Effect of milk fat globule membranes on emulsion stability of recombined sterilized milk

Abstract

Recombined oil-in-water emulsions containing 3% protein and 3% milk fat were prepared from low-heat nonfat dry milk, whey protein concentrate and anhydrous milk fat. The effect of casein to whey protein ratios of 80:20, 60:40, 40:60 and 0:100, emulsifiers, homogenization pressure, and sterilization on the stability of the emulsion was investigated. Increasing the concentration of whey proteins increases the stability of the emulsion because of the ability of whey proteins to unfold and react with other proteins, probably due to intradroplets interactions increasing the viscoelasticity of the interfacial membrane. However, emulsions stabilized with 100% whey proteins had heat aggregation unless emulsifiers were added in the emulsion. Incorporation of emulsifiers into the formulations significantly increased the emulsion stability. Monoglycerides were more effective for decreasing the volume-surface average diameter and increasing surface area of the particles, but the emulsion stability was lower with this emulsifier compared to lecithin and the mixture of emulsifiers. Monoglycerides promote coalescence or flocculation of the fat globules, but emulsion stability was greatest in emulsions that contained monoglycerides compared to the control. Lecithin did not cause the dvs or surface area of the particles to change compared to the control, and had better stability than monoglycerides. This might be because lecithin did not displace as much protein from the oil-water interface at the particle surface as monoglycerides, and the zwitteronic nature of the lecithin might have affected the results. The mixture of emulsifiers had a synergistic effect on the stability of the emulsions. The emulsions prepared with the mixture were more stable than emulsions prepared with only the monoglycerides or lecithin. This synergistic effect might be explained by the better emulsifying properties of monoglycerides and the protective effect of lecithin on the interfacial membrane. Homogenization at 90MPa compared to homogenization at 20MPa caused the stability of the emulsions to increase. The most stable sterilized emulsions were those that had casein to whey protein ratios of 60:40, 40:60 or 0:100, were homogenized at 90MPa, and contained lecithin or mixture of emulsifiers.