Alternative storage environments for shelled peanuts

Authors: Butts, Christopher - Chris; Lamb, Marshall; Sorensen, Ronald - Ron; POWELL, SHANE - Birdsong Peanuts; COWART, DARLENE - Birdsong Peanuts; HORM, KATIE - Mars Chocolate North America; ANTHONY, BRIAN - Mars Chocolate North America; BENNETT, JOHN - Mars Chocolate North America

Submitted to: Peanut Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/31/2017
Publication Date: 10/27/2017
Citation: Butts, C.L., Lamb, M.C., Sorensen, R.B., Powell, S., Cowart, D., Horm, K., Anthony, B., Bennett, J. 2017. Alternative storage environments for shelled peanuts. Peanut Science. No. 2, pp. 111-123. doi.org/10.3146/PS17-2.1.

Interpretive Summary: Previous research has shown that peanuts shelled in the late spring and through the summer had an elevated risk of mold growth placed into conventional cold storage at 38 F. Studies showed that when the warm peanuts were placed in cold storage, the air in the top of the container went through a transition period where the relative humidity exceeded 80% causing the peanut moisture content to increase to levels suitable for mold growth. In an effort to reduce this risk, the potential for raising cold storage temperatures from 38 to 55 F was examined. Studies were conducted both in small chambers with small samples and in commercial facilities using full scale commercial packaging and storage facilities. In the small scale studies, a total of 120 samples were divided equally and placed in one of three storage conditions: 38 F, 55 F, and 70 F. The relative humidity was held to about 65% in all three temperature environments. Samples were taken from each environment every 60 days for 360 days and tested for flavor, chemical characteristics, and seed germination. In the commercial tests, three one-ton packages of shelled peanuts were placed in a storage facility maintained at 33 F and 65% relative humidity and three one-ton packages were placed in a storage facility maintained at 55 F and 65% relative humidity for 60 days. Samples were taken at 0, 30, and 60 d storage. Samples were tested for moisture content and water activity. After 60 d of storage, these containers were removed and replaced with containers of new peanuts and the tests repeated. The commercial test also ran for one year. The peanuts stored at 55 F showed no ill effects on flavor, chemical, or germination characteristics in either the small chamber or commercial studies. Insects became a problem in the small-chamber at 70 F after being stored for approximately 140 d. Increasing the temperature of shelled peanut storage facilities from 38 to 55 F could energy required to maintain these facilities by as much as 50%.

Technical Abstract: Studies were conducted in small chambers and commercial storage facilities to evaluate the effect of storing shelled peanuts at 3, 13, and 21 C (38, 55, 70 F) for one year. Shelled medium runner peanuts from the 2014 crop were placed in the three different environments in Feb 2015, sampled at 60-d intervals until Feb 2016 (364 days). Difficulty maintaining the desired relative humidity of 65% in the 3°C unit, led to unacceptable mold growth and severely degraded seed germination. Peanuts stored at 21 C developed an infestation of Indian meal moth after 238 d in storage rendering the samples unsuitable for sensory analysis from that point forward. The infestation most likely occurred due to hatches of eggs that were present in the original samples. Sensory analyses showed very little fade of the intensity of the Roasted Peanut flavor characteristic in either storage environments. No unacceptable increases in free fatty acids or peroxide values were noted at the end of the 1-yr storage period for peanuts stored at 13 C remaining well below 1%. Commercial studies were conducted from Feb 2015 through Mar 2016. Six 60-d runs were conducted where three totes of medium runner peanuts from the same manufacturing lot were placed in commercial cold storage facilities maintained at 3 and 13 C. There were no differences in the initial moisture content of peanuts when placed in the two storage environments. However, after 30 and 60-d storage, the peanuts stored at 13 C tended to be an average of 0.3% dryer than those stored at 3 C. The peanuts had the highest increase in moisture between June and August 2015, with the moisture content after 30 and 60 d storage at 3 C averaged 8.1 and 7.7%, respectively. The peanuts stored in the 13 C environment averaged 7.6 and 7.3% moisture content after 30 and 60 d in storage, respectively.