Developing Milk Protein Based Structure for New Dairy Products.

摘要

Cheddar cheese has a desirable texture that is described as moderately firm and springy, which forms a cohesive mass of smooth particles during mastication and also has a slow instrumental breakdown pattern. Sensory texture is perceived during oral processing and is related to the physical properties and structure of the food material. In general, properties such as fracture stress and strain are related to sensory firmness and deformability respectively. Percent recoverable energy, Young's Modulus and water holding are related to springiness, stiffness and moisture release respectively. Breakdown patterns are related to crumbliness. The overall goal of this thesis was to develop a high protein, nofat, soft-solid model gel that has a Cheddar cheese-like texture. The research investigated texture development of model dairy protein gels by monitoring 1) changes in whey protein gel material and sensory properties caused by partial replacement of whey protein with casein micelles or dispersed casein, 2) the influence of embedded crystalline particles on breakdown properties of casein-whey protein gels, and 3) the influence of proteinphospholipid particles, a neutracuetical ingredient, on whey protein gel material properties. Secondarily, relationships among microstructure and material or sensory properties were investigated.;In the first phase, known casein-whey protein interactions were used to alter the material properties of whey protein gels and yield a range of soft-solid sensory textures by combining casein micelles or dispersed caseins with whey proteins in heat set gels. Replacing whey protein with casein drastically reduced fracture stress but minimally altered recoverable energy. Water holding capacity was decreased by casein addition. Breakdown patterns were shifted from brittle-like to ductile-like for dispersed casein at pH 5.5 or micellar casein at pH 6. Additionally, sensory evaluation showed that whey protein-casein gels broke down more rapidly into a more cohesive mass during mastication than did the whey protein gels without casein. Overall, it was demonstrated that material and sensory properties of whey protein gels can be altered to a more Cheddar cheese-like texture using caseins as a texture modifier while maintaining a high total protein concentration. Shifts in microstructure observed by confocal microscopy could not explain the changes in mechanical or sensory textures.;In the second phase, crystalline particles of starburst-like morphology were embedded in whey protein-dispersed casein gels. The dispersed casein solution was prepared by addition of citrate chelator in a 0.7:1 or 1:1 molar ratio of chelator to calcium in milk protein concentrate solution. Crystalline particles minimally influenced the breakdown pattern, but increased fracture stress and reduced fracture strain. Breakdown patterns were influenced however by chelator to calcium ratio. Breakdown patterns for gels with 0.7:1 chelator to calcium ratio were slow where as those with 1:1 ratios were fast. Overall, the results demonstrate the feasibility of shifting the breakdown pattern of whey protein-dispersed casein gels to one more similar to Cheddar cheese by altering the molar ratio of chelator to calcium in the dispersed casein solution.;Finally, in the third phase, the influence of protein-phospholipid particles on whey protein gel properties and their status as an active or inactive filler particle were investigated. Composite gels showed typical response for an active filler by increasing the gel strength with increasing particle phase volume. However, relative to whey protein gels of equivalent protein concentration, composite gels had reduced gel stiffness (Young's Modulus), strength (fracture stress), deformability (fracture strain), and broke into numerous pieces upon fracture. These results suggest that this particle may be used to alter gel properties by increasing fracturability but would this would be at the cost of reducing gel firmness and deformability relative to gels of equivalent protein concentration.