranges; pectinesterase; pressure treatment; Sonication; ultrasonic treatment
• ISSN: 0021-8561; 1520-5118
• DOI: 10.1021/jf980566v

Pectinmethylesterase of navel oranges shows two fractions greatly differing in thermostability. The most thermostable fraction accounts for ∼10% of total activity. The thermal inactivation of this fraction follows first-order kinetics both in 5 mM, pH 3.5, citrate buffer and in orange juice at the same pH, showing a z value of 5.1 °C and an activation energy (E a) of 435 kJ mol-1 K-1. The heat resistance of the enzyme is ∼25-fold higher in the juice than in citrate buffer. When ascorbic acid, sucrose, glucose, and fructose are added to the citrate buffer at the concentrations found in orange juice, the heat resistance of the enzyme increases 3-fold. The addition of pectin at 0.01% concentration multiplies it by a factor of 50. Manothermosonication (MTS), the simultaneous application of heat and ultrasound under moderate pressure (200 kPa), at 72 °C, increases the inactivation rate 25 times in buffer and >400 times in orange juice. MTS inactivation shows a higher z value (35.7 °C) and lower E a (56.9 kJ mol-1 K-1) than simple heating. Keywords: Orange pectinmethylesterase; manothermosonication; thermostable enzymes; orange juice