Section 7: Drying and Storing Groundnuts
Dry Groundnuts Quickly
In order to maintain quality of groundnuts and prevent growth of mold, groundnuts should be dried as quickly as possible. If groundnuts are not immediately removed from plants, pods should be turned facing the sky with soil shaken from the roots and pod as thoroughly as possible. This will allow air to flow across pods and will decrease the amount of time needed for drying (Figure 7.1). If groundnuts are dug and pods removed at the same time, pods should be placed on tarps or materials that provide a barrier between the pods and soil. This will also increase the speed of drying and will protect pods from insect damage and possible mold contamination.
The drying step is often the most important step in managing aflatoxin contamination. Practices in the field can also affect contamination by aflatoxin, but poor drying can cause an explosion of mold and high contamination going into storage. Groundnuts should be dried to a moisture of less than 10% before placing in storage. Groundnuts in the field are often dried to approximately 10% before they are stripped from the vines. This stripped is often done with sticks which often damages the pods. For smallholder farmers this percentage can be difficult to estimate. Many farmers use a technique of shaking a handful of pods, which may make a rattling sound when dried. Pods that make this sound may need to be dried even a bit more to assure they are safe from mold growth. Moisture meters are available and could be used on a village or community level. It is important to dry pods more slowly and handle pods with care if they are going to be used for seed the following year.
Store Groundnuts Properly
The first step in maintaining kernel quality and reducing the risk of aflatoxin contamination is to dry groundnuts to a low moisture content as quickly as possible and move the dried groundnuts into storage as quickly as possible. Storage of groundnuts remaining with the shell is recommended because the shell offers a protective layer against pests that are found in storage areas and can protect kernels from physical damage. While difficult to achieve, especially for small-holder farmers, storing groundnuts in protective bags placed away from walls and off of the floor promotes air flow and can keep relative humidity lower. Air flow in a shady area can also moderate temperatures. Decreases in groundnut kernel quality and increases in mold growth leading to possible aflatoxin contamination occur when relative humidity and temperatures are high. If plastic storage bags that can be hermetically sealed are available, the quality of groundnut kernels can be maintained and the potential for increased aflatoxin during storage minimized. If these are used it is important that moisture of groundnuts is 8% or less and that bags remain sealed. If groundnut moisture is high and bags are sealed, mold and subsequent aflatoxin contamination can increase at a high rate.
Importance of Minimizing Aflatoxin in the Field, During Drying and in Storage
Careful attention to management practices at pre-harvest and post-harvest steps is needed to provide a safe product that can be further processed, marketed to consumers and exported. Proper practices and care of groundnuts prior to storage can have a significant effect on the potential for an increase in aflatoxin contamination while in storage. Incorporating practices that improve plant health in the field not only increases yield but also decreases contamination by mold and subsequent aflatoxin contamination. Practices such as increased fertility and protection from pest damage in the field results in less mold going into the drying step. Pest-resistant varieties and good rotation sequences along with other practices improve plant health. Rapid drying and less exposure of groundnuts to soil where mold is often found can decrease the abundance of aflatoxin production molds going into storage. It is important to store groundnuts elevated off the ground (e.g., on a wooden pallet), and under cool and dry conditions if at all possible. Mold can grow exponentially when relative humidity and temperatures are high. NEVER moisten or add any water to the pods when shelling. This increases the likelihood of higher aflatoxin contamination. Sealed bags create a protected environment not only from moisture but also from arthropod and vertebrate pests. It is important that groundnuts are dried to the desired level before sealing bags. Sealing bags with groundnuts at higher moisture could lead to disaster.
Practices to Minimize Aflatoxin Contamination
In general, the growth of healthy groundnut plants in the field will reduce aflatoxin contamination of the crop prior to harvest. Stressed plants are more likely to suffer from higher levels of aflatoxin. Thus, the first step in aflatoxin management is the production of a healthy, high yielding crop which should also contribute to increased profits. This fact cannot be overstated in an overall aflatoxin management program that the cost-efficient production of high yielding and profitable groundnuts is the best approach to gain an initial advantage in this effort.
Figures 7.3 and 7.4 compare practices that improved plant health in the field (e.g., fertilizer, minor suppression of disease and aphids, and extra weeding) with the traditional farmer practice. In this research conducted in rural villages, groundnuts following both practices in the field were dried on the ground or on tarps which protected groundnuts from soil and allowed groundnuts to be covered or moved to shelter quickly if rain occurred.
Groundnuts were then placed in poly bags or were placed in bags that could be sealed. The results from six villages revealed that improved practices at each step in the process contributed to reductions in aflatoxin when groundnuts were removed after 4 months of storage. Quality of shelled kernels was also higher when an improved practice was implemented. The highest quality and least amount of aflatoxin was observed when the improved practice was used at each step. While the increase in groundnut yield more than offset the costs of a tarp and sealed bags, farmers may not be able afford these inputs in full but may be able to incorporate at least one or two improved practices in the system. The result would be fewer damaged kernels and less aflatoxin for processors to deal with further down the value chain.
