Effect of Vacuum Packaging on the Biochemical, Viscoelastic, and Sensory Properties of a Spanish Cheese during Chilled Storage.

The unique qualities of Spanish cheeses, such as the San Simón da Costa (SSC) cheese, are protected by the Protected Designation of Origin (PDO) status. The technological importance of chilled storage at 4 °C of vacuum-packaged (V) and natural (N) (unpackaged) cheeses was examined. For this purpose, the physico-chemical, biochemical, mechanical (puncture tests), viscoelastic (oscillatory and transient tests) and sensory properties of V and N cheeses were compared and analysed. During chilled storage, the caseins in V cheeses did not undergo proteolytic reactions. Low temperature maintained a low intensity of proteolytic phenomena for up to 6 months. Lipolysis was more intense in the N than in the V samples. The moisture content decreased in the N cheeses during chilled storage, and thus, the casein matrix concentration and ionic strength increased, resulting in an increase in the gel strength (S) parameter and complex modulus (G*), and the conformational stability-high stress amplitude (σmax). The low and similar values of the n' and n'' exponents (mechanical spectra) and the n parameter (transient tests) indicated the high degree of the temporal stability of the cheese network in both the N and V samples, irrespective of storage time. Likewise, the similar values of the phase angle (δ) for the N and V cheeses during storage indicate energy-stable bonds in the SSC cheese matrix. The attributes of the oral tactile phase (firmness, friability, gumminess, and microstructure perception), mechanical parameters and viscoelastic moduli enabled the discrimination of the packaged and unpackaged cheeses. Cheeses chilled and stored without packaging were awarded the highest scores for sensory attributes (preference) by trained panellists.

Influence of pH on viscoelastic properties of heat-induced gels obtained with a ß-Lactoglobulin fraction isolated from bovine milk whey hydrolysates.

A ß-Lactoglobulin fraction (r-ßLg) was isolated from whey hydrolysates produced with cardosins from Cynara cardunculus. The impact of the hydrolysis process on the r-ßLg structure and the rheological properties of heat-induced gels obtained thereafter were studied at different pH values. Differences were observed between r-ßLg and commercial ß-Lg used as control. Higher values for the fluorescence emission intensity and red shifts of the emission wavelength of r-ßLg suggested changes in its tertiary structure and more solvent-exposed tryptophan residues. Circular dichroism spectra also supported these evidences indicating that hydrolysis yielded an intermediate (non-native) ß-Lg state. The thermal history of r-ßLg through the new adopted conformation improved the microstructure of the gels at acidic pH. So, a new microstructure with better rheological characteristics (higher conformational flexibility and lower rigidity) and greater water holding ability was founded for r-ßLg gel. These results were reflected in the microstructural analysis by scanning electron microscopy.

Structural and thermo-rheological analysis of solutions and gels of a ß-lactoglobulin fraction isolated from bovine whey.

A ß-Lactoglobulin fraction (r-ßLg) was isolated from milk whey hydrolysates produced with cardosins from Cynara cardunculus. The impact of the technological process on the r-ßLg structure and how in turn this determined its heat-induced gelation was investigated. Results were analysed taking pure ß-Lg (p-ßLg) as control sample. The process induced changes in the r-ßLg native conformation causing exposure of hydrophobic groups, lower thermal stability and also, shorter thermal treatments needed to give rise to non-native and aggregated species. At pH 3.2, r-ßLg and p-ßLg solutions exhibited two gelation steps, with the advantage that r-ßLg protein may form stable gels at lower temperature than p-ßLg. At pH 7.2, a specific thermo-viscoelastic stability to 73 °C was found, which corresponded to the gel point in both protein solutions. The difference was that while for p-ßLg solution in sol state δ<45° (solid-like), however for r-ßLg solution δ>45° (fluid-like).