Adding Citrate to Ice Cream Mix for Enhanced Protein Functionality
High-pressure processing has been shown to greatly improve the structure and texture of ice cream by modifying casein micelles, the net effect of which is to enhance protein functionality through increased air adsorption and enhanced protein-protein interactions in the aqueous phase. The addition of citrate to milk also modifies casein micelles, enhancing soluble casein levels through the chelation of calcium from within the micelle. This has been shown to enhance foamability in skim milk. It has been documented that citrate will decrease fat partial coalescence in ice cream mix, through enhanced soluble protein adsorption to the fat globule. Given these established relationships, the effect of citrate addition to ice cream mix was re-examined to determine if advantage could be gained from enhanced soluble proteins at air interfaces or within the serum phase, to either provide enhanced structure and air bubble stability and/or enhanced mouthfeel and texture.
In this study, citrate triphosphate/citric acid was added to a typical ice cream mix at 0.1M/kg milk solids-not-fat (SNF) or 0.2M/kg SNF, balanced to keep the pH at 6.8, in the presence of either 0.15% saturated or unsaturated monoglyceride. Ice cream mix was batch pasteurized and batch frozen. Analyses included fat droplet size, soluble protein and protein adsorption to fat droplets in the mix; and structural collapse during melting, fat destabilization and structural analyses by transmission electron microscopy in the ice cream. Results indicated that serum proteins were enhanced in the mix due to citrate addition. However structural collapse during melting was enhanced by citrate in the presence of either surfactant, due to reduced fat partial coalescence. Adsorbed protein levels to the fat droplet were reduced by the addition of citrate, but TEM analyses indicated that the proteins were more homogeneously distributed around the fat droplets in the mix and emulsifiers were less able to displace these proteins than they were native casein micelles. Thus the soluble caseins over-stabilized the emulsion by creating a more continuous thin layer around the fat globules, which prevented the formation of a partially coalesced fat globule network necessary for air stabilization in ice cream. Consequently, while the citrate did successfully modify the casein micelles by increasing soluble casein, it did not result in enhanced foamability or protein structure in the aqueous phase.
Keywords: casein, citrate