Properties and structure of coconut milk emulsions

Coconut milk is the natural oil-in-water emulsion extracted from the endosperm of mature coconut (Cocos nucifera L.) endosperm. The emulsion is stabilized by coconut proteins, but it poorly stable due to the insufficient quantity and quality of the proteins present. In order to improve the stability and quality of coconut milk products, various processes and food additives are normally used. However, the underlying emulsion science is still unclear.;The first objective was to investigate the effects of homogenization and heat treatment. Fresh milk had large but non-flocculated via a bridging mechanism. Homogenization reduced the droplets size, but increased the degree of flocculation, via a bridging mechanism. Extensive flocculation and slight coalescence was observed in coconut milk after treatment at temperatures above the denaturation temperature of coconut proteins. Flocculation was responsible for increased viscosity and retarded creaming.;The second objective was to determine the influence of pH, and ionic strength. Coconut milk flocculated when the pH was to close to the isoelectric point of coconut proteins as the electrostatic repulsion between droplets is reduced due to the loss in surface charge. The addition of NaCl induced flocculation only when the surface charge of the emulsion droplets was insufficient to prevent aggregation due to the screening effect.;The third objective was to understand the changes in bulk quality and surface properties of coconut milk emulsions due to the addition of model surface-active stabilizers [sodium caseinate, whey protein isolate (WPI), sodium dodecyl sulfate (SDS), or polyoxyethylene sorbitan monolaurate (Tween 20)]. When added after the homogenization, small-molecule surfactants broke up the flocs while protein stabilizers did not. The addition of any surface-active stabilizer before homogenization increased the efficacy of homogenization step and produced stable submicron sized emulsion droplets. The improved stability in all cases resulted from the displacement of interfacial coconut proteins by the added stabilizers.;The final objective of this work was to determine the effect of various thermal treatments on the stability of the stable emulsions prepared with surface-active stabilizers. Coconut milk homogenized with proteins were stable to the freeze-thaw cycles while those prepared with small-molecule surfactants were not. The caseinate and SDS emulsions were able to withstand the heat treatments whereas WPI and Tween 20 samples extensively coalesced following autoclave treatment.