Compositional Phase Diagram, Rheological and Structural Properties of Systems Containing UHT Skim Milk, Sunflower Oil, Saturated Monoglycerides and Co-Surfactants

The phase behavior of UHT skim milk, sunflower oil, saturated monoglyceride and co-surfactants mixtures was studied by determining the state compositional diagram of systems having different ratio among ingredients. Synchrotron XRD analysis, polarized light microscopy and rheological analysis were used to study the monoglyceride structure organization. To better understand the influence of UHT skim milk constituents on monoglyceride structuring behavior simulated milk ultrafiltrate solutions (SMUF), added or not with whey proteins and caseins, were considered as water phase. The capacity to incorporate water was highly affected by the water phase compositions and availability of negative charges allowing the swelling of bilayers. The complex interplay among proteins and salts dispersed in the medium led to the formation of stable liquid emulsions when the co-surfactants/monoglyceride mixture (CO-MG) and oil contents were below 3.5 and 45% (w/w), respectively. On the contrary, gels were obtained below 65% (w/w) of oil and CO-MG content higher than 1% (w/w). These systems were structured by the formation of a network among monoglyceride crystalline lamellas. The relative ratio among ingredients affected the rheological properties of the systems: as the oil and/or CO-MG content increased, the gel strength also increased, in concomitance with mean droplet diameters.