The cashew tree has been cultivated for food and medicine for 400 years. Cashews have served nutritional, medicinal and wartime needs. More recently, they have been used in the manufacture of adhesives, resins and natural insecticides. During World War II, the cashew tree became highly prized as the source of a valuable oil drawn from the shell.
Figure 4: Cross section of a cashew fruit
The cashew kernel is a rich source of fat (46 percent) and protein (18 percent) and is a good source of calcium, phosphorus and iron. It has a high percentage of polyunsaturated fatty acids, in particular, the essential fatty acid linoleic acid. The tart apple is a source of vitamin C, calcium and iron. The bark, leaves, gum and shell are all used in medicinal applications. The leaves and bark are commonly used to relieve toothache and sore gums, and the boiled water extract of the leaf or bark is used as a mouth wash. A paste of bark ground in water is used in topical applications for the cure of ringworm; in this form it can however act as an irritant and should not be applied to sensitive skin or to children. The root has been used as a purgative. Fibres from the leaves can be used to strengthen fishing lines and nets, and as folk remedies for calcium deficiency and intestinal colic, as well as a vitamin supplement. The water-resistant wood is used for boats and ferries, while the resin, in addition to having industrial uses, is used as an expectorant, cough remedy and insect repellent.
The cashew nut kernel is constituted of three different portions - the shell, the kernel and the adhering testa (Figure 4). The primary product of cashew nuts is the kernel, which is the edible portion of the nut and is consumed in three ways:
The relative importance of these uses varies from year to year and country to country, but it is estimated that at least 60 percent of cashew kernels are consumed as salted nuts. Separately packed cashew nuts are a good selling line, mainly as an appetiser to cocktail drinks. Salted cashews are part of the snack food market. They compete mainly with other nuts, although chips, salted popcorn and other savoury snacks can impinge on the nut market. The price of cashew nuts is much higher than the price of peanuts or other snacks so that sales must be based on a strong taste preference by the consumer. Cashew nuts are generally considered a luxury product, and an element of their appeal may lie in this status.
The cashew nut shell contains a viscous and dark liquid, known as cashew nut shell liquid (CNSL), which is extremely caustic. It is contained in the thin honeycomb structure between the soft outer skin of the nut and the harder inner shell. The CSNL content of the raw nut varies between 20 and 25 percent.
Cashew nut shell liquid (CNSL) is an important and versatile industrial raw material. There are more than 200 patents for its industrial application, in particular, its use as raw material for phenolic resins and friction powder for the automotive industry (brake linings and clutch disks). In drum-brake lining compounds, cashew resins are used as fillers, and may also be used as binders. In disc pads, the role of cashew resin is restricted to the use of friction dust as a filler. The advantage of the cashew resins compared with synthetic phenolic resins is that they are more economical and produce a softer material, which gives a quieter braking action (CTCS, 1993).
CNSL is also used in mouldings, acid-resistant paints, foundry resins, varnishes, enamels and black lacquers for decorating vases, and as insecticides and fungicides. In tropical medicine, CNSL has been used in treating leprosy, elephantiasis, psoriasis, ringworm, warts and corns.
Like cashew nuts, CNSL also has an excellent international market and its imports have reached almost US$10 million annually, corresponding to the sale of the raw liquid. However, the exporting country would earn much more foreign currency if manufactured products were exported.
After extracting the CNSL, the cashew nut shells can be burned to provide heat for the decorticating operation or can be used in the manufacture of agglomerates. Together with the testa, it may be used either in the manufacture of dyestuff or to provide durability to hammocks and fishing lines.
In cashew-producing countries, the nut is only one of the products enjoyed by the local populations. The cashew "apple" or false fruit is an edible food rich in vitamin C. It can be dried, canned as a preserve, or eaten fresh from the tree. It can also be squeezed for fresh juice, which can then be fermented into cashew wine which is a very popular drink in West Africa. In parts of India, it is used to distill a cashew liquor referred to as feni. In some parts of South America, local inhabitants regard the apple, rather than the nut kernel, as a delicacy. In Brazil, the apple is used to manufacture jams, and soft and alcoholic drinks.
The cashew tree bears a false fruit known as the cashew apple from which the nut protrudes. The cashew apple is between three and five inches long and has a smooth, shiny skin that turns from green to bright red, orange or yellow in colour as it matures. It has a pulpy, juicy structure, with a pleasant but strong astringent flavour.
The cashew apple is very rich in vitamin C (262 mg/100 ml of juice) and contains five times more vitamin C than an orange. A glass of cashew apple juice meets an adult individual's daily vitamin C (30 mg) requirement. The cashew apple is also rich in sugars, and contains considerable amounts of tannins and minerals, mainly calcium, iron and phosphorous. Furthermore, the fruit has medicinal properties. It is used for curing scurvy and diarrhoea, and it is effective in preventing cholera. It is applied for the cure of neurological pain and rheumatism. It is also regarded as a first-class source of energy.
Until recently, the potential of cashew apple had not been investigated due to its highly astringent and acrid taste which is believed to originate in the waxy layer of the skin and which causes tongue and throat irritation after eating. Cashew fruit can be made suitable for consumption by removing the undesirable tannins and processing the apples into value-added products, such as juices, syrups, canned fruits, pickles, jams, chutneys, candy and toffee. The recommended methods for removing the astringent properties of the cashew apple include steaming the fruit for five minutes before washing it in cold water, boiling the fruit in salt water for five minutes, or adding gelatin solution to the expressed juice.
The fruit should be picked from the tree by hand to avoid bruising the delicate flesh. They are then carefully washed and the nuts are removed for processing. Cashew apples should be processed within two to three hours of picking, since they undergo rapid deterioration when kept for a longer time.
Currently only six percent of cashew apple production is exploited, since the producer only has a guaranteed market for cashew nuts. It is also extremely difficult to use the whole fruit commercially as the apple ripens prior to the nut. The quality of nuts detached from the green fruit, is unacceptable for commercialization. The ripe apple can be eaten or used for jam making, for the production of fruit juices or for making alcoholic beverages. The development of processing options for the cashew apple, has also been limited by its high degree of perishability, and consequent difficulties in transportation from growing areas to distant processing plants.
In gathering the fruits and transporting them to be processed, the prime purpose should be to have the fruit arrive in the very best condition possible. Cashew apples should be sorted, and only mature, undamaged cashew apples should be selected for use in recipes. These should be washed in clean water prior to use. Recipes for the use of cashew apple are listed in Appendix A2.
Cashew wine is made in many countries throughout Asia and Latin America. It is a light yellow alcoholic drink, with an alcohol content of 6-12 percent.
Cashew apples are cut into slices in order to ensure a rapid rate of juice extraction when they are crushed in the juice press. The fruit juice is sterilized in stainless steel pans at a temperature of 85oC in order to eliminate any wild yeasts. The juice is filtered and treated with either sodium or potassium metabisulphite, to destroy or inhibit the growth of undesirable types of micro-organisms such as acetic acid bacteria, wild yeasts and moulds.
Wine yeast (Saccharomyces cerevisiae - var ellipsoideus) should be added. Once the yeast has been added, the juice is thoroughly stirred and allowed to ferment for about two weeks. The wine is separated from the sediment and clarified by mixing fining agents, such as gelatin, pectin or casein, with the wine. Filtration is carried out with filter-aids such as fullers earth. The filtered wine is transferred to wooden vats.
The wine is pasteurized at 50-60oC. The temperature should be controlled, so that it does not rise exceed 70oC, since alcohol vaporizes at a temperature of 75-78oC. The wine is then stored in wooden vats and subjected to ageing. At least six months should be allowed for ageing. If necessary, the wine should be clarified again before bottling. During ageing and subsequent maturing in bottles, many reactions, including oxidation, occur. The formation of traces of esters and aldehydes, together with the tannin and acids already present enhance the taste, aroma and preservative properties of the wine (Wimalsiri et al, 1971). The product is packaged in glass bottles with corks and should be kept out of direct sunlight.
|Selection||Mature, sound cashew apples|
|Slicing||To increase extraction of juice|
|Sterilization||At 85º C|
|Inoculation||With S. cerevisiae|
|Ageing||In wooden vats for 6 months|
Cashew fruit are not readily consumed in the raw state because of their high content of astringent compounds. If these are removed and the fruit is sweetened, it can be converted into a useful dried product. The fruit must therefore be extensively processed prior to drying.
Fruits are prepared according to the following process:
Source: Brown, 1992.