Extracellular polysaccharides as target compounds for the immunological detection of Aspergillus and Penicillium in food

H.J. Kamphuis

    Research output: Thesisinternal PhD, WU

    Abstract

    <p>This thesis is devoted to the immunological detection of <em>Aspergillus</em> and <em>Penicillium</em> in food products. More specifically, the immunogenicity, antigenicity, production and structure of the water-soluble extracellular polysaccharides (EPS) of these moulds have been studied, and a latex-agglutination assay, based on the detection of EPS has been developed.<p>For the detection of moulds many methods are available, each of them with specific advantages and disadvantages, mostly related to reliability and applicability ( <strong>Chapter 2</strong> ).<p>An overview of the immunogenicity and antigenicity of EPS produced by moulds is presented in <strong>Chapter 3</strong> . The role of β(1,5)-galactofuranoside sequences as epitopes of galactomannans from <em>Aspergillus</em> and <em>Penicillium</em> is documented. Antigenically specific polyclonal antibodies raised against <em>P.digitatum</em> EPS are directed towards β(1,5)-linked galactofuranosyl residues. These antibodies react specifically with EPS from <em>Aspergillus</em> and <em>Penicillium.</em><p>Synthetic tetramers and heptamers of β(1,5)-linked galactofuranosides are conjugated to tetanus toxoid and polyclonal antibodies are raised in rabbits against these synthetic immunogens ( <strong>Chapter 4</strong> ). Antibodies obtained after immunisation with the heptamer conjugate possess the same genus specific antigenicity as the antibodies raised against <em>P.digitatum</em> EPS. No reactions are observed with the Penicillium subgenus biverticillium species and species belonging to genera other than <em>Aspergillus</em> and <em>Penicillium</em> . In contrast, antibodies raised against the tetramer conjugate reacted only with six out of 24 tested <em>Aspergillus</em> and <em>Penicillium</em> strains.<p>From Glucanex, a <em>Trichoderma harzianum</em> enzyme preparation, an exo-β-D- galactofuranosidase is purified. This enzyme is used to hydrolyse specifically the immunodominant β(1,5)-linked galactofuranosyl residues from <em>Aspergillus</em> and <em>Penicillium</em> EPS. This enzyme alleviates the antigenicity of the EPS completely ( <strong>Chapter 5</strong> ).<p>Additionally, the reductive cleavage method for determination of the glycosidic bonds revealed that the β(1,5)-linked galactofuranosyl side chains in <em>P.digitatum</em> EPS carry side-chains of β(1,6)-1inked galactofuranosyl residues. These results allowed to propose a new structural model for the antigenically active galactofuranoside side chains of <em>Penicillium</em> galactomannans.<p>In <strong>Chapter 6</strong> , the production of antigenic EPS by <em>P. aurantiogriseum</em> and <em>P. digitatum</em> has been described under various growth conditions. Antigenic EPS was produced under almost all conditions investigated. However, both <em>P.aurantiogriseum</em> and <em>P.digitatum</em> do not produce antigenic EPS on lactate as the carbon source. Also, <em>P.camemberti</em> isolated from a mould fermented cheese (Camembert) does not produce antigenic EPS on lactate, althought, <em>P.camemberti</em> produces antigenic EPS on other substrates. The monosaccharide composition of the EPS produced by <em>P.aurantiogriseum</em> and <em>P.digitatum</em> under various conditions varies considerably.<p>Immunopotent acid-labile β(1,5)-linked galactofuranosyl residues of <em>Aspergillus fumigatus, Aspergillus niger</em> and <em>Penicillium digitatum</em> EPS were acid-hydrolysed ( <strong>Chapter 7</strong> ). Antibodies are raised against these acid-treated extracellular polysaccharides. It was supposed that these acid-treated EPS preparations would elicit antibodies with a broader specificity, making them useful in the detection of nearly all or all moulds occurring in food products. However, the antibodies obtained are more species specific and are generally directed to glucosyl and/or mannosyl residues of the EPS.<p>Antibodies raised against <em>P.digitatum</em> EPS <em></em> are used for the development of a rapid and reliable latex-agglutination assay for the detection of <em>Aspergillus</em> and <em>Penicillium</em> in food and feed ( <strong>Chapter 8</strong> ). The reliability of the assay is enhanced by using a synthetic epitope, a tetramer of β(1,5)-Iinked galactofuranosides. With this tetramer false-positive results can easily be recognised.<p>Finally, in <strong>Chapter 9</strong> the applicability of the developed latex-agglutination assay is tested in both comparative and collaborative studies. The significance of extracellular polysaccharides produced by moulds for the detection of moulds in food and feed is discussed.
    Original languageEnglish
    QualificationDoctor of Philosophy
    Awarding Institution
    Supervisors/Advisors
    • Rombouts, F.M., Promotor, External person
    • Notermans, S.H.W., Promotor, External person
    Award date29 Sep 1992
    Place of PublicationS.l.
    Publisher
    Print ISBNs9789054850199
    Publication statusPublished - 1992

    Keywords

    • food contamination
    • food microbiology
    • aspergillus
    • penicillium
    • polysaccharides

    Fingerprint Dive into the research topics of 'Extracellular polysaccharides as target compounds for the immunological detection of Aspergillus and Penicillium in food'. Together they form a unique fingerprint.

    Cite this