Optimization of emulsification and microencapsulation of evening primrose oil and its oxidative stability during storage by response surface methodology

Microencapsulation is a technique by which small droplets of liquid or solid particles are coated with a thin film of wall materials to protect susceptible ingredients in food products to assure their quality or effectiveness. Microencapsulation of liquid lipid into powdery matrixes of wall materials includes two unit operations: emulsification of the lipid with an aqueous solution of wall material and drying of the emulsion. The effects of hydrophile-lipophile balance (HLB) value, emulsifier content and oil content on the evening primrose oil-in-water emulsion stability were studied by response surface methodology (RSM). The HLB value, emulsifier content and oil content all had significant effects on the emulsion stability (P < 0.05). Of them, the HLB value and emulsifier content contributed more effects than the oil content. The optimized HLB value, emulsifier content and oil content were used to mix with wall materials: gum arabic (GA), maltodextrin (MD) and/or sodium caseinate (NaC). The oil was encapsulated with these materials individually or in combination by spray-drying, and their oxidative stability during storage was compared. The microcapsules with a single wall material were relatively susceptible to oxidation than those with multiple wall materials. The most desirable composition of the mixture of GA, MD and NaC by RSM was 17.2, 75 and 7.8%, respectively. Practical Applications: Response surface methodology (RSM) provided a valuable means to help us understand the relative or interactive effects of three important parameters: HLB value, emulsifier content and oil content on the emulsion stability of the oil-in-water (o/w) system. The information obtained would be useful for the preparation of similar o/w emulsion system as needed in some product development for foods. In addition, the effects of gum arabic, maltodextrin and sodium caseinate on the oxidative stability of microencapsulated oil were also studied by RSM. The results revealed the relative or interactive effects of these materials and gave the optimal conditions in minimizing the oxidative instability in this study. Since these wall materials are readily available and widely used in a variety of products, the information provided by this study would be useful for product-developing professionals to use these materials more efficiently in terms of obtaining optimal microencapsulated products against lipid oxidation and cost effectiveness.