A. Marcos

Proteolysis of Cabrales cheese and other European blue vein cheese varieties

The extent and level of proteolysis were evaluated in Cabrales and five other European blue vein cheese varieties, Bleu de Bresse, Danablu, Edelpilzkase, Gorgonzola and Roquefort, by analysing their different N-containing constituents and determining the degree of casein hydrolysis. The electrophoretic patterns of the caseins in the cheeses confirmed their strong proteolysis, components featuring the lowest electrophoretic mobility offering the greatest resistance to subsequent hydrolysis. Component α s1 — I was detected in all varieties studied with the exception of Roquefort cheese.

Measurement and calculation of water activity in Blue cheese

Wateractivity ( a w ), pH, and several chemical components were determined in 20 samples of Blue cheese belonging to the varieties Bleu de Bresse, Cabrales, Danablu, Edelpilzkase, Gorgonzola and Roquefort. The a w in these cheeses could be calculated from chemical data on a water content basis (g/100 g H 2 O) by two simple equations: where SN is the soluble nitrogen. Differences between calculated and measured a w using these relationships were similar to those obtained with a more complex equation described by Ruegg & Blanc (1983).

Equations for calculation of water activity in cheese from its chemical composition: a review.

Abstract This paper reviews the relations between the chemical composition of cheese and its water activity (Aw) found by linear regression analysis, including twelve regression equations proposed for the chemical prediction of such activity in different types of cheese. Equations, both applicable to all types of cheese with Aw > 0·90 and others valid only for fresh, bacterial- and mould-ripened or processed cheeses, are reviewed.

Chemical prediction of water activity in processed cheese

By linear regression analysis, a highly significant negative correlation ( r = −0·96) was found between the mean ash concentration values (g/100 g moisture) and water activity ( a w ) of six types of processed cheeses (low-fat, semi-fat, fat, extra-fat, double fat and special). The regression equation a w = 0·9951 − 0·0032* (ash), applied to 40 cheese samples, yielded a w values which differed by a w units from those measured experimentally in 75% of the samples. The maximum differences between the calculated and experimental a w values (found in only two samples) were ±0·01 a w units.

Improved equation for cryoscopic estimation of water activity in cheese

Abstract Cryoscopes employed in dairy plants for routine quality control of milk can be used for the determination of the water activity (Aw of cheese according to the equation: A w =1·0155+0·1068. fp where fp is the freezing point in °C of an aqueous extract of cheese solutes obtained under standard conditions. This linear regression equation was obtained for 139 pairs of Aw and fp measurements. The differences between the measured and calculated Aw values in the range 1·00–0·90 were only greater than 0·02 Aw units in a small number (6·5%) of the samples with the lower Aw values. Hence this cryoscopic approach can be applied by the cheese industry as a straightforward quality control technique.

Calculation of water activity in surface mould-ripened soft cheeses from their chemical composition

Abstract The water activity (Aw) of 24 samples of 12 different brands of Brie cheese and another 12 of Camembert cheese was measured at 20°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 g moisture) and Aw (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 Aw at 20°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) Aw values were similar to those yielded by the four measurement methods used.

Determination of water activity in Brie and Camembert cheese varieties by four different methods.

Abstract The water activity (A w ) of single samples from 12 brands of Brie cheese and 12 brands of Camembert cheese was measured at 20°C by using four methods based on different principles, namely psychrometry, cryoscopy, dew-point hygrometry and isopiestic equilibration. The average A w values found (± standard deviation) for the Brie and Camembert cheese were 0·965 ± 0·005 and 0·967 ± 0·009, respectively. The mean difference between methods was less than 0·005 A w units, while the mean deviation from the average A w values was ± 0·005 A w units. The mean deviations from the average A w for the entire population of samples of the two cheese varieties were 0·000, +0·001, +0·001 and −0·003 A w units for the gravimetric (isopiestic), psychrometric, cryoscopic and hygrometric methods, respectively. The average pH values measured (± standard deviation) were 6·96 ± 0·44 and 7·01 ± 0·47 for the Brie and Camembert cheese, respectively.

Cryoscopic approach to water activity measurement of non-liquid foods : application to cheese

Abstract The initial freezing points (fp) of aqueous cheese extracts were related (r = 0·99) to the water activity (A w ) of the starting non-extracted cheeses by the equation A w = 1·0162 + 0·0981 fp. Comparisons of the cryoscopic procedure for A w evaluation in cheese with a reference method (thermocouple psychrometer) show that differences between the methods were, in the majority of cases, lower than 0·02 A w units and, consequently, the cryoscopic approach may be used in the cheese industry as a quality control technique. Cryoscopic measurements gave better estimates of A w than chemical analysis.

Estimation of water activity in mould ripened cheese from chemical composition

Abstract The water activity (aw) of mould ripened cheeses conforms to the equation aw = 1·0058 − 0·0045[ash] − 0·0107[NPN], with a square of multiple correlation coefficient, R2, = 0·90. This equation was established by multiple regression analysis of data point sets of the variables x (g ash/100 g moisture), y (g non-protein nitrogen/100 g moisture) and z (aw at 20°C) obtained from 30 individual samples of surface-mould ripened soft cheeses of three different varieties, and from 40 individual samples of internal-mould ripened blue cheeses of six varieties. Application of this equation to 30 individual samples of soft cheeses yielded calculated aw values within ± 0·005 and ± 0·010 aw units of the experimental water activities of 73% and 97% of the samples, respectively, while its application to the 40 individual samples of blue cheeses yielded water activities within ± 0·01 and ± 0·02 aw units of their experimental counterparts in 73% and 98% of the samples, respectively.

Comparison of methods for determination of high water activities. Application to dairy products and juices.

Water activity was determined in various dairy products (ice creams, yoghourts and flavoured milks) and several juices by three different methods: psychrometric, cryoscopic and gravimetric. The differences between the AW values provided by the three methods were also calculated. Such differences were always smaller than 0·005 Aw units, which allows the use of a straightforward method (gravimetric) together with two instrumental methods (psychrometric and cryoscopic) for the determination of high Aw values (in the range 0·999–0·900) in the aforesaid types of products.