Measurements of oleic acid among individual kernels harvested from test plots of purified runner and spanish high oleic seed

Authors: DAVIS, JACK - Jla Global; LEEK, JAMES - Jla Global; SWEIGERT, DAN - Hershey Company; Dang, Phat; Butts, Christopher - Chris; Sorensen, Ronald - Ron; Lamb, Marshall

Submitted to: Peanut Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/1/2017
Publication Date: 10/27/2017
Citation: Davis, J.P., Leek, J.M., Sweigert, D.S., Dang, P.M., Butts, C.L., Sorensen, R.B., Lamb, M.C. 2017. Measurements of oleic acid among individual kernels harvested from test plots of purified runner and spanish high oleic seed. Peanut Science. Vol. 44, No. 2, pp. 134-142. doi.org/10.3146/PS16-21.1.

Interpretive Summary: The amount of oleic fatty acid in peanuts is a major contributor to the shelf life of roasted peanuts and peanut products. In general, the higher the percentage of oleic fatty acid the longer peanuts and peanut products can be stored on the shelf without the development of off flavors. Peanut varieties, or cultivars, have been developed that have a high concentration of the oleic fatty acid. However, peanuts that are supposed to have the high oleic characteristic, when chemically analyzed, did not have the elevated concentration of oleic fatty acid. This could be due to unintentionally mixing high oleic and normal oleic peanuts during handling and processing or it could be because of environmental conditions during growth or the maturity of the individual seed or a combination of all three. In this study, runner and spanish peanut seed with the genetic characteristic to produce plants that resulted in high oleic peanuts were scanned using an near infrared scanner, and only peanut actually having a high concentration of the oleic fatty acid were planted. The peanut seed were planted in small plots where the soil temperature could be controlled. The soil in one plot was allowed to fluctuate according to the normal day/night fluctuations, i.e. no control. A second plot had chilled water cooling coils buried about 6 inches deep and were used to cool the soil about 6 F below the untreated plot. A third plot had heating cables buried in the soil that were controlled to heat the soil 8 F above the untreated plot. All three plots were irrigated so that the peanuts did not undergo any drought stress. To look at the effect of peanut maturity on the development of the oleic fatty acid, the peanuts in half of each of the plots had the flowers removed by hand between 100 and 110 days after planting. This hand removal of flowers, prevent the peanut plants from adding new peanuts that would not reach maturity before harvesting and forced the plant to use the energy to mature the peanuts. In general, the higher percentage of mature kernels, the higher the percentage of oleic fatty acid. Average percent oleic fatty acid in the peanuts increased as the kernel size increased primarily because generally speaking, as kernel size increases the percentage of mature kernels increases. No 1 sized kernels had 77% oleic acid, Medium-sized kernels had 80.6% oleic acid, and the Jumbo-sized peanuts had 81.4% oleic acid. Similarly, the warm soil temperatures caused the percent oleic acid to increase, because the percent of mature kernels increased. Finally, the percent of mature kernels in the peanuts on the plants where the flowers were removed by hand increased and therefore, increased the percent oleic acid by about 2% compared to the peanuts where the flowers were not removed. Peanut market type and environment both influenced the oleic fatty acid content through their effect on the range individual seed maturity.

Technical Abstract: Normal oleic peanuts are often found within commercial lots of high oleic peanuts when sampling among individual kernels. Kernels not meeting high oleic threshold could be true contamination with normal oleic peanuts introduced via poor handling, or kernels not meeting threshold could be immature and not fully expressing the trait. Beyond unintentional mixing, factors contributing to variation in oleic acid concentration in peanut kernels include market type, environment, maturity and/or kernel size; however, the relative influence of these factors, and their interactions, is not quantitatively well understood on the single kernel level. To better understand these factors while simultaneously excluding variation from unintentional mixing, seed from a high oleic spanish cultivar and seed from a high oleic runner cultivar were carefully purified via NIR technology and subsequently planted in environmentally controlled test plots to in turn analyze progeny for oleic acid chemistry. Post flowering, plot sections were either chilled (3-4 C below ambient), maintained at ambient or heated (4-6 C) above ambient) in the pod zone to characterize soil temperature effects on oleic acid chemistry development. Fully randomized (4 reps) plots included the purified high oleic spanish and runner cultivars, three soil temperatures, seed maturity (profile board), commercial kernel size classifications, and a late season flower termination protocol. At harvest, the oleic acid concentration of approximately 20,000 individual kernels were measured via NIR technology. Significant market type, temperature, maturity and size effects on high oleic chemistry among kernels were observed. Implementation of a late season flower termination protocol significantly, and positively, influenced high oleic chemistry of runner peanuts, minimizing immature kernels not meeting high oleic threshold and resulting in elevated and more consistent distributions in this key chemistry; distributions that were more similar to those of the more botanically determinate, but lower yielding, spanish market type. Data from this study improves understandings of expected natural variation in high oleic chemistry and suggests late season flower termination of runner peanuts as a viable strategy to maximize high oleic chemistry on the single kernel level.