Effects of different wall materials on the physicochemical properties and stability of ARA oil microcapsules

The purpose of this research is to microencapsulate the ARA oil by spray-drying using different wall materials. A systematic investigation was implemented to characterize the effects of microcapsules on the structure, physical and chemical properties, and stability. The ARA microcapsules were used as the core material, where whey protein (W), whey protein-glucose (WG), and whey protein-glucose syrup-lactose (WGL) were used as the wall materials. An analysis was made on the encapsulation efficiency, water content, solubility, bulk density, angle of repose, particle size distribution, micro-morphology, oxidation stability, and thermal stability of the microcapsules. The properties of the microcapsules were compared from different wall materials. The results showed that the higher encapsulation efficiency of WGL was 98.64%, indicating a significant difference between W and WG (P＜0.05). The encapsulation efficiency was increased and the embedding effect of microcapsules was good. The WGL was measured to observe a water content of 2.85% and a bulk density of 0.54 g/mL. There was no significant difference among the three kinds of ARA oil microcapsules. Microcapsule powders that are obtained in this research study were very stabile and compressible.The solubility of WGL was higher and the angle of repose of WGL was lower, which were significant differences between W and WG (P＜0.05). The solubility of WGL reached 89.83%, it was increased and the quality of microcapsules was good. The angle of repose of WGL was 35.87°, which angles of repose of WGL were 7.36° and 4.38° lower than those of W and WG. As such, the smaller the angle of repose of the WGL was, the smaller the frictional force, and the better the fluidity was, the larger particle size was, indicating the normal distribution and a narrow region. The physicochemical properties of WGL were superior to W and WG, which was beneficial to the storage stability of microcapsules. The microcapsule product shared the spherical microstructure, free-cracks, free-pores, dense structure, fullness, and complete particle morphology, which basically achieved the intended purpose of embedding. The iodine titration was used to determine the peroxide values of W, WG, and WGL. Specifically, the peroxide values of WGL increased from 2.42 to 19.92 and 32.75 mmol/kg at 25 ℃ and 50 ℃, respectively. The peroxide values of WGL were significantly lower than those of W and WG (P＜0.05), indicating that WGL with higher oxidative stability. The accelerated storage test of the ARA oil after embedding showed that the WGL improved the oxidative stability of ARA oil. The wall material of WGL was better than those of W and WG for embedding ARA oil, which hindered the influence of external conditions on ARA oil and isolated oxygen, thus slowing down the oxidation rate. The reason was the dense and void-free structure of the WGL. Therefore, the oxidative deterioration of ARA oil microcapsules was effectively delayed during storage and prolonged the shelf life. The maximum melting temperature and mass retention rate of WGL were 107 ℃ and 27.55%, respectively, according to the differential scanning calorimetry and thermal gravity analysis. The WGL shared better thermal stability than W and WG. Therefore, there were higher temperatures and energy required for the phase transition of the WGL, indicating better thermal stability. The WGL can be expected to store the stability of microcapsules at room temperature. In conclusion, the properties of WGL are better than those of W and WG, indicating a better embedding and protective effect on ARA microcapsules. The finding can also provide a strong reference for the selection of the appropriate wall materials to encapsulate ARA microcapsules.