Comparison of microencapsulation properties of spruce galactoglucomannans and arabic gum using a model hydrophobic core compound

In the present study, microencapsulation and the physical properties of spruce (Picea abies) O-acetyl-galactoglucomannans (GGM) were investigated and compared to those of arabic gum (AG). Microcapsules were obtained by freeze-drying oil-in-water emulsions containing 10 wt % capsule materials (AG, GGM, or a 1:1 mixture of GGM-AG) and 2 wt % α-tocopherol (a model hydrophobic core compound that oxidizes easily). Microcapsules were stored at relative humidity (RH) of 0, 33, and 66% at 25 °C for different time periods, and their a-tocopherol content was determined by HPLC. X-ray microtomography analyses showed that the freeze-dried emulsions of GGM had the highest and those of AG the lowest degree of porosity. According to X-ray diffraction patterns, both freeze-dried AG and GGM showed an amorphous nature. The storage test showed that anhydrous AG microcapsules had higher α-tocopherol content than GGM-containing capsules, whereas under 33 and 66% RH conditions GGM was superior in relation to the retention of α-tocopherol. The good protection ability of GGM was related to its ability to form thicker walls to microcapsules and better physical stability compared to AG. The glass transition temperature of AG was close to the storage temperature (25 °C) at RH of 66%, which explains the remarkable losses of α-tocopherol in the microcapsules under those conditions.