title: Measurement of pH micro-heterogeneity in natural cheese matrices by fluorescence lifetime imaging.
abstract: Cheese, a product of microbial fermentation may be defined as a protein matrix entrapping fat, moisture, minerals and solutes as well as dispersed bacterial colonies. The growth and physiology of bacterial cells in these colonies may be influenced by the microenvironment around the colony, or alternatively the cells within the colony may modify the microenvironment (e.g., pH, redox potential) due to their metabolic activity. While cheese pH may be measured at macro level there remains a significant knowledge gap relating to the degree of micro-heterogeneity of pH within the cheese matrix and its relationship with microbial, enzymatic and physiochemical parameters and ultimately with cheese quality, consistency and ripening patterns. The pH of cheese samples was monitored both at macroscopic scale and at microscopic scale, using a non-destructive microscopic technique employing C-SNARF-4 and Oregon Green 488 fluorescent probes. The objectives of this work were to evaluate the suitability of these dyes for microscale pH measurements in natural cheese matrices and to enhance the sensitivity and extend the useful pH range of these probes using fluorescence lifetime imaging (FLIM). In particular, fluorescence lifetime of Oregon Green 488 proved to be sensitive probe to map pH micro heterogeneity within cheese matrices. Good agreement was observed between macroscopic scale pH measurement by FLIM and by traditional pH methods, but in addition considerable localized microheterogeneity in pH was evident within the curd matrix with pH range between 4.0 and 5.5. This technique provides significant potential to further investigate the relationship between cheese matrix physico-chemistry and bacterial metabolism during cheese manufacture and ripening.
authors: Teagasc Food Research Centre Moorepark, Fermoy, Ireland.
authors: Zuzana
authors: Z
authors: Burdikova
authors: Department of Biology, W. M. Keck Center for Cellular Imaging, University of Virginia Charlottesville, VA, USA.
authors: Zdenek
authors: Z
authors: Svindrych
authors: Department of Sport Medicine, Third Faculty of Medicine, Charles University Prague, Czech Republic.
authors: Jan
authors: J
authors: Pala
authors: Teagasc Food Research Centre Moorepark, Fermoy, Ireland.
authors: Cian D
authors: CD
authors: Hickey
authors: Department of Life Sciences, Faculty of Science and Engineering, University of Limerick Limerick, Ireland.
authors: Martin G
authors: MG
authors: Wilkinson
authors: Institute of Macromolecular Chemistry, Academy of Sciences of the Czech Republic Prague, Czech Republic.
authors: Jiri
authors: J
authors: Panek
authors: Teagasc Food Research Centre Moorepark, Fermoy, Ireland.
authors: Mark A E
authors: MA
authors: Auty
authors: Department of Biology, W. M. Keck Center for Cellular Imaging, University of Virginia Charlottesville, VA, USA.
authors: Ammasi
authors: A
authors: Periasamy
authors: Teagasc Food Research Centre Moorepark, Fermoy, Ireland.
authors: Jeremiah J
authors: JJ
authors: Sheehan
keywords: C-SNARF-4; FLIM; Oregon Green; cheese matrix; fluorescence lifetime; natural cheese; pH micro-heterogeneity