2012, EN, English, Thesis edition: Contribution of intrinsic factors to heat resistance of ascospores of Byssochlamys Nguyen, Anh Linh, Chemical Sciences & Engineering, Faculty of Engineering, UNSW

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Physical Description
  • Thesis
  • PhD Doctorate
Published
  • Awarded By:University of New South Wales. Chemical Sciences &​ Engineering, 2012
Language
  • EN
  • English

Edition details

Title
  • Contribution of intrinsic factors to heat resistance of ascospores of Byssochlamys
Author
  • Nguyen, Anh Linh, Chemical Sciences &​ Engineering, Faculty of Engineering, UNSW
Other Contributors
  • Fleet, Graham, Chemical Sciences &​ Engineering, Faculty of Engineering, UNSW
  • Hocking, Ailsa, CSIRO Food &​ Nutritional Sciences
  • Tran-Dinh, Nai, CSIRO Food &​ Nutritional Sciences
Published
  • Awarded By:University of New South Wales. Chemical Sciences &​ Engineering, 2012
Physical Description
  • Thesis
  • PhD Doctorate
Subjects
Summary
  • Byssochlamys is a fungus that causes spoilage of heat processed fruit products by producing heat resistant ascospores. This thesis investigated heat resistant properties of ascospores of Byssochlamys fulva and Byssochlamys nivea. Heat inactivation of the ascospores at temperatures of 82.5 – 90oC showed activation, shoulder, exponential reduction and tailing phases. The D values of the ascospores increased significantly with culture age over the period of 4 – 24 weeks, and the average increase was 3.5 – 7- fold for B. fulva strains and 2 – 4-fold for B. nivea strains. Ascospores of B. fulva were more heat resistant than those of B. nivea. Ultrastructure of the ascospores examined by electron microscopy comprised a cell wall, a thick intermediate space (IMS) and a dense cytoplasm. Examining the arrangement of materials in the ascospores with differential scanning calorimetry provided evidence of a glassy state. Aging improved the robustness of the ascospore structure whereas heating reduced its integrity. Older ascospores occasionally had more sub-layers in the IMS. Ascospores of B. fulva had a more resilient structure and more elaborated outer coating than those of B. nivea. Flow cytometry revealed heterogeneity in preparations of dormant and heat treated ascospores at different ages. Heating affected the integrity of the ascospore wall, which was manifested as increased autofluorescence, permeability to SYTO 9 and clumping of the ascospores. Sub-populations of activated and sub-lethally injured ascospores mostly appeared after heat treatments. Proteomic analysis of ascospores by 2D gel electrophoresis showed that less than 4% of their total proteins significantly changed their expression after heating and aging. Most of the changed proteins were metabolic enzymes, which possibly had been resynthesised and stored in dormant ascospores. For B. nivea, three proteins were identified as heat shock proteins 60, 70 and general stress protein 39. Latent protein synthesis, denaturation and defragmentation of proteins into peptides possibly caused changes in the protein expressions. The results showed that population, structural and molecular factors contribute simultaneously and synergistically to the heat resistance of Byssochlamys ascospores. Data obtained provide a platform for further studies to understand the biological mechanisms of heat resistance of their ascospores and for the food industry to develop more effective heat processes to inactivate these fungi.
Terms of Use
Language
  • EN
  • English
Related Resource
  • SHELF:T/​2012/​49 (Ask at Level 2 Information Desk, UNSW Library)
Identifier
  • oai:unsworks.unsw.edu.au:unsworks:10218

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