| Dairy creams with 50 and 55% milk fat were prepared by adding whey protein concentrate (WPC) at the levels of 0, 1, 2, and 3% (w/w) or at 2% (w/w) and homogenizing at 0, 3.4, 6.8, and 10.2 MPa. All creams were UHT processed at 142°C for 2 sec. These higher fat content (HFC) creams, stored at 25°C for 64 days, were evaluated for stability by determining fat separation, rheological properties, fat globule distribution, fat globule membrane integrity, and acid degree values (ADV). Added WPC reduced fat separation. The milk fat globules (MFG) were small and well dispersed initially but as time progressed, they coalesced and resulted in fewer globules. Apparent viscosities, storage modulii (G'), and loss modulii (G″) were independent of the fat content. Fat separation, apparent viscosities, G ', and G″ increased over time. More whey proteins (alpha-La and beta-Lg) were detected in the milk fat globule membranes (MFGM) than the casein fractions, and creams with higher amounts of added WPC had more whey proteins in the MFGM. The MFGM disintegrated over time. Homogenization reduced fat separation. Homogenized HFC creams had lower apparent viscosities but higher G' and G″ . Fat separation and apparent viscosities increased over time. Higher homogenization pressures resulted in more whey protein adsorption on the MFGM. Larger MFG were observed in non-homogenized HFC creams. The 55% HFC creams showed higher degree of coalescence than did 50% HFC creams. Non-homogenized HFC creams had MFG with discontinuous MFGM and with few protein aggregates (PA). Creams homogenized at 6.8 and 10.2 MPa had smaller, well-dispersed globules that had well-defined MFGM and had large masses of PA in the inter-globular spaces. 50% HFC creams had lower ADV than did 55% HFC creams and addition of WPC did not influence ADV. Homogenized 50% HFC creams had lower ADV than non-homogenized 50% HFC creams. Shelf stable, higher fat, liquid dairy creams (up to 55% milk fat) could be prepared by the addition of 2 or 3% of WPC and homogenizing at 6.8 or 10.2 MPa but the stability of such HFC creams is time dependent. |
