Table 12. Chemical composition of groundnut shell, haulms and oil cake.

2.9.2 Groundnut quality characteristics

Harvested crop is allowed to dry in the field in developing countries and the vagaries of weather affect the seed and haulms quality. The uses of groundnut are diversified, as are the quality parameters based on these uses. Kernel size is one of the most important factors that decide the quality of groundnuts for table use. Normally cultivars with a hundred-seed mass of 60 g or more are considered as large-seeded groundnut and they are preferred in the domestic and international markets. The percent sound mature kernels (SMK) should be as high as possible, which prompts consumer and producer acceptance. Oval or elongated kernels are preferred over round kernels as mechanical blanching (removal of testa) is easier with the former type. Uniformly-sized kernels are preferred, as they are appealing to the consumer and to the processing industries. Normally, pink or salmon testa colours are preferred over dark testa-coloured seed. At present variegated testa colour is not acceptable for table purposes. However, if variegated groundnut in future is bred specifically for the table purposes with higher sugar content and improved textural quality, the product may attract the international consumer market. Table 13 summarizes seed quality characteristics of the two American standard varieties. This data is provided for the benefit of scientists, traders and producers in the developing countries.

Table 13. Comparative shelling, oil quality and flavour evaluations of groundnut.

Edible groundnut has to satisfy very strict standards in West Africa. Some of these quidelines are specific, whereas others lead to an overall improvement of groundnut production. This is particularly true in terms of health pertaining to aflatoxin control and seed technology. Edible groundnut is a driving force and a benchmark for the entire product range. Market and producer demands are concerned with the following:

Reliable and reproducible tests have been developed to measure the above parameters. Current research in the Savannah region of West Africa is helping to develop post-harvest technology for more effective improvement of groundnut products. Disinfecting stocks, refrigerated seed storage and vacuum storage of seed have been developed. Industrial production of ready-to-use seed will be undertaken in Senegal soon. Action is being taken on technological screening, packing and storage procedures, skinning, ready-prepared seeds, electronic sorting among other industrial tasks. Mixed research and development operations are underway, notably in seed production and processing (Schilling and Misari, 1992).

The quality of Indian stored groundnut kernels is considered low due to higher percentage of free fatty acids. Free fatty acids tend to accumulate during storage and transport. The practice of wetting pods prior to decortication or shelling accelerates the development of free fatty acids. If there is damage to the kernels in shelling, free fatty acids develop at a faster rate. Shrivelled and immature kernels also contain more free fatty acids than fully developed kernels. Free fatty acid contend may be reduced by harvesting mature pods, drying the produce properly, careful decoration to avoid breakage and splits, better storage and avoiding unnecessary handling.

Relationship between blanching quality and seed physical characteristics

The blanching process that primarily involves the removal of skin (testa) is a major step in processing groundnuts for many edible end products. Several factors affect the blanching quality of groundnut. Grain hardness, grain volume and flotation indexes are considered important factors that could influence the blanching quality of groundnut genotypes. Methods of determination of seed hardness using Instron Food Testing Machine (IFTM) and floatation index by gravimetric procedure have already been standardized. At ICRISAT effects of temperature of heating on seed hardness (texture) were examined, it was observed that groundnut heated at 200°C for 8 minutes is suitable for the testing the texture and blanching quality of different genotypes (ICRISAT, Annual Report, 1995).

Oil quality

At ICRISAT screening groundnut germplasm has demonstrated the large range in the oil content (31 to 55 percent) with an average of 50 percent. The chemical and physical properties of groundnut oil as compiled by Cobb and Johnson are shown in Tables 14 and 15. The stability or shelf-life of oil is important globally, but deserves more attention in developing countries where storage conditions are not ideal. A major influence on oil storage stability is its fatty acid composition, especially the proportion of unsaturated fatty acids. Cultivar, maturity stage and environmental conditions influence fatty acid composition of groundnut oil. Groundnut oil is relatively more stable than safflower and sunflower oil which both have higher content of polyunsaturated fatty acids (PUFA). However about 80 percent of the lipid in groundnuts is unsaturated, with about 50 percent monounsaturated fatty acids and about 30 percent polyunsaturated fatty acids and consequently groundnut oil has a longer shelf-life. It is light yellow with slightly nut-like flavour and low viscosity fluid. Unsaturated lipids are susceptible to oxidation and are indicated by its relatively high iodine value and refractive index. All cultivars contains 12 fatty acid, 3 of which present in amount exceeding 5 percent of the fatty acid composition i.e. palmitic, oleic and linoleic acids. Fatty acid composition of groundnut cultivars at ICRISAT showed that the oleic (O) to linoleic acid (L) ratio (O:L) varied between 0.91 and 1.23 among various cultivars and is an indicator of oil stability. A minimum O: L ratio of 1.6 has been recommended for groundnut by food processing industry purchasers in the United Kingdom (Jambunathan, 1991). Though scientifically there is no definite basis for this 1.6 value. The primary dietary essential fatty acid for man is linoleic acid. The amount of dietary linoleic acid found to prevent both biochemical and clinical evidence of deficiency in several animal species and humans is 1 to 2 percent of dietary calories.

Table 14. Fatty acid composition of oil.

Table 15. General properties of groundnut oil.

The committee on Dietary Allowances (1980) believes that in view of the possible hazards of high intake of polyunsaturated oils an upper limit of 10 percent of dietary energy as polyunsaturated fatty acids is advisable (FAO, 1977). Groundnut oil, due to its lower linoleic acid content (33.2 percent of total fatty acids) than corn oil (58 percent), safflower oil (79.5 percent) or mixtures of soybean oil and cottonseed oil (46.7 percent), satisfies the recommendation of the Committee on Dietary Allowances. The ratio of ά-tocopherol to polyunsaturated fatty acids could be used as a measure of the adequacy of dietary Vitamin E and that ratio should be 0.6 or higher; later on a ratio of 0.2 has been suggested to be satisfactory indicator of Vitamin E adequacy (Pattee and Young, 1982).

The enhanced stability of oils obtained from runner types of groundnut is mainly due to their higher linoleic acid and slightly higher tocopherol contents, there is some evidence that crude groundnut oils contain some non-tocopherol antioxidant and/or synergist (Fore, et al., 1953). The stability of oil in groundnut-based foods may be increased by low temperature and humidity storage, packaging under vacuum or inert gas and addition of antioxidants to these foods (Shewfelt and Young, 1977). It is also suggested that the selection or development of raw groundnuts with low levels of linolenic acid is also a means for extending product shelf-life. A low O/L ratio may result in rancidity because of release of free radicals and peroxides. The stability or shelf life is important in both developing and developed countries, but deserves more attention in developing countries.

Fatty acid composition is very vital for oil quality and shelf-life of the stored products. To develop a rapid and cost-effective method for determination of fatty acids, three methods were compared at ICRISAT i.e. microanalytical, direct transmrthylation and standard FAME (fatty acid methyl ester) method. For screening large numbers of samples for O/L ratio, the direct transmethylation method could be used. This method is rapid and less expensive than the other two methods. Thirty-five mutant lines obtained by the use of ethyl methane sulfonate (EMS), including their parents (standard cultivars) as controls, were analyzed for oil, sugars, protein and fatty acid composition. The O/L ratio of these lines ranged between 0.99 and 3.06 and some mutant showed high O/L ratios. The protein content of these lines also varied markedly from 15.7 to 29.1 percent. Preliminary results indicated that short-duration genotypes had lower oil (40.0 to 50.9 percent) and higher protein content (20.4 to 29.5 percent) when compared to long-duration types. It was observed that starch content decreased and protein content increased, when plants were exposed to low root temperature and high pod temperature (ICRISAT, Annual Report, 1996).

A simple device to determine oil content of groundnut seed

Oil content and specific gravity of groundnut kernels have an inverse relationship. Utilizing this principle, an arachilipometer was developed to determine the oil content of groundnut samples (Figure 23). Compared to NMR spectrometry, which is widely used to determine oil content in groundnut, the arachilipometer technique is very simple and economical (Misra and Yadav, 1997).

 Figure 23: Arachilipometer developed and designed and developed at NRCG.

Nutritive quality

Proteins: There is growing demand for protein throughout the developing world. Groundnuts are good sources of proteins and have high-energy value (average 564 calories/100 g seed), thus in the developing countries groundnut is very important crop to meet the demand of oil and protein in daily diet. Groundnut germplasm collection at ICRISAT demonstrated protein content ranges between 15 to 34 percent depending upon the cultivar, location and year. The genetic variability in the mechanism of protein synthesis during development of seed suggests that there is potential for the development of groundnut cultivars possessing nutritionally desirable proteins by manipulating protein synthesis.

Amino acids: The contents of amino acids in groundnut seed very according to type of groundnut, cultivar, location, year and length of maturation period of seed. With advancing the maturity of groundnut seed, amount of free amino acids decreases, while protein content increases. Arginine undergoes the greatest reduction in content upon maturation; thus it is proposed that argenine content could be used to determine the degree of maturity of groundnut seed and also suggested that free amino acids can be incorporated into protein at different rates. Thus high-protein cultivars contained higher amounts of free amino acids than the low protein cultivars, during seed maturation. This implies that certain polypeptides or proteins with a specific amino acid composition are selectively deposited in the maturing seed at different time intervals and at different rates among the various groundnut cultivars. Conarachin proteins that are high in essential amino acids were observed to be deposited during early stages of maturity while the arachin protein that are low in essential amino acids deposits during the later stages of maturation (Basha, et al., 1980).

According to FAO (1970), the limiting amino acids in groundnut are lysine and methionine, but there are reports, which indicate that lysine, metheonine and threonine are equally limiting (Miller and Young, 1977). Tryptophan has also been included as a possible limiting amino acid in groundnut (Milner, 1962). Much published information is available on the amino acid composition of groundnut (FAO, 1970). The ranges reported for the amino acids, lycine, methionine and threonine as per cent of protein are 2.1 to 3.9, 0.35 to 1.0 and 2.3 to 2.7, respectively.

Carbohydrates: In groundnut sucrose is the major sugar measuring from 2.86 to 6.35 percent among different cultivars, followed by stachyose and raffinose (Pattee, et al., 1974). Slight loss in sugar contents is found upon roasting and there is about 15 percent loss in sucrose and inositol and about 33 percent loss in glucose and fructose. Please see Table 16 and 17. Fructose and glucose occurs in small concentrations, but it was found that the sucrose undergoes hydrolysis to the two monosaccharides, fructose and glucose, which in turn reacts with some free amino acids to form the characteristic flavour of roasted groundnuts.

Table 16. Effect of roasting on sugar content (mg g^-1 fat-free groundnut meal) of Spanish type groundnut.

Table 17. Nutritional characteristics of groundnut kernel.

Sensory quality

Sensory quality is the summation of all physical and chemical characteristics of edible seed or their products that influence human senses and result in acceptability judgements by the consumer. Several volatile components isolated from roasted groundnuts were described as contributors to "nutty" odour or a "nut-like". Some of which are 2-crotolsctone, 3-methyl-2-carotolactone, 5-hydroxy-4-nonenoic acid, pyrazines, 2-isopropyl-4, 5-dimethylthiazole and 2-propyl-4, 5 diethylthiazole, most of them have been characterized as having green nutty aroma (Ho, et al., 1982). Several flavour evaluation lies on the use of human subjects as the detectors of sensors of food-flavour. For roasted nuts, the Quality Committee of APREA (1971) has adopted the CLER flavour score method. Twenty roasted half-seed are tested individually and a score is assigned to each seed. The total of these scores will represent the treatment flavour score. It is suggested that standardized sensory methodology should be followed to evaluate the flavour of food products. Such methodologies are outlined in several publications (Rodriguez, 1976; Larmond, 1977).

Studies in Japan showed a negative correlation exist between whole pod mass and eating quality. For the same level of yield varietal differences in eating quality exist, which enables the selection of a high-yielding variety with better eating quality. The correlation between sweetness and eating quality and seed hardness and eating quality increases as sweetness and seed hardness is augmented. On the other hand, eating quality is more closely correlated with sweetness. The correlation between external quality and eating quality was so low that good external quality as determined by pod and seed is not necessary associated with good eating quality. Based on the studies it was suggested that the sucrose content and hardness of the seed, which are most closely related to the eating quality, could be used as indicators for the evaluation of the eating quality in tests (Gocho, 1992).

Seed hardness decreased with the delay in harvesting time and selection for seed hardness should be determined 85 days after flowering. Sucrose content of seed decreases when the harvesting time was delayed. The eating quality also shows a similar trend. Therefore, sampling time for this character is very important. The sucrose content should be analyzed at the optimum sampling time of the lines, based on the harvesting time, namely 75 days after flowering for early-maturing varieties, 80 to 85 days for medium maturing varieties and 95 days in late-maturing varieties (Pattee and Young, 1982).

2.9.3 Oil processing

Food processing constitutes a major economic sector in developing countries, especially in urban areas where low-income families are not equipped to carry out the basic processing of agricultural and animal products. Food processing also allows the consumption of seasonal agricultural products over the whole year and therefore minimizes the important price fluctuations resulting from the periodic gluts and shortages of the fresh products. In addition, food processing could generate substantial foreign exchange. Thus extraction of oils from the kernel of groundnuts is a well-established industrial activity in a number of developing countries. Since the early 1950s, most groundnut-growing countries have favoured indigenous oil extraction in preference to the export of kernels. They have thus support the setting up of factories for this purpose, which, are large-scale plants situated in or near urban areas. Commercially oil is extracted from groundnut by three methods including hydraulic pressing, screw pressing and solvent extraction.

Power ghani mill

The ghani mill originated from India where these indigenous oil crushers have been improved over the time. The original animal-powered ghani consists of a wooden mortar and a pestle. The mortar is fixed to the ground while the pestle attached to one or a pair of bullocks (or buffaloes or camel) is rotated in the mortar where the kernels are crushed by the generated fraction and pressure. The oil runs through a hole at the bottom of the mortar while the residue or cake is scooped out. Depending on the size of the mortar and the type of kernels, an animal-powered ghani can process 5 to 15 kg of kernels at a time. An improved version of the ghani has been developed in India, known as the Wardha Ghani (see Figure 24). It is larger as well as more efficient than the traditional ghani and can crush charges of kernels of up to 15 kg in approximately 1.5 hours or close to 100 kg per day. Two or three family members are required for the operation of the mill. It is essential that one of the workers should have the necessary qualifications for running, maintenance and repair of the ghani unit. An engine-powered ghani is now replacing, to a large extent, the bullock-powered ghani. In this type of ghani, either or both the mortars and pestles are made of cast-iron. Power ghanis are often work in pairs. The crushing capacity of a two-ghanis unit is approximately 500 kg to 600 kg of kernels per day.

Some of the technical advantages of the power ghanis, as compared to bullock-powered ghanis include a higher oil extraction rate per unit of raw materials representing an increase of approximately 1 to 2 percent of the extraction rate. There is a higher output per unit of time and less space is used than in the case of bullock-powered ghanis. The quality of the oil produced by the power ghanis is identical to that produced by the bullock-powered ghanis. Power ghanis are now increasingly replacing bullock-powered ghanis (ILO, 1990).

 Figure 24: Line diagram of Wardha Power Ghani.

Improved power ghanis have oil extraction efficiency, which fairly close to that of small-scale expellers and often constitute a viable alternative to the latter, especially in rural areas. While this has been the case in India and in a number of Asian countries, there is no guarantee that ghani mill meet the same approval in other developing countries. For example, the introduction of ghani in Tanzania has met with little success. It is therefore, important to analyze all the requirements for the successful adoption of ghani mills prior to investigating in such units. For example it is important to investigate whether qualified labour is available in ruler areas, whether the miller or local mechanics can carry out the maintenance of ghani without much difficulty and whether power ghanis may be manufactured locally or must be imported. A large number of designs of powered ghanis have been developed and marketed in India. The detailed information regarding the drawings and name and addresses of manufacturers may be obtained by writing to: Appropriate Technology Development Association, P.O. Box No. 311, Gandhi Bhawan, Mahatma Gandhi Road, Lucknow-226001, India.

Oil extraction by pressing

The unit is a double ghani-mill, powered off a single 3-hp motor. Each ghani takes a charge of about 35 kg, which is processed in approximately one hour by the rotary movement of the iron pestle in the bowl. Thus such a unit may process 560 kg of kernel per day. Separate engines may also power the two ghanis. In this case, 2-hp motors are needed. The pestle in power ghanis rotates at approximately 10 to 12 revolutions per minute as compared to 3 to 5 revolutions for bullock-powered ghanis.

Oil filtration: To remove small impurities, oil must be filtered using an ordinary cloth stretched over a frame onto a tank of sufficient capacity. The filtered oil should be left in the tank for a few hours in order to allow the settling down of any fine impurities. The oil than is transferred into tins or bottles with a funnel from a tap on the tank. The tap should be attached over the sediment layer. The cake can be removed from the ghani manually. It may need little or no further breaking-up. The broken up cake meal can be loaded into bags manually. In general, the cake may spoil rapidly after a few days, unless it is properly treated, packaged and stored.

Advantages and disadvantages of ghani crushing

When ghani crushing was widespread, fresh oil was in greater demand than it is today. Flavour, which was traditionally an important attribute of all oils, was best in oils produced from mild ghani crushing. Since vegetable oils are naturally sterile, problems of hygiene in ghani oil are unlikely. Ghani cake is also known to be exceptionally hard and dry and is not prone to mould infestation unless inadvertently wetted. However, the ghani has disadvantages, which are mainly economic in nature. Traditional ghanis have a maximum capacity of about 50 kg per day and modern powered units only about twice that much. As a result, running costs are disproportionately high. If animals are used, they need to be trained and they are expensive to feed. Artisan training is also essential. Ghani oilcake as pressed out of the unit after crushing is externally hard and is not accepted by the trader for further solvent extraction, as are expeller oilcake (Achaya, 1993).

Baby expeller mills

The baby expeller mills as defined in the joint memorandum of International Labour Office (ILO) and the United Nations Industrial Development Organization in 1990 have 45 to 55 kg per hour capacity. Therefore, by working only a one-day shift, as is normal for small plants, the unit can process between 350 and 450 kg of raw material per day. In a few cases such units do work 2 or 3 shifts per day and may then process up to one tonne of raw materials. Before crushing the seed remedial drying may be carried out in the open air or under a covered shade in case of adverse weather conditions. A drying ground of approximately 20 m² is sufficed. This mill may use a crusher of the swing beater type with a capacity of 100 kg of material per hour, a 2-hp power requirement and revolving at 1 400 rpm. The seeds can be heated in open pans over enclosed fireplace to ensure fuel economy. The raw materials may be mechanically stirred through, for example, a linkage to the expeller or crusher drive. The length of time required is about 20 to 30 minutes and temperature 60 to 90°C. Trial and error will show the best conditions in terms of oil yield and quality. Cooking or scorching of seed is needed for three reasons: to facilitate oil extraction, to lower or increase the moisture of seed and to reduce the wearer in the screw press. The best temperature and moisture content depends on the extraction system, however the temperatures attained during cooking should not exceed 120°C as otherwise the protein quality may be adversely affected. In general, the required cooking temperature is a function of the cooking time, the type of oil extraction technology, the moisture content of the row material and the type of seed. The cooking or scorching of seeds should be carried with care in order to avoid the deteriorating groundnut kernels. Overheating reduces the oil extraction rate and yields lower quality oil. Since small rural processors neither may nor afford scorching equipment with automatic control of temperature and moisture of the material, they should arrive at the right cooking conditions through learning and experience.

Oil extraction by pressing: Pressing can be achieved a single, duo or duplex expeller. Their drive can be provided by either an electrical motor or via a pulley and v-belt from a separate diesel engine. Various specialist manufacturers, notable in Japan and in India, produce small capacity expellers. When using a single expeller, the decision on whether to pass the seed once or twice should be based on economic considerations. A second pressing raises the oil extraction rate and therefore, yields additional revenues, but also increases processing costs. Thus, a second pressing is justified only when the increase in revenues is at least equal to the increase in cost. In general, at relatively low extraction rate of small expellers, small rural mills in developing countries find it profitable to press the row materials twice, the first time at low pressures and therefore, high hourly output and the second time at higher pressure through an adjustment of the choke.

The extraction of groundnut oil in small expellers is a highly skilled job as it is necessary to add groundnut shells to the kernels in order to prevent the forming of groundnut butter. The adding of shells is necessary because groundnut kernel unlike copra have little fibre. The need for skilled labour should therefore be taken into consideration while choosing among various types of expellers. Expellers require periodic maintenance and repairs, the principal wearing pieces being the liner bars, the worms and the distance pieces. The periodicity of maintenance and repairs is a function of the rate at which the abrasive action of the row materials and that of foreign matter i.e. sand, pieces of iron wear the above piece of the equipment. The abrasive action of foreign matter is particularly harmful and can considerably shorten the life of various parts of expellers.

Filtration: Alternatively and whenever it is economically feasible, the mill may use a small chamber filter press with 10 plates of 18 x 18 cm, with attached oil pump. The pump makes 170 rpm and has a power requirement of 0.5 hp. Such a press may process up to 50 litres per hour and should therefore be sufficient for the filtering of the daily out put of oil. Filtration takes place through paper and filtre cloth. The mill owner should have the necessary skills for the running of the equipment, as well as for maintaining and repairing the latter. The daily out put of oil is 156 kg and cakes 215 kg. Two or three family members should suffice for the running of the unit. The mill owner should have the necessary skill for the running of the equipment, as well as for maintaining and repairing (ILL, 1990).

Solvent extraction plant

Even the most perfect expeller leaves at least 6 percent of the oil in the expeller cake. It is possible to recover these losses using a solvent extraction plant and can reduce the residual oil in cake to less than 1 percent. A major drawback of this process, especially in view of the bias of the memorandum towards small-scale production, is that it is by nature suited to large-scale extraction. The range of production leaves employed in solvent extraction plants is between 50 to 200 tonnes per day. Other drawbacks include high investment costs, the need for highly skilled labour, low employment generation and danger of explosion if the plant is not kept in perfect conditions. While solvent extraction plant may not constitute a viable rural industry, a number of these plants may be profitably established for the processing of both oil seeds and the cake produced by small oil extraction units. This will however, require a good cake collection system and a sufficient supply of oil seeds in order to maintain the solvent extraction plant running at sufficiently high capacity utilization rate.

Oil in human consumption

Groundnut oil is used primarily as a cooking and salad oil. Small quantities of groundnut oil are used in the manufacture of shortening and margarine. Groundnut oil is excellent fat for pan-frying or deep fat frying. Pastries shortening, oleomargarine, mayonnaise, salad dressing and other food products can be easily made with this bland vegetable oil. For use in mayonnaise, it should retain its natural yellow colour, for oleomargarine, it should be colourless, for shortening and other plastic fats, for all purposes it should contain an antioxidant. Groundnut oil is also marketed as crude oil for soaps and detergents. It forms the base for many face creams, shaving creams, hair lotions and other cosmetics because it is believed to energize the skin. It is used extensively for massaging polio patients. It is also used as a carrier of adrenaline in the treatment of asthma and other ailments.

Adequate amounts of dietary fats are essential for health. In addition to contribute to meet energy needs, intake of dietary fat must be sufficient to meet requirements for essential fatty acids and fat-soluble vitamins. The minimum intake consistent with health varies throughout a person's life and among individuals. Adequate intake of dietary fat is particularly important prior to and during pregnancy and lactation. Increasing the viability and consumption of dietary fats is often a priority for overcoming the problems of protein-energy malnutrition. The role of dietary fats and oils in human consumption is one of the most important areas of concern and investigation in the field of nutritional science. The findings of investigations on this subject have wide-ranging implications for consumers, healthcare providers and nutrition educators as well as food producers, processors and distributors. New evidence concerning the benefits and risks associated with particular aspects of dietary fat is constantly emerging in both the scientific literature and the popular media. At the invitation of FAO and the World Health Organization (WHO), an international group of experts in nutrition, public health, food science and technology gathered in Rome in 1993 to consider the latest scientific evidence about dietary fats and oils. Following are the general conclusions and recommendations of the expert consultation on fats and oils in human nutrition (FAO, 1994).

• For most adults, dietary fat should supply at least 15 percent of their energy.
• Women of reproductive age should consume at least 20 percent of their energy from fat.
• Concerted efforts should be made to ensure adequate consumption of dietary fat among populations where less than 15 percent of the dietary energy supply is from fat.

Excessive dietary fat intake has been linked to increased risk of obesity, coronary heart disease and certain type of cancer. The mechanisms by which these are linked are complex, varied and in many instances not clearly understood. Elevated levels of serum cholesterol and low-density lipoprotein (LDL) constitute major risk factors for atherosclerosis and coronary heart disease. The degree of risk for these and other factors may vary according to, inter alia, type and level of fatty acid intakes, percentage of energy from total fat, dietary cholesterol, lipoprotein levels, intakes of antioxidants and dietary fibre, activity levels and health status. Low fat diets are often lower in cholesterol and higher in antioxidants and dietary fibre. Among adults, there are no nutritional advantages in consuming high fat diets once essential energy and nutrient needs are met.

Anti-nutritional and other factors in groundnut

Lusas (1979) has briefly reviewed various anti-nutritional factors present in groundnut. Trypsin inhibitor activity in groundnuts has been reported as one half to approximately one fifth of the activity found in soybeans. Trypsin inhibitor activity in groundnut is significantly enough to cause pancreatic hypertrophy in rats receiving 15 percent of protein intake from groundnuts. Lectins shown to possess a remarkable array of biological activities have been found in groundnuts. An interesting aspect of the lectins in groundnut is that, roasting of groundnut does not destroy the lectins. Oil seed proteins constitute the most highly allergenic food groups. Groundnuts also have been shown to be highly allergic and shown some hypersensitivity reactions in children. Groundnut oil has been attributed to contain potent anti-inflammatory compounds, however, Calloway, et al. (1971) observed that groundnuts are absolutely non-flatulent. Later on varietal differences were noticed for the differences exist in groundnut in their ability to cause flatulence. In this connection, the consumption of new raw groundnuts is not advisable; groundnuts always should be consumed fried, boiled or roasted. Plant breeding programmes should also focus on developing varieties of groundnut with minimal content of allergenic proteins and antinutritional factors.

Groundnut oil and atherosclerosis

The atherogenecity of groundnut oil is well established, as is the fact that the structure of the component triglycerides of groundnut influences its atherogenecity. It is also atherogenic in the rabbit and rhesus monkeys. This property is not related to the degree of unsaturation of its component fatty acids. Some studies suggest that the atherogenic potency may be due to the triglycerol structure of the groundnut oil. If the atherogenic property is indeed due to the triacylglycerol structure, there seems to exist some genetic potential among cultivars for development of non-atherogenic lines of groundnut.

2.9.4 Secondary products

Boiled groundnuts

Newly harvested groundnut pods are boiled or steamed in East and Southeast Asia before they are eaten as a vegetable. On a commercial scale, the boiled pods are dried, packed in airtight plastic bags and sold. Sweet-tasting Valencia types with 3 to 4 seeded pods; tan-rose or tan coloured seeds with high protein and low oil content are the most preferred. Unshelled immature pods can also be boiled in medium brine and eaten fresh or alternately canned and frozen and marketed commercially. At ICRISAT groundnut germplasm was screened for the boiling type of groundnuts with three controls, JL 24, Gangapuri and TMV 3. Six germplasm accessions identified were comparable to JL 24 and Gangapuri for shelling percentage, 100-seed mass, oil and protein content, O/L ratios and polyunsaturated/saturated acid ratios. Some lines significantly out yielded TMV 3, which has been released as Khon Kane 60-2 for boiling purpose in Thailand.

Roasted groundnuts

 Figure 25: Fresh or dried groundnuts are roasted.

Groundnut is roasted either by applying dry heat (see Figure 25) or using some vegetable oil. Mature groundnut can be soaked in brine and subsequently roasted. Dry roasted groundnut can be used in the preparation of groundnut butter, confectionery or bakery products. Roasting reduces the moisture content, develops a pleasant flavour and makes the product more acceptable for consumption. The reduction in moisture during roasting prevents moulding and reduces staling and rancidity.

It is important to note that excessive heating during roasting lowers the nutritional quality of proteins. Roasted groundnuts are ground into a paste and mixed with honey and cocoa in South America. A considerable amount of raw groundnut paste is made in South Africa near Cape Town and used as a spread on bread.

Salted groundnuts

Salted groundnuts are very popular in Western India and prepared by soaking the groundnut kernels (HPS) in water with 4 percent common salt (NaCl) solution for 12 hours (please see Figure 26). Soaked kernels are dried and roasted with sand. If the skin is pealed off and the roasted kernels are packed in attractive packs it may add to their value. Kernels like these are sometimes served on Indian AirLines flights.

 Figure 26: Salted groundnuts, very popular in West India, are being processed.

Frozen unshelled groundnut product

Quick-freezing and low temperature storage technique is widely used for food processing keep freshness and quality of the product. This technique was applied to fresh, unshelled groundnut to develop a new type of product, which could maintain fresh taste and nutritive values even after several months of storage. Immature pods were harvested around 10 to 20 days before full maturity, washed and steamed at 105°C for 5 minutes to stop enzyme activity. After vacuum packing (at -760 mm Hg for 10 min) in 0.08 mm polyvinyaldichloride film, the pods were immediately frozen groundnut investigated after 2 months of storage and compared to those of conventionally dried groundnuts. When thawed after 2 months storage, the kernels were very palatable with softness and fresh taste. This study suggested that frozen groundnut can be consumed after the steaming and freezing technique described above. However, such groundnut will require transportation under cold storage to deliver this product safely to consumers.

Groundnut milk

Groundnut milk can be prepared by soaking kernels in 1 percent sodium bicarbonate (NaHCO₃) solution for 16 to 18 hour, drain off the water and grind the kernels in aqueous medium. Steep the wet mass for 4 to 5 hour and filtre through cheesecloth to remove the product. In India groundnut milk called Miltone® is a commercial reality. Miltone® consists of groundnut milk extended with buffalo milk. Groundnut milk can be used in the preparation of yoghurt-like products, ice cream and other products. Following steps may be followed to prepare groundnut milk (Figure 27).

1. Shelled groundnuts

2. Add groundnuts to boiling water, remove from heat and let soak for 7 minutes

3. Drain, remove skins, soak the cotyledons in 2% NaHCO₃ overnight

4. Rinse cotyledons with tap water, blend in warming blender with water (1:5 w/v) for 4 to 5 minutes

5. Filtre the homogenate through 4 layers of cheese cloth

6. Add whey powder to the filtre at 4% level (w/v), mix thoroughly for 1 hour and boil for 10 minutes

7. Groundnut milk

Figure 27 Preparation of groundnut milk.

Source: Singh, B. 1992, ICRISAT

Preparation of mishi

Mishi is concentrated, spiced yoghurt prepared from whole milk in Sudan and usually consumed along with bread. Mishi can also be prepared from peanut milk by following the steps given in Figure 28.

Detailed studies show that aflatoxin B₁ is the most commonly occurring form. All the aflatoxins can be toxic at certain concentrations and may cause primarily liver cancer in animals and human. They can also cause lack of appetite, loss of weight, haemorrhage, ascites and abortion. Young animals are more sensitive and vulnerable to aflatoxicosis than older ones. There are two types of aflatoxin toxicity: direct toxicity and relative toxicity; both can be acute or chronic. This issue has become a subject for concern in agriculture on global scale. Many countries have assigned high priority to research to find a solution to aflatoxin contamination of groundnut. It is a serious problem in the warm to hot subtropical moist regions of the world and is more serious during and following alternative dry and wet periods, i.e. drought followed by showers. Fungal growth and aflatoxin production in the pods is favoured, when temperature range from 20 to 30°C and the relative humidity in the pod microenvironment ranges from 85 to 95 percent. Invasion of fungus to groundnut can occur during flower and peg formation, gradually as the pod mature and rapidly as the pod become over mature. Mature intact pods with thick sclerotize cellular components and kernels with compact seed coat (testa) are less susceptible. Seed coat is a barrier to fungal infection, as in seed with higher Ca content in seed coat decreased the growth of A. flavus. The results revealed that Ca content in seed coat is more important than Ca in pericarp (Field Crop Research, 1997 pp. 9). The presence of a "natural barrier" to invasion of undamaged pods was also considered and suggested possible antagonism and competition by Trichoderma viridi and Penicillium spp. With in the endocarp community (Garren, 1966).

Preharvest contamination: Late season drought spell, particularly in the semi-arid region is a major factor associated with aflatoxin contamination. Reduced metabolic activity associated with decreased pod moisture content under drought stress seems to increase susceptibility of groundnuts to A. flavus infection. However, another possible role of drought stress in pre-harvest fungal infection could involve suppression of microbial competitors of aflatoxin producing fungus by elevated temperatures in the pod zone (Mehan, et al., 1991). Pod splitting is another factor contributing to aflatoxin contamination. Pod maturing under fluctuating soil moisture conditions during seasons of inadequate or irregular rainfall, are prone to pod splitting. Seed in split pods are frequently invades by A. falvus and subsequently become contaminated with aflatoxins. It is well established that A. flavus invasion can occur in soil during pod development and maturation; the fungus directly penetrates the pod wall or enters passages created by pod pests and diseases/lesions. However, the exact mode of infection of groundnut pod has not been fully elucidated. To control the invasion of A. flavus under the drought situations efforts are needed to under stand the mechanism of A. flavus invasion at different levels of pod moisture and genotype variations for the pod characteristic to develop cracks under varying soil moisture regimes.

Post-harvest contamination

During drying: In most of the groundnut-producing countries the weather remains warm, wet during the drying period and the risk of aflatoxin contamination is increased. At harvest groundnut pods contain moisture content about 45 to 55 percent and a complex of microorganisms, the endocarp microflora, which includes A. flavus also. When moist pods are lifted and cured/dried in windrows or heaps there may be considerable invasion of seed by A. flavus and other fungi already existed in the shell. This process is encouraged, if drying is slow because seed remain in very susceptible range of 12 to 30 percent moisture content for extended period. A rain shortly after lifting is not particularly harmful, but a rain after the groundnuts are partially dried, followed by poor drying is likely to result in aflatoxin contamination (Troeger, et al., 1970). Rains in the evening may keep the groundnuts wet all night, thus providing fungi with needed moisture to multiply. Rains early in the morning are less likely to slow down drying and accelerate mould growth, because of effective daytime drying. In Nigeria, in the areas where rains continue after harvest, field drying of groundnuts is serious problem of aflatoxin contamination (McDonald and Harkness, 1965). The use of inverted windrows compared to random windrows or heap has shown to speed the curing and drying process (Pettit, et al., 1971). Groundnut pods positioned at the top of inverted windrows reside where air currents move more rapidly and the atmosphere humidity is low as compared with positions close to soil surface. Thus the pod at the top of inverted windrows has less chances of invasion by A. flavus than the pods close to soil surface.

Lower levels of A. flavus infection and aflatoxin contamination have been reported in groundnuts dried in inverted windrows than in inverted random windrows (Porter and Garren, 1970). Thus inverted windrows shorten the time required to cure groundnuts in field and help to reduce the number of kernels invaded by A. flavus and other fungi. However, to avoid infection and aflatoxin contamination because of prolonged periods of rain, groundnut should be threshed as soon as possible with final drying achieved under controlled conditions, if groundnut is cultivated in large scale. In case the drying facilities are inadequate groundnuts should be left in the inverted windrows rather than combined and held for drying. Even during periods of rain, the risk of aflatoxin contamination is probably less for groundnuts in inverted windrows than for those held in dryers without proper ventilation (Dickens, 1977). In India lot of work on the aflatoxin problem has been conducted by the ICRISAT, from other developing countries the reports are sporadic, however, more systematic studies are required to prevent the invasion of A. flavus during curing and drying.

During storage and shipment: The number of ecological studies of storage fungi involving quantitative mould count of populations is limited. In Egypt, groundnut seed were adjusted to 8.5, 13.5, 17.5 and 21 percent moisture levels and stored for 6 months at 5, 15, 28 and 45°C and A. flavus was found to be the dominant fungus followed by A.niger, A.terreus and P.funiculosum (Moubasher, et al., 1980). The main factors influencing the growth of A. flavus and other storage fungi in groundnut are moisture (relative humidity), temperature, storage period and gaseous composition of the storage atmosphere. High mycofloral counts have been associated more often with high initial moisture contents of groundnuts going into storage than with any other factor. The literature on the influence of moisture, temperature and other factors on the growth of A. flavus in groundnuts have been comprehensively reviewed by Diener and Davis (1977). A. flavus infection and aflatoxin contamination may increase in groundnuts during storage until their moisture content drops below 9 percent. Natural accumulation of carbon dioxide (CO₂) and decreased levels of oxygen (O₂) in closed storage reduce mycoflora development. Fungus growth and sporulation were reduced with each 20 percent increase in CO₂ from 40 to 80 percent. No growth occurred in 100 percent CO₂. Visible growth and free fatty acid (FFA) formation by A. flavus were inhibited at 86 percent. RH decreased by 20 percent at 17°C and 60 and 40 percent CO₂ at 25°C. FFA levels decreased as RH decreased from 99 percent to 92 percent to 86 percent (Lander, et al., 1967). Low temperatures and uniform moisture distribution reduce mould growth and insect activity. Aeration is necessary to reduce aflatoxin contamination during storage. High relative humidity and temperature, rainwater leakage and insect infestation are critical factors that contribute to aflatoxin contamination of groundnuts in storage.

Groundnut meal has traditionally been an important component of poultry and other livestock feeds both in groundnut producing and importing countries. The economics of some of the developing countries are strongly dependent on export of groundnuts and groundnut products. Therefore, every effort should be made to reduce aflatoxin contamination and so maintain trade in groundnuts and groundnut products. The problem of mould damage and mycotoxin contamination can be minimized by improving facilities for storage at port and transient points and on ship. Use of airtight polyethylene bags with silica gel may reduce the proliferation of A. flavus by lowering the relative humidity of the storage microenvironment.

Need of aflatoxin contamination control in developing countries

In developing countries the problem of the aflatoxin contamination is more serious and farmers are still following the old practices of harvesting, curing, drying and storage, more over the environment during harvesting and storage remains congenial for the mould growth. Farmers need to be educated about the ill effects of the aflatoxin production and to follow a package of practices for the control of invasion by the fungus A. flavus. Therefore several National and International Organizations in the developing countries are organizing the programmes for the control of the aflatoxin in groundnuts.

In October 1987 ICRISAT organized International Workshop on Aflatoxin Contamination of Groundnut. To present overview of the work and problems of aflatoxin contamination in the developing countries, showed that in many developing countries there is only limited or no facilities for monitoring groundnut and groundnut products for aflatoxin contamination. There are also possible synergistic interaction between aflatoxin and infectious hepatitis virus B and there is evidence that the effects ingestion of aflatoxin are much more serious in the case of children suffering from severe protein malnutrition and unfortunately this is a common condition in some countries where aflatoxin occur.

African Groundnut Council (AGC) in 1975, on the basis of scientific information on A. flavus and other mycotoxin producing fungi launched an aflatoxin control programme in collaboration with EEC (European Economic Community) and UNDP (United Nations Development Programme) with technical assistance from the FAO. In Zambia, groundnut kernels meant for export are routinely monitored for aflatoxin contamination. A committee to coordinate action on the aflatoxin problem in Nigeria was constituted in 1961 with representatives from four ministries, the Institute for Agricultural Research (IAR) Zaria, The Nigerian Stored Products Research Institute (NSPRI) and Northern Nigeria Marketing Board. This committee was charged with the responsibility of assessing the extent of the aflatoxin problems in groundnut in the country and of initiating and coordinating all actions leading towards its elimination.

The IOPEA has started, in small way in India, its endeavour to educate farmers about sound post harvest practices in Gujarat, which is one of the largest groundnut-producing states in the country. In Andhra Pradesh the farmers do not seems to be as conscious as their counterparts in Gujarat about proper drying, storage and moisture levels. In both the states in UNDP sub-programme on "Promoting Groundnut as Food Crop for Sustained Nutritional Security" implemented by National Research Centre for Groundnut to educate the farmers regarding the proper drying and storage methods and the serious consequences of aflatoxin contamination. More organizations are now joining the campaign to educate farmers regarding the quality concept like in Gujarat NGOs are joining hands with NRCG to promote the cultivation of Bold seeded groundnuts especially in the Kutch-Bhuj area.

Developing countries mainly face the problem of mould growth and aflatoxin contamination in commodities transported over long distance through the sea route and need immediate attention of the researchers, producers and traders. If the contamination occurs during transit, often no insurance coverage for the risk is available. Because of the different methods of sampling followed in the exporting and importing countries, it is often difficult to define the exact responsibility of the development of aflatoxin as having taken place during transit.

Management of aflatoxin contamination

Following strategies may be followed to minimize the aflatoxin contamination: