Effects of variation in cheese composition and maturation on water activity in Cheddar cheese during ripening

Changes in the water activity (a_w) of experimental Cheddar cheeses with different compositions were measured over a 270 d ripening period. The ranges of key compositional parameters were typical of those found in commercial Cheddar cheese: moisture (35.6-38.6%), fat (29.9-33.4%), salt (1.4-2.0%), salt-in-moisture (3.8-5.2%), moisture-in-non-fat substances (MNFS, 52.4-56.3%) and pH (5.0-5.7). Linear regression analysis indicated that at ripening times ≤30 d, the a_w was inversely correlated with salt-in-moisture, while at 270 d it was positively correlated with levels of moisture and MNFS, but negatively with fat content. The a_w decreased significantly (P < 0.001) during ripening, from a mean of ∼0.965 at 1 d to ∼0.956 at 270 d. The preponderant factor responsible for the decrease in a_w was the increase in proteolysis, as measured using pH 4.6 soluble N and free amino acids.