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. The purified seed were planted in environmentally controlled test plots to analyze the progeny for oleic acid chemistry. Post flowering, plot sections were either chilled (3.8 -5.0 C below ambient), maintained at ambient or heated (3.8-5.0 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 24,000 individual kernels were measured via NIR technology. Market type, temperature, maturity and size had a significant effect on high oleic chemistry among kernels. Late season flower termination significantly, and positively, influenced high oleic chemistry of runner peanuts, minimized the number of immature kernels not meeting high oleic threshold and resulted 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 our understanding of expected natural variation in high oleic chemistry and suggests late season flower termination of runner peanuts is a viable strategy to maximize high oleic chemistry on the single kernel level.
High oleic peanuts have conservatively twice the post-roast shelf life of conventional peanuts as measured by descriptive flavor panels (Braddock
When sampling from kernel to kernel to kernel within a sample of high oleic (or conventional) peanuts, regardless of potential contamination with conventional oleic kernels, a natural distribution in oleic acid/linoleic acid content is observed among the individual kernels. As peanuts mature, it's established that the oleic acid (%) increases while linoleic acid (%) decreases, hence the overall O/L ratio increases with maturity (
With these two sources of variation in mind, i.e. true contamination of high oleic lots with normal oleic seed, and the natural variation associated with maturity, it's not clear what factors are the predominate cause of commercial lots of high oleic peanuts being sampled and subsequently not meeting established purity limits. It's also important to recognize that measuring this chemistry is both expensive and time consuming. The primary chemical method is gas chromatography (GC) based which requires a skilled operator and 100 extractions/injections of a typical sample. Refractive index methods are developed which correlate well with the primary GC method, and while faster and cheaper than the GC method (
Terminating flowers generated after about 90 days after planting, which have no potential to generate viable peanuts, has been shown to improve farmer stock yield and grade (
The objectives of these experiments were to better understand factors influencing single kernel oleic acid (%) distributions, including seed maturity, seed size, growing environment and/or late season flower termination.
Two high oleic peanut cultivars were planted for this study. The first, ‘13AU-12’ is an advanced runner breeding line from the joint Auburn University/National Peanut Research Laboratory breeding program. The second cultivar, ‘AT-9899’ is a high oleic spanish cultivar. Some seed lots of ‘AT-9899’ were found to be contaminated with conventional oleic peanuts in 2009. In 2010 work was carried out to recover and purify this line (
High speed NIR data was collected on individual seed using a Luminar™ AOTF NIR Spectrometer (SeedMeister), and the Snap32!™ software package by Brimrose Corporation of America. The raw spectral data was imported into The Unscrambler® version 10.3, by CAMO Software, for post-processing and chemometric analysis. A percent-oleic acid prediction result was generated for each seed using a Partial Least Squares (PLS) regression model previously developed and validated for use with spanish and runner peanut seed.
The calibration data set consisted of 378 runner and spanish redskin peanuts ranging from 41% to 83% oleic acid (ratio in oil fraction of the peanut). The PLS model was developed by pairing the spectral data from each kernel with its corresponding oleic acid result from Fatty Acid Methyl Ester (FAME) analysis by gas chromatography. Analysis of an independent validation set of seeds resulted in a Root Mean Squared Error (RMSE) of 4.4. The uncertainty of the prediction results could then be estimated to be ± 9% oleic acid at a 95% confidence interval (CI). Later in the process of data collection, a second validation was performed to include selected seeds from the study to verify that the calibration accuracy was being maintained. The RMSE was 4.3 for the verification, which was the same as the initial validation set.
Prior to planting, seeds were screened via NIR. Only seed measuring greater than 75% oleic acid were saved for planting. A total of 2189 spanish and 2648 runner seeds were screened as summarized in
Summary of NIR sorting of individual runner and spanish seed prior to planting. Only seed sorted with an oleic acid content greater than 75% as measured by NIR were planted for the current study.
After planting, harvesting, sorting, and shelling as described below, individual redskin peanuts were scanned via NIR to measure the percent oleic acid. Sample data was collected for each maturity or size subset by scanning 100 seed from labelled bags. For some kernel classifications such as the yellows or No1-sized, 100 kernels were not available but all kernels available were measured. For the harvested samples sorted by maturity and size, a total of 12,426 and 11,697 kernels, respectively, were scanned via NIR. Kernels were randomly hand-selected, after discarding only the ones that were not suitable for NIR analysis due to extremely small size or defects.
Each unique 100-kernel sample set was given a descriptive filename corresponding to its organizational grouping (eg Yellow No 1). After completing data collection and processing, the numbered and categorized prediction results were organized into an Excel spreadsheet for further analysis. Excel and JMP Pro 12.0.1 of SAS Institute Inc. were used for statistical data analysis. Treatment means were compared using the Tukey-Kramer HSD Test.
Runner and spanish peanuts screened having more than 74% oleic acid were planted at a seeding rate of 20 seed/m in environmental control plots located at the USDA ARS NPRL in Dawson GA on 26 May 2014. Soil type was a Tifton sandy loam (Fine-loamy, kaolinitic, thermic Plinthic Kandiudults). Experimental units were 0.91-m rows within the environmental control plots. The average plant population after emergence was approximately 17.1 plants/m for both seed types. Plants were fully irrigated based on soil moisture sensing (MPS-2, Decagon Devices, Pullman, WA). Soil nutrition, fungicides, herbicides, and insecticides were applied throughout the growing season in accordance with recommended production practices. Soil temperature adjustments and hand flower removal were initiated approximately 90 days after planting (DAP) on 18 Aug 2014 as described in the following paragraph. Spanish peanuts were dug 122 days after planting on 15 Sep 2014. Runner peanuts were dug 138 days after planting on 30 Sep 2014.
Treatments for both spanish and runner peanuts included three soil temperature treatments: ambient (untreated control), heated or chilled; two late season flower terminations: control or hand removal. All experimental units were replicated 4 times. The schematic of the plot layout is shown in
Heating cables and chilled water coils were used to heat and cool, respectively, the soil in the pod zone portions of the environmental control plots (
Late season flowers, i.e. flowers added by the peanut plants after about 90 days, were hand removed for select treatments. Trained personnel hand removed flowers each morning between 6:30 and 8:00 AM by visually looking for and pinching off new flowers.
At harvest, plots were split and half the material was processed to simulate common, best commercial processing while the other half was processed for maturity sorting. Peanuts experimentally processed to simulate industrial practices, by hand digging, then inverting in windrows, and field curing for approximately 3 days. After windrow curing, peanuts were harvested with a plot thresher (Kingaroy Engineering Works, Kingaroy, Queensland, AU). Peanuts were mechanically cured until the kernel moisture content was less than or equal to 10% using air heated 8C above ambient, but no greater than 35C in laboratory-scale dryers (
The remaining peanuts were hand dug, turned, loose soil shaken off, and pod blasted to remove the exocarp (
Half the test plots from this study were harvested, handled and shelled to simulate common, best industrial practices, including windrow drying, mechanical curing, and shelling/sizing according to industry standards. The other half were immediately pod blasted on the day of harvest, sorted according to maturity based on the exposed mesocarp color, mechanically dried, and then shelled. These two portions of the study are referred to as simulated commercial processing and maturity sorting. The current manuscript primarily focuses on plots processed via simulated commercial processes, although data generated via maturity sorting is used to complement findings.
Total shelled material recovered per 0.9 m of experimental row, defined as the total mass of Jumbo's, No1's, sounds splits and oilstock for spanish, or the total mass of Jumbo's, Medium's, No1's, sound splits and oilstock for runners, is summarized in
Mean1 and standard deviation of total shelled material (grams) recovered per m experimental row grouped by market type, soil temperature and late season flower termination.
The relative (%) of various size classifications after shelling are summarized in
A total of 11,697 individual seeds were scanned for oleic acid (%) via NIR after harvesting, handling and shelling to simulate commercial practices. Summary statistics for the 6901 runner and 4796 spanish kernels are provided in
Summary of oleic acid (%) for individual runner and spanish peanuts. At harvest, these samples were collected after simulating commercial processing as described in the manuscript.
Runner (
Summary statistics for oleic acid (%) of individual
Summary statistics for oleic acid (%) of individual
The increased oleic acid (%) of spanish kernels coupled with their decreased variation are ideal for many confectionary applications; however, the decreased yield of spanish varieties is an obvious economic disadvantage. Late season flower termination could be a strategy to not only improve farmers' stock yield and grade, but improve single kernel maturity distribution for runner peanuts. Late season flower termination increased (p<0.05) the overall mean compared to control runner peanuts (to a value closer to that of spanish) and decreased variation around this population (
Flowers appearing later than approximately 90 days after planting (late season flowers) do not have enough time to make viable, mature peanuts given typical cultural practices. When this occurs, the plant is allocating photosynthetic resources into these flowers that could be used to mature the existing pods, hence the hypothesis that late season flower termination improves maturity distributions and single kernel oleic acid content on. Peanuts were also harvested and sorted according to mesocarp color into maturity classes (
A primary consideration in the industrial trade of high oleic lots is the percentage of kernels within a lot that do not meet the threshold fatty acid chemistry limits set for high oleic peanuts. While values may vary slightly, a typical threshold is an O/L ratio of 11.0 or greater (
Distribution (N=159) of runner peanuts less than 70% oleic acid for various categories.
For current experiments, late season flowers were hand removed; however, work over three years and multiple growing locations (small plot work) demonstrated that the input diflufenzopyr (BASF Biosciences) was effective at terminating late season flowers with corresponding approximate 400-500 lb/acre yield increases with irrigation while also improving farmer stock grade (
Strong market type, soil temperature, size and maturity effects on oleic acid (%) among individual kernel populations of spanish and runner peanuts were observed. Implementation of a late season flower termination protocol strongly, and positively, influenced high oleic chemistry of runner peanuts. Data from this study provides an unprecedented understanding of expected natural variation in high oleic chemistry on the single kernel level
The authors gratefully acknowledge Mrs. C.M. Baker for conducting the NIR measurements. The authors also acknowledge the technical support staff at the National Peanut Research Laboratory including, Staci Ingram, Larry Powell, Hank Sheppard, Dan Todd and others for designing and installing the instrumentation and control systems, planting, managing, and harvesting the peanuts, then processing the samples after harvest.
Director of Technical Services, JLA International, Albany, GA USA, a subsidiary of IEH Laboratories, Lake Forest Park, WA 98155 and Adjunct Faculty, Dept. of Food, Bioprocessing & Nutrition Sciences, North Carolina State University, Raleigh, NC 27695
Chairman of the Board, JLA International, Albany, GA USA, a subsidiary of IEH Laboratories, Lake Forest Park, WA 98155
Dan S. Sweigart, The Hershey Company, Hershey, PA 17033
Research Biochemist, Research Agricultural Engineer, Research Agronomist, and Supervisory Research Food Technologist, respectively, USDA, ARS, National Peanut Research Laboratory, Dawson, GA 39842
Professor, Crop, Soil, and Environmental Sciences, Auburn University, AL 36849