fatty acids ,All stage producing peanuts to trade 6

fatty acids ,All stage producing peanuts to trade this product 6







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.

2.7.1 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.

2.7.2 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).

2.8 Processing

2.8.1 Chemical composition of groundnut

The world is experiencing a shortage of edible oil and proteins. Groundnut plays a useful role in alleviating these deficiencies as it is a rich source of edible oil and protein. Groundnut has an outer thick woody shell. Inside normally there are 2 or 3 embedded seeds (kernel). The seed consists of 2 cotyledons and the germ covered by an outer thin skin called the testa. The colour of the testa may be red, brown, purple or white depending upon the type and variety. Testa constitutes about 4 to 5 percent of the weight of the kernel. The cotyledons constitute the bulk of the seed in the range of around 92 to 94 percent of the weight. The germ constitutes around 3 to 4 percent of the seed weight. The testa protects the seed against pests and diseases. Cotyledons are the storage organs, which supply food the germ during germination. As a result of these functional differences, the chemical make-up of the parts of the kernel also differ. Composition of groundnuts parts, oil cake and haulms is revealed in Tables 11 and 12.


Table 11. Chemical composition of kernel (g 100-1 g).

Total carbohydrates48.3-52.26.0-24.9
Reducing sugar1.0-
Crude fibre21.4-34.91.6-1.81.6-1.9

Source: Cobb and Johnson (1973), NDDB (1982)


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

Crude fibre22.11-35.35
Oil cake 
Crude protein45-60
Mineral matter4-5.7
Crude fibre3.8-7.5

Source: Reddy, P.S., 1988.

2.8.2 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.

Grade ComponentsRange of parameter
Total Shelled Pods (%)100
Good Seed (riding 17/64″ screen)52-71%
Good Seed (riding 15/64″ screen)62-74%
Loose Shelled Kernels (LSK)0.5-1%
Split and Shrunken Seed (%)5-9
Pick Outs (%)1-7
Shelling Outtern (%)72-80
Moisture of Seed (%)6.22-6.62
Oil (%)48.7-48.8
Oil Colour (Abs 450 mu)0.035-0.054
Iodine Value94.9-95
Percent Linoleic Acid29.6-29.6
Percent Oleic Acid50.1-50.8
Organoleptic Score (CLER score)58-67

Source: Norden, et al., 1969. 

fatty acids
fatty acids


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:

  1. Shelling percentage,
  2. Germination capacity,
  3. Prevention of aflatoxin,
  4. Seed and pod size and shape,
  5. Skinning and splitting performance, and
  6. Organoleptic qualities after roasting.

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.

Fatty acidRangeAverage
Saturated fatty acids  
Myristic (C 14:O)0.01-0.230.09
Palmitic (C 16:O)9-24.912.6
Stearic (C 18:O)0.0-5.51.7
Arachidic (C 20:O)2-10.24.2
Behenic (C 22:O)0.7-3.92.1
Lignoceric (C 24:O)0.0-2.80.3
Unsaturated fatty acids  
Palmitoleic (C 16: 1)0.6-3.31.4
Oleic (C 18:1)38.7-56.247.9
Linoleic (C 18:2)16.2-38.429.9
Eicosenoic (C 20:1)0.74-2.273.9



Table 15. General properties of groundnut oil.

Melting point0-3°C
Iodine value82-106
Thiocyanogen value58-75.5
Saponification value188-195
Acetyl value8.5-9.5
Reichert-Meissl value0.5
Polenske value0.5
Free fatty acids0.02-0.6%
Unsaponifiable matter0.3-0.7%
Refractive index (ND20)1.4697-1.4719
Density at 15°C0.917-0.921
Density at 25°C0.910-0.915
Mean viscosity at 20°C71.07-86.15 centipoises
Heat of fusion21.7 cal/g (unhydrogenated) and 24.7 cal/g


Colour: VisualLight yellow
Lovibond, 1 in.Yellow: 16-25; Red: 1-2
Taste and odourSlightly nut-like

Source: Cobb and Johnson (1973), NDDB (1982) 


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 shelflife. 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.

The oil from fresh and ripened kernels should have less than 1 percent free fatty acids. A higher concentration indicates damage to the tissues especially during storage. The ά- and β- tocopherols (Vitamin E) are nutritionally important both in the seed for direct consumption and in oil. The aflatoxins do not become a major hurdle in the oil industry as they are associated with the protein bodies and are easily removed by proper filtering. With solvent extraction this problem could totally be overcome. However, there are few reports that oil not properly filtered contains some traces of aflatoxin.

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 shortduration 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).

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