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2.8 Storage

Smallholder farmers store groundnut in-shell, in earthen pots, mud bins, bamboo baskets or in other types of wicker receptacles. These containers are often plastered with mud and cow dung with little or no use of pesticides. For long-term storage the containers are sealed with mud after the addition of ashes, ground pepper, dried neem leaves or other local herbs to control storage pests. In Andhra Pradesh groundnuts are stored in big earthen pots and the mouth of the container is sealed with the sand or mud or cow dung. Daily storage of groundnuts in gunny bag is a common practice requiring utmost care to protect the produce from the pests. For consumption and seed purposes, groundnuts are stored for longer periods up to 8 to 10 months. Farmers generally have inadequate facilities and use their houses to keep bags of groundnuts over long periods of time. This finding calls for an effort on the part of governments in the developing countries to improve facilities for storage. Farmer level storage conditions for groundnut in gunny bag is shown in Figure 21.

 Figure 21. Storage of groundnuts in gunny bags under farmers' storage conditions.

Groundnuts following proper drying are either packed in gunny bags or stored in heaps in big rooms in the farmhouse. Eighty percent of the farm produce reaches the market to be crushed for oil extraction by the millers via the local market or cooperative societies. Due to storage problems, the oil mills also do not store groundnuts for a long time. When pods are stored at ambient farm storage conditions, they interact with the storage humidity (RH percent) and temperatures. At high RH >80 percent and temperatures >40°C the process of ageing accelerates and the kernels start deteriorating.

Groundnut pods are generally stored at the moisture content between 6 and 8 percent. In India summer season groundnut is harvested in the month of May to June, and the environmental RH increases immediately after storage, and may reach up to 80 to 90 percent on the onset of monsoon in the month of June to July. Consequently the pod moisture also increases and may reach between 10 and 15 percent, depending on the RH of storage environment. Pod moisture percent >10 percent is harmful for the maintenance of seed viability and quality. The RH of the storage environment may be reduced with the help of dehumidifiers or use of desiccants like silica gel and calcium chloride (anhydrous or fused). On the other hand the rainy season produce is harvested in the month of October to November, when monsoon resides and the temperature and RH of the storage environment become favourable for the storage of groundnuts. Thus the storage environment between December and March remains quite favourable, under such situations farmers can store their produce in ordinary gunny bags at the ambient storage conditions, provided care is take to protect the produce from the storage pests. It is recommended that the summer season produce either should be processed immediately after harvest or may be stored for 1 to 2 months taking utmost care. For example the produce may be stored in polyethylene bags with desiccant like silica gel or calcium chloride (CaCl2, anhydrous) and sealed.

In the assembling markets, decorticating factories and oil mills, produce is generally stored in the form of pods, either loose or in bags. The period of storage may be very short. Beside storage in godowns, pods are often heaped loose or stacked in bags in the open in places where the risk of damage by rain is minimal. If it does rain, the sacks are covered with tarpaulin. Wooden planks or matting must be arranged on the floor to prevent damage from damp. The pile of bags in the godowns should be kept to 4 to 5 feet below the roof to allow free circulation of air. The period of storage of individual lots in most cases may not exceed two to three months. Storage conditions may very in the terminals markets and ports. At these centres invariably storage is in the form of kernels, which are most often packed in gunny bags. Sometimes, it becomes imperative to store kernels at ports for longer periods, waiting for the shipment, such situations lead to serious damage to the kernels.

Groundnuts are semi-perishable and are subject to quality losses during storage through microbial proliferation, insect and rodent infestation, biochemical changes, i.e. flavour change, rancidity, viability loss; physical changes, i.e. shrinkage, weight loss, and absorption of odours and chemicals. When subjected to suitable storage environments, clean groundnuts can be stored for several years. High moisture and temperature regulates the rate of deterioration of kernels in storage. During shelling serious losses in milling quality may result, if groundnut kernels are dried below 7 percent moisture content (w.b.) or stored at a temperature less then 7°C. Thus, best storage conditions for normal dry bulk storage of unshelled groundnuts is about 7.5 percent kernel moisture content (w.b.) at 10°C and 65 percent RH. If these storage conditions are maintained, unshelled groundnuts can be stored without significant loss in quality for about 10 months (Patee and Young, 1982).

Some groundnut varieties have been noted to have poor storability for example in Gujarat cultivar GG 2 loses its viability rapidly than any other cultivar. The methods of cultivation, harvesting, curing, and post-harvest handling of the groundnuts may affect their storability. In developing countries the conditions of most farmers stock warehouses are not good, practically they don't have the warehouses. The warehouses require ventilation and/or aeration system to help in maintaining the quality of groundnuts. These systems remove excessive heat and moisture, equalize groundnut moisture content and temperature throughout the mass of stored groundnuts and reduce the differences between the ambient and groundnuts temperature. The aim should be to keep the conditions of the air in the pile of groundnuts within the limits and to prevent moisture migration and condensation inside the storage structure. In Ghana mature groundnut kernels, following harvesting and drying are stored in jute bags and kept in barns built of mud or thatch. The major problems in stored groundnuts in Nigeria include weather, insects, rodents, and infestation by toxicogenic fungi. In South Africa the recommended maximum drying temperature is 35°C, however, commercial cultivars react differently to drying temperature. In India groundnuts in-shell and seed of cv. Big Japan and M 13 were stored in polyethylene bags for up to 14 months (Sinha, et al. 1997). Groundnut stored in polyvinyl bag at 7 percent moisture content showed the highest germination. Seed treated with an insecticide/fungicide, were stored successfully for one year without significant loss of viability in laminated polyvinyl bags (Krishnappa, et al. 1998).

Certain factors known to accelerate the ageing process are: i.) soil moisture content during pod development, harvest stage; ii.) drying methods mainly the temperatures during curing of pods, and iii.) ambient relative humidity during storage. Based on these principles a simple and economic storage technology has been developed to prevent the exposure of pods to high humidity during monsoon season. In this technology CaCl2 is used as a desiccant in side a polyethylene-lined gunny bag containing the groundnut pods (Figure 22).

 Figure 22. Storage of groundnuts in gunny bags under farmers' storage conditions.

The summer season's produce stored with CaCl2 in polyethylene-lined gunny bag showed 80 percent germinability with high seedling vigour, even after 10 months of storage. On the other hand produce stored in ordinary gunny bags without calcium chloride could retain only 10 percent germinability (Nautiyal and Joshi, 1991). Two factors known to influence the preservation of groundnut seed are temperature and relative humidity. To preserve groundnut seed for one year at 21 °C, moisture content of 5 percent or less is necessary. The farmer's stock groundnut may be stored to 8 to 10 percent seed moisture content in mechanically and naturally ventilated miniature metal warehouses for six months.

Rapid loss of groundnut seed viability during storage is a common problem in seed production. It was found that the specific iso-esterases are prone to deterioration during ageing of groundnut seed (Aung and McDonald, 1995). In several developing countries, studies of the farmers stock of groundnut seed showed that improvement in seed quality and farmers` seed management is required immediate attention to maintain healthy seed stock. It is also emphasized that availability of quality seed at the time of sowing is sometimes a problem. If storage facilities are created at the farmers' level or village level and farmers are made aware regarding the benefits of the quality seed this problem may be solved to a certain extent. Thus seed production activity at village level may be advantages over existing centralized large-scale production and procurement by state owned organizations in various developing countries.

High temperature drying i.e. >40°C adversely affects the seed viability and oil quality. Groundnuts for edible or culinary purpose should be kept separately from those required for industrial use, and greater care is necessary to handle and store them. In Gambia for instance, a type known as Philippine Pink, grown especially for edible use, is kept separately in the buying and marketing organization. The smallholder farmers usually produce groundnut for their consumption and store it in mud bins, basket, and earthen pots or in gunny bags for 6 to 8 months. The medium-holder farmers produce groundnut for their consumption as well for the sale in the local market, they mostly store it loose in a room, or bags, metal bins. The millers store the groundnut in gunny bag or large heap in the open courtyard for at least 2 to 3 months. These widely contrasting storage practices may explain the range of storage loss in the developing countries. The type of storage plays a fundamental role in storage efficiency. If a concrete or mud storage structure can absorb water or allow the water vapours to pass through, in the case of a jute bag, the biochemical changes and mould attack are minimal, but the risk of insect infestation increases. Aeration greatly minimizes mould growth, insect activity, and respiration of the seed. Further aeration provides a cooling action and equalizes the temperature through the mass of the kernels stored. Bad odours developed by stored kernels can be easily and effectively removed.

Following are the findings of investigations on various aspects of storage of groundnut under commercial conditions in India (MAD, 1949):

  1. All produce intended for storage should be well dried to have not more than 5 percent moisture.
  2. Groundnuts always should be stored as pods rather than as kernels.
  3. If storage is done as kernels, pods should be decorticated carefully to avoid splits and broken kernels. The period of storage should be reduced to the minimum possible.
  4. Storing of kernels on hard floor or hard bedding material and piling of bags to great height should be avoided to minimize caking up of kernels and damage to gunnies. Dry-sand bedding to a depth of about a foot covered by Hessian cloth appears to be best.
  5. Produce from the summer crop should not be stored for long period as it deteriorates more rapidly than that from the winter or rainy season crop. The summer produce is best utilized for the crushing for oil.
  6. For storing small quantities of kernels, bin appears to be most suitable.

2.8.1 Semi-underground storage of farmers' stock groundnut

Throughout history reasonable success has been achieved in storing various foods underground. A small semi-underground warehouse was constructed by waterproofing and placing 7.6 cm thick pre-cast concrete tank 304.8 cm long by 152.4 cm deep in the ground with the top of the tank at ground level. Two courses of 20.3 cm concrete blocks were installed above the walls and the warehouse was covered with sheet-metal gable roof having a 45° slope. The warehouse had a groundnut storage capacity of approximately 10.2 m-3. A fan located in the south gable changed the headspace air once every two minutes. Thermocouple and relative humidity sensors placed at various locations throughout the warehouse indicated temperatures and relative humidity at these locations. Free fatty acid and total carbonyl analyses indicated acceptable quality maintenance in the underground storage and compared with groundnut in conventional storage. Temperatures were more uniform in the underground warehouse than the conventional warehouse (Smith, et al. 1987). Thus this semi-under ground warehouse for storing farmers stock groundnut offer the potential for maintaining quality of groundnut in storage.

 

2.8.2 Durability of farmers' stock groundnut in mechanically and naturally ventilated miniature warehouses

Farmers stock groundnut from the same field dried either 8 or 10 percent seed moisture content were stored for 6 months (October through March) in mechanically and naturally ventilated miniature metal warehouses. The initial temperatures for the 8 percent moisture content groundnut were 2 to 3°C higher than those for the 10 percent moisture content groundnut. This difference was maintained until February. Relative humidity, 10 percent points higher in the 10 percent initial moisture content groundnut began to equilibrate in December and similar buy late January. Final moisture of the groundnut from the two mechanically ventilated warehouses was about 7 percent compared to 7.5 percent in the two naturally ventilated warehouses. Only small changes in total carbonyls and free fatty acids observed during storage in the warehouses and sensory evaluation after storage indicated no significant differences among treatments. No aflatoxin was detected in any seed category before or after storage. Results indicated that quality of farmer's stock groundnut at 10 percent or less can be maintained when stored in a properly constructed and operated mechanically or naturally ventilated warehouse (Smith, et al. 1989).