Effects of postharvest handling practices on quality of groundnuts and aflatoxin contamination

The increased cases of aflatoxin contamination are exacerbated by poor post-harvest management practices, coupled with adverse climatic conditions at harvest and post-harvest stages. This study therefore was carried out to improve safety and quality of groundnuts from aflatoxin contamination, through use of proper postharvest handling practices. Specifically the study determined the effects of harvesting dates and drying methods on aflatoxin contamination. Field experiments were carried out both at Chitedze and Chitala Agricultural Research Stations in Malawi during 2017/2018 growing season. A randomized complete block design in a split plot arrangement with three harvesting dates as the main plot and four drying methods as the sub-plots replicated three times was used. Groundnut was assessed for kernel infection by Aspergillus flavus, and level of aflatoxin contamination. Significantly low levels of about 0.5μg/ Kg of A. flavus infection and aflatoxin contamination were observed at 90 days after sowing (DAS). Higher aflatoxin contamination of up to 5μg/ Kg was observed at 80 DAS, and 10 days late after physiological maturity (100 DAS). This study also identified Mandela cock, aframe drying rack as effective drying method that can reduce aflatoxin contamination in groundnuts by 75 %. Moreover, Mandela cock drying method was shown as the most effective compared to A-frame and drying rack drying method. Current study therefore recommends for adoption of timely harvesting at physiological maturity, and drying using either Mandela cock or A-frame and drying rack. Further studies need to be carried on biological control of aflatoxin contamination

Reducing Aflatoxins in Groundnuts through Integrated Management and Biocontrol

The groundnut, or peanut (Arachis hypogaea L.), is an important food and fodder crop in the farming systems of developing countries. The seed is high in oil (close to 50 percent for many varieties) and protein (~26 percent) and an important source of vitamins and dietary fiber. Groundnuts, like all legumes, are also important due to their ability to fix atmospheric nitrogen, a critical and often limiting nutrient for crops in degraded soils. Global groundnut production is concentrated in Africa (40 percent) and Asia (55 percent). As discussed in other briefs in this series, high aflatoxin levels pose human health risks and are also a barrier to expanding trade in and commercial use of groundnuts and other crops

Predicting aflatoxin content in peanuts using ambient temperature, soil temperature and soil moisture content during pod development

Higher than acceptable aflatoxin levels in peanut kernels (Arachis hypogaea L.) and related products is a worldwide food safety concern. Strict regulatory standards by major importers of peanuts limit the marketability of peanuts for many developing tropical countries including Zambia. The incidence of preharvest aflatoxins is strongly linked to soil and weather conditions during pod-development. This study aimed to formulate statistical models to predict total aflatoxin content in peanut kernels using selected environmental factors during pod development. Field experiments were conducted for two years during which the peanut crop was exposed to 84 combinations of ambient temperature, soil temperature and soil moisture content measured during the last 30 days of pod development. These data were used to formulate regression models to predict total aflatoxin content in peanut kernels. Simple linear regression models had R2 values of 0.30 for maximum ambient temperature, 0.24 for soil temperature and 0.38 for soil moisture content. Combining soil moisture content and soil temperature in a multivariate regression model could explain 54% of the variation in total aflatoxin content while a combination of soil moisture content and maximum ambient temperature could only explain 46% of the variation in total aflatoxin content

Identification and Toxigenicity of Aspergillus spp. from Soils Planted to Peanuts in Eastern Zambia

It is not known which aflatoxigenic species are present in Zambia. Therefore, soil samples were collected during May to June 2012, at the end of the growing season in Eastern Province, from 399 farmers' fields that had been planted to groundnut (Arachis hypogaea L.) in Nyimba, Petauke, Mambwe, and Chipata Districts. Population densities of Aspergillus spp. were estimated by plating 10−3 soil dilutions on modified dichloran rose Bengal (MDRB) media. To test for toxigenicity, colonies were randomly selected from MDRB dilution plates, single-spored, transferred to vials with yeast extract sucrose (YES) liquid media, and grown for a week at room temperature. Agra Strip ® lateral flow cards were then used to test the filtered extracts, from the YES cultures, for total aflatoxin at 4 and 20 parts per billion (ppb). We identified Aspergillus flavus (small and large sclerotia strains), A. parasiticus, A. niger, A. nomius, A. oryzae, A. tamarii, and A. terreus. 100% of the S-strain A. flavus isolates produced aflatoxin at 4 and 20 ppb, whereas 86% and 56% of the L-strain A. flavus isolates produced aflatoxins at 4 and 20 ppb, respectively. All the A. nomius isolates produced aflatoxins at 4 and 20 ppb. 79% and 64% the A. parasiticus isolates produced aflatoxins at 4 and 20 ppb. To our knowledge, this is the first peer reviewed report from Zambia documenting the population densities of A. flavus across different agroecologies. In addition, it is also the first report on the identification of different Aspergillus spp., such as A. nomius, A. terreus, A. oryzae, and A. tamarii from Zambia. This information, taken together with cropping practices, soil characteristics, agroecological and climatic data, can form a basis for developing holistic pre-harvest aflatoxin mitigation strategies

Simulation model for solar energy harnessing by the solar tunnel dryer

Models were developed to predict global solar radiation and the energy harnessed by a solar tunnel dryer, and simulated in Visual Basic 6.  In addition, the simulated data were compared with actual data.  Using a 10% absolute residual error interval, the developed model achieved 78.4% and 83.3% performance for global solar radiation and energy harnessing, respectively.  Further, the relationship between global solar radiation and the ten years mean satellite solar radiation, and that between the actual and simulated plenum chamber temperatures were linear, with coefficients of determination (R2) of 0.788 and 0.962.  Thus, it shows that there is the existence of strong correlation between satellite and predicted global solar radiation, and between predicted and actual plenum chamber temperatures.  Furthermore, Student’s t-test did not show any significant difference between simulated and actual data for solar radiation and energy harnessing.  Finally, this study shows that the developed model can be used to predict solar radiation and the energy harnessed by the solar tunnel dryer.Keywords: modeling, tunnel-dryer, global, direct, solar-radiation, plenum-temperature Citation: Kituu G. M., D. Shitanda, C. L. Kanali, J. T. Mailutha, C. K. Njoroge, J. K.Wainaina, and J. S Bongyereire. Simulation model for solar energy harnessing by the solar tunnel dryer.  Agric Eng Int: CIGR Journal, 2010, 12(1): 91-98

Effects of Compost Manure on Soil Microbial Respiration, Plant-Available-Water, Peanut (Arachis hypogaea L.) Yield and Pre-Harvest Aflatoxin Contamination

Peanut production in Zambia is often characterized by low yields and high aflatoxin incidence in harvested kernels. Soil amendments such as farmyard manure have shown potential to increase yields and reduce pre-harvest aflatoxin incidence. The aim of the current study was to evaluate the effects of composted cattle manure on soil properties that relate to yield and pre-harvest aflatoxin contamination of peanut kernels. Research evaluated the effects of composted cattle manure on soil respiration, plant-available water (PAW), peanut yield and pre-harvest aflatoxin contamination in a field experiment conducted in two successive rain-fed cropping seasons starting in December, 2015 and ending in April 2017, in Chongwe District, Zambia. Six (6) levels of compost were incorporated into the top 10 cm of the soil at rates of 0, 4.5, 12.0, 19.5, 27.0, and 34.5 metric tons/ha 1 wk before planting. There was a strong positive relationship between levels of compost and soil microbial respiration (R2=0.84) and PAW (R2=0.86). Secondly, compost manure was associated with increases in pod (R2=0.65) and kernel (R2=0.61) yield. The kernel yield potential of the planted cultivar was achieved at the rate of 12 metric tons per ha. Thirdly, there was a reduction in total aflatoxin levels with increasing levels of compost (R2=0.85). The improvement in peanut yield and the decrease in aflatoxin concentrations in kernels can be attributed to the improvement in soil moisture retention capacity and soil microbial activity arising from manure amendments. This study demonstrated the potential of compost manure to increase soil microbial activity, PAW, peanut yield and minimize aflatoxin contamination at field level

Uncommon occurrence ratios of aflatoxin B1, B 2, G 1, and G 2 in maize and groundnuts from Malawi

We report an unusual aflatoxin profile in maize and groundnuts from Malawi, with aflatoxin G1 found routinely at equal or even higher levels than aflatoxin B1. Aflatoxin B1 (AFB1) ratio in a contaminated sample is generally greater than 50 % of total aflatoxin (sum of aflatoxin B1, B2, G1, and G2). In Malawi, the aflatoxin occurrence ratios were determined by examining LC-MS/MS and HPLC fluorescence detection (FLD) data of 156 naturally contaminated raw maize and 80 groundnut samples collected in 2011 and 2012. Results showed that natural aflatoxin occurrence ratio differed. In 47 % of the samples, the concentration of AFG1 was higher than that of AFB1. The mean concentration percentages of AFB1/AFB2/AFG1/AFG2 in reference to total aflatoxins were found to be 47:5:43:5 %, respectively. The AFG1 and AFB1 50/50 trend was observed in maize and groundnuts and was consistent for samples collected in both years. If the AFB1 measurement was used to check compliance of total aflatoxin regulatory limit set at 10, 20, 100, and 200 μg/kg with an assumption that AFB1 ≥ 50 % of the total aflatoxin content, 8, 13, 24, and 26 % false negative rates would have occurred respectively. It is therefore important for legislation to consider total aflatoxins rather than AFB1 alone

Predicting the impact of outdoor vector control interventions on malaria transmission intensity from semi-field studies

BACKGROUND: Semi-field experiments with human landing catch (HLC) measure as the outcome are an important step in the development of novel vector control interventions against outdoor transmission of malaria since they provide good estimates of personal protection. However, it is often infeasible to determine whether the reduction in HLC counts is due to mosquito mortality or repellency, especially considering that spatial repellents based on volatile pyrethroids might induce both. Due to the vastly different impact of repellency and mortality on transmission, the community-level impact of spatial repellents can not be estimated from such semi-field experiments. METHODS: We present a new stochastic model that is able to estimate for any product inhibiting outdoor biting, its repelling effect versus its killing and disarming (preventing host-seeking until the next night) effects, based only on time-stratified HLC data from controlled semi-field experiments. For parameter inference, a Bayesian hierarchical model is used to account for nightly variation of semi-field experimental conditions. We estimate the impact of the products on the vectorial capacity of the given Anopheles species using an existing mathematical model. With this methodology, we analysed data from recent semi-field studies in Kenya and Tanzania on the impact of transfluthrin-treated eave ribbons, the odour-baited Suna trap and their combination (push-pull system) on HLC of Anopheles arabiensis in the peridomestic area. RESULTS: Complementing previous analyses of personal protection, we found that the transfluthrin-treated eave ribbons act mainly by killing or disarming mosquitoes. Depending on the actual ratio of disarming versus killing, the vectorial capacity of An. arabiensis is reduced by 41 to 96% at 70% coverage with the transfluthrin-treated eave ribbons and by 38 to 82% at the same coverage with the push-pull system, under the assumption of a similar impact on biting indoors compared to outdoors. CONCLUSIONS: The results of this analysis of semi-field data suggest that transfluthrin-treated eave ribbons are a promising tool against malaria transmission by An. arabiensis in the peridomestic area, since they provide both personal and community protection. Our modelling framework can estimate the community-level impact of any tool intervening during the mosquito host-seeking state using data from only semi-field experiments with time-stratified HLC

A Case for Regular Aflatoxin Monitoring in Peanut Butter in Sub-Saharan Africa: Lessons from a 3-Year Survey in Zambia

A 3-year comprehensive analysis of aflatoxin contamination in peanut butter was conducted in Zambia, sub-Saharan Africa. The study analyzed 954 containers of 24 local and imported peanut butter brands collected from shops in Chipata, Mambwe, Petauke, Katete, and Nyimba districts and also in Lusaka from 2012 to 2014. For analysis, a sample included six containers of a single brand, from the same processing batch number and the same shop. Each container was quantitatively analyzed for aflatoxin B1 (AFB1) in six replicates by using competitive enzyme-linked immunosorbent assay; thus, aflatoxin contamination level of a given sample was derived from an average of 36 test values. Results showed that 73% of the brands tested in 2012 were contaminated with AFB1 levels >20 μg/kg and ranged up to 130 μg/kg. In 2013, 80% of the brands were contaminated with AFB1 levels >20 μg/kg and ranged up to 10,740 μg/kg. Compared with brand data from 2012 and 2013, fewer brands in 2014, i.e., 53%, had aflatoxin B1 levels >20 μg/kg and ranged up to 1,000 μg/kg. Of the eight brands tested repeatedly across the 3-year period, none consistently averaged ≤20 μg/kg. Our survey clearly demonstrates the regular occurrence of high levels of AF B1 in peanut butter in Zambia. Considering that some of the brands tested originated from neighboring countries such as Malawi, Zimbabwe, and South Africa, the current findings provide a sub-Saharan regional perspective regarding the safety of peanut butter

Aflatoxin B1 contamination of groundnut Arachis hypogaea L. in eastern Zambia

Groundnut is a rich source of protein and it is the second most widely grown crop in eastern Zambia. A survey was conducted in 2012 to determine the incidence of aflatoxin B1 contamination in groundnuts from several districts important in groundnut production in eastern Zambia. Nyimba and Mambwe districts are in the Luangwa Valley and are comparatively hotter and drier than Chipata and Petauke districts which lie in the cooler plateau. 399, 1 kg unshelled groundnut samples were collected from farmers’ fields and also from homesteads upto 1 month after harvest. Aflatoxin B1 was assayed in each shelled sample by weighing and comminuting 100 g subsample and extracting aflatoxin from six 20 g aliquots. ELISA was used to estimate aflatoxin levels and the six values averaged to give the sample contamination. 34 and 27% of samples from Nyimba (maximum=4,980 ppb and arithmetic mean [AM] =1.1) and Mambwe (maximum=69 ppb and AM=0.7), respectively, had aflatoxin levels greater than 20 ppb. In comparison, 38 and 28% of samples from Petauke (maximum=3,258 ppb and AM=0.9) and Chipata (maximum=1,077, and AM= 0.8), respectively, had aflatoxin levels greater than 20 ppb. At the beginning of the season, priority is given to planting maize and cotton, while planting groundnut is delayed, increasing the risk of the crop being exposed to end-of-season drought. The aflatoxin contamination levels we report are a barrier to trade and the well being of consumers