Understanding the oxidation of hemp seed oil and improving its stability by encapsulation into protein microcapsules

Hemp seed oil (HSO) is an edible oil low in saturated fat and rich in polyunsaturated fatty acids (PUFAs) such as omega-6 and omega-3 fatty acids. When they are in contact with oxygen in the air, PUFAs are easily oxidized even at room temperature due to the multiple double bonds that facilitate the formation of reactive radicals when exposed to air. This study aimed to evaluate the oxidation of HSO under different conditions and to examine the encapsulation of HSO with zein as a new method to prevent its oxidation. Peak time of weight gain monitored with thermogravimetric analysis and oxidation products detected with high-performance liquid chromatography were used to determine the oxidation of fatty acids and HSO. It was found that the thermal decomposition of fatty acids prevailed over autoxidation beyond a certain temperature (at about 100-140°C). Encapsulating HSO into zein microcapsules, which isolates oil droplets from contact with oxygen in the air, effectively prevented its oxidation. The induction period of HSO oxidation was delayed by 7.3-9.3 times with the zein-to-HSO ratio of 0.5-1.25. In contrast, 0.5% (w/w) α-tocopherol could prolong the induction period up to 2.5 times indicating that the encapsulation method was much more effective than α-tocopherol in preventing the oxidation of HSO. This method may also be applied for other oils susceptible to oxidation such as omega-3 oils. PRACTICAL APPLICATION: This research compares the effects of three schemes that stabilize hemp seed oil from oxidation: (1) lowering temperature to slow down the oxidation reaction, (2) adding antioxidant to deactivate the initiation of oxidation reaction, and (3) encapsulating oil droplets into protein microcapsules to keep the oil from contact with oxygen. The experimental result showed the encapsulation of oils in protein microcapsules is more effective than the other two. The stabilization approaches applied to hemp seed oil can also be applied to other edible oils that are unstable.