Location: Market Quality and Handling Research
Title: Refractive Index and Density Measurements of Peanut Oil for Determining Oleic and Linoleic Acid Contents Authors
Submitted to: Journal of the American Oil Chemists' Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 25, 2012
Publication Date: February 8, 2013
Citation: Davis, J.P., Sweigart, D.S., Price, K.M., Dean, L.L., Sanders, T.H. 2013. Refractive Index and Density Measurements of Peanut Oil for Determining Oleic and Linoleic Acid Contents. Journal of the American Oil Chemists' Society. 90(2)199-206. Interpretive Summary: Peanut seed are approximately 50% oil of which > 80% is either oleic or linoleic acid. The oleic/linoleic acid ratio largely influences oxidative stability and hence peanut shelf life. This ratio varies tremendously among cultivars and there is a strong need across multiple segments of the industry for a simple and cost effective method that can rapidly provide this information. Data in this publication, for the first time, establishes the relationships among oleic acid, linoleic acid, density and refractive index of peanut oil, and the excellent potential of using measurements of refractive index, or density, to rapidly and cost effectively differentiate peanut seed based on oleic and linoleic acid contents.
Technical Abstract: Peanut seed are approximately 50% oil of which > 80% is either oleic or linoleic acid. The oleic/linoleic acid (O/L) ratio largely influences oxidative stability and hence peanut shelf life. Traditional peanut seed have O/L ratios near 1.5-2.0; however, many new cultivars are “high oleic” with O/L ratios = 9. During peanut seed handling, contamination among lots may occur. A cost effective method to rapidly differentiate peanut seed based on O/L ratio is needed across multiple segments of the industry, and measurements of oil density and oil refractive index (RI) were evaluated for this potential. Fatty acid profiles of samples from normal and high oleic seed lots, and blends of these oils, were determined by traditional gas chromatography analysis and this data compared to corresponding oil density and RI measurements. Oleic acid content, linoleic acid content, density and RI were all strongly linearly (R2 >0.98) correlated for oil blends with O/L ratios from ~2-16. Threshold density or RI values both showed excellent potential for rapidly differentiating samples with an O/L = 9; however, sample volume requirements preclude density measurements on single seed.