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United States Department of Agriculture

Agricultural Research Service

Research Project: Improvement & Maintenance of Flavor & Shelf-Life, Functional Characteristics & Biochem/Bioactive Process, & Use of Genetic/Genomic Resource

Location: Market Quality and Handling Research

Title: Density and Refractive Index Measurements of Peanut Oil to Determine Oleic and Linoleic Acid Content

Authors
item Davis, Jack
item Price, Kristin
item Dean, Lisa
item Sanders, Timothy

Submitted to: Journal of the American Oil Chemists' Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 25, 2012
Publication Date: November 4, 2012
Citation: Davis, J.P., Price, K.M., Dean, L.L., Sanders, T.H. 2012. Density and Refractive Index Measurements of Peanut Oil to Determine Oleic and Linoleic Acid Content. Journal of the American Oil Chemists' Society. 90:199-206.

Interpretive Summary: 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 2.5; however, many new cultivars are “high oleic” with O/L ratios = 9. During peanut seed handling, contamination of high oleic seed with normal oleic seed is common, and an industry recognized, problem. A cost effective method to rapidly differentiate peanut seed based on O/L ratio is needed across multiple segments of the peanut industry, and in the current study, measurements of oil density and oil refractive index (RI) were evaluated for this potential. Both methods showed excellent potential at rapidly predicting the oleic and linoleic acid chemistry of peanut oil; however, sample volume requirements preclude density measurements on single seed. Both methods have the potential to provide substantial cost savings to multiple segments of the peanut industry for differentiating oleic and linoleic acid content, and information in this study better positions these novel technologies for this purpose.

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 2.5; however, many new cultivars are “high oleic” with O/L ratios = 9. During peanut seed handling, contamination with normal oleic seed 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 highly linearly (R2 >0.98) correlated for oil blends. Selected density or RI values can be used to predict if a sample had an O/L = 9. Both measurements have excellent potential at rapidly predicting oleic and linoleic acid chemistry of peanut oil; however, sample volume requirements preclude density measurements on single seed.

Last Modified: 11/23/2014