A study of 124 cultures of S. paracitrovorus from milk, cream and butter confirms the characterization of the group as those streptococci that produce a definite but variable increase in the acidity of milk and a high volatile acidity, which is greatly increased by the adding of citric acid to the milk to be fermented.
Organisms having the same general appearance in litmus milk as S. paracitrovorus. US but which fail to give a high volatile acidity or to show an increased volatile acidity when citric acid is added to the milk are readily isolated from dairy products. Cultures of S. paractirovorus destroyed the citric acid in the milk in which they had grown, while the organisms failing to produce a high volatile acidity, did not. In general S. paracitrovoros q produced considerable COe but there was no clear cut difference in the CO2 production of these organisms and of other types so that it seems a determination of the CO2 produced will not afford a means of identifying S. pancitrovorus cultures.
Certain of the S. paracitrovorus cultures show considerable resistance to heat and are undoubtedly capable of withstanding the usual pasteurization exposures. Ropiness was observed in one culture of S. paracitrovorus out of the 124 studied. No satisfactory basis was found for the division of the S. paracitrovorus cultures into types; further work may, however, provide such a basis. S. paracitrovorus is rather widely distributed in milk and cream. It seems to be more common than S. citrovorus.
Hammer, B. W. and Baker, M. P.
"Studies on Streptococcus Paracitrovorus group,"
Research Bulletin (Iowa Agriculture and Home Economics Experiment Station): Vol. 6
, Article 1.
Available at: https://lib.dr.iastate.edu/researchbulletin/vol6/iss81/1