Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)


School of Animal Science

First Advisor

John U. McGregor


Lipid autoxidation of whole milk powder (WMP) during storage lowers its organoleptic quality and causes accumulation of oxidation products. This study evaluated the effectiveness of high-oryzanol (2.5%) rice bran oil (RBO) as an antioxidant in WMP. The powder was fortified with 0.1% and 0.2% RBO and its oxidation studied during accelerated storage at 45°C and 0.31 water activity for 40 days. Free radicals were determined by electron spin resonance spectroscopy. Oxidation was estimated by determining thiobarbituric acid reactive substances (TBARS) and cholesterol oxidation products using gas chromatography. The effect of RBO on flavor and consumer preference of freshly manufactured milk powder was also evaluated. The oryzanol content of the WMP was 0.00 mug/g, 49.16 mug/g and 180.11 mug/g for 0.0%, 0.1% and 0.2% RBO fortified samples respectively. The alpha-tocopherol content was 0.00, 3.72 and 7.54 mug/g for 0.0%, 0.1% and 0.2% RBO fortified samples respectively. Addition of RBO significantly affected the color of the powder. The fortified powders had darker, more yellow color than control samples. Consumer tests showed that 0.2% RBO caused a detectable flavor change in milk powder, but at 0.1%, it had no significant effectonflavor. The RBO at 0.1% and 0.2% caused a significant reduction in free radicals during manufacture and after 10 days storage. High-heat powder had higher concentrations of free radicals than low-heat powder. Lipid oxidation was not significantly affected by RBO immediately after manufacture, but was significantly reduced by 0.1% and 0.2% RBO after storage for 10 or more days. The TBARS for all powder samples increased up to 30 days storage but reduced on further storage, probably due to their reaction with proteins. Rice bran oil did not have a significant effect on the accumulation of COP. The data on COP however was not conclusive, due to wide variability that may have resulted from thermal degradation of COP in the GC column during analysis. Results indicated that RBO reduced oxidation of WMP. Further work is necessary to determine the optimum application rate and method for process optimization.