Evaluation of oxidative stability of rice oil from brown rice flour under thermal oxidation and light irradiation.

Effects of autoxidation and light irradiation on the oxidative stability were evaluated in rice oil from two brown rice flours including 'Baromi2' and 'Samkwang'. 'Baromi2' is a newly developed variety for rice flour production while 'Samkwang' is a typical rice variety as a control. Degree of oxidation and volatile profiles were evaluated in rice oil stored at 60 °C or under fluorescent light at 25 °C. The oil yields of 'Baromi2' and 'Samkang' were 2.63 and 1.78%, respectively whereas rice oil from 'Baromi2' had lower degree of unsaturation than 'Samkang'. Rice oil from 'Samkwang' possessed higher volatile compounds and more oxidized products during autoxidation whereas rice oil from 'Baromi2' had more oxidation products under light irradiation. Hexanal and 2-heptenal were major headspace volatile from heated rice oil while 2-heptenal and 1-octene-3-ol were main volatiles from light irradiated rice oil, which implies the involvement of singlet oxygen in rice oil during photooxidation.

Effects of association colloidal structures on the oxygen solubility in oil-in-water emulsion matrix.

Although association colloidal structures are believed as major oxidation places, relationship of oxygen molecules with association colloids have not been evaluated in oil-in-water (O/W) emulsion. Oxygen solubility was determined in O/W emulsion containing dispersed phases with different charges of emulsifiers, numbers of dispersed droplets, and surface areas of dispersed droplets. The rates of lipid oxidation were also examined. O/W emulsion made of positively charged emulsifier had higher oxygen solubility than negatively charged and neutral emulsifiers. As number and surface area of oil droplet in O/W emulsion increased, higher oxygen solubility was observed, implying that dispersed phases could be places for oxygen molecules. O/W emulsion made of positively charged emulsifier had higher lipid oxidation than neutral emulsifier. O/W emulsion with more interfaces had lower oxidative stability, implying interfaces of association colloids could affect rates of lipid oxidation. Dispersed phase in O/W emulsion can be places for oxygen molecules.