CALCULATION OF WATER ACTIVITY IN SURFACE MOLD-RIPENED SOFT CHEESES FROM THEIR CHEMICAL-COMPOSITION

The water activity (A(w)) of 24 samples of 12 different brands of Brie cheese and another 12 of Camembert cheese was measured at 20-degrees-C by four methods (psychrometric, cryoscopic, dew-point hygrometric and isopiestic equilibration). The cheeses were also analysed chemically for their moisture, salt (NaCl), ash and non-protein nitrogen (NPN) contents. A linear regression analysis of data pairs of the variables [NaCl], [Ash] or [NPN] (in g/100 moisture) and A(w) (average values of the four methods) yielded the following relations A(w) = 0.9813 - 0.0045 [NaCl] A(w) = 0.9769 - 0.0019 [Ash] A(w) = 0.9793 - 0.0101 [NPN] On the other hand, a multiple linear regression analysis of sets of g ash/100 g moisture, g NPN/100 g moisture and average A(w) at 20-degrees-C led to the equation A(w) = 0.996 - 0.0029 [Ash] - 0.0106 [NPN] All four equations can be used alone or in conjunction to predict the water activity of surface mould-ripened soft cheeses. The differences between the calculated and measured (average) A(w) values were similar to those yielded by the four measurement methods used.