The Effect of Manipulating Fat Globule Size on the Stability and Rheological Properties of Dairy Creams

Abstract

Recombined cream (RC, 23 % fat w/w) and standardised commercial cream (CC, 28 % fat w/w) were studied to understand the effects of manipulating fat globule size at the micron-/nano-scale on the stability and rheological properties of cream. All samples were adjusted to a fat: protein ratio of 5:1 and a fat: emulsifier (Tween 80) ratio of 30:1 to stabilize emulsion. For both CC and RC, different emulsions with droplet sizes covering micron- (3.9 μm), sub-micron (0.5 – 0.6 μm) and nano-metric scales (0.13 – 0.29 μm) were obtained using either the homogeniser (7/3 MPa) or the microfluidiser (85 MPa and 42 MPa). Fat globules from both RC and CC had high zeta potential values (-28 to -43 mV) and maintained their reduced size after 1 month of storage at 4 °C, providing evidence of emulsion stability. Droplet size had a significant effect on rheological characteristics of all creams produced. Nano-sized RC tended to have a rigid structure (solid/gel-like form) as compared to micron-sized RC (liquid-like form) as reflected by higher phase angle. Surprisingly, the rheological properties of CC exhibited an opposite tendency to that of RC. This implies that the observed rheological properties of CC and RC could not be fully explained by the discrepancy in droplet size. Differences in interfacial properties between RC and CC might also play a role in the rheological behaviour of the creams. Results indicated the stable high milk fat emulsions could be successfully created by reducing the globule size. These findings would be useful in understanding how micron-/nano-sized emulsions can be utilised in further application or processing of creams.