Effects of processing conditions on the texture and rheological properties of model acid gels and cream cheese.

Manufacture of cream cheese involves the formation of an initial acid-induced gel made from high-fat milk, followed by a series of processing steps including shearing, heating, and dewatering that complete the conversion of the acid gel into a complex cheese product. We investigated 2 critical parameters for their effect on the initial gel: homogenization pressure (HP) of the high-fat cheese milk, and fermentation temperature (FT). The impact of a low (10 MPa) and high (25 MPa) HP, and low (20°C) and high (26°C) FT were investigated for their effects on rheological and textural properties of acid-induced gels. Intact acid gels were sheared and heated to 80°C, and then their rheological properties were analyzed to help understand the effect of shearing/heating processes on the gel characteristics. The effect of HP on fat globule size distribution and the amount of protein not involved in emulsion droplets (i.e., in the bulk phase) were also studied. For cream cheese trials, a central composite experimental design was used to explore the effect of these 2 parameters (HP and FT) on the texture, rheology, and sensory properties of experimentally manufactured cream cheese. Storage modulus (G') and hardness values of cream cheeses were obtained from small amplitude oscillatory rheology tests and texture profile analysis, respectively. Quantitative spectrum descriptive sensory analysis was also performed. Consistency of acid gels (measured using a penetration test) increased with an increase in FT and with an increase in HP. Although stiffer acid-induced gels were formed at high FT, after the heating and shearing processes the apparent viscosity of the samples formed at high FT was lower than those formed at low FT. For the cream cheeses, significant prediction models were obtained for several rheological and textural attributes. The G' values at 8°C, instrumental hardness, and sensory firmness attributes were significantly correlated (r > 0.84); all these attributes significantly decreased with an increase in FT, and HP was not a significant parameter in the prediction models developed for these attributes. Significant interactions were observed between the HP and FT terms for these prediction models. Higher HP increased the amount of protein adsorbed at interface of fat globules but decreased bulk phase protein content (which may be important for crosslinking this gelled emulsion system). At higher FT temperature, coarser gel networks were likely formed. The combined effect of a coarser acid gel network at high FT, and less bulk phase casein available for crosslinking the acidified emulsion gel with an increase in HP, could have contributed to the lower stiffness/firmness observed in cream cheese made under conditions of both high FT and high HP. Stickiness of cream cheese greatly increased under conditions of high FT and high HP, whereas the sensory attributes cohesiveness of mass and difficulty to dissolve decreased. This study helped to better understand the complex relationships between the initial acid-induced gel phase and properties of the (final) cream cheese.