CASHEW NUT NUTRITIONAL ASPECT
Cashew is a highly nutritious and concentrated food form providing a extensive amount of energy. The cashew nut kernel has a pleasant taste and flavour and can be eaten raw, fried and sometimes salted or sweetened with sugar (Manay et al, 1987). It also contributes to an important source of invisible fat in the diet, being widely used in a variety of ways. There has been a growing demand for cashew in many temperate countries where the demand is increasing (Russel, 1979). The nut contains an acrid compound which is a powerful vesicant that is abrasive to the skin. The cashew shell contains 25% of this reddish-brown oil, industrially known as Cashew Nut Shell Liquid (CNSL) which is a by-product of the roasting process.
The kernel is considered as high nutritive quality and the growing conditions or the variety of cashew may have an influence on kernel composition (Ohler, 1979). The overall composition of the kernel is protein 21%, fat 46% and carbohydrates 25%.
TOTAL NUTRIENT CONTENT
The total nutritive value of 100 g of cashew nut is presented in Table 1. Table 1: Nutritive Value in 100 g of Cashew Nut
Wide differences in the protein content ranging from 13.13 to 25.03% have been reported from various regions of India. It has been suggested that protein content is considered as one of the most important factors in future breeding and selection programs on cashew nut. The amino acid composition of kernel protein has been reported by various experts (Table 2).
Analysis of cashew nut kernels from different regions of India has revealed that there are variations in the reducing sugar content from 1% to 3% and the non-reducing sugars from 2.4% to 8.7%. Starch content ranged from 4.6% to 11.2% and the oil content also showed a wide variability from 34.5% to 46.8%.
FATTY ACID COMPOSITION
The fat and oil content of cashew nut contributes substantially to its energy content and consists mostly of Glycerides of oleic acid (73.8%) and linoleum acids (7.7%) (Ohler, 1979). Table 3 gives the composition of fats in cashew kernels. Table 3. Fatty Acid Composition of Cashew Kernels (%)
It may be mentioned that the high proportion of oleic and stearic acid contents may limit its use in the diets advocating low energy intake. The high content of MUFA oleic, however, might be beneficial in cases of bowel enteropathy. Also, from the point of view of essential fatty acid requirements, the ratio of linoleic to linolenic (values for cashew nut not available) acid is considered important. Studies at the National Institute of Nutrition (NIN) have shown that cereals and pulses on average contribute 3% and 2% respectively, of invisible fat, providing 1.5% LA and 0.08% ALNA and pulses furnish 1.3% LA and 0.28% ALNA to the diet. On this basis, habitual rural Indian diets were found to provide 7 en % of invisible fat (both from cereals and pulses) (Ghafoorunissa, 1989).
WHO/FAO (1977) had recommended an LA intake of over 3 en %, the requirement of LA being around 8g/capita/day. In rural diets, the invisible fat present in cereals, pulses and milk can meet about 66% of the daily LA requirements. To furnish the remaining 33%, different amounts of vegetable oils would be required from various sources of nuts and oil seeds. In the Indian context, figures available for two edible oils furnishing the recommended intake of LA works out to be 11 g or 4 en % in the adult diet, wherein the fat intake of total calories would be 11% or 30 g.
The judicious use of cashew in the diet in suitable proportions so as to enhance dietary quality with respect to fat and protein should, therefore, be possible. Owing to its high protein content, it could be used along with cereals/staples and pulses in small amounts in association with vegetables to improve the dietary profile. The level of oil present in the cashew to ensure energy density in the diet appears to be adequate, but whether it can meet the diets LA requirements needs to be studied further.
The vitamin content of cashew nut kernels shown in Table 4 indicates that 0.5 to 1.4 mg per 100 g of thiamin and 0.58 mg per 100 g of riboflavin, a good proportion of vitamin E and traces of other vitamins are present in cashew.
Table 4. Vitamin Content (mg per 100 gm) of Cashew Kernels
It may be mentioned that the vitamin E content of cashew nut could be a beneficial factor, in view of the wider use in the diet of the elderly and those who run the risk of cardiovascular disease. Vitamin E is also a powerful anti-oxidant and its role in lipid metabolism has been well-established. Fats containing a lesser amount of tocopherol in the unsaponifiable fraction have been reported to be more atherogenic as compared to most crop species containing the higher concentration of tocopherols (Kurup, 1989).
Thus, the amounts of cashew to be incorporated and the economic feasibility in utilizing for local diets need to be critically examined. Cardiovascular diseases which affect individuals mostly around middle age are common among the more affluent. The use of small amounts of cashew nut in the diet could, therefore, be a deterrent to controlling cardiovascular ailments.
The mineral content of cashew kernel (Table 5) appears to be minimal as compared to the higher mineral content of the cashew apple, especially the high Vitamin C content (240 mg). Most citrus species such as orange have only 45 mg of Vitamin C. However, the cashew apple is yet to be utilized on a large scale to alleviate Vitamin C nutrition requirements in the tropical countries where the crop is grown.
Cashew is also one of the few sources of phenols (contains about 60 % of anacardic acid by weight). This acid is responsible for the vesicative activity of the shell liquid extract and can cause acute dermatitis. It is therefore essential to ensure that as little contamination as possible of CNSL should occur during processing of kernels. In traditional medicine, however, this extract has been used successfully (Ohler, 1979).
The high price of cashew kernels will certainly stimulate the planting programs in various countries. Since the cashew nut market competes with other nuts, there is bound to be increased production of all nuts. The present cost of processing cashew is much higher than compared to other nuts which allow little flexibility in cashew kernel prices. It is, therefore, necessary to develop more efficient and cost-effective processing systems for cashew (Russel, 1979).
Table 5. Mineral Content of Cashew Kernels (%)
In contrast, groundnut (Arachis hypogaea) which is also an important oil crop of Brazilian origin, is now cultivated in tropical and warm temperate climates. The Portuguese were initially responsible for introducing the crop to Goa, India and the rest of Asia and Africa. With 31 % of the world’s production, India ranks first in groundnut production today. Groundnuts are not only rich in proteins which are easily digestible and consequently, a higher biological value but are also rich in B-complex vitamins. Like other edible nuts, it is used in different ways and it is an essential item in several confectionery products, and in supplementary feeding programs such as in weaning food formulations in combination with cereals and pulses in many developing countries. Various cultivars of groundnut tested in Andhra Pradesh, Southern India have shown high contents of P and K, possibly due to varietal differences (Pillai et al, 1984). There is a similar need to investigate the variability in the mineral content of cashew nut varieties in order to produce better varieties and optimize their use.
Whilst groundnut, when processed into margarine is gaining popularity as a substitute for butter in the USA and elsewhere, specifically due to its alternate use in instances of lactose intolerance, it is fast replacing dairy products due to the absence of cholesterol. The principal use of groundnut, however, is in the production of oil (Cummins, 1986).
COMPARATIVE NUTRITIVE VALUE OF GROUNDNUT VS CASHEW NUT
The comparative proximate composition of groundnut and cashew nut is given in Table 6. The nutritive value of both nuts is apparently similar with the exception of iron, where cashew nut has twice the level of groundnut and the chromium content which is higher in cashew. The bio-availability of these minerals needs to be studied as cashew also has high oxalate content. This aspect needs to be investigated in view of its possible application in meeting the iron requirements of vegetarian diets which are usually deficient in iron. The presence of chromium can also help in formulating better diets for diabetics.
Table 6. Comparative Nutritive Value of Cashew Nut and Groundnut
The fatty acid composition of groundnut is presented in Table 7. The oleic acid content of groundnut is much lower than that of cashew nut, while linoleic acid is three times the level in cashew nut. The WHO/FAO expert group has recommended that 30-35 percent of the Calorie requirements should be met from fats and oils in the ratio of 1:1 of saturated to unsaturated. It is also generally accepted that the total fat in human diets should not exceed 30en % or even lower in sedentary individuals (Fats and oil News, 1988, Grundy et al, 1987). The dietary fat (both visible and invisible) which were so far considered as an important nutrient component merely as a concentrated source of energy, has in recent years assumed tremendous nutritional significance with close links to the quality of fat in relation to its constituent fatty acids. In view of this, it may be of interest to nutritionists and food scientists to evaluate the merits and demerits of the usage of cashew nuts and groundnuts in the diet in suitable proportions to improve the nutritional fat quality and optimize its dietary benefits and applications.
Table 7. Total Fatty Acid Composition of Groundnut Oil