Journal of Dairy Research

pH-Sensing 96-well microtitre plates for the characterization of acid production by dairy starter cultures

Gernot T John a1, Detlef Goelling a2, Ingo Klimant a3, Holger Schneider a2 and Elmar Heinzle a1c1
a1 Technische Biochemie, Saarland University, 66123 Saarbrücken, Germany
a2 Danisco Cultor Niebüll GmbH, D-25899 Niebüll, Germany
a3 Institut für Analytische, Chemo- und Biosensorik, Universität Regensburg, D-93040 Regensburg, Germany

Article author query
john g   [PubMed][Google Scholar] 
goelling d   [PubMed][Google Scholar] 
klimant i   [PubMed][Google Scholar] 
schneider h   [PubMed][Google Scholar] 
heinzle e   [PubMed][Google Scholar] 


A new method for characterization of acid production by dairy starter cultures is presented. Microplates with integrated optical pH sensors are developed. Two fluorophores, a pH-sensitive and a pH-insensitive one are immobilised at the bottom of a polystyrene 96-well microtitre plate. The pH-insensitive fluorophore serves as an internal reference and makes calibration unnecessary. The sensor measures pH accurately in optically well-defined media. Particles and fluorophores contained in the bulk medium disturbed the measurements. Despite these disturbances it was possible to clearly sense differences in inoculum type and in inoculum sizes of cultures of Lactococcus lactis and of Streptococcus thermophilus at 30 and 37°C. Besides a pH-related signal there is information about other changes during milk fermentation. The cultivation results were compared with those from the established CINAC-method. From this comparison it can be concluded that the new method can be used reliably to characterize particularly a large number of strains for screening purposes but also for quality control.

(Received October 6 2001)
(Accepted February 13 2003)

Key Words: Optical pH sensing; microtitre plate; dairy starter culture; acid production; Lactococcus lactis; Streptococcus thermophilus.

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