Growth and metabolic activity of a cheese starter in CO2-acidified and non-acidified refrigerated milk

 The growth and activity of two Lactococcus strains and one Leuconostoc strain in CO₂-acidified and non-acidified refrigerated milk were evaluated separately and as a mixed culture to determine their suitability for use as a starter in the manufacture of Afuega’l Pitu, an acid-coagulated Spanish cheese, from refrigerated CO₂-acidified milk. The growth of the strains studied and their production of organic acids were similar in CO₂-acidified and non-acidified refrigerated or fresh milk, indicating that CO₂ treatment does not affect the metabolic activity of the strains. However, refrigeration enhanced the production of acetaldehyde, ethanol and diacetyl in CO₂-acidified and non-acidified milk. The level of diacetyl was also greater in refrigerated CO₂-acidified milk than in refrigerated non-acidified milk. It was concluded that refrigerated milk acidified with CO₂ can be satisfactorily used in the manufacture of Afuega’l Pitu cheese, and that this technique can be also used in the production of other acid-coagulated cheeses. Received: 1 July 1997 / Revised version: 1 September 1997