Pectinesterases from the orange fruit : their purification, general characteristics and juice cloud destabilizing properties

C. Versteeg

    Research output: Thesisinternal PhD, WU

    Abstract

    Twelve forms of pectinesterase were detected in citrus fruits. Two forms, representing over 90% of the total pectinesterase activity in Navel oranges, were purified. These pectinesterases, named Pectinesterase I and II have isoelectric points of 10.05 and>11.0, respectively. Both pectinesterases have the same molecular weight of 36 200 but differ in amino acid composition. A third pectinesterase, with a higher molecular weight (about 54 000) was partly purified. The optimum pH of these three pectinesterases is about 7.5, but their pH-activity profiles differ and depend on the degree of esterification of the pectin. The high molecular weight pectinesterase is still active at pH 2.5. The <em>K</em><sub><font size="-1">m</font></sub> values of both purified pectinesterases decrease with decreasing degree of esterification of the pectin substrate and increase with decreasing pH. Pectinesterase II has a tenfold higher affinity for pectin than Pectinesterase I and is more strongly inhibited by pectate. The heat stabilities were determined: the <em>D</em><sub><font size="-1">90</font></sub> °C and Z values in orange juice are 0.00037 min and 6.5 °C for Pectinesterase 1, 0.0015 min and 11 °C for Pectinesterase II and 0.375 min and 6.5 °C for the high molecular weight pectinesterase. The orange juice cloud destabilizing properties of the pectinesterases at 5 °C and 30 °C are remarkably different. The activity measurements were done, amongst other methods, by an improved gas chromatographic methanol assay. The literature on pectinesterase was reviewed.
    Original languageEnglish
    QualificationDoctor of Philosophy
    Awarding Institution
    Supervisors/Advisors
    • Pilnik, W., Promotor, External person
    • Rombouts, F.M., Co-promotor, External person
    Award date28 Sep 1979
    Place of PublicationWageningen
    Publisher
    Print ISBNs9789022007099
    Publication statusPublished - 1979

    Keywords

    • esterases
    • orange juice
    • oranges
    • pectins

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