Oxidative Stability of Tree Nut Oils

Abstract

The oxidative stability of selected tree nut oils was examined. The oils of almond, Brazil nut, hazelnut, pecan, pine nut, pistachio, and walnut were extracted using two solvent extraction systems, namely, hexane and chloroform/methanol. The chloroform/methanol system afforded a higher oil yield for each tree nut type examined (pine nut had the highest oil content, whereas almond had the lowest). The fatty acid compositions of tree nut oils were analyzed using gas chromatography, showing that oleic acid was the predominant fatty acid in all samples except pine nut and walnut oils, which contained high amounts of linoleic acid. The tocopherol compositions were analyzed using high-performance liquid chromatography, showing that alpha- and gamma-tocopherols were the predominant tocopherol homologues present; however delta- and beta-tocopherols were also detected in some samples. The oxidative stability of nonstripped and stripped tree nut oils was examined under two conditions, namely, accelerated autoxidation and photooxidation. Progression of oxidation was monitored using tests for conjugated dienes, peroxide value, p-anisidine value, and headspace volatiles. Primary products of oxidation persisted in the earlier stages of oxidation, whereas secondary oxidation product levels increased dramatically during the later stages of oxidation. Hexanal was the major headspace aldehyde formed in all oxidized samples except walnut oil, which contained primarily propanal. Results showed that chloroform/methanol-extracted oils were more stable than hexane-extracted oils in both the accelerated autoxidation and photooxidation studies. Oils of pecan and pistachio were the most stable, whereas oils of pine nut and walnut were the least stable.

Lipid components and oxidative status of selected specialty oils

“…In walnut oil, γ-and d-Tp contents were in accordance with the data published by except for α-Tp. The predominant isomer γ-Tp represents 69% of the total tocol contents (373 µg/g) which is a similar finding to published data Miraliakbari and Shahidi, 2008).…”

“…This can be a reason for the com paratively lower Rancimat value of walnut oil than grape seed oil even though they had close levels of total PUFA, MUFA and SFA. Miraliakbari and Shahidi (2008) also noted walnut oil as the least stable and most unsaturated while almond and hazelnut exhibited intermediate stability in a study on the oxidative stability of tree nut oils. Also, grape seed oil contained 216 µg/g α-tocopherol compared to walnut oil which contained only 71 µg/g oil.…”

Physicochemical Properties of Plukenetia volubilis L. Seeds and Oxidative Stability of Cold-pressed Oil (Green Nut Oil)

“…PV was higher in all oils exposed to UV light than in those not exposed. As was reported previously (Kato et al, 2008;Seto et al, 1990;Miraliakbari and Shahidi, 2008;Shibasaki, 2000) fats and oils are readily photooxidized when exposed to UV light at wavelengths less than 300 nm. Similarly, in our experiments, we observed that PV increased with UV exposure time.…”

“Pine Mouth” Syndrome: Cacogeusia Following Ingestion of Pine Nuts (Genus: Pinus). An Emerging Problem?

“…It is unclear if a specific species of Pinus is to blame. If a link between pine nut ingestion and cacogeusia is real, an exact mechanism is unclear: symptoms may be related to decomposing lipids, as pinus oils are known to be unstable and degrade quickly [14]. The role of toxins and other contaminants has not been fully evaluated.…”