Oxidative stability and sensory evaluation of microencapsulated flaxseed oil

Cold pressed flaxseed oil was microencapsulated by spray drying using an emulsion containing modified starch. The fatty acid composition, moisture, water activity, wettability, water holding capacity, water solubility, crystallinity, and particle size distribution of the microcapsules were determined. The stability of the microcapsules and the crude oil were assessed. An acceptance test was used for the sensory evaluation of a powdered supplement containing the microcapsules. The fatty acid composition was not significantly affected by the microencapsulation. The moisture, water activity, wettability, water solubility and crystallinity were appropriate for dry powders. The microcapsules had no cracks and showed better oxidative stability compared with the crude oil. Storage under vacuum prevented oxidation of the microcapsules. In sensory evaluation, all quality scores of the supplement containing microcapsules were mid range or higher. The microencapsulation improved the oxidative stability of the oil and this procedure was satisfactorily applied in powdered food. (Authors abstract)

A drawback of oils containing a high amount of PUFAs is their rapid oxidation, which involves the formation of toxic products, such as peroxides, or undesirable off flavour compounds.
Microencapsulation is a technology that allows sensitive ingredients to be physically enveloped in a coating to protect these ingredients or ‘‘core materials’’ from adverse reactions, volatile loss or nutritional deterioration.  Several techniques, including spray drying, spray cooling, fluidised bed drying, extrusion and centrifugal extrusion can be used to produce microcapsules. Microencapsulated flaxseed oil could be used in the formulation of several food products aiming to improve nutritional value by increasing contents of n3 fatty acids, without adversely changing sensory attributes. Furthermore, microencapsulated flaxseed oil could protect the flaxseed oil against oxidation compared with the bulk oil, thus increasing products’ shelf life. The objective of this study was to evaluate the ability of modified starch to act as a microencapsulating agent for flaxseed oil by spray drying. In addition, the physicochemical properties and oxidative stability of the powders during storage were investigated. A sensory evaluation was performed by incorporating the microencapsulated oil into a commercial nutritional supplement.

The paper provides an overview of the results of microencapsulation yield; total oil content and microencapsulation efficiency; fatty acid composition of crude oil and microcapsules. Characterisation of the microcapsules including moisture and water activity (Aw); wettability; water absorption index and water solubility index; powder X-ray diffraction; particle size are described in the paper.  The study demonstrated that spray dried powders encapsulating flaxseed oil could be produced using modified starch as a wall material at a 2 to1 ratio. The microencapsulation yield and microencapsulation efficiency were satisfactory and similar to other microencapsulated oils, produced with the same wall to core material ratio. The amorphous state and physical properties, such as moisture, water activity, wettability and water solubility index, indicated that the powder can be readily dissolved in water. Quantification of lipid oxidation products showed that microencapsulation by the spray drying technique protected the flaxseed oil against oxidation compared with bulk oil, especially in the case of the vacuum packed microcapsules. Microencapsulated flaxseed oil improved the nutritional quality of the supplement. The sensory test showed that all quality scores were mid-range or higher, indicating that the fortified supplement was acceptable. In conclusion, the process of encapsulation itself not only improved the oxidative stability of the oils but also rendered them physically usable for easy product incorporation. (Editors comments)