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S.K. Majumder. Central Food Technological Research Institute, Mysore, India
Abstract
Food availability versus the pest complex
Choice of disinfestation systems
Soil quality and environment, and their influence on post-harvest quality of food grains and other agricultural products
Disinfestation in post-harvest ecosystems
References
Millets are nutritionally deficient compared to cereals. Root crops are also similar to millets. Insects, moulds, and mites that attack these commodities and bring about big-deterioration, even at comparatively low moisture or water activity, are responsible for producing in situ undesirable metabolities, apart from depletion of calorie and selective nutrilites. Enzyme of seeds are activated under ecosystems of underground pit storage and above-ground silo storage systems. Changes in bulk densities, production of frass, microbial and entomogenous debris, related mycotoxins and entomotoxins are responsible for the lowering of nutritional quality besides posing health hazards to animals and man.
Prevention of such depredations by pests and big-deterioration can lead to predictable nutritional and energy supplies. In tropical and subtropical ecosystems, pre-harvest prophylaxis to ensure post-harvest nutrition availability is a primary requirement. It is pre-emptory to apply selectively deterrent pesticides for annhilating fungi and insect pests, and repellents for birds and rodents, to protect the ripe grain panicles. This will reduce the gap between the predicted harvest forecast and actual harvest.
The post-harvest threshold as a pea of the system of crop production must be treated in conjunction with prophylactic and curative approaches, as pre-harvest internal infestations are non-retrievable episodes that nullify efforts to achieve nutritional self-sufficiencies or surplus food supplies.
Appropriate, safe (free from health or environmental hazards). and tropically matching technologies available in the world are catalogued for adoption under the agro-climatic and socio-ecosystems. Preharvest prophylaxis; solar and crib drying; thermally compatible storage structures, non-toxic seed or raw grain protectants, Meta-H-Halloysite; nutritional grain/processed product protectants; small-scale and large-scale disinfestation technologies are stated.
All agricultural products are perishable. Cereals, pulses, and oilseeds are relatively durable commodities, in contrast to fruits and vegetables and other green agricultural products. Insects, moulds, mites, and rodents attack the commodity in the field and in the post-harvest period (Cotton 1963). Their depredations not only deplete quantity, but also damage the quality of the commodities. More insidious effects of the big-deterioration caused by insects, moulds, and mites are reflected in the production of entomotoxins and mycotoxins (Majumder 1975, 1978). Crops like sorghum, bajra, ragi, pulses and beans, maize, groundnut, and many others are attacked by field pests and field fungi. They directly bring about shedding and, hence, shattering of grains during the harvesting operations. Yields of crops are, therefore, affected very adversely, and discrepancies arise between production forecasts and the quantity actually harvested. When infestation is high (at the pre-harvest stage), post-harvest quality is proportionately reduced and shelf-life is also lowered. Thus, on the one hand, a direct reduction in yield occurs, and, on the other hand, the harvested quality suffers.
Agro-climatic situations also affect post-harvest quality and the storage characteristics of food grains and fruits and vegetables. The higher the thermal and humidity effects of the environment during the production of the crop, the lower will be the resistance to infection and infestation during the postharvest period. Drying in the field in the post-harvest period poses difficult problems, as the water activity and consequent enzymatic activities within the tissues remain at higher potentials. Such postharvest practices as underground pit storage for millets and related crops, or above-ground storage of other cereals in bins and silos, activate the enzymes of the seeds and also accelerate moisture migration, together with thermogenesis (Majumder 1972). Under prevalent agricultural and climatic systems, underground pit storage and above-ground silos do not come up to the requirements for maintenance of quality of agricultural commodities. Quality attributes are reflected in bulk densities, production of frass, microbial and entomogenous debris, related mycotoxins and entomotoxins. Biological value, digestibility, and available protein-calorie contents are adversely affected during storage under non-optimum conditions, such as exist in the humid tropics. The chronic and acute toxicities that follow the consumption of deteriorated grains are still not well understood (Howe 1965), but they do possess deleterious constituents and pose health hazards to man and animals. The selective removal of proteins, minerals, fats, and vitamins, the most nutritious components of grains, by insect pests and fungi is on record.
Cereals and millets carry only marginal amounts of proteins, fasts, crude fibres, minerals, and vitamins. However, they are rich in total carbohydrates and in calorie contents. The depletion of specific tissues of the seeds such as the germ, bran, and endosperm have their individual influence on nutritional availability and calorie supply. In tropical and subtropical ecosystems, maintenance of these marginal food and nutritional supplies assumes great importance in view of the profiles of food intake and the delicate balance between nutritional requirements and supplies. These aspects have been very neglected fields of study.
In the approach to the maintenance of quality, particularly of the edible portions of the cereal food grain, millets, fruits, and vegetables under tropical and subtropical ecosystems, pre-harvest sanitation prophylaxis and curative measures are not only essential but determine the interface contributions between pre-harvest and post-harvest systems. Pre-harvest prophylaxis with selectively deterrent pesticides for annihilating fungi, insect pests, and mites is absolutely essential (Majumder et al. 1961). Ripe grain panicles are attacked by rodents in the field prior to harvest. They not only consume them but carry away an excess for storage and consumption during the lean season. In order to maintain the theoretical quantum forecast of harvest, rodent and bird repellents are also required. Tropical environments provide continuous sources of infestations by storage pests in the fields prior to harvesting. The proximity of farm houses to agricultural land means a high pest population index because of rodent burrow cultures in fields. Selective compounds with little or no effect on domestic animals and man are available. The technologies and logistics of applications for such formulations are required to ensure planned and integrated systems of pre-harvest and post-harvest agricultural and food productions. These measures can definitely reduce the constraints that now exist for achieving the maximum productivity from land and post-harvest conservation.
Harvested grains must be treated with technologies that are appropriate to the agricultural practices in tropical and subtropical areas. Marginal farmers, subsistence producers, and organized cultivators require technologies for post-harvest drying, threshing, packaging, and storage systems that are in consonance with their economic status and level of skills. Harvesting of panicles for cereals and of haulms for groundnut and tuber crops without mechanical injury is one essential requirement to prevent infection and cross-infestation during post-harvest handling. The development of new technologies and the designing of harvesting tools should, therefore, take into account the physiological and morphological features of these crops. Drying in cribs using solar energy, oven heat or fire appliances has been the potential contrivance available to average farmers. The good design of such cribs will go a long way towards preventing losses at the threshold of agricultural production. Bringing the moisture to a level that will not encourage storage fungi and mites can surely solve the problem of mycotoxin production in food grains and other crops. Gaseous pasteurization with ammonia, ethyl formate fumigations, and treatment with organic acids have very promising effects on the preservation of the quality of wet harvested commodities (Majumder 1972; Majumder and Venugopal 1973). The effect of ammonia on aflatoxin is fairly well established and disinfection techniques that do not pose any residue or contamination problems can be utilized easily even under field conditions.
Apart from natural edaphic factors that influence the agronomical characteristics of crops, the soil environment, which contains pesticides, heavy metals and mycotoxins, seems to have a profound influence on the uptake, translocation and concentration of xenobiotics and other foreign chemicals in the edible tissues of plants. The tissues that are not utilized for human consumption are utilized as fodder and feed for animals, and often the residues are consumed by wild animals and birds. In addition to this inherent translocation, along with solutes that concentrate pesticide residues in tissues, edible by either people or animals, agricultural practices demand the application of pesticides, growth regulators, weedicides and other chemicals during the growth, development, and production of crops. Residues of pesticides lingering in the soil sometimes have adverse effects on crop yields (Karanth et al. 1981).
Preferential uptakes from the soil by different crops have been studied. Some crops have an inherent tendency to concentrate chemicals even beyond the permissible limits prescribed under food regulations. Coriander absorbs much more chlorinated hydrocarbon pesticides from the soil than do amaranthus, knolkhol, chillies, cucumbers, and tomatoes. Tomatoes grown in highly polluted soils showed growth retardation resulting from phytotoxicity, yet there was no actual intake of pesticide in the edible tissues. Other crops like the French bean, brinjal, and ragi were not adversely affected by these pesticide residues in the soil. Paddy exhibited reduced growth when certain chlorinated hydrocarbons were present in the rhizosphere region. Under experimental conditions the half-life of test chemicals was calculated to be of the order of twenty days. The possibility of using French bean, paddy, ragi, and brinjal as rotation crops in soils containing chlorinated pesticide has been suggested. Another approach to mitigate the adverse effect of pesticide residues in the soil is based on the use of crude enzymes, prepared from germinating plants. which have the capability to dehydro-halogenate chlorinated pesticides, including benzene hexachloride (BHC). The above studies have thus indicated that the decontamination of soils containing high levels of chlorinated pesticides, including BHC residues, might be carried out using certain safe techniques and soil amendements, to achieve crop products free of pesticide residues. If the contents of pesticides in soils are monitored, the antagonistic properties of pesticide combinations could be exploited, both for beneficial effects on plant growth, and also to obtain a remission in the pesticide residue uptake from soils. Combinations, such as gardona + HCH, and fenitrothion + HCH, worked in this way in pot cultures (Deo et al. 1980).
Another phenomenon that has been examined relates to the isomerization of some inactive isomers of chlorinated hydrocarbon pesticides to their active forms. Similarly, active forms could be isomerized to non-active isomers in aqueous medium which could be abiotic or biotic. Fruits or cereal panicles when sprayed with pesticides at recommended dosages may not carry residues beyond the permissible limits, but deposits on the leaf surfaces, sheaths, flowers, and other tissues show a several-fold increase in concentration beyond permissible limits due to the surface/weight ratio. The leaf is broad and outspread and thus receives heavy deposits of spray. The weight of leaves being smaller in proportion to surface area, the concentration could, arithmetically, go beyond permissible limits. This factor poses health hazards and related problems to grazing animals. The need for decontamination of fruits, vegetables, grains, and other agricultural crops from pesticide residues prior to consumption is becoming more relevant in today's context (Visweswariah et al. 1977). The water runoff and effluent in a farm environment contain pesticide residues, either in emulsified form, suspended. or in soluble form. Fish culture is posing difficult problems due to the big-magnification phenomenon and high toxicities of pesticides towards them. Sources of water that are contaminated with farm runoff, need purification prior to utilization for drinking purposes, fish culture, algal production, and even for irrigation purposes. The implications of pesticide residues in harvested crops, in their nutritional and toxicological aspects, need deeper studies.
In the tropics, post-harvest disinfestation should include two basic features: (a) freedom from infestation from within the seed or grain materials; and (b) effectiveness of the treatments to prevent cross-infestation from outside sources. In order to fit into the interfaces and interphases of agricultural and post-harvest systems, integrated application of the following techniques and products will be required to prevent big-deterioration at all stages of production, processing, handling, storage, and distribution (Majumder 1970). At the same time, it would minimize the risks of pesticide contamination of food and pollution of the environment.
I. Rural Sectors
- malathion formulations on grains or pods or synthetic pyrethroids or primiphos methyl prior to maturity and harvesting of grains;
- bacterial insecticides on paddy and vegetables.
- field drier, crib drier, and algate drier;
- maize hand-sheller;
- groundout and paddy drying of haulms and stalks, respectively;
- control of fungi on wet harvested grains.
The above techniques, which have already been standardized and tested in the tropics, could cover up to 70 per cent of all food-grain production in a county like India. Such pre-harvest and post-harvest integration of disinfestation techniques in the rural sector has the possibility of augmenting food and nutrition supplies to a significantly larger extent than any other effort from existing production.
II. Urban and Household Sectors
- Durofume process that includes a tropicalized fumigant for disinfestation and prevention of cross-infestation. with high-viscosity insecticidal treatment of stacks;
- ballooning technique for storage of moisture-sensitive commodities that prevents ingress of moisture from humid atmospheres;
- rodentproof design of storage structures.
- Heat disinfestation for processed dry products and Entolation of milled powdered products;
- serial fumigation for inpackage disinfestation and inpackage injection fumigation;
- nutritional grain protectants for inducing immunity against insect attack by selective metabolic aberration of insects;
- multiple fumigation process for mixed commodities in large warehouses;
- insect and rodent proofing of cartons and packages for dry foods and macaroni;
- dehydrobin to mitigate moisture condensation in metal bins during storage of grains;
- laminated pouches/cartons;
- silo-cum-elevators under large mill and bulk handling conditions;
- air curtains in warehouses and processing plants;
- warehouse rodent proof designs;
- entomological sanitation of surroundings.
- Decontamination of fruits, vegetables and grains from pesticide residues;
- household spray emulsion and sprayer, repellent spray for domestic pest control;
- spot fumigant tablets, paste, and powder for disinfestation of rations in domestic store;
- calcium phosphate-based grain protectants for long-term storage of food grains, and processed and formulated products;
- pyrethroid formulations for store. kitchen and toilets;
- anti-termite pre-construction and post-construction treatments with newer products;
- flyproofing/mosquito proofing using mechanical or chemical methods;
- vector control methods for controlling flies, mosquitoes. etc. with bacterial pesticides.
Special mention should be made of the recent development of non-toxic pesticides, which are either selective deterrents or toxic to insects. These are based on specificities in the physiology, morphology. biochemistry, and immunology of insects, which are, luckily, different from higher animals. Whenever these highly specific pesticides could not be effectively used for the control of insects, moulds, mites, and rodents, other techniques which have ecological compatibility have been selected, and find a place in the above list.
Most of the products and technologies listed do not pose environmental residue and other pollution problems. The basic principle of integrating pre-harvest phases with the post-harvest operations can serve as a prophylactic system. Accordingly, a preventive approach to the problems of big-deterioration caused by fungi, insect, mould, and mites has been the general theme of the present paper. Nutritional augmentation has been inherent in the approach, since grains are protected not only from adverse changes brought about by tropical humid environmental conditions, but from pests which reduce nutrients. The problems of mycotoxins, entomotoxins, calorie depletion, nutritional loss, and related factors have been taken into account in selecting both the particular selective compound and the method of conservation for use at various points in the pre- and post-harvest continuum.
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Majumder, S.K., and J.S. Venugopal. 1973. "Fumigation and Gaseous Pasteurisation. " Academy of Pest Control Sciences, CFTRI. Mysore, pp. 37-104.
Visweswariah, K., G.S. Raju, and S.K. Majumder. 1977. "Decontamination of Water from Pesticides." Indian Journal of Environmental Health, 68: 30 37.