Physical and rheological parameters of skim milk gels fermented with slime producing (ropy) cultures and non-ropy cultures were compared. The skim milk gels were made from steamed reconstituted nonfat dry milk inoculated with 2% of a single strain starter culture and incubated at 32, 37, and 45°C until pH 4. 5 + 0.05 was attained.
Skim milk gels fermented by slime-producing strains of Streptococcus thermophilus, Streptococcus cremoris, and Lactobacillus bulgaricus exhibited similar rheological and physical characteristics. Electron micrographs of the ropy skim milk cultures showed that slime produced by the organisms was associated with the cell surface as well as the protein matrix of the systern.
Skim milk gels fermented by the slimeproducing strains exhibited decreased susceptibility to syneresis as compared to skim milk which had been fermented with non-ropy strains at the same temperatures. Excessive slime production (when cultures were incubated for a longer time at a lower temperature) resulted in a coagulum with decreased relative firmness and apparent viscosity. However the skim milk gels fermented by the ropy strains at the higher incubation temperatures exhibited greater viscosity than skim milk fermented by non-ropy strains at the same temperatures.
Schellhaass, S. M. and Morris, H. A.
"Rheological and Scanning Electron Microscopic Examination of Skim Milk Gels Obtained by Fermenting With Ropy and Non-Ropy Strains of Lactic Acid Bacteria,"
Food Structure: Vol. 4
, Article 11.
Available at: http://digitalcommons.usu.edu/foodmicrostructure/vol4/iss2/11