The effects of fat content and the supplementation of milk with Sodium Caseinates (SCN) and Whey Proteins Concentrates (WPC) on the rheological and sensory properties of stirred yogurt made from buffalo milk were investigated. Whether the heat treatment of the milk affected the rheological behavior and the sensory characteristics of the samples was also evaluated. Principal Component Analysis (PCA) was used to assess in detail the relative contribution of whey proteins, caseins and fat on the rheological properties and sensory characteristics of the samples. Furthermore, it related the instrumental and objective sensory data to consumer perception (hedonic response of non-trained panelists). The objective acidity and white color intensity were positively correlated and increased with increasing casein content. Fat interacted synergistically with caseins to increase all the hedonic attributes, apart from odor. As far as rheological properties are concerned, elastic modulus (G'), instantaneous elasticity (G g ), retarded elasticity (G R ) and Newtonian viscosity (η 0 ) were positively correlated with increasing casein content. However, tan δ was negatively correlated with the aforesaid attributes and increased with increasing fat content. Whey proteins in the presence of fat determined the magnitude of flow behavior index (n). The lactic acid concentration (%) and the b component of color (yellow color intensity) were affected positively by SCN and WPC addition but in the absence of fat. In all regression equations the effect of process temperature was found to be insignificant. Finally, the consumer-optimized composition of the fat and the added SCN can be used to formulate a marketable product.

In the present study the physicochemical (acidity, color measurements), rheological (viscosity measurements and viscoelastic properties) and sensory (objective and hedonic) properties of stirred yogurt made from buffalo milk were evaluated. Yogurt samples with two fat globule sizes (large: 2.9 μm; small: 0.87 μm) were prepared with or without the addition of Whey Protein Concentrates (WPC) or Sodium Caseinates (SCN), and stored at 4 C for testing at day 1 and 7 after preparation. SCN addition resulted in increased lactic acid concentration, rheological properties (except loss tangent -tan δ), white color intensity and sensory viscosity. The effect of WPC on the aforesaid properties was lower when compared to SCN. Small fat globule size also increased the rheological properties apart from tan δ, brightness and sensory viscosity of yogurt samples. Increasing storage time resulted in reduced viscosity, increased acidity and rheological properties apart from tan δ and apparent viscosity. The greater decline rates were obvious for Newtonian viscosity at zero shear rate (η 0 ) and instantaneous elasticity (G g ) in yogurts with added SCN and WPC and large globule size and lower or negligible in samples without additives. In contrast, tan δ increased at a lower rate when SCN were added in products with large fat globules. Storage time increased the value of flow behavior index (n) in yogurts with large fat globules and, more rapidly, the value of elastic modulus (G') in the presence of SCN and WPC. The small globule size in the absence of additives produced the lowest response of b and, when WPC was present, the lowest white color intensity. The sensory viscosity reduced the most during storage in yogurt samples with no protein addition.