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Technological considerations in evolving strategies for varietal development of food grains

About 70 per cent of food grains produced in India are retained for farm-level consumption and the rest moves along a chain of agencies before it reaches the consumption points. Post-harvest conservation by modern procedures is therefore a crucial need to prevent the dissipation of national efforts to raise food production levels. The incidence of bunt in wheat, chalky grains in rice, and Gibberella infection in maize, and the impairment of processing qualities as a result of pre-harvest infection have engaged the attention of scientists in recent years. The expertise in food conservation built up during the last 30 years has found increasing application, but basic information to evolve varieties with desirable storage, processing, and nutritional or organoleptic qualities is important in meeting future needs. Variable production levels in different years emphasize the need for varieties that give maximum yields during processing and suffer minimum losses during post-harvest handling and storage.

Processing

Food grains harvested from standing crops are dried and processed before cooking and consumption. Milling is used to obtain rice from paddy, dhals from pulses, and flours from wheat and millets. The wastages inherent in some traditional practices have been minimized through improved processing technology and equipment design. The physico-chemical features of food grains need attention in varietal development programmes.

Rice

About 50 per cent of all cereal production consists of rice, represented by numerous varieties exhibiting diverse per hectare yields and physico-chemical features. Research and developmental efforts have focused on the best utilization of paddy varieties grown in the country through:

1. minimizing qualitative and quantitative losses during harvest and post-harvest handling and drying stages;
2. improving the milling yields of rice by appropriate drying and milling procedures, and the development of milling equipment;
3. adapting processing procedures to improve nutrition and acceptability;
4. utilizing by-products; and
5. product development for diverse needs.

The investigations at the Central Food Technological Research Institute (CFTRI) have conclusively shown that inherent grain structure and harvest/post-harvest drying practices directly influence the milling behaviour of paddy.

Paddy is currently harvested at 16 to 18 per cent moisture level because of difficulties in getting labour, drying space, and other amenities during harvest periods. Harvesting at this stage results in shattering and sun-checking of grains ultimately reflected in heavy breakages and reduced milling yields. Harvesting at higher grain moisture levels of say 20 to 24 per cent (indicated by the presence of 1 per cent milky grains), and a controlled drying procedure with an intermediate conditioning stage, is suitable for farm level use, and also reduces milling breakages.

Breeding of crack-resistant varieties, the second approach, overcomes frequent process alterations and equipment designs. Crack-resistant and low-shattering selections from pushpa, vani. and madbu varieties have been identified, tested and released by the CFTRI for mini-test trials through the University of Agricultural Sciences, Bangalore, Further, a chalky variant of Alur sanna (a rice variety), which seems to cook into discrete, fluffy grains even without ageing, has also been identified by the CFTRI for further trials (CFTRI 1981).

The influence of physico-chemical characteristics on the storage, packing, and processing of rice has been examined as an aid in post-harvest conservation. For example, grains with low length: breadth ratio exhibit higher bulk density (and lower porosity), indicating that a given volume of round grains has a greater weight than slender grains. Similarly, the friction coefficient of grains increases with moisture level, contributing to handling and packing problems. Brown rice and highly milled rices, characterized by low friction coefficients, pack well, while intermediate milled rice, particularly from parboiled paddy, packs badly because of high friction and low bulk density (DES 1975). Yellow discoloration of rice preharvest has also been a problem in some parts of the country.

Varieties of rice with a high amylose content cook into dry and flaky products, while those with a low content into pasty products. The gelatinization temperature (GT) of starch has proved to be an important quality criterion and low-GT rices are preferred for puffed products (Bhattacharya 1979). Data such as these are extremely useful in developing varieties capable of yielding cooked products that suit the diverse food habits of Indian populations.

Breeding of varieties with a higher bran oil content, and weak or no bran-lipase activity, is also indicated in relation to the edible oil requirements of the country. Breeding for low husk content would lead to higher yields of edible material, but the storage qualities of such varieties would need scrutiny.

Coarse grains

Coarse grains consisting of jowar, maize, bajra, and other millets account for about 25 per cent of total cereal production. They are dryland crops capable of withstanding variable climatic conditions. Recent years have witnessed the evolution and commercial cultivation of hybrids, new varieties, and composites characterized by good yields, disease resistance, and adaptability to different cropping systems (table 7).

TABLE 7. Some New Hybrids and Varieties of Millets Evolved or Recommended in Recent Years

Sources. Ganga Prasada Rao 1976; Joginder Singh 1976; Murthy 1976.

Coarse grains yield cooked products of harder texture than rice and wheat because of a fibrous bran layer that is relatively resistant to water permeability during the cooking process, and also of hard and horny subaleurone layers. Milling procedures and equipment (Desikachar 1976) have been evolved that remove 10 to 15 per cent of grain layers as bran to obtain grains and flours without serious impairment of nutritional qualities (tables 8 and 9). Large-sized and damaged starch granules present in the grains of certain varieties of maize, jowar, and bajra are conductive to higher water uptake by flours and soft cooked products (CFTRI 1977-1981).

TABLE 8. Chemical Composition of Products of Milling from Jowar

Source: Desikachar 1976.

TABLE 9. Chemical Composition of Maize and Its Milled Fraction

Source: Desikachar

In making roti (unleavened bread) from coarse grain flour, the rolling of dough into circular sheets is difficult because of the absence of gluten. The steaming of dough minimizes rolling problems, but detailed studies on the histo-chemistry of starch and its hydration features may help in identifying grains with desirable sheeting properties.

Wheat

Over 90 per cent of the wheat produced in the country is ground in chakkis to obtain flour of about 95 per cent extraction, used for making various unleavened breads such as chapati and poor). Only about 2 million tonnes pass through roller flour mills to yield maida and white flour used in bakery products. New varieties in various stages of development and cultivation are systematically screened for characteristics needed for the manufacture of bread and biscuits (Shankar and Amla 1979). Comprehensive data have become available from the Indian Agricultural Research Institute (IARI), the CFTRI, and the Food Grains Research Centre at Hapur.

A programme has been undertaken at the CFTRI to gain an insight into the protein characteristics of wheat and their relationship to the quality of chapati, the most important means of utilizing wheat in this country. Some attempts have also been made to define chapati quality by sensory methods and to correlate the data with instrumental methods of analysis (CFTRI 1977-1981). Translation of these criteria into physico-chemical characteristics could help in evolving varieties specially suited for chapati.

Pulses

Pulses are the principal means of raising the protein quality of Indian cereal-based dietaries. Pulse production has not exceeded 12.5 million tonnes, although consumption requirements for 1980181 can be estimated at 15 million tonnes (at 60 9 per capita per day for a 684 million population). To minimize the wastages in traditional milling practices and hence nutrient losses, improved procedures and milling equipment have been evolved for commercial use. This technology has been used by industry for the milling of pigeon-pea almost throughout the year. independent of the climatic conditions, which play an important role in traditional practices (Kurien 1979).

Milling conditions are also being optimized for mung bean, chick-pea, urd bean, cow-pea, kidney bean, horse gram, winged bean, and peas by suitable adaptation or modification of the technology developed for pigeon-pea at the CFTRI.

Wide variations in physical properties and chemical composition of each of these pulses and their varieties are to be expected in different regions and cropping systems. These properties would influence the milling behaviour of pulses, necessitating expensive changes in technologies and equipment. Intra-and inter-varietal differences in physico-chemical properties should be exploited to upgrade the milling quality of the grain, without sacrifice of yield and duration.

Storage

Food grains in the hot and humid countries of Asia suffer qualitative and quantitative losses from insects, micro-organisms and rodents during post-harvest handling and storage. Impairment of organoleptic and nutritional qualities. and health hazards arising from insect and fungal metabolises, are well-known effects of inadequate grain protection measures and undesirable storage conditions. Food grains handled by government agencies benefit from improved storage practices, but not those remaining in farm storage.

To eliminate or minimize such losses, pesticidal chemicals and their formulations are used widely for prophylaxis or destruction of insect pests both pre- and post-harvest. Pesticide residues are monitored and regulated under Indian food laws to ensure safety to consumers. Increasing hazards from the pesticide residues on food grains accumulating in the human system. either by direct consumption or through animal-based foods, have led to an intensification of research on non-toxic insecticides, biological methods of control, and breeding of varieties resistant to pre-harvest infestation.

A mass of experimental data on the varietal resistance of different food grains to storage pests has been put out from various parts of the world. More often than not, the susceptibility or resistance of high-yielding varieties to storage pests is tested just before release for commercial cultivation. Attention to pest resistance is important at all stages of the breeding programme. Maintaining desirable genetic characteristics on a national scale of cultivation is difficult and expensive.

Sixty-seven varieties of rice have been tested for field infestation by Angoumois paddy moth (Sitotroga cerealella) and graded for susceptibility (Kittur and Patel 1972).

Genetic resistance of certain rice varieties to this storage pest has also been reported from the United States (Cogburn 1977). Information on susceptibility or resistance of wheats grown in India to storage pests such as the rice weevil (Sitophilus oryzae), or khapra beetle (Trogoderma granarium), Rhizopertha dominica, and Tribolium castaneum have also been generated to help in breeding and cultivation (Bhatia and Gupta 1969; Gupta and Kalyan 1971; Chakrabarty and Mathew 1972; and Singh and Mathew 1973).

In maize, Angoumois paddy moth is found to damage varieties with a high amylose content (Fergason et al. 1970). Reports from Africa indicate that local varieties are more resistant to insect infestation than improved varieties and hybrids, because of hard kernels and complete coverage of cobs by sheaths (Adams 1977; Dobie 1977). Resistance and susceptibility of India maize varieties to Trogoderma granarium and Phizopertha dominica have also been tested. Six genotypes (M-25-1, CSH-1, CSH-2, CSH3, CSH-4, and CSH-5) of Indian jowar have also been tested and the degrees of resistance to storage pests ascertained (Krishnamurthy et al. 1976).

Varietal resistance of pulses to storage pests has also been indicated in India. Trials on chick-pea have shown that grains of indigenous varieties G-24 and G-30 are more tolerant than new varieties to the pulse beetle (Callosobruchus chinensis) because of a wrinkled surface and tough coat (Gupta and Mishra 1970).

Continuous efforts are necessary to develop and maintain pest-resistant germplasm of different food grains so as to economize on the costs of storage and infestation control.

Breeding for Improved Nutritional Quality

Breeding for nutritional quality has mainly been directed to improving the protein content, which may or may not be reflected in increased levels of specific essential amino acids. The dwarf wheats cultivated in India contain 12.5 - 16 per cent protein and 2.21 - 2.9 9 of lysine per 100 9 protein (Deosthale et al. 1969). The protein content of improved sorghum varies from 7 to 10 per cent, and that of lysine from 0.9 to 2.6 9 per 100 9 protein. Lysine is the amino acid that limits the nutritional quality of sorghum protein; however, there is overwhelming evidence to show that excess of dietary leucine (another essential amino acid) results in a conditioned nicotinic acid deficiency. More recent studies have shown that the leucine/isoleucine ratio may be as important as the leucine level in causing pellagra. Deficiency of lysine is also relevant in bajra and ragi as in other cereals (Srikantia 1976).

Tannin present in the testa of sorghum grains at about 1 per cent level is known to reduce protein digestibility and availability by binding some of its fractions. Most Indian varieties contain less than 0.1 per cent tannin and it may not be of much significance. However, recently the National Institute of Nutrition indicated that the big-availability of iron from a variety of jowar that contained 136 mg/100 9 of tannin was lower than in one containing 20 mg/100 g of tannin. Of the common cereals, the big-availability of iron from jowar is least and iron deficiency anaemia is common among poorer sections of the population. A low tannin content in jowar is therefore a desirable breeding feature (Srikantia 1976).

Very little attention seems to have been given to the carbohydrates of food grains be they cereals, millets, or pulses, although animal experiments indicate that flatulence can occur by feeding food grains containing stachyose (CFTRI Annual Report 1980/87), and that protein quality can be affected by the level of digestibility of dietary starches. For example, feeding the field bean and some of its carbohydrate fractions to rats affected the absorption of calcium and nitrogen. Detailed carbohydrate profiles of food-grain varieties appear relevant in breeding programmes in terms of nutrition, processing and culinary practice (Srikantia 1979).

Conclusions

The impact of scientific advances in raising food-grain production levels and building buffer stocks could in future years be diluted by agro-climatic uncertainties and population growth. Accordingly, efforts have been intensified to develop sturdy varieties capable of withstanding adverse conditions, resisting infestation, and giving high per hectare yields.

Research and development in post-harvest conservation of food grains have begun to provide a fund of information on physico-chemical characteristics that influence milling yields, cooking behaviour, and sensory qualities. Inherent crack-resistant feature of paddy for better milling yields and low breakage of rice, the influence of carbohydrate make-up and starch characteristics on cooking qualities and digestibility of rice and millets, imbalances in amino acid profiles causing nutritional deficiencies like pellagra, and hard texture coupled with a wrinkled surface in grain as a deterrent against pest infestation, are some specifics that merit consideration in breeding programmes.

Commendable advances in breeding, post-harvest conservation and nutrition have been made, but only through isolated efforts. Technologies and equipment have also been developed to process varieties under commercial cultivation, but may not cope with the diversities in physico-chemical characteristics of different food-grain varieties. Constant interaction among breeders, post-harvest technologists, nutritionists, and extension specialists is necessary to integrate the developments in various disciplines and evolve a systems approach that will result in raised production levels and optimal utilization without sacrifice of nutritional or sensory qualities.

While the evolution of varieties characterized by high productivity and disease resistance will continue to have a high place in breeding programmes, genetic translation of such desirable attributes as milling yield, cooking quality, acceptability, nutritive value, and post-harvest infestation is a challenge to the scientific community.

Co-ordination between the areas of agriculture, food technology, and nutrition needs to be reflected in practice (and not just as policy) in the evolution of food-grain varieties possessing the best possible attributes of production, utilization, and nutrition. Such interaction has a very crucial role to play in the food system.

Acknowledgement

The authors wish to thank Dr. D.R. Bhattacharya and Mr. B.R. Srihari for their helpful suggestions.

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