15C-7 |
Microstructure of high hydrostatic pressure yogurt |
F. M. HARTE, Biological Systems Engineering Department, Washington State University, Grimes St. - Smith Hall, Pullman, WA 99164-6120, B. G. Swanson, Department of Food Science and Human Nutrition, Washington State University, Pullman, WA 99164-6376, and G. V. Barbosa-Cánovas, Biological Systems Engineering Department, Washigton State University, Grimes St. - Smith Hall, Pullman, WA 99164-6120.
Due to syneresis and lack of adequate texture, thickeners and stabilizers are added during the manufacture of yogurt. High hydrostatic pressure (HHP) is a promising technology for the manufacture of additive-free yogurt. Although yogurt made from HHP treated whole milk showed similar rheological properties and water holding capacity to that made from thermally processed milk, how HHP processing affects the casein micelle structure and casein- The objective was to study microstructural changes and b- Lactoglobulin retention patterns in yogurt made from thermally and HHP treated whole milk, using immunolocalization transmission electron microscopy (TEM). Fortified (1% (w/w) WPC, 5.7% low heat skim milk powder) raw milk was subjected to the following treatments: control (no treatment), thermal processing (85oC, 35 min), and combinations of HHP (193; 676 MPa) and holding time (5; 30 min). After treatments, set yogurt was made using traditional methods. Yogurt was subjected to immunolocalization for b- Lactoglobulin, and observed under TEM. Round, individual casein micelles (~200 nm radius) were observed in yogurt obtained from thermally treated milk. Yogurt processed at low pressure and low holding time (193 MPa, 5 min) showed bigger round casein micelles (~250 – 400 nm radius), forming compact aggregates that were similar to those from the control yogurt. Yogurt from 193 MPa and 30 min exhibited round micelles of intermediate size (~200 – 300 nm). Smaller (~100 – 150 nm) and oval-shaped casein micelles were observed in yogurt from 676 MPa HHP treated milks. Increased b- Lactoglobulin retention was observed in yogurt made from 676 MPa treated milk when compared to 193 MPa and control. Although further research is needed, the use of thermal treatment to achieve extensive b- Lactoglobulin denaturation and short HHP processing to promote disruption of individual casein micelles is a promising option in the development of yogurt having a thinner gel matrix and thus increased water holding capacity.
Session 15C, Dairy Foods
|