| Summary: | The quest for designing a stable encapsulation system for natural bioactive in food products has never stopped. The development and innovation of analytical instruments allows for new factors influencing the system design to be explored. It is believed that the partitioning of bioactive within an emulsion affects the stability of the system, and so understanding it may inform the development of stable formulations as carriers for health promoting bioactives.
This research is focussed on analysing the partitioning characteristics of a bioactive carried in emulsion systems, using a powerful but as yet relatively unexplored technique in food-related studies; in-situ confocal Raman microspectroscopy (CRM). Stable food-grade palm oil-in¬water (O/W) emulsions were engineered for the encapsulation of natural ~-carotene, using whey protein isolate (WPI) as the emulsifier and carrier. High-pressure emulsification was employed for processing and improving the physical stability of the emulsions. This was followed by in-situ spectroscopic measurement of changes in the system upon variations in its formulation, storage condition and treatment procedure.
The Raman technique was first validated against a conventional method involving solvent extraction of p-carotene and quantification by visible absorption spectrophotometry. It is shown that CRM enables in situ quantification of the ~arotene content of oil droplets within emulsion systems. The Raman image obtained shows that the bioactive molecules were dispersed into both the oil and aqueous phases of the emulsions, but at a much higher concentration in the former.
Next, it was found that increasing the p-carotene concentration (from 0.1 to 0.3 g/kg emulsion) at a fixed gross composition of an emulsion (10% palm 0Iein:2% WPl) reduced the concentration of ~-carotene in the oil droplet, whereas increasing the WPf concentration (2- 20 g/kg emulsion) had the opposite effect. A storage study was then conducted using these variables to determine the stability and partitioning characteristics of ~-carotene throughout 30 d storage at 20 and 40°C. It was found that a higher composition of J3-carotene was in the aqueous phase at the end of the storage period, suggesting that ~-carotene oxidation occurred faster in the oil phase and that p-carotene was more protected against oxidation by WPJ in the aqueous phase.
Additionally, using only CRM, it has been shown that the use of small molecule Tween 40, as compared to that of the dairy protein (WPI) as the emulsifier, resulted in lesser partitioning of the bioactive molecules into the aqueous phase of emulsions. In contrast, the partitioning of f}-carotene into the aqueous phase increased with the rise in the solid fat content of the lipid phase of the emulsions, achieved by manipulating the ratio between the liquid palm olein and its solid fraction; palm stearin.
Moreover, the variation in partitioning of j3-carotene molecules between the phases of emulsions was examined following the use of pre-treated (heat and pressure) WPI as an emulsifier. Generally the partitioning of j3-carotene into the aqueous phase of emulsions increased when the protein emulsifier was heat- or high pressure-treated prior to emulsion formation. However, increasing the concentration of high pressure-treated WPI reduced the j3-carotene partitioning into the aqueous phase.
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