In-shell Peanuts Research Articles

Anti-mildew and fresh-keeping effect of Lactiplantibacillus paraplantarum P3 cell-free supernatant on fresh in-shell peanuts during storage process

Lactiplantibacillus paraplantarum P3 (L. paraplantarum P3) cell-free supernatant (CFS) with good antifungal effect was sprayed on fresh in-shell peanuts stored at 5 °C and 30 °C to explore its effect on the microorganisms and quality of fresh in-shell peanuts during storage process. Results showed that L. paraplantarum P3 CFS effectively maintained good quality of fresh in-shell peanuts by not only reducing fungi amount and the mildew rate, but also improving the morphology, color and flavor. Besides, L. paraplantarum P3 CFS activated plant mitogen-activated protein kinase signaling pathway and plant hormone signaling pathway to produce more ethylene, gibberellin regulatory proteins and other substances to enhance plant resistance to pathogenic microorganisms. L. paraplantarum P3 CFS could also induce the biosynthesis of glycerophospholipid and arginine to increase the stress resistance of fresh peanuts. This study provides research data for the application of L. paraplantarum P3 CFS in the preservation and antimildew of fresh in-shell peanuts.

Utilization of a Resonant Cavity for Characterization of Single In-Shell Peanuts

Utilization of a Resonant Cavity for Characterization of Single In-Shell Peanuts

Dielectric properties of in-shell peanuts with radio frequency and microwave heating treatment and RF heating performance

Radio frequency (RF) heating technology has potential advantages for drying or sterilization of in-shell peanuts, with a critical need for understanding the dielectric properties governing energy conversion. In this study, the dielectric properties of peanut shells and kernels were measured over the frequency range of 10 MHz ∼ 3 GHz, spanning temperatures from 20 to 80 °C. Results showed that the dielectric constant of all the samples decreased rapidly with increasing frequency, the loss factor of peanut shells and kernels with lower moisture content exhibited an initial decrease within the RF band followed by a slight increase within the microwave (MW) band, while loss factor of peanut kernels with higher moisture content decreased continuously with increase in frequency. A high temperature will enhance the sample polarization, while an elevated moisture content will provide the more polar molecules and release the more ions, so that both of them have the positive effect on the dielectric properties. It should be noted that the disruption of the coarse fiber structure and clumping phenomenon in the samples might mitigate the temperature effect. The numerical simulation results of RF heating based on the cubic regression model of dielectric properties showed that: since the loss factor was more sensitive to temperature and moisture content than dielectric constant, the loss angle tangent of the samples increased significantly with increasing moisture content, which subsequently hindered the heating rate of the samples. Meanwhile, this simulation results derived the optimal conditions, with the fastest heating rate at 20% moisture content and the most uniform RF heating (UI=0.16331) at 30% moisture content. Consequently, the loading thickness of in-shell peanuts should be controlled within 11 cm when designing a 27.12 MHz RF dryer. This research has a profound meaning to promote the efficiency of RF heat treatment of in-shell peanuts.

Characteristics of the modern nut market

Despite seasonal fl uctuations depending on annual climatic conditions, the nut market is showing steady growth. The increase in nut production is explained by the rise in their consumption as a raw material for confectionery products, as well as for direct consumption as an alternative source of basic and physiologically active substances. In total, 5,367,530 tons of nuts were produced in the 2022–2023 marketing year (excluding peanuts). Almonds lead the world production. It is followed by walnuts, cashews, pistachios, and hazelnuts. Pine nuts are the only nut produced in the Russian Federation on an industrial scale. According to Russian data, in the 2022/23 season, the country produced about 35 thousand tons of pine nuts in shell, which is half of the world production of this type. Global production of inshell peanuts annually is about 50 million tons.

A stable and major QTL region on chromosome 2 conditions pod shape in cultivated peanut (Arachis hyopgaea L.)

Peanut pod shape is a heritable trait which affects the market acceptance of in-shell peanut products. In order to determine the genetic control of pod shape, six component traits of pod shape (pod length, pod width, pod length/width ratio, pod roundness, beak degree and constriction degree) were measured using an image-based phenotyping method. A recombinant inbred line (RIL) population consisting of 181 lines was phenotyped across three environments. Continuous distributions and transgressive segregations were demonstrated in all measured traits and environments. Significant correlations were found among most component traits with broad-sense heritability ranging from 0.87 to 0.95. Quantitative trait locus (QTL) analysis yielded 26 additive QTLs explaining 3.79 to 52.37% phenotypic variations. A novel, stable and major QTL region conditioning multiple shape features was detected on chromosome 2, which spans a 10.81-Mb genomic region with 543 putative genes. Bioinformatics analysis revealed several candidate genes in this region. In addition, 73 pairs of epistatic interactions involving 92 loci were identified for six component traits explaining 0.94–6.45% phenotypic variations. These results provide new genetic loci to facilitate genomics-assisted breeding of peanut pod shape.

The Effect of Microwave Irradiation on the Representation and Growth of Moulds in Nuts and Almonds.

Microwave (MW) irradiation is a non-destructive method that can be applied as an alternative method to inhibit the growth of microorganisms. The present study evaluated the effect of MW irradiation on the occurrence of moulds in nuts and almonds. Samples of unshelled natural almonds, pistachios, and in-shell peanuts were treated with different doses of MW irradiation (2400–4000 W). The effect of MW irradiation on mould counts was evaluated by cultivating immediately after irradiation and after 3 and 6 months of storage. The most represented genera in all analysed samples were Aspergillus (68%), Penicillium (21%), and a small amount of Cladosporium (3%). Mould numbers significantly decreased after MW treatment. The treatments with MW irradiations at 3000 and 4000 W significantly reduced the mould colony counts, and their effect persisted during storage; irradiation at 2400 W was partially effective. The strongest effect of MW irradiation was observed in in-shell peanuts. MW irradiation seems to be a promising method for maintaining the microbiological quality of nuts.

COMPUTATIONAL FLUID DYNAMICS MODELED AIR SPEED THROUGH IN-SHELL PEANUTS IN DRYING WAGONS COMPARED TO MEASURED AIR SPEED

Abstract.HighlightsPeanut drying wagon internal airflow simulation and visualization.Comparison of computer fluid dynamic (CFD) solutions to measured air speed.Modeling of airflow through masses of in-shell peanuts. Information is lacking about airflow through masses of drying in-shell peanuts in drying wagons because of the difficulties encountered in making direct measurements. Information about airflow is needed to improve efficiency of drying peanuts to make peanut crops more profitable. Computational Fluid Dynamics (CFD) modeled airflow through in-shell peanuts loaded in drying wagons was validated using actual airflow measurements. CFD models allow for the investigation of airflow within peanut loads and the air plenum of drying wagons. Airflow through a wagon load of in-shell peanuts treated as a solid mass with distributed resistance was modeled using airflow behavior following Darcy’s law. CFD model simulations were undertaken using measured air speed, wagon air plenum static air pressure, and fan performance curve data. CFD modeling was based on actual air speed measurements made at 40 locations on the top surface of wagon loads of in-shell peanuts. The 40 measurement locations represented the top center of 40 blocks which the peanut load was divided into to investigate air speed. To match actual measurements to CFD model results, CFD models were configured with the same 40 blocks as those of the actual measurements. In CFD models, the permeability of the peanuts in each of the 40 blocks could be varied in a trial-and-error fashion to increase or decrease the air speed at the top surface of the peanut load to match that of the actual air speed measured for each of the blocks. Model results reproduced the measured air speed to within the accuracy limits of the air speed measurements. The air speed and static air pressure distribution in the wagon air plenum was found not to be uniform even when all blocks had the same permeability. Model results revealed wagon air plenum air speed patterns and static air pressure distribution could explain the general air speed distribution of slower air speeds at the top surface of the peanut load near the wagon air inlet wall and the increasing air speed along the length of the wagon. Permeability variations within the peanut load were found to explain localized variations in air speed at the top surface of the peanut load. Keywords: Air speed, Airflow, Modeled results compared to measured, Computational fluid dynamics modeling, Drying wagon, In-shell Peanuts, Peanut bulk permeability, Peanut curing, Peanut drying .

Storing Peanuts in Grain Bags

HighlightsExisting bag loading equipment may be used to load both in-shell and shelled oil stock peanuts.Grain bags can be loaded at 1.2 t/m of in-shell peanuts and 2.3 t/m of shelled oil stock peanuts.Existing extraction equipment requires modification to unload shelled oil stock peanuts due to poor flow characteristics.Grain bags not suitable for storing in-shell peanuts due to significant moisture migration and quality reduction under typical Georgia conditions.Abstract.Edible grade farmers’ stock peanuts and shelled oil stock peanuts were stored in hermetically sealed silo or grain bags to determine their suitability for short-term storage. The objectives of the study were to evaluate equipment for loading and unloading the grain bags, the capacity of the grain bags, and the changes in quality. In May 2015, approximately 90 Mg of farmers’ stock (in-shell) peanuts from the 2014 crop were unloaded from a commercial warehouse, transported to Dawson, Georgia, and loaded into two 2.7 m diameter grain bags. Similarly, 85 Mg of shelled oil stock peanuts were loaded into two 2.7 m diameter grain bags. Farmers’ stock bags were unloaded after 30 and 60-d storage. A vacuum extractor and a skid steer loader were used due to wet peanuts in the top of the bag. Both oil stock bags were unloaded after 60-d storage. A skid steer loader was used to unload the oil stock bags because shelled oil stock peanuts did not flow adequately to use the conventional bag extraction equipment. Oxygen content in the farmers’ stock peanuts decreased from ambient levels (21%) to an average of 8.6% after 15-d storage. After 20-d storage, the oxygen content in the oil stock had decreased to 14%. A layer of high moisture peanuts due to moisture migration and subsequent condensation in the top of both of the farmers’ stock bags resulted in the peanuts being unsuitable for human consumption and reduced the value from $342/Mg to approximately $125/Mg for oil stock, a 63% reduction in value. No moisture problems were observed in the oil stock bags when they were unloaded. Based on these studies, sealed grain bags would be unsuitable for temporarily storing farmers’ stock peanuts under typical Georgia conditions. Sealed grain bags could possibly be used to store oil stock peanuts for 60 d, but suitable unloading equipment would have to be found or developed. Keywords: Grain bag, Groundnut, Handling, Hermetic, Peanut, Silo bag, Storage.

Hopper Bottom Semi-Trailer Modified for In-Shell Peanut Drying: Design, Fabrication, and Performance Testing

HighlightsComputational fluid dynamics modeling of airflow through the peanut load improved the design process.Peanuts dried using the modified hopper bottom semi-trailer passed inspection at 9.1% moisture content in preliminary tests.Final moisture gradient in the modified hopper bottom semi-trailer consisted of even layers from front-to-back with moisture increasing with depth.Current inspection probe sampling pattern biases inspection moisture measurements lower by not sampling the hopper bottom.Abstract. Hopper bottom semi-trailers (HBST) modified to dry loads of in-shell peanuts would provide several advantages to peanut producers and peanut processing facility operators. Producers who have HBST for transporting grain would have an additional use for their HBST and would reduce harvest delays during peak harvest times when trailer availability is limited from peanut processors. Additionally, smaller processing facilities would gain the economic advantages of semi-trailers without the investment in hydraulic lifts to unload peanut drying van semi-trailers. Before this study, no HBST had been modified to add peanut drying functionality. The objectives of this study were to design, fabricate, and test the performance of drying modifications to a HBST. After review of the functional components needed to dry peanuts and existing structural constrains of the HBST, the components fabricated were an air inlet connection, an enclosed transition space, an air plenum vent, and air exhaust vents on the undersides of the hopper tubs. The number, size, and location of the air exhaust vents were determined using a computational fluid dynamic model. Three test loads of peanuts were dried in the modified HBST during the 2020 peanut harvest season. Measurements were taken at intervals throughout the peanut drying process to assess drying and to monitor air temperature and relative humidity. Results of a test load indicated that the moisture content decreased from 12.9% wet basis (w.b.) to 12.0% w.b. after 8.5 h of drying. Average moisture content was reduced to 11.1% w.b. following an additional 8.6 h without the dryer operating. The sample load official grade moisture content was 9.1% w.b after the rest period. The most important finding was that a moisture gradient persisted in the loads of peanuts after active drying and rest period. The peanuts located at the top of the load had a moisture content of 9% w.b. while those with the highest moisture content of 14% w.b. were at the bottom of the load. The official inspection sampling procedure did not detect the moisture content differences in the test loads. The finding of a persistent moisture gradient will require more investigation and modification of the HBST. Keywords: Computational Fluid Dynamics, CFD, Design, Drying, Hopper-bottom semi-trailer, Moisture distribution, Moisture gradient, Peanuts, Retrofit.

Experimental and Modeling Study of Peanut Drying in a Solar Dryer with a Novel Type of a Drying Chamber

ABSTRACT The aim of the present study is to investigate the experimental performance of a solar dryer by using a novel type of a drying chamber for increasing the drying performance and ensuring homogeneous drying. The drying system (SDS) consisted of a new type of a drying chamber and a solar air collector, which were designed, made, and tested in Osmaniye, Turkey. The analyses of Computational Fluid Dynamics were carried out to demonstrate the advantage of the designed drying chamber over the tunnel type drying chamber, which is commonly used in peanut drying. The drying experiments were conducted using in-shell peanut to observe the performance of the system. The drying procedure was performed in the form of open sun drying (OSD), and the results of drying kinetics such as moisture ratio (MR), drying rate (DR), and heat transfer coefficient (hc) obtained from both drying methods were compared. The MR and DR values obtained during the drying experiments were estimated using different models such as mathematical, multiple linear regression (MLR), decision tree (DT), and the support vector machine (SVM). It was observed from the numerical results that the products can dry more homogenously and effectively with the newly designed drying chamber compared to the conventional tunnel type drying chamber. The results of the drying experiments showed that the products dried earlier and more regularly through the SDS compared to the OSD. The DR and hc values were found 0.0051E-01 (gw/gdm)/min and 1.5727 W/m2°C for SDS and 0.0039E-01 (gw/gdm)/min and 1.4664 W/m2°C for OSD, respectively. The models that best estimated the experimentally obtained MR and DR values for peanuts dried with the SDS proved to be the Random Tree Model (R2 = 0.9972) and Quintic Model (R2 = 0.8551), respectively.

Nutritive Value and Inherent Anti-Nutritive Factors in Processed Peanut (<i>Arachis hypogaea</i>)

Processing conditions and even the form of the food being processed as they affect nutrient availability is critical to develop structured foods to meet the nutritional needs of end users. The effect of heat treatments (roasting, boiling and autoclaving) on the physical, nutritional and functional properties of in-shell and shelled peanut (Arachishypogaea) was determined. Unprocessed shelled peanut served as the control. Nutrient and anti-nutrient compositions of peanut samples were determined by standard methods, while physical (colour) and functional properties were also carried out. Analysis of variance was used to analyze the treatment groups and Duncan's multiple range tests to determine significant difference at p≤0.05. The result of proximate composition revealed that raw peanut had protein (32.7%), ash (1.37%), fibre (5.15%), fat (42.9%) and carbohydrate (12.1%). However, processing methods significantly increased the fat and ash contents. Peanut is high in calcium, magnesium and potassium but low in iron and zinc; processing significantly increased the elemental concentration of peanut. Phytate, tannin, oxalate, alkaloid, trypsin inhibitor and flavonoid were determined in the peanut samples and all were significantly affected by the processing method employed. However, boiling of shelled peanut was more effective in reducing the anti-nutrients than roasting and autoclaving. The aflatoxin concentration was in a range of 2.06-8.05 ppb. Shelled peanuts subjected to the processing methods had lower aflatoxin levels compared with in-shell processed peanuts. There exist variation in bulk densities (packed and loosed), water and oil absorption capacities as a result of processing method employed. The colour of peanut was significantly affected by the processing method. In general, processing of shelled peanut resulted in flour with better nutritional quality and functionality than in-shell peanut. The findings showed that boiling has proved to be an efficient method in processing of peanut.

Species Composition, Temporal Abundance and Distribution of Insect Captures Inside and Outside Commercial Peanut Shelling Facilities.

Insect populations were studied within two commercial peanut shelling facilities located in the southeastern United States. Commercially available pheromone/kairomone-baited dome traps and pheromone-baited flight traps were deployed throughout processing and shipping portions of the shelling plants and serviced weekly over one year. Lasioderma serricorne, Tribolium castaneum, Typhaea stercorea, Carpophilus spp., Plodia interpunctella and Cadra cautella were the most common captures across locations. Lasioderma serricorne made up 87% and 88% of all captures in dome traps in plants one and two, respectively. While L. serricorne was not captured during the winter months in flight traps, it was captured with near 100% frequency in dome traps, suggesting that populations persisted throughout the year inside the facilities. Tribolium castaneum populations were active year round. Across insect species and trap type, temperature was a significant covariate for explaining variation in insect counts. After accounting for the effect of temperature, there were always more insects captured in the processing portions of the facilities compared to the shipping areas. A negative linear relationship was observed between captures of L. serricorne and T. castaneum and trap distance from in-shell peanuts entering the shelling facilities. Conversely, fungivores were more evenly distributed throughout all parts of the shelling plants. These data suggest that management efforts should be focused where in-shell peanuts enter to reduce breeding and harborage sites for grain feeding insects.

Detection of Irradiated In-Shell Peanuts (Arachis hypogaea) by Screening PPSL and Confirmatory TL Luminescence Methods

In this work, the luminescence methods of pulsed photo-stimulated luminescence (PPSL, as screening) and thermoluminescence (TL, as confirmatory) were used for identification of non-irradiated and low-dose irradiated (1–5 kGy) in-shell peanuts from light emissions of silicate minerals incorporated in the shell. The minerals were irradiated with 90Sr beta particles, 60Co and 137Cs gamma rays. Screening PPSL response detected peanut shell as irradiated from 80 Gy for 60Co and 30 Gy for 137Cs gamma rays. Irradiated (60Co and 137Cs) peanut shell samples were positively detected with PPSL after 4.5 and 14 months. A complex TL glow curve composed of at least two maxima was exhibited by the minerals. Using the TL1/TL2 ratio, the in-shell peanuts were identified as irradiated from 50, 120, and 100 Gy of 90Sr, 60Co, and 137Cs radiation, respectively. Moreover, the TL glow curve shape was also used to identify the peanut shell minerals as irradiated at lower dose of radiation. After 34 days of storage, the peanut shell minerals showed enough TL emissions for their identification as irradiated.

Impact of peanut roasting on Salmonella spp. survival

This study evaluated the efficiency of the dry and oil roasting processes in the inactivation of a pool of five serotypes of Salmonella isolated from the peanut supply chain (Miami, Muenster, Yoruba, Javiana and Glostrup). The Weibull model was fitted to the data to describe the thermal inactivation of Salmonella in peanut matrices. The time to achieve 5-log reduction of the pathogen during dry roasting at 125 °C was significantly different between the matrices (p < 0.05), being 1.5-fold more on the blanched peanuts than on the in-shell peanuts. Only the 145 and 160 °C protocols resulted in reductions > 5-log MPN/g of Salmonella for both matrices, with T5d of 56 and 39 min for blanched peanuts and 46 and 44 min for in-shell peanuts, respectively. For the oil roasting, the Weibull model predicted the first decimal reduction after 7.2 s and 0.012 s at 115 °C and 145 °C, respectively. To achieve reduction of 5 log Salmonella it would take 3.0 min at 115 °C, and 0.40 min at 145 °C. The results demonstrated that temperature, heat process and in some cases the type of matrix influence the thermal resistance of Salmonella on peanuts.

Effects of peanut drying and blanching on Salmonella spp.

In order to evaluate the behavior of Salmonella during peanut drying and blanching, a study was conducted with Runner type peanuts. Samples of raw in-shell or unblanched peanuts were inoculated by spraying with a pool of five Salmonella serotypes isolated from the peanut supply chain (Miami, Muenster, Yoruba, Javiana and Glostrup). The in-shell peanuts were submitted to drying at 35 and 40 °C up to 18 h. After this time, the Salmonella counts went down ca. 2.0 log MPN/g at 35 and 40 °C. According to the Weibull model the time needed to achieve Salmonella 3-log reduction (T3d) and 5-log reduction (T5d) on the in-shell peanuts would be ca. 49 and 117 h at 35 °C and 35 and 79 h at 40 °C, respectively. The results showed that there was no statistical difference (p > .05) between either of the temperatures employed in the process. The blanching process was performed in two steps: pre-roasting (step 1) and skin removal (step 2). Reduction of up to 2.1 log MPN/g was observed after blanching at 100 °C/15 min plus 15 s of air impact. The skin removal process did not result in recontamination of the final sample. The Weibull model predicted 3- and 5-log reductions of Salmonella in 37.0 and 68.9 min for blanching at 95 °C, and in 39.1 and 114.9 min at 100 °C. The results demonstrated that drying and blanching processes did not generate large reductions of Salmonella in the peanut samples. Thus, the product resulting from these steps may be a possible source of cross-contamination for the processing plant and the final product.

Sensory and Chemical Stabilities of High-Oleic and Normal-Oleic Peanuts in Shell During Long-Term Storage.

Quality preservation of peanuts is important for the food industry using peanuts as an ingredient. Peanut processors are concerned as to the best ways to preserve peanut quality for long-term storage. Raw high oleic peanuts kept in the shells show better preservation of their sensory and quality properties during storage. In-shell peanuts constitute an appropriate alternative to preserve chemical and sensory properties of this product.

Long-term kinetics of Salmonella Typhimurium ATCC 14028 survival on peanuts and peanut confectionery products.

Due to recent large outbreaks, peanuts have been considered a product of potential risk for Salmonella. Usually, peanut products show a low water activity (aw) and high fat content, which contribute to increasing the thermal resistance and survival of Salmonella. This study evaluated the long-term kinetics of Salmonella survival on different peanut products under storage at 28°C for 420 days. Samples of raw in-shell peanuts (aw = 0.29), roasted peanuts (aw = 0.39), unblanched peanut kernel (aw = 0.54), peanut brittle (aw = 0.30), paçoca (aw = 0.40) and pé-de-moça (aw = 0.68) were inoculated with Salmonella Typhimurium ATCC 14028 at two inoculum levels (3 and 6 log cfu/ g). The Salmonella behavior was influenced (p<0.05) by aw, lipid, carbohydrate and protein content. In most cases for both inoculum levels, the greatest reductions were seen after the first two weeks of storage, followed by a slower decline phase. The lowest reductions were verified in paçoca and roasted peanuts, with counts of 1.01 and 0.87 log cfu/ g at low inoculum level and 2.53 and 3.82 log cfu/ g at high inoculum level at the end of the storage time. The highest loss of viability was observed in pé-de-moça, with absence of Salmonella in 10-g after 180 days at low inoculum level. The Weibull model provided a suitable fit to the data (R2≥0.81), with δ value ranging from 0.06 to 49.75 days. Therefore, the results demonstrated that Salmonella survives longer in peanut products, beyond the shelf life (>420 days), especially in products with aw around 0.40.

Solar Drying: A Means of Improving the Quality of Peanuts in Ghana

ABSTRACT An indirect, passive, wooden dryer, with a galvanized steel panel (4.5 m2) and four wire mesh shelves (2.62 m2 each), was constructed in Kumasi, Ghana. The dryer was evaluated for its capacity in drying of freshly-harvested in-shell peanuts on a single layer (8.5 Kg), and then up-scaled to four layers (4x18 Kg). Equal amounts of peanuts, dried simultaneously on a concrete floor under the open sun, served as comparisons. The moisture content of solar dried peanuts decreased from 35.85-5.25% and 32.00 %-4.25% in the single-layer and four-layer drying, respectively, in 4 days. Faster drying rates were observed when peanuts had relatively higher moisture contents with R2 values ranging from 0.72-0.95. The average daily solar radiation ranged from 360-592.99 W/m2 and daily energies generated were from 42.24-69.16 MJ. The drying efficiency ranged from 1.50-6.47% in the single-layer drying and 23.07-24.93% in the four-layer drying whereas the thermal efficiency was 3.15-21.60% in the single-layer drying and 3.08-24.93% in the four-layer drying. Peanuts from the solar dryer had lower free fatty acid and peroxide values but higher germination percentage compared to open sundried peanuts. The study suggests that solar drying can be used effectively for improving peanut safety and preserving peanut quality in Ghana.

Variation in fungal microbiome (mycobiome) and aflatoxins during simulated storage of in-shell peanuts and peanut kernels.

Internal transcribed spacer 2 (ITS2) sequencing was used to characterize the peanut mycobiome during 90 days storage at five conditions. The fungal diversity in in-shell peanuts was higher with 110 operational taxonomic units (OTUs) and 41 genera than peanut kernels (91 OTUs and 37 genera). This means that the micro-environment in shell is more suitable for maintaining fungal diversity. At 20–30 d, Rhizopus, Eurotium and Wallemia were predominant in in-shell peanuts. In peanut kernels, Rhizopus (>30%) and Eurotium (>20%) were predominant at 10–20 d and 30 d, respectively. The relative abundances of Rhizopus, Eurotium and Wallemia were higher than Aspergillus, because they were xerophilic and grew well on substrates with low water activity (aw). During growth, they released metabolic water, thereby favoring the growth of Aspergillus. Therefore, from 30 to 90 d, the relative abundance of Aspergillus increased while that of Rhizopus, Eurotium and Wallemia decreased. Principal Coordinate Analysis (PCoA) revealed that peanuts stored for 60–90 days and for 10–30 days clustered differently from each other. Due to low aw values (0.34–0.72) and low levels of A. flavus, nine of 51 samples were contaminated with aflatoxins.

Microwave moisture meter for in-shell peanut kernels

A microwave moisture meter built with off-the-shelf components was developed, calibrated and tested in the laboratory and in the field for nondestructive and instantaneous in-shell peanut kernel moisture content determination from dielectric properties measurements on unshelled peanut pod samples. The meter operates at a single frequency of 5.8 GHz and uses free-space transmission measurement principles for determining the dielectric properties of the peanut pods. From these properties, a dielectric-based algorithm provides peanut kernel moisture content from measurements on pods. Field tests at a peanut buying station showed that moisture content of peanut kernels can be determined with a standard error of performance of 0.82% when compared to the official moisture meter which required the pods to be shelled before kernel moisture content can be determined. When performance of both the microwave moisture meter and the official meter were compared to the oven-drying standard method, values of the standard errors of performance were 0.53% for the microwave moisture meter and 0.87% for the official moisture meter.