Chapter 15 - Microbiome Changes During Ripening

Abstract

Microorganisms, including bacteria, yeast, and molds, are present in cheese throughout ripening. The majority contribute in a positive manner to the maturation process either directly through their metabolic activity or indirectly through release of enzymes into the cheese matrix through autolysis. The cheesemaker encourages growth of such organisms. Although diverse, the microbiota associated with cheese ripening may be conveniently divided into two groups, that is, the starter lactic acid bacteria and the secondary microbiota. Starter bacteria are primarily responsible for acid production during manufacture and, therefore, need to be capable of producing sufficient acid to reduce the pH of milk rapidly; a useful rule of thumb is a pH < 5.3 in milk in 6 h at 30–37°C depending on the cheese variety. The secondary microbiota does not play any active role during cheese manufacture, but is involved with the starter bacteria in the ripening process. Using this approach, Lactococcus, Streptococcus thermophilus, Lactobacillus delbrueckii, and Lactobacillus helveticus are regarded as starter bacteria. Enterococcus has been regarded as a starter by some researchers; however, as most strains isolated from cheese are not significant acid producers, they are more frequently regarded as part of the secondary microbiota. The secondary microbiota may be divided into a number of primary groups, including (1) nonstarter lactic acid bacteria consisting of nonstarter lactobacilli, Pediococcus, Enterococcus, and Leuconostoc; (2) propionic acid bacteria; (3) molds; and (4) bacteria and yeast, which grow on the surface of smear-ripened cheeses.