Canola Oil Encapsulated by Alginate and Its Combinations with Starches of Low and High Amylose Content: Effect of Quercetin on Oil Stability

Co-extrusion encapsulation in combination with antioxidant (quercetin, vitamin E or BHT) addition was employed to reduce deterioration of unsaturated canola oil. Alginate only (A), alginate–Novation 2300 starch with 1.4 % amylose (A-N), and alginate–Gelose 80 starch with 89.8 % amylose (A-G) were used as encapsulants, and storage trials of encapsulated oil beads were conducted at 20 °C and 38 °C. Microscopy examination confirmed that the freshly prepared 1 %A, A-N, and A-G beads generally had spherical shape, with the 1 %A beads possessing smoother surfaces. The average diameter and wall thickness of the freshly prepared beads decreased in the order of A-G (380 μm) > 1 %A (348 μm) > A-N (310 μm) beads, and 1 %A (70 μm) > A-N (60 μm) > A-G (50 μm) beads, respectively. After the treatment at pH 3 for 2 h, these three types of beads remained intact but shrank significantly with the A-G beads exhibiting the largest contraction. From the bead storage trials, primary oil oxidation dominated over secondary oil oxidation and oil hydrolytic rancidity. Quercetin was more powerful in suppressing primary oil oxidation than vitamin E and comparable to BHT. Overall, the three types of shell formulations were suitable for protecting unsaturated oil, with the A-N and A-G shells forming the best and worst barriers, respectively. The 1 %A shell could be an alternative to A-N for a prolonged storage at 38 °C. Fourier-transform infrared spectra of the beads were consistent with the bead formulations, indicating roughly similar chemical composition before and after storages despite some detected spectroscopic differences. High-performance liquid chromatography analyses showed the differences in the degradation pathways of added quercetin and the changes of the alginate or alginate-starch shell during storage. Results suggest that core oil stability depends on a complex interplay between shell components, added antioxidants, and storage conditions. Encapsulated oil beads provide a convenient vehicle for delivering health-promoting unsaturated oil, antioxidants, and starch fiber polysaccharides to consumers either as a supplement or food ingredient. Alginate-starch shells can be formed to offer different protective barriers with different physical characteristics and nutritional value.