Food Structure


Mixed dairy gels (including a control without fat) of skim milk powder (SMP) and whey protein isolate (WPI) containing fat globules were formed by heating protein emulsions to 90°( and by acid release from glucono- 0-lactone to provide a pH of 4.3-4.4 . Fat globules with artificial protein membranes (FGAPM) were prepared by homogenization of a butter oil /water mixture in the presence of WPI while fat globules without membranes were stabili zed with polyoxyethylene sorbitan monolaurate (Tween 20). Both emulsions were added at a 4% (w/w) leve l to solutions having 3% SMP and 8.3% WPI. The gel contai ning FGAPM had significantly higher compressive streng th than the control without fat (2.4 versus 1.8 kPa , respectively) and microst ru ctural ly it was a mixed gel in which the FGAPM, casein and whey protein aggregates formed a copolymer network. Addition of fat globules without membranes led to a filled gel weaker th an the control without fat (1.4 versus 1.8 kPa, respectivel y). Bonding of the protein membrane in FGAPM to the gel network and presence of in dividually di spersed fat globules without membranes was demonstrated by trans mission electron microscopy. The difference in microstructure is proposed to be responsible for the mechanical properties of each gel.

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