Effects of maturity on the development of oleic acid and linoleic acid in the four peanut market types

Authors: Dean, Lisa; EICKHOLT, CLAIRE - North Carolina State University; LAFOUNTAIN, LISA - North Carolina State University; Hendrix, Keith

Submitted to: Journal of Food Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/19/2020
Publication Date: 6/10/2020
Citation: Dean, L.L., Eickholt, C.M., Lafountain, L.J., Hendrix, K. 2020. Effects of maturity on the development of oleic acid and linoleic acid in the four peanut market types. Journal of Food Research. 9(4):1-9. https://doi.org/10.5539/jfr.v9n4p1.
DOI: https://doi.org/10.5539/jfr.v9n4p1

Interpretive Summary: Food products that contain significant levels of oil can develop rancid flavors due to oxidation of the fatty acids in the oils. The more unsaturated the fatty acids, the more susceptible the food is to the onset of rancidity. Peanuts normally contain 45 to 50% oil. The major fatty acid in peanut oil are oleic (a monounsaturated fatty acid) and linoleic (a polyunsaturated fatty acid). The ratio of the 2 fatty acids is usually between 1 and 3 and is reported as the "O/L" ratio. New varieties of peanuts have been developed with O/L ratios of 9 or higher with some reported as high as 40. These varieties have been proven to be less prone to oxidation and thus have a longer shelf life which is very appealing to food producers using peanuts. Confection and roasted snack peanut producers have come to prefer these varieties. There is no visual difference between peanuts with normal and high O/L ratios, therefore time consuming and expensive chemical testing is needed to determine the O/L ratio present. Keeping lots of the two types separate in the supply chain from the farm to the peanut buying point to the shelling operation to the end user has to be very rigorous. Never the less, mixed lots of normal and high O/L peanuts have been reported. This research studied the effects of maturity on the final O/L ratio of the four market types of peanuts (runner, virginia, spanish and valencia), to determine if mixed lots were the end result of normal peanut metabolism in some cases rather than physical mixing and human error. It was found that immature peanuts do have lower O/L ratios than mature ones, especially in larger seeded peanut varieties such as those of the virginia cultivar and could be the cause of lots of peanuts being found to be less than 100% pure high O/L. These results give the production chain a new focus on how to keep lots pure by removing immature seed whenever possible.

Technical Abstract: The commercialization of high oleic peanut varieties with the fatty acids, oleic and linoleic present in a ratio greater than 9 has increased the shelf stability of many products containing peanuts significantly. With no visual traits to determine levels of the fatty acids present, mixing of the high oleic peanut types from the normal oleic types has been a problem in the peanut supply chain. This study investigated the effect of the development of the fatty acids in peanuts over their maturation with respect to the different market types (Runner, Viriginia, Spanish, Valencia) to determine if the maturation stage of the peanut could be responsible for the presence of normal oleic peanuts in lots of h igh oleic peanuts and thus decreasing the purity of the lots. Peanuts had different levels of the main fatty acids present as the oil content increased with maturation. Due to the presence of a natural desaturase enzyme in peanuts, oleic acid is converted to linoleic as the peanut develops resulting in a ratio of oleic acid to linoleic acid of 3 or lower in normal oleic peanuts. In peanuts from high oleic cultivars, the genes encoding for this enzyme are mutated or slow to develop. As this gene is activated in the later stages of peanut maturity, this study proves immature peanuts of the high oleic type may not have the proper ratios of oleic to linoleic to ensure shelf stability despite being from high oleic cultivars. This study describes how the concentra tions of oleic and linoleic acid changed with maturation of the peanut seeds and affects the purity of individual lots of high and normal oleic types of peanuts. This effect of maturity was seen to be greater in the large seeded V irginia cultivars compared to the smaller seeded market types.