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United States Department of Agriculture

Agricultural Research Service

Research Project: PROTEIN PROCESSING USING HIGH-PRESSURE GASES AND SUPERCRITICAL FLUIDS Title: Improving Physical Properties of Co2-Precipitated Casein Films by Reducing Protein Particle Size

Authors
item Dangaran, Kirsten
item Cooke, Peter
item Tomasula, Peggy

Submitted to: Journal of Food Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 7, 2006
Publication Date: June 1, 2006
Citation: Dangaran, K.L., Cooke, P.H., Tomasula, P.M. 2006. Improving physical properties of co2-precipitated casein films by reducing protein particle size. Journal of Food Science. 71(4:E196-201.

Interpretive Summary: CO2-precipitated casein has unique properties compared to commercially-available types of casein. Casein is one of the major proteins in milk. Developing applications that take advantage of the properties of CO2-casein could increase the utilization of dairy proteins. Edible films and coatings made from CO2-casein are two such applications. The edible films and coatings would protect food from damage and would extend the shelf-life of a product. Protecting food from losing water and becoming dry during storage is an important function of edible films and coatings, and films made from CO2-casein are better than most films made from agricultural materials at preventing water loss. We found that the water barrier property plus the appearance and the mechanical properties of the CO2-casein could be improved if the particle size of the protein was reduced. Films became more transparent and glossier as particle size was reduced. The films were stronger and were better at preventing water loss than CO2-casein films made with a larger protein particle size. All the improvements to the CO2-casein films made by reducing particle size help increase the success of the protein as a protective and aesthetic coating for foods.

Technical Abstract: Casein precipitated with high pressure-CO2 (CO2CAS) has unique properties compared to commercial acid-precipitated casein. CO2CAS is less water-soluble and films made from it are less susceptible to high humidity environments; however, the films are also opaque and hazy. The appearance of CO2CAS films is important especially if applied as a food coating. To improve the appearance properties, the particle size of CO2CAS film plasticized with glycerol was reduced. The effect of protein particle size reduction on tensile properties, water vapor permeability (WVP) and gloss was studied using ASTM methodology. As particle size of the CO2CAS was reduced from 126 µm to 111 µm, tensile strength and modulus of the films increased while WVP decreased. With the same particle reduction, gloss increased from 55.3 gloss units on average to 73 gloss units, but films were still hazy. With a particle size less than 86 µm, CO2CAS films were glossy and transparent, however, tensile strength decreased and WVP increased. Depending on desired application, the properties of CO2CAS films can be optimized by changing particle size.

Last Modified: 4/17/2014
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