Abstract

Hydroxypropyl-inulin (HPI) was synthetized from inulin by etherification. The hydroxypropylation of inulin (degree of substitution 0.7) was confirmed by H-1 NMR. The replacement of hydroxyl groups in inulin by an ether linkage increased its hydrophobicity, making HPI suitable as a novel encapsulating agent of fish oil (FO) by both conventional and water-free spray drying. FO microparticles were designed according to a composite central plus star statistical design. A FO-in-water emulsion was prepared as infeed for encapsulation by conventional spray drying (FO-csd), whereas FO was dispersed in methanol for encapsulation by water-free spray drying (FO-wfsd). The encapsulation efficiency of FO was similar in both FO-csd and FO-wfsd microparticles (80.5% and 82.6%, respectively), despite the different encapsulation mechanism. FO-wfsd microparticles showed lower glass transition temperature (Tg), hygroscopicity, moisture and water activity (a(w)) than FO-csd microparticles. Only the superficial FO was released from FO-wfsd microparticles (at pH 4.6 and 6.5) and FO-csd (at pH 6.5), which is desirable in the design of healthy food liquid matrices. Furthermore, FO-csd microparticles showed lower oxidative stability than FO-wfsd microparticles evaluated by the formation and distribution of polar compounds, suggesting that water had a higher plasticizing effect than methanol and provided FO microparticles with poor film-forming properties. The type of solvent determined the FO encapsulation mechanism but slightly affected the physico-chemical properties of the microparticles, the oxidative stability and the FO released pattern.