Walnut oil

Walnut oil is oil extracted from walnuts, Juglans regia. The oil contains polyunsaturated fatty acids, monounsaturated fatty acids, and saturated fats.^[1]^[2]

Composition

According to gas chromatographic and HPLC analysis, virgin walnut oil consists of linoleic acid (60–62%). It also contains many phenolc compounds including γ-tocopherol, tanins, and flavanoids. Several of these exhibit antioxidant properties.^[2] According to another source, walnut oil is composed largely of polyunsaturated fatty acids (72% of total fats), particularly alpha-linolenic acid (14%) and linoleic acid (58%), oleic acid (13%), and saturated fats (9%).^[1]

Walnuts typically contain high concentrations of phenolics including ellagic acid.^[3]

Culinary use

Walnut oil is edible and is generally used less than other oils in food preparation, often due to high pricing. It is light-coloured and delicate in flavour and scent, with a nutty quality.^[4] Although chefs sometimes use walnut oil for pan-frying, most avoid walnut oil for high-temperature cooking because heating tends to reduce the oil's flavour and produce a slight bitterness. Walnut oil is preferred in cold dishes such as salad dressings.^[4]

Cold-pressed walnut oil is typically more expensive due to the loss of a higher percentage of the oil. Refined walnut oil is expeller-pressed and saturated with solvent to extract the highest percentage of oil available in the nut meat. The solvents are subsequently eliminated by heating the mixture to around 400 °F (200 °C). Both methods produce food-grade culinary oils. Walnut oil, like all nut, seed and vegetable oils can turn rancid.

Over 99% of walnut oil sold in the US is produced in California.^[5]

Artistic use

Linoleic acid, the major component of walnut oil, is a "drying oil", which means that in air it polymerizes, forming strong strong but flexible films, useful in oil paints and varnishes.^[6] Walnut oil was one of the most important oils used by Renaissance painters. Its short drying time and lack of yellow tint make it a good oil paint base thinner and brush cleaner.

Some woodworkers favour walnut oil as a finish for implements that will come in contact with food, such as wooden bowls, because of its safety. Rancidity is not an issue because walnut oil dries when applied to wood in a thin coating. People who mix oil and wax to formulate wood finishes value walnut oil as an ingredient because of the edibility of both ingredients. The oil typically is combined with beeswax in a mixture of 1/3 oil to 2/3 beeswax.^[7]

References

^ ^a ^b "National Nutrient Database for Standard Reference, Release 28". USDA National Nutrient Database. 2017. Retrieved 3 November 2017.
^ ^a ^b Ojeda-Amador, Rosa M.; Salvador, María Desamparados; Gómez-Alonso, Sergio; Fregapane, Giuseppe (2018). "Characterization of virgin walnut oils and their residual cakes produced from different varieties". Food Research International. 108: 396–404. doi:10.1016/j.foodres.2018.03.066.
^ Bodoira, Romina; Maestri, Damián (2020). "Phenolic Compounds from Nuts: Extraction, Chemical Profiles, and Bioactivity". Journal of Agricultural and Food Chemistry. 68 (4): 927–942. doi:10.1021/acs.jafc.9b07160. PMID 31910006.
^ ^a ^b Ben-Erik van Wyk (2014). Culinary Herbs and Spices of the World. University of Chicago Press. p. 154. ISBN 9780226091839.
^ "Walnut industry". California Walnuts. 2017.
^ Ulrich Poth (2002). "Drying Oils and Related Products". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a09_055. ISBN 978-3527306732.
^ Schimek, Erik (2010-03-19). "Finishing with Walnut Oil and Beeswax". Erik Organic. Archived from the original on 2011-05-08. Retrieved 2011-11-10.