X-ray technology to determine peanut maturity

Authors: Sorensen, Ronald - Ron; Butts, Christopher - Chris; Lamb, Marshall

Submitted to: Peanut Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/13/2020
Publication Date: 9/29/2020
Citation: Sorensen, R.B., Butts, C.L., Lamb, M.C. 2020. X-ray technology to determine peanut maturity. Peanut Science. 47(2)38-45. https://doi.org/10.3146/PS20-2.1.

Interpretive Summary: The indeterminate growth of peanut may create indecision on timing to dig for maximum maturity as well as economic value. Peanut producers and manufacturers recognize that digging too early or too late can reduce yield and grade as well as processing characteristics. Two results of digging early, aside from lower yields, are increased amount of immature peanuts entering storage facilities that may increase the risk of mold production (Aspergillus flavus), and immature peanuts can cause off-flavors during roasting. Conversely, digging late may reduce yield by leaving pods on the soil surface (pod loss) caused by mechanical or biological damage to over-mature plants with diseased or weakened pegs due to age. Therefore, harvesting peanut at the optimum time would have greatest peanut yield, least peanut loss, and reduce the risk of mold growth in the warehouse and for the development of off-flavors during roasting. As peanuts mature, the hull color beneath the exocarp turns color starting at immature white, going to yellow, orange, brown, and finally mature black. Peanut placement on a color board using hull scrape color is highly dependent on each individual making the observation as to which color profile each individual pod should be placed. Individuals may see hull color differently allowing for personal bias to select specific profiles compared to another individual. Moving pods from one maturity column to another, especially in the black class may give the grower a “false positive or negative” digging date. X-ray technology has been an accepted practice for many years in food processing, pharmaceuticals, and manufacturing industry for contaminate detection, inspection, counting, material integrity, and damaged product. It is proposed that X-ray technology may have the capability of looking at the peanut kernel through the hull to possibly determine density similar to looking at bone density through live tissue. The objective of this project was to determine if x-ray could be used as a quick, non-destructive, and precise method to determine peanut maturity. Peanut sampling began about 110 days after planting and was sampled every 7 to 10 days, depending on weather conditions, until peanuts were over 150 days after planting. There were a total of 7 different harvest dates. At each sampling date approximately 10 feet of crop row were hand dug in each cultivar, washed with tap water, and pods removed manually. Blasting consists of removing the pod exocarp using a high pressure washer with water. Once the exocarp was removed, pods are placed into individual columns based on the subjective classification of their mesocarp color. Once boarded, individual profile columns were x-rayed, saved in individual mesh bags, dried with forced air dryers (same as above) and re-x-rayed. At the end of the season, pods were combined by cultivar and by column color profile and x-rayed again. The x-ray machine was a proprietary product designed specifically for the National Peanut Research Laboratory by TOMRA Sorting NV (Research Park Haasrode 1622 Romeinse straat 20, 3001 Leuven, Belgium). Software algorithms and parameters were designed over a 6-year period to enable the x-ray to identify individual peanut pods/kernels from foreign material with the end result being a farmer stock grade. Software algorythms use the x-ray component to classify peanuts by size, density, and gray scale to determine an acceptible grade compared with manual classification using USDA official grading procedures. It was hypothesized there would be an increase in x-ray value with increased maturity level of peanut. Since this did not occur for green picked peanuts (wet peanuts) and values for immature peanuts were similar in value to mature peanuts was probably related to kernel moisture and kernel size. Once dried, x-ray values increased linearly for the two runner and

Technical Abstract: Indeterminate growth of peanut (Arachis hypogaea L.) creates indecision for best digging date for maturity and economic return. The current standard to determine peanut maturity is the Hull Scrape method. This method uses human observations to place hull scraped peanuts on a color maturity profile board. Human observations may lack precision and repeatability from individual to individual. X-ray technology has the capability of viewing peanut kernels through the hull to possibly ascertain density and maturity. The objective was to determine if x-ray could be used as a quick, non-destructive, and repeatable method to determine peanut maturity of runner, spanish, and virginia market types. Fresh dug peanut pods had 25 percent greater peanut area and gray scale values compared with hull scraped pods (runner and virginia only) and showed no difference in x-ray value between immature and fully mature peanut. Dried peanut showed a linear response of x-ray value versus peanut maturity (hull color). Virginia market type had much higher x-ray values followed by runners, then spanish. The relationship between peanut maturity and x-ray value peaked at the Orange class for runners (Georgia-06G, Georgia-13M), and Spanish (AT9899) while virginia (Georgia-11J) tended to peak at the Brown class. This research demonstrated that x-ray technology may be used to measure peanut density and possible maturity but needs further examination past Orange and Brown maturity class. Final x-ray values determined by this proprietary x-ray equipment may not be transferable due to specific x-ray power, detector precision, background color/scatter, and other electronic nuances.