Fruits are normally eaten fresh when mature but for long preservation and wider distribution, they are processed into juice. The few fruits that can be processed into juice are pineapple, mango, guava, citrus fruits, etc
3.3.1 Orange/Grape-fruit Processing
Fruits are sorted by hand to remove rotten, broken, diseased fruits. The sorted fruits are washed and may be de-oiled by passing the washed fruits through another metal column consisting of a series of revolving graters which rasp the thin skin layer under jets of water. The oil/water emulsion is then collected, screened and centrifuged to recover the oils. The juice is extracted by pressing; and screened to obtain a cleaner juice. Granulated sugar may be added if necessary.
The juice is pasteurized, filled into sterilized cans, closed, cooled and dried for packing and storage.
Stored commodity includes crop produce/products, dried and smoked fish, meat, tides and skins, tuber products and household goods e.g. clothes, carpets, books etc. Crop produce obtained from field and horticultural crops are grouped into four classes:- durables, semi-durables, perishables and others.
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3.3.2 Oil fruits
Since the oil palm gives the economically most important tropical oil fruit, the technologies for its extraction can serve as an example in this category.In the traditional process, the fruit is first removed from the bunches, generally after the bunches have fermented for a few days. The fruit is then cooked and pounded or trampled. The mashed mass is mixed into water. The oil and oil containing cell material is separated from the fibre and the nuts by rinsing with excess water and pressing by hand. The oil-containing mass, now floating on the top, is collected and boiled. In this step, the oil separates from the rest and collects on the surface. It is skimmed off and finally dried.The actual execution of the process may vary somewhat from area to area; most
traditionalprocesses, however, have in common the superfluous use of water. Using this process, generally not more than 50% of the oil is obtained.
The problems are:
- the digestion by means of pounding or trampling,
- the separation of the oil and oil containing material from the fibres and the nuts by means ofwater and the liberation of the oil by cooking afterwards.
The potential for improvement of this technology and thereby the development of small scale extraction equipment in principal depends on
- better cooking by means of steam,
- better digesting using a reheating step with steam and
- effective pressing in a batch press or continuously working screw press.
The modern process of extracting palm oil, used on a larger scale, starts with the steam sterilization of the bunches. The bunches are threshed and the fruit is digested mechanically, while heated with steam. The mass is then pressed in hydraulic presses or continuously in screw presses. The oil is separated from the press fluid by heating and is finally dried.
3.3.3 Oil seeds
In addition to the distinction made between traditional and modern methods, the processes for oil seeds should also be divided into so-called wet and dry extraction methods. Of the traditional wet
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processes, the extraction of coconut oil from fresh coconuts is the best known. It starts with grating the meat, after which the oil as well as the proteins and impurities are extracted as milk from the fibrous residue by pressing (by hand or foot) and rinsing with fresh water. The milk is left to stand to form an oil rich cream on top. The cream is boiled to separate the oil from water and other impurities. The oil can be skimmed off. It still contains a protein- rich residue that can be filtered off after drying and used for human consumption.Other oil seeds, like groundnuts, palmkernels and Sheanuts are roasted and crushed as fine aspossible (e.g. first by pounding, followed by crushing between stones or a stone and an iron bar). The crushed mass is mixed with water, and the oil is obtained by cooking the mixture, causing the oil to float. The oil is finally skimmed off and dried by heating. Sheanut oil is often obtained by beating air into a mixture of crushed seeds with some water using a hand-operated butter making process. The milk or cream floating on top of the beaten mass at the end of the process is then cooked to evaporate the water and dry the oil.The weak points of these processes are the grating or crushing steps. They are time consuming and exhausting work, yet crushing is generally not fine enough. Thorough crushing can improve the oil recovery considerably. In many areas, engine-driven disc mills are used by women in small commercial enterprises to get their seed crushed.
4.0 Conclusion
Ineffective or inappropriate food processing technologies, careless harvesting and inefficient post-harvest handling practices, bad roads, moribund rail systems, bad market practices and inadequate or complete lack of storage facilities, packing houses and market infrastructures are some of the factors responsible for high post-harvest food losses in West African countries.
5.0 Summary
The common element in all sectors of the food processing is conversion of raw material into a product of higher value. In some situations, processing is a one-step conversion of raw material to a consumer product. The history of food processing lay emphasis on the role of establishing and maintaining microbial safety in foods, as well as the desire to establish and maintain economic shelf-life for foods. Processing methods are used worldwide as they improve the digestibility and nutritional quality of the grains.
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6.0 Tutor Marked Assessment (TMA)
- Describe processing of cassava - Describe processing of yam
- Describe the production of instant yam flour - Explain processing of oil seeds
- Differentiate between decorticated and de-germinated meal
7.0 References and further Readings
1. Adaskaveg, J.E., H. Forster, and N.F. Sommer. (2002). Principles of postharvest pathology and management of decays of edible horticultural crops. p. 196-195.
2. Batten, D. J. and Loebel, M. R. (1984). Agfacts: Lychee harvesting and post-harvest handling. New South Wales Department of Agriculture, Australia.
3. Batten, D. J. (1989) Maturity criteria for litchis (lychees). Food Quality Preference1, 149-55
4. Barrett, D. M. (2000) processing of horticultural crops No. 37 pg.466-479
5. Charles A. O. (2008). The Role of Traditional Food Processing Technologies: In National Development: the West African Experience. International Union of Food Science &
Technology. Sub-Saharan
5. Hall, D. W. (1969)."Food Storage in Developing Countries," J.R. Soc. Arts, 142: 562-579 (1969)
6. Harris, K. L., C. J. Lindblad (1976) Postharvest Grain Loss Assessment Methods - A Manual of Methods for the Evaluation of Postharvest Losses American Association ofCereals Chemists, 1976
7. Jelle H. (2003). The storage of tropical agricultural products; Agrodok 31 Agromisa Foundation, Wageningen,
8. Kader A.A. (1983). Postharvest technology of horticultural crops, third edition.
University of California, ANR Publication 3311.
9. Kitinoja, L., Kader, A. A. (2002). Small Scale Postharvest Handling Practices: A Manual for Horticultural Crops (4th edition). July 2002
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10. McGregor, B.M. (1989) Tropical Products Transport Handbook. USDA Office of Transportation, Agricultural Handbook 668.
11. MISSING FOOD: The Case of Postharvest Grain Losses in Sub-Saharan Africa. World Bank Report No. 60371-AFin
12. Proctor, D. L. (1994) Grain storage techniquesEvolution and trends in developing countries.FAO AGRICULTURAL SERVICES BULLETIN No. 109
13. Thompson, J.F., Spinoglio, M. (1994). Small-scale cold rooms for perishable commodities. Family Farm Series, Small Farm Center , University of California , Davis . 14. Schulten . G. G. M. (2002) Post-harvest losses in tropical Africa and their
prevention.Royal Tropical Institute, Amsterdam, Netherlands 15. http://www.fao.org/docrep
16. http://postharvest.ucdavis.edu 17. http://www.crcpress.com/product 18. http://www.actahort.org/books
19. http://sciencedirect.com/science/journal 20. http://www.stewartspostharvest.com
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