Preparation of Multi-layered Microcapsules from Nanofibrils of Soy Protein Isolate using Layer-by-Layer Adsorption Method

Abstract

Nanofibrils were formed from soy protein isolate (SPI), which was isolated from black soybean, and commercial SPI by heating 2% w/w SPI suspensions at pH 2 and 80°C for 16 h. Nanofibrils from both types of SPI have branches and curvy structures with diameters between 10 and 20 nm. These fibrils, together with high methoxyl pectin (HMP), were used to make up to seven layered microcapsules at pH 3.5. Initially, negatively charged HMP (0.1 %w/w) was adsorbed onto oil droplets stabilized by unheated SPI (0.1 %w/w) which was positively charged. Onto this base, following layers were added by alternately adsorbing positively charged SPI nanofibrils and negatively charged HMP until the desired numbers of layers were achieved. Both types of SPI resulted in similar morphology of microcapsules. The microcapsules had a diameter between 12 and 18 μm with shell thickness of around1.7 μm and a final charge of +3.5 mV. This research showed that SPI nanofibrils can be used effectively as building blocks for constructing multilayer microcapsules that have much thicker shells for the same number of layers as examples from literature.