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 change in the intensity of the Roasted Peanut flavor characteristic in either storage environments. There were no unacceptable increases in free fatty acids or peroxide values during the 1-yr storage period for peanuts stored at 13 C. The percent free fatty acids in peanuts stored at 13 C remained well below 1% throughout the 1-yr study. 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. This study has shown that shelled peanuts can be stored for up to one year with no detrimental effects at temperatures up to 13 C and relative humidity ranging from 55 to 70%. Based on this research, the recommended temperature for storing shelled peanuts can be increased to 13 C, while maintaining the relative humidity between 55 and 70%.
Peanut shelling companies will have at least one of their shelling facilities processing peanuts almost year round to minimize any carryover of farmers' stock peanuts from one crop year to the next. In the shelling process, farmers' stock peanuts are cleaned removing foreign material, and then shelled, separating the kernels from the hulls. After additional processing to segregate the shelled peanuts into various commercial sizes and sorting to remove additional foreign material and damaged kernels, the shelled peanuts are loaded into flexible intermediate bulk containers (totes). Each tote holds approximately 1 t (1000 kg) of similarly sized and type peantus (e.g. Medium Runners). Totes are assembled, labelled, and positively identified into a single lot consisting of 20 totes. Each tote in the lot is sealed and labelled with a coded adhesive tag around the filler neck of the tote then placed in dry storage or in a cold storage facility where the entire lot remains until they are shipped to the peanut product manufacturer. Once the tote is labelled and sealed with the Federal-State Inspection Service lot identification tag, the tote may not be opened until it reaches the buyer.
As early as 2005, researchers were made aware of complaints of shelled peanuts received by some European customers having spots on the surface of the kernels after oil roasting. In response to the complaints, scientists determined that the spots were caused by injury to the kernel due to fungal invasion (Sobolev,
More recently, complaints of mold being found on the peanuts in the tops of the totes by domestic and international customers have been received.
During the shelling process, peanuts reach a temperature that is in equilibrium with the ambient temperature in the shelling plant due to the large amount of moving air used in the shelling, sorting, and sizing processes. As the shelled peanuts are loaded into the totes, ambient air accompanies the peanuts into the bag. The totes are placed into cold storage facilities maintained according to the good management practices between 1 and 5 C and 55 and 70% relative humidity (
The psychrometric chart is a graphical representation of the thermodynamic properties of moist air and can be used to visualize how the temperature and humidity conditions change when air is heated, cooled, or mixed with air of differing conditions.
If the conditions for cold storage were changed from 3 to 13 C with the same relative humidity condition of 65% (
The primary objective of this research was to investigate the effect of alternative temperature environments for storing shelled peanuts on peanut quality and storage facility pest management. Specific objectives were two-fold:
Determine the effect on peanut water activity, seed germination/vigor, free fatty acids, peroxide values, and flavor over time at various temperature and humidity conditions.
Monitor temperature, humidity, and peanut “wetness” in totes of shelled peanuts in commercial storage facilities held at conventional cold storage conditions (3 C, 65%) and alternative storage conditions (13 C, 65%).
Approximately 600 kg of mill run runner medium-sized peanuts were obtained from a single shelled lot of the 2014 peanut crop. Sample bags were fabricated from woven polypropylene fabric used in the manufacture of the flexible intermediate bulk containers (totes) for storing and handling shelled peanuts (
Lexicon of peanut flavor attributes used in the sensory evaluations of samples from alternative storage environments for shelled peanuts.
Sampling schedule for small chamber tests of alternative shelled peanut storage environments.
Using peanuts from normal shelling operations, six totes were filled with mill run runner type peanuts according to conventional practice. Immediately after filling, but prior to closing, a 200-g sample was removed from the top of the tote to determine the moisture content (% w.b.) and the water activity (aw). A datalogger (Hobo Model U23-001, Onset Computers, Bourne, MA) to record temperature and relative humidity and a leaf wetness sensor (Model LWS, Decagon Devices Inc., Pullman, WA) were placed in a small mesh bag containing 200-300 g of shelled peanuts from the tote, then worked into the top 5 cm of peanuts in the tote. The lead wires of the leaf wetness sensor extended out through the filler neck of the tote. The leaf wetness sensors are a resistance grid embedded in a leaf shaped composite to simulate the leaf surface and have been used in agronomic research to monitor the presence of condensation on leaves in a plant canopy. While these sensors do not have the same heat transfer and surface shape or texture as the shelled peanuts, it was hypothesized that they might indicate the presence of condensation on the peanuts in the top of the totes.
Three totes were stacked in a cold storage facility maintained at 3 C and 65% relative humidity (
Sampling and test schedule for storing shelled peanuts in alternative environments at commercial storage facilities.
Summary statistics of the temperature and relative humidity in each of the small chamber storage environments are shown in
Summary statistics for the temperature and relative humidity in the small controlled environment chambers for the shelled peanut storage study.
The relative humidity in the small controlled environment chambers (13 and 21 C) was considerably more stable than in the walk-in cooler (3 C).
There were no significant changes in the quality of the peanuts stored in the 13 C chambers. However, active mold growth was observed in one of the three the samples retrieved from each of the 3 and 21 C chambers after 180 d storage. The mold growth in the 3 C sample was directly related to the excessive relative humidity (
Analysis of variance (PROC GLM, SAS v9, Cary, NC) indicated that storage time had a significant effect (α = 0.05) on 10 out of 17 of the flavor attributes, free fatty acid, peroxide value, and the seed germination (
Analysis of variance of raw sensory attributes, free fatty acid, peroxide value, and seed germination due to storage time, storage temperature, and sample.
Because there was no dependence on storage temperature, the attribute intensities were averaged over all storage temperatures at each sampling date (
Mean flavor attribute intensities* averaged over all storage temperatures.
The percent free fatty acids (FFA) and peroxide values (PV) are both indicators of oxidative degradation of the oil in the peanuts. The FFA tended to increase during the 364 d storage period for all storage temperatures (
Mean percent free fatty acid after storage at three different temperatures in controlled environment chambers.
There was no significant increase in PV in the peanuts stored at 13 C throughout the storage period (
Mean peroxide values (meq) after storage at three different temperatures in controlled environment chambers.
Seed germination was initially 74.5% when placed in storage (
Mean percent germination after storage at three different temperatures in controlled environment chambers.
As shown in
Summary of storage and initial peanut temperature ( C) and relative humidity (%), initial and final moisture contents (%) of shelled peanuts stored for 60 d in commercial facilities maintained at 3 and 13 C.
After shelling and filling, the initial peanut temperature fluctuated seasonally as expected (
Peanut moisture content after 0, 30, and 60 d in commercial storage maintained at 3 and 13 C averaged over all six runs.
In general, the peanut moisture content after 60 d storage tended to be higher when the initial peanut temperature exceeded 20 C (
Peanuts will rehydrate to an EMC of 7.5% if maintained in an 70% relative humidity environment (
Percent of the storage time that the relative humidity measured on the outside of and in the top of each tote was greater than or equal to 75% when stored for 60 d in commercial facilities maintained at 3 and 13 C.
During Runs 1-4, 2014 crop peanuts were placed in cold storage and had already reached an EMC of less than 7%.
If peanuts are in a desorption (drying) phase, they will equilibrate to a higher moisture content than they would in a sorption (rewetting) phase and held at the same relative humidity (
If a commercial cold storage facility were to change its operating parameters so that the temperature is maintained at 13 C and the relative humidity maintained at 60%, let's examine the effect on operating costs. As stated in the introduction, the average number of cooling degree days would be reduced from 5629 to 2525 C-days. Cooling degree days are an indicator of the energy required to maintain a building at a fixed temperature accounting for the heat transfer from outside the building through conduction. An additional energy load occurs due to infiltration of warm outside air into the cooled space. This infiltration occurs through intentional introduction of outside air, unintentional leaks, and traffic in and out of the cold storage facility. The cooling load associated with cooling the infiltrating air consists of a sensible portion (the amount of heat required just to change the temperature) and a latent portion (the amount of heat associated with the condensation and removal of water from the air). For this analysis, we will assume that the amount of infiltration is primarily due to traffic moving product in and out of cold storage and will be the same whether the facility is maintained at 3 or 13 C. In both scenarios, the target relative humidity will be 60%. Using the weather stations at Albany, Attapulgus, Dawson, and Vienna, Georgia (
If a commercial facility were to raise its operating temperature from 3 to 13 C and maintain 60% RH, both the latent and sensible cooling load could be reduced by approximately 50%. Due diligence in other good management practices such as sanitation and pest control would have to be maintained.
Tests were conducted to examine the change in peanut flavor, chemistry, germination and the risk of mold growth when storing shelled peanuts at 3, 13, and 21 C. Small chamber tests showed that there was no significant reduction in flavor, chemistry, or germination when stored up to 1 year at 13 C. There were no significant reductions in flavor, chemistry, or chemistry when peanuts were stored at 21 C. However, infestation by Indian meal moth prevented sensory and germination evaluations after 180 d storage. Controlling the relative humidity in the 3 C chamber within the recommended range of 55-70% was difficult and resulted in mold growth deeming them unacceptable for sensory testing. Tests at commercial storage facilities indicated that the risk of mold growth when storing shelled peanuts could be significantly reduced if the storage temperature were increased from 3 C to 13 C while maintaining relative humidity between 55 and 70%. The commercial testing also indicated that the relative humidity should be maintained closer to 55% than 70% when placing a significant amount of new crop peanut to reduce the risk of mold growth. Raising the storage temperature from 3 to 13 C could reduce the energy costs of operating the cold storage facility by as much as 55%. Based on this research, the recommended temperature for storing shelled peanuts can be increased to 13 C, while maintaining the relative humidity between 55 and 70%.
The authors kindly acknowledge the cooperation of the staff in the shipping department of the Birdsong Peanuts shelling plant located in Colquitt, GA for loading the shelled peanuts, stacking and unstacking the totes to provide access for sampling during the middle of each 60-d storage cycle. The authors also acknowledge David DeShazo at JLA International in Albany, GA for conducting the sensory panel and chemistry evaluations. The germination samples were evaluated as a courtesy by the Georgia Department of Agriculture's Seed Lab located in Tifton, GA.
First, second, third authors: Agricultural Engineer, Supervisory Research Food Technologist, Research Agronomist, USDA-ARS National Peanut Research Laboratory, Dawson, GA 39842; Fourth and fifth authors: SE Food Safety and Quality Manager, Director of Food Safety and Quality, Birdsong Peanuts, Blakely, GA 39823; Sixth, seventh and eighth authors: : Raw Materials Technologist, Global Strategic Raw Materials Manager, Global Research and Development Nut Manager, Mars Chocolate Elizabethtown, PA 17022