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Chapter 16

Preparation and Use of Avocado Oil and Its Products

Julius K. Muigai and Francis M. Mwaura

The Avocado (Persea americana) belongs to the family Lauraceae, a family of mainly tropical trees and shrubs. Other well-known members are laurel, cinnamon, sassafras and greenheart (Samson, 1986). Avocado is native to tropical America. It is a shallow-rooted evergreen tree that grows up to 20 m tall. Its leaves are simple, ovate and spirally arranged. The white flowers are borne in clusters on auxiliary panicles. The avocado fruit is generally pear-shaped with a large, round to egg-shaped central seed. The flesh is buttery in texture, contains a high percentage of oil and protein and has a high calorific value (Rice et al., 1986).  Avocado is common throughout the tropics and subtropics (Martin et al., 1987).

Avocado trees perform well in areas with warm, frost-free climates. The flowers are sensitive to low temperatures and frost during blooming results in substantial crop loss. Optimum growth occurs in fertile, well-drained soils, although they are tolerant to a wide range of soil types except those with excessive salinity (Koch, 1983). The trees respond well to fertilizers especially phosphorus in the early stages of growth, and to nitrogen and potassium in the later growth stages. Soil pH levels and root disease conditions affect the tree’s ability to absorb nutrients. Avocado has a number of pests and diseases but the most serious is Phytopthora cinnamomi which causes root rot, seedling blight and stem canker (Gachanga and Ilg, 1990). For better crop establishment, farmers are encouraged to use disease or pest prevention that includes treatment of rootstock before planting, use of root-rot resistant grafting stock, and planting on ridges in deep, well drained soils.

Three different subspecies, Mexican, Guatamala and West Indian, are recommended for the subtropical, semitropical and tropical climatic areas respectively. These races can be distinguished from one another using several attributes (Table 1). Hybrids between the varieties are common and of commercial importance. The attributes preferred by breeders in the selection of avocado cultivars are high and regular yields of medium-sized fruits containing small seeds and buttery flesh.  Uniform ripening, fruit shelf life and tree size and shape (smaller trees of spreading habit) are also considered (Samson, 1986).

Table 1. Properties of some avocado varieties (after Samson, 1986)

Farmers generally recognize the avocado varieties by cultivar rather than races. Some of these cultivars include, Hass, which belongs to Guatemalan race and is self-fertile. The fruit is warty, medium sized, roundish and purple at full maturity. The fruit has a tough, pebbly skin, ships well, has good shelf life and enjoys wide consumer acceptance (Koch, 1983). Fuerte, is a Mexican-Guatemalan hybrid with shiny-green pear-shaped fruit that weighs 250 to 450 g with a high oil content (18-26 %). Booth 8 has large, pear-shaped fruit that turn purple on ripening. Other varieties grown in Kenya are Reed, Puebla, Pinkerton and Simmonds (Mugambi, 2002).  Kenyan farmers produce avocado for food, local markets and export. The fruits are largely grown in the Central Highlands and have been found to be the second in prevalence on farmers’ field after Grewia robusta (Betser et al., 1999).  

One industrial process involving avocado is the recovery of its oil. Avocado oil has a pleasant smell and multiple uses in cosmetics, healthcare products and as a fine lubricant. Both raw and processed avocado oil represent a potential source of income for farmers while its use as lighting fuel may contribute to the reduced dependence upon fossil fuels as an alternative to paraffin (kerosene).

Avocado Oil Extraction

1. Collect mature, off-grade avocado fruits

2. Ripen for 2 days

3. Cut the fruit into pieces and remove the seed (Figure 1)

4. Sun dry the fresh pieces of avocado until brown to black in colour (Figure 2)

5. Wrap the dried pieces in a cloth then use a clamp to squeeze the oil

6. The extracted oil is ready for use as a fuel and burns well in an open lamp

A liter of oil is extracted from between 9 to 11.5 kg, or about 40 to 50 avocado fruits. In Kenya, avocado oil was tested for some of its chemical and physical properties by the Kenya Bureau of Standards and the Kenya Institute of Research and Development (Box 1). Because the avocado fuel produced from this process does not light well with the regular lantern lamps, a special lamp has been designed for the use of avocado fuel (Figure 3).

The harvesting cost of avocados is negligible as many fruit fall to the ground at maturity. Off-grade avocados are inexpensive during harvest seasons or freely obtained from neighboring farms with surplus production.

Avocado production follows peak seasons and the processing of fuel oil from avocado competes with other local uses such as food. Even the low-grade fruits enjoy demand in local market as an inexpensive food and over-ripe fruits have a distinct taste that is preferred by some consumers. The fruit is highly nutritious and lacks harmful fats and cholesterol. The oil is also used locally as herbal medicine for certain health conditions and in the preparation of cosmetics that are not discussed in detail within this chapter.

Conclusion

Improving the marketing of avocado fruits will reduce post-harvest losses and improve household income. The efficiency of oil extraction needs to be improved especially for trees that are not rich in oil such as Hass and other Guatemalan varieties.

The use of a pressing machine to replace the current manual extraction methods will improve the efficiency of oil extraction. The extraction and use of avocado oil as fuel is innovative but its progress is limited by the economics of the undertaking. Already avocado has a number of uses that offer higher returns than fuel. With the current extraction technique, one litre of avocado oil has a value of KSh 200 while the equivalent quantity of paraffin costs only KSh 35. The need to improve on the avocado oil lantern may increase the effectiveness of the avocado oil technology and stimulate demand for its processing among low income households. Better filtration of the avocado oil would allow for its fuller industrial processing particularl into cosmetics.

References

Betser, L., Mugwe, J. and Muriuki, J. 1999. Of-farm Production and Marketing of High Value Tree Products in the Central Highlands of Kenya. Proceedings of a Workshop on Off-Forest Tree Resources of Africa Held in Arusha, Tanzania 12-16 July 1999. pp. 227-241.

Gachanja, S. and Ilg, P. 1990. Fruit Tree Nurseries. Ministry of Agriculture, Nairobi, Kenya.

Koch D.F. 1983. Avocado Growers Handbook. Housall Publications, California, USA. 

Martin, F.W., Campbell, C.W. and Ruberte, R. M. 1987. Perennial Edible Fruits of the Tropics: An Inventory. Agriculture Handbook No. 642. United States Department of Agriculture. Washington DC, USA. 252 pp.

Mugambi, D.M. 2001. Market Status of Avocado and Associated Products in Kenya. RELMA Working Paper No. 12. RELMA, Nairobi, Kenya.

Rice, R.P., Rice, L.W. and Tindall, H.D. 1986. Fruit and Vegetable Production in Africa. Macmillan Publishers, London, UK.

Samson, A.R. 1986. Tropical Fruits. Longman Press, New York, USA

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