1.1 Background of the study
Cassava (Manihot esculenta) is an important food in the tropical areas of African, Asia and Latin Africa (IITA,1990). It is estimated (IITA, 1990) that the crop provides about 40% of all the calories consumed in Africa and ranks seconds only to cereal grains as chief source of energy in Nigerian diet (Ngodddy, 1989). Cassava plays important role in alleviating African Food Crisis. It is poor in protein (1.20%) and high in cyanide (> 10 mg/100g fresh weight), (IITA, 1990;Janssens, 2001).
Raw cassava has been reported tocontain two cyanogenicglycosidesknow as linamarin,lotaustralin and amygdalin.(Onabolu, 1989, Cereda and Mattos, 1996, Dicer, 1993). Linamarine and lotaustralin are glucoside of acetone cyanohydrins and ethyl-methy-ketone-cyanohydrin, respectively (Cereda and Mattos, 1996). Linamarin produces the toxic compound (hydrogen cyanide, HCN), which can be hazardous to the consumers. Amygdalin is also a cyanide which on metabolism produces hydrogen cyanide, a potent toxin. Beta-glucosidase, one of the enzymes that catalyzes the release of cyanide from amygdalin , is present in the human small intestine and in variety of common foods. Cassava processing by fermentation is one the most widespread techniques used in Africa and is considered an efficient means of reducing cyanogenic potential in the resulting food (Brainbridge, 1994).
“Lafun” is a fermented cassava flour popular among the people in the South West states of Nigeria. (Cereda and Methos, 1996). The traditional method of processing cassava into “lafun” is unique for its ability to reduce the toxic cyanogenic compound to at least safe level (Numfor, 1983) and impacts a smell to the product (Cereda and Mathos, 1996). Cassava flour (lafun) is a dry product, which can be preserved for a long time under the prevailing local environment.
Gaari is also a fermented cassava product,it is a convenience food with a short preparation time. Its cheapness, ease of storage and preparation for consumption have combined to make it extremely popular among the urban dwellers in Nigeria and other West African countries. “Gaari” can be prepared in a variety of ways. It can be dispersed in cold water and consumed directly with sweeteners, groundnut and fish. The most widespread method of gari consumption is preparing it into a paste by pouring into a measured quantity of boiling water. The paste, popularly called “eba”in Nigeria is eaten by dipping small balls of it into soup or stew and swallowing with or without mastication (Cereda and Mattos 1996).
“Gaari” is by far the most popular form in which cassava is consumed in West Africa (Onwueme, 1978). In Nigeria, it is consumed primarily by the Urban dwellers and the scale of “gaari” processing in West Africa has been found to involve individual family units producing less than 0.5 ton/hr. The end product (gaari) is consumed in varying amounts by approximately 50 million Nigerian (NRCRI, 1987). Whether “gaari” can be relied upon as staple food will to a large extent depend on how well it can be processed in safe forms (Bokanga, 1995). The use of cassava as a food is limited by its perishability, low protein content and potential toxicity (Cooke and coursey, 1981). Processing methods have devised to reduce their toxicity and at same time convert the highly perishable roots to more stable products. These processes include sun drying, soaking and fermentation followed by drying or roasting.
1.2 Aim and Objectives
The aim of this project is to determine the amygdalin and cyanide contents of commercially available cassava products in Oyo State (Ogbomoso, Oyo, Ibadan).
- To determine the amount of amygdalin and cyanide in commercially available cassava products (lafun and gaari) in Oyo State.
- To quantify the amount of cyanide in commercially available cassava products (lafun and gaari) in Oyo State.
The potential toxicity of cassava is related to the capacity of all part of the plant to release hydrogen cyanide from stored cyanogenic glucoside. The residual cyanogens, linamarin and acetone cyanohydrins, are the apparent source of cyanide toxicity to animals and human, when converted to cyanide inside the body. For an adult human, consumption of 50 to 100mg or 2mmol of HCN within 24hours can completely block cellular respiration leading to death (Rosling, 1994). Consumption of cassava products with high concentration of cyanogens can lead to cyanide poisoning, goitre, konzo and tropical neuropathy. Improperly processed cyanogenic plant foods can cause cyanide poisoning. (Tylleskaret al., 1991).
1.4 Scope of the study
This study is limited to the determination of amygdalin and cyanides in cassava products (gaari and lafun) produced in Oyo State, Nigeria.