Peanut oil stability and physical properties across a range of industrially relevant O/L ratios

Authors: DAVIS, JACK - Jla Global; PRICE, KRISTIN - Former ARS Employee; Dean, Lisa; SWEIGART, DANIEL - Hershey Company; COTTONARO, JAYNE - Hershey Company; SANDERS, TIMOTHY - Retired ARS Employee

Submitted to: Peanut Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/1/2015
Publication Date: 1/30/2016
Citation: Davis, J.P., Price, K.M., Dean, L.L., Sweigart, D.S., Cottonaro, J.M., Sanders, T.H. 2016. Peanut oil stability and physical properties across a range of industrially relevant O/L ratios. Peanut Science. 43:(1)1-11.

Interpretive Summary: Peanut varieties with high levels of oleic acid and corresponding low levels of linoleic acid are desired by the peanut industry due to their decrease tendency to become rancid compared to normal varieties. This difference in fatty acids present causes differences in handling properties for the industry of the oil produced from these peanuts. In this study, blends of high and normal oleic containing oils were created to make a range of contents. The fatty acid contents, refractive index, density and viscosity of the blends were found to be closely related to each other. Oxidative Stability was measured and found to increase with oleic acid content and the highest value was 7 times longer than the lowest. Other rancidity measurements and sensory tests were made after storing the oils under conditions known to create rancidity. Rancidity was found to be less with increased oleic acid content and less off flavors were found, while viscosity increased. From the data, oil processors will be able to predict certain attributes such as shelf life based on the ratio of the oleic acid content to the linoleic acid content of the oils.

Technical Abstract: High oleic cultivars are becoming increasing prevalent in the peanut industry due to their increased shelf life compared to conventional cultivars. High oleic peanuts are typically defined as having oleic acid/linoleic acid (O/L) ratios = 9, whereas most traditional varieties have O/L ratios near 1.5-2.0. In practice,this ratio can vary substantially among commercial material;accordingly, the goal of this study was to better understand the shelf life and physical properties of 16 model oil blends with O/L ratios systematically prepared from 1.3 – 38.1. Across these samples, % oleic acid, % linoleic acid, refractive index, density and dynamic viscosity were all highly (R2 > 0.99) linearly correlated. Increasing concentrations of oleic acid and concomitant decreases in linoleic acid were associated with decreasing oil density, decreasing refractive index, and increasing viscosity. Oxidative stability index (OSI), an established method for predicting relative oil shelf life, increased more than 7X from an O/L of 1.3 to 33.8 and this response was well described by a 2nd order polynomial. Oil stability was also assessed by storing oil blends at 24°C/50% R.H. for 24 weeks and periodically sampling these oils to measure peroxide value (PV) and describe oil flavor via sensory analysis. Excellent correlations were observed among:off-flavor (oxidized/cardboard/rancid) development during storage;PV development during storage; O/L ratio and OSI. While viscosity was greatest for high oleic samples when comparing fresh oils, after storage under abusive conditions viscosity increased exponentially with decreasing O/L ratio due to oxidation/polymerization reactions. Overall, these data will aid processors in selection of high O/L peanuts for various food applications and better determine final product shelf life.