Physical properties of emulsion stabilized by kappa casein before and after treatment with chymosin
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In order to determine the effect of lipid concentration on the properties of k-casein stabilized emulsions, butteroil was added to solutions that contained 0.3% k-casein to achieve milk fat concentrations of 3, 10, and 20%. These mixtures were adjusted to pH 6.5 and heated to 65?C. They were then homogenized at 20 and 100 MPa and particle size was measured; viscosity and yield stress were measured before and 30 minutes after the addition of chymosin. These experiments were repeated twice. Homogenization of the emulsions at 100 MPa produced smaller particles than homogenization at 20 MPa. Emulsions with 20% milk fat showed the largest particle size. Before treated with chymosin, these emulsions had the greatest viscosity and yield stress, however the differences with the other lipid concentrations were greater after chymosin treatment. A gel with yield stress less than 10 Pa occurred in emulsions with 3 or 10% milk fat. The emulsion with 20% milk fat after chymosin treatment provided the best possibility for the formation of a gel because it had the highest viscosity and yield stress. The effect of protein concentration on the properties of the emulsions was determined in emulsions that contained 20% milk fat and 0.5, 0.7, and 1.0%. These emulsions were prepared as previously described. Emulsions homogenized at 100 MPa had smaller particles than emulsions homogenized at 20 MPa. An increase in protein concentration caused the particle size to decrease. Emulsions homogenized at 100 MPa were more stable than emulsions homogenized at 20 MPa and the emulsion with 1.0% k-casein was the most stable emulsion. The protein load of k-casein stabilized emulsions ranged from 3 to 6 mg/m2. The viscosity and yield stress prior to chymosin treatment showed no properties of gelation. After treated with chymosin, these emulsions produced a weak gel with yield stress values that ranged from 14 to 16 Pa.