Use of pectinesterase for detection of hydrocolloids addition in natural orange juice

In natural orange juice, pectin is the major constituent responsible for cloud stability. In adulterated and imitation orange juices, for technical reasons, cloud stability is effected by different natural or synthetic hydrocolloids. Pectinesterase, an enzyme specific for pectin hydrolysis, was used to detect substitution of natural pectin of orange juice by other hydrocolloids. Natural orange juice, imitation orange juice and mixtures of them were used in this study. In pasteurized orange juice samples, pectinesterase was added at 20 mg/100 ml of juice. Mixtures were heated at 50°C in a water bath for 24 h and the percentage of clarification, as well as the amount of precipitate formed after centrifugation were measured. A linear correlation was found to exist between natural orange juice percentage in the natural–imitation orange juice mixtures and precipitate formed. A second order relation was found to exist between the percentage of the natural orange juice in the natural–imitation orange juice mixtures and the degree of clarification of orange juice. The method was used successfully for the detection of addition of extraneous hydrocolloids in orange juice for adulteration purposes.