Water activity (aw) is a critical physico-chemical parameter that influences microbiological and biochemical properties during cheese ripening. This study assessed the use of Raoult’s law in estimating aw based on four chemical components (moisture, NaCl, total free amino acids [ΣFAAs] and lactate) across 14 commercial Swiss hard and semi-hard cheeses. A strong correlation (r = 0.979) was observed between the measured and calculated aw values. Non-protein nitrogen was tested as an alternative to ΣFAAs but yielded a lower correlation. Additionally, o-phthaldialdehyde (OPA) analysis emerged as a simple, cost-effective alternative to ΣFAAs for estimating aw values, achieving a comparable correlation coefficient (r = 0.980). The study proved that although moisture and NaCl were primary determinants of aw, ΣFAAs (or OPA reactive substances) resulting from proteolysis and lactate were also crucial for accurate aw values prediction in ripened hard/semi-hard cheeses. This study provides a robust model for aw prediction in ripened cheeses, particularly when instrumental measurements are unavailable.
