Minimizing Postharvest Losses in Yam (Dioscorea spp.): Treatments and Techniques
Yam belongs to the genus Dioscorea (Family Dioscoreaceae) and is the second most important tropical root crop in West Africa after cassava. Besides their importance as a food source, yams also play a significant role in the socio-cultural lives of some producing regions such as the celebrated New Yam Festival in West Africa. Yams originated in the Far East and spread westwards. Today, yams are grown widely throughout the tropics. West and Central Africa account for about 94% of world production, Nigeria being the major producer.
The most popular and preferred form of consuming yam is the tuber form, either boiled, pounded, roasted or fried. Better financial returns are obtained by selling the yams as tubers rather than as processed yam flour. Thus, farmers prefer to store most of their yams after harvest. Methods of storage vary from delayed harvesting, storage in simple piles or trenches to storage in buildings specially designed for that purpose, and application of modern techniques.
Causes of storage losses of yam tubers include sprouting, transpiration, respiration, rot due to mould and bacteriosis, and attack by insects, nematodes and mammals. Sprouting, transpiration and respiration are physiological activities which depend on the storage environment (mainly temperature and relative humidity). These physiological changes affect the internal composition of the tuber and result in destruction of edible material and changes in nutritional quality. Storage losses in yam of the order of 10-15% after the first three months and approaching 50% after six months storage have been reported.
A number of treatments and techniques have been developed to reduce these physiological activities and also to protect the tuber from postharvest diseases. These include treatment with chemicals, plant extracts, palm wine and gamma irradiation; storage techniques used include cold storage, improved underground storage and improved yam barns. This chapter discusses research into yam postharvest handling aimed at improving the availability of tubers throughout the year.