Selective determination of pectinesterase activity in foodstuffs using a pervaporator coupled to an open-closed dynamic biosensing system

A selective automated method for monitoring pectinesterase (PE) activity in food is presented. The proposed method is based on indirect monitorisation of the methanol released by pectin demethoxylation catalysed by PE using a n open-closed dynamic system coupled to a pervaporator. The use of analytic al pervaporation as previous separation technique provides enough selectivi ty to determine PE in both fresh and processed foods without interferences. The biochemical system involved a two-step enzymic derivatisation reaction using alcohol oxidase (AOD) and horseradish peroxidase (POD) and fluorimet ric monitorisation of the reaction product at lambda (ex) = 310 nm and lamb da (em) = 415 nm. The method shows a linear range between 5 x 10(-5) and 0. 2 U ml(-1), with a precision, expressed as R.S.D,, better than 4.8% and a s ampling frequency of 4 h(-1). The usefulness of the method was tested by de termining PE activity in natural and manufactured juices and applying the s tandard addition method with recoveries between 92.3 and 101.8%. (C) 2001 E lsevier Science B,V, Ah rights reserved.