Storage and Thermal Effects on the Oxidative Stability and Emulsion Characteristics of Hemp (Cannabis sativa L.) Oil-in-Water Emulsions

Abstract

It has been well established that hemp oil has potential for functional food products and nutraceutical formulations due to its fatty acid profile. However, is its commercial application is limited as a result of its corresponding oxidation susceptibility. To assess the suitability of micro-encapsulation to improve oxidative stability, oil-in-water (1% v/v) emulsions treated with surfactant were exposed to temporal and thermal conditions and examined for resistance to rancidity. Hemp and avocado emulsions were prepared by an ultrasonication procedure (40% amplitude, processing time 5 min), and a 0.5% (w/v) soy protein and 0.5% (w/v) lecithin suspension was incorporated into treated emulsions as the surfactant. Samples were subjected to conditions of 25°C and 4°C for the 42-day storage trial, as well as short exposure to a 72°C condition for the thermal trial. The diphenyl-1-pyrenylphosphine assay was performed and sulfhydryl group levels were quantified as oxidative parameters. Average particle size, polydispersity, and zeta potential were analyzed as the emulsion characteristics. All emulsions were relatively resistant to further oxidation during the thermal trial. Over the course of the storage trial, emulsions with surfactant exhibited smaller particle sizes and lower polydispersity, compared to non-treated emulsions. Although this encapsulation technology appears promising for physical emulsion traits, there was a tendency for emulsions with surfactant to have higher oxidation levels. Soy lecithin should be re-examined as a food grade emulsifier for highly unsaturated oils, as it may become oxidized itself or catalyze oxidation of the oils, contributing to lipid oxidation levels. Hemp oil’s instability during storage and processing will continue to limit its food applications until suitable encapsulation techniques and surfactant materials are identified.