Application of High Pressure Homogenization and Ultrafiltration for the Manufacture of Skim Milk Acid Gels and Isolation of Casein

The dairy industry has experienced an important growth around the world in the last decades. Along with this growth, advances in scientific research and technology have opened the possibility for new applications of dairy products. These topics are discussed in Chapter I as a literature review and introduction.

Emerging non-thermal technologies can offer many advantages when compared to thermal technologies. High Pressure Homogenization (HPH) is an emerging technology applied in the study of dairy science. Chapter II of this thesis describes the study of HPH (0-350 MPa) in combination with thermal processing (90°C, 5 min) to improve the rheological properties and stability of low fat model yogurts. In samples obtained from combined treatments (HPH and thermal treatment, regardless the order) a reduction in gelation times (~28 min) was observed compared with just HPH treated samples (~48 min); also G’ values were higher and pressure dependant (~250 and ~320 Pa in samples from combined treatments with HPH from 100 to 350 MPa, respectively) compared with samples just HPH-treated (~18 Pa). Whey holding capacity was higher in samples obtained from HPH milk at 350 MPa compared to all other treatments. The results showed the potential benefits of this technology, which could lead to a reduction in the need of stabilizers and additives. Future studies are needed to completely elucidate the specific mechanisms and kinetics responsible for those improvements. The individual components in milk offer unique functional properties of interest for food and non-food applications; one of the most important is the casein protein fraction. However, casein isolation as a native and pure ingredient is not an easy task. A method for isolation of casein micelles from whey proteins, using ultrafiltration (0.22 μm) in a continuous system with three different salts (calcium chloride, sodium phosphate, and potassium citrate) and concentrations (0 to 100 mM), is presented in Chapter III of this thesis. Our goal was achieved by altering the balance in the mineral fraction of milk with sodium phosphate (50 mM) during ultrafiltration. However, further studies are required to improve the technique and study the functionality of the isolated caseins.