title: Acquisition of the yeast Kluyveromyces marxianus from unpasteurised milk by a kefir grain enhances kefir quality.
abstract: Kefir is a fermented milk beverage consumed for nutritional and health tonic benefits in many parts of the world. It is produced by the fermentation of milk with a consortium of bacteria and yeast embedded within a polysaccharide matrix. This consortium is not well defined and can vary substantially between kefir grains. There are little data on the microbial stability of kefir grains, nor on interactions between microbes in the grain and in the milk. To study this, a grain was split, with one half of each stored at -20°C and the other half passaged repeatedly in whole unpasteurised milk. Grains passaged in the unpasteurised milk recovered vigour and acquired the yeast Kluyveromyces marxainus from the milk which was confirmed to be the same strain by molecular typing. Furthermore, these passaged grains produced kefir that was distinguished chemically and organoleptically from the stored grains. Some changes in ultrastructure were also observed by scanning electron microscopy. The study showed that kefir grains can acquire yeast from their environment and the final product can be influenced by these newly acquired yeasts. Kluyveromyces marxianus is considered to be responsible for some of the most important characteristics of kefir so the finding that this yeast is part of the less stable microbiota is significant.
authors.affiliation: School of Microbiology, University College Cork, Cork, Ireland Teagasc Research Centre, Moorepark, Fermoy, Co. Cork, Ireland.
authors.forename: Loughlin
authors.initials: L
authors.lastname: Gethins
authors.affiliation: Teagasc Research Centre, Moorepark, Fermoy, Co. Cork, Ireland Alimentary Pharmabiotic Centre University College Cork, Cork, Ireland.
authors.forename: Mary C
authors.initials: MC
authors.lastname: Rea
authors.affiliation: Teagasc Research Centre, Moorepark, Fermoy, Co. Cork, Ireland Alimentary Pharmabiotic Centre University College Cork, Cork, Ireland.
authors.forename: Catherine
authors.initials: C
authors.lastname: Stanton
authors.affiliation: School of Microbiology, University College Cork, Cork, Ireland Alimentary Pharmabiotic Centre University College Cork, Cork, Ireland.
authors.forename: R Paul
authors.initials: RP
authors.lastname: Ross
authors.affiliation: Teagasc Research Centre, Moorepark, Fermoy, Co. Cork, Ireland.
authors.forename: Kieran
authors.initials: K
authors.lastname: Kilcawley
authors.affiliation: School of Food Science and Nutrition, University College Cork, Cork, Ireland.
authors.forename: Maurice
authors.initials: M
authors.lastname: O'Sullivan
authors.affiliation: BioSciences Imaging Centre, Department of Anatomy and Neuroscience, Cork, Ireland.
authors.forename: Suzanne
authors.initials: S
authors.lastname: Crotty
authors.affiliation: School of Microbiology, University College Cork, Cork, Ireland j.morrissey@ucc.ie.
authors.forename: John P
authors.initials: JP
authors.lastname: Morrissey
mesh_terms: D000818:Animals; D043302:Cultured Milk Products / Q000382:microbiology; D005285:Fermentation; D063427:Food Quality; D006801:Humans; D000070716:Kefir / Q000382:microbiology*; D007716:Kluyveromyces / Q000235:genetics / Q000378:metabolism*; D059013:Microbial Consortia; D008892:Milk / Q000382:microbiology*; D061352:Pasteurization; D012441:Saccharomyces cerevisiae / Q000378:metabolism*; D013649:Taste
keywords: Kluyveromyces; fermented beverage; flavour; kefir; milk; yeast