Microencapsulation of Phytosterols by Spray Drying

Abstract

Phytosterols (PS) are vegetable sterols with a similar structure to cholesterol. Although PS are poorly absorbed into the blood stream, they are widely recognized as lowering absorption of cholesterol and their serum levels. It has been found that PS exert their hypocholesterolemic effect if they are dispersed. Indeed, the PS must be administered finely divided in order to facilitate their exposure to the bile salts, preferably in particles smaller than 25 μm to reduce the sandy mouth feel and favor their incorporation into the micellar phase in the intestine. Several authors focused on particle-size reduction to improve the PS dispersibility by several techniques. However, all of them are complex and time- and energy consuming because they require more than one step (homogenization or milling, including cooling or heating) to obtain the desired particle size. Furthermore, for solid PS, several abrasive effects of the homogenizer valves or parts of the milling equipment have been found. PS and their derivatives (stanols, esters, and stanol esters) have been included in fat- or oil-based food products, which are clearly restricted in diets for hypercholesterolemia. Therefore, the incorporation of PS in aqueous-based formulations (like beverages, soups, and others) is an attractive field of application. The hydrophobic and water-insoluble nature of PS, which make them poor candidates for stable dispersions, hinder their applicability on intermediate or final aqueous-based products. In this context, the microencapsulation by spray drying appears as a good choice to provide a physical barrier between the PS and the aqueous medium. In this chapter, the microencapsulation of PS by spray drying was studied to obtain particles (microcapsules) with small sizes (lower than 25 μm) in order to keep the suspension stable. The feed suspensions to be spray dried were analyzed in details (e.g., composition, treatment conditions, rheological behavior, and interfacial properties). The influence of these factors on the microcapsule structure and on the particle size of PS in suspension was particularly investigated. The main operating variables were also rationally studied in order to identify the optimum set in terms of low particles size and high process yield, encapsulation efficiency, and PS retention in the powder of microcapsules. Several parameters involved in the microcapsules formation were affected by the spray-drying conditions. Finally, the microcapsules of PS were incorporated in aqueous matrices and the stability of the product suspension was analyzed. The microencapsulation of PS by spray drying using a mixture of Arabic gum and maltodextrin was successfully achieved. Moreover, by including a surface active material in low concentrations (especially sodium lauryl sulfate at 2%, m/v), better results were obtained (low mean particle size and relatively high encapsulation efficiency and PS retention). Infrared spectroscopy, powder X-ray diffraction, and differential scanning calorimetry of the raw materials and microcapsules indicated that no changes in chemical structure nor strong interaction between microcapsules components took place.