Emulsions were prepared with 5% (w/v) solutions of sodium caseinate (Na Cas) and soy oil at oil/protein ratios of 0.25-3.0 by homogenization at 10--50 MPa. Emulsions were spray-dried to yield powders with 20--75% oil (w/w). Emulsion oil droplet size and interfacial protein load were determined. Microencapsulation efficiency (ME), redispersion properties, and structure of the powders were analyzed. The size of emulsion oil droplets decreased with increasing homogenization pressure but was not influenced by oil/protein ratio. Emulsion protein load values were highest at low oil/protein ratios. ME of the dried emulsions was not affected by homogenization pressure but decreased from 89.2 to 18.8% when the oil/protein ratio was increased from 0.25 to 3.0, respectively. Mean particle sizes of reconstituted dried emulsions were greater than those of the original emulsions, particularly at high oil/protein ratios (>1.0), suggesting destabilization of high-oil emulsions during the spray-drying process.
Emulsions of gum arabic solutions (10% w/w) and soya oil at oil/gum ratios of 0.25−5.0 were prepared
by homogenization at 20 MPa. The resulting emulsions were subsequently spray-dried to produce
powders with oil contents ranging from 20 to 82% (w/w). Lipid globule size distributions and
viscosities of the emulsions were determined, and particle size and percentage of extractable oil
were determined for the spray-dried powders. The ability of the powders to redisperse in water
was also examined. The average lipid globule size (D
4,3) (0.57 μm) did not vary significantly (P >
0.05) as the oil/gum ratio was increased from 0.25 and 1.0, but it did increase at higher ratios to a
maximum of 2.02 μm. The average particle size of the spray-dried emulsions was within the range
9−17 μm, and the microencapsulation efficiency decreased from 100 to 48% when the oil/gum ratio
was increased from 0.25 to 5.0, respectively. Powders with an oil content <50% dispersed readily
in water.
Keywords: Gum arabic; emulsions; microencapsulation; lipid globule size distribution
Effects of glycerol, xylitol, and sorbitol on selected physical properties of whey protein isolate (WPI) films were examined. Increasing glycerol or sorbitol content led to increases in moisture content, water vapor permeability, and % elongation; and decreases in tensile strength, elastic modulus, and glass transition temperatures of the films. Increasing levels of xylitol had no effect on permeability, moisture content, or glass transition temperature of the films, but decreased % elongation, tensile strength, and elastic modulus. Moisture content of the films correlated well with glass transition temperatures. Differences in measured physical properties of films with plasticizer type and concentration may be attributed to differences in the hygroscopic and crystalline properties of the plasticizers.
Transglutaminase (TGase) is an enzyme that cross-links many proteins, including milk proteins. In this study, the effects of TGase on some physico-chemical properties of milk were studied. TGase-treated milk was not coagulable by rennet, which was due to failure of the primary (enzymic) stage of rennet action rather than the non-enzymic secondary phase. Dissociation of TGase-treated casein micelles by urea or sodium citrate or removal of colloidal calcium phosphate by acidification and dialysis was reduced, presumably due to the formation of cross-links between the caseins. Casein micelles in TGase-treated milks were also resistant to high pressure treatment and to hydrolysis by plasmin. Results of the present study show that milk proteins are fundamentally modified by the action of TGase, which may have applications in the manufacture of functional proteins for use as novel food ingredients.
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