Describe the effect of cassava processing on cyanide level

Cassava tubers are traditionally processed by a wide range of methods, which reduce their toxicity, improve palatability and convert the perishable fresh root into stable products. These methods consist of different combinations of peeling, chopping, grating, soaking, drying, boiling and fermenting. While all these methods reduce the cyanide level, the reported loss in cyanide content differs considerably due to analytical methods, the combination of methods and extent to which the process(es) is(are) carried out.
The specific effects of various processing techniques on the cyanide content of cassava are discussed below:

1.Peeling

Many methods of processing cassava roots commence with the peeling of the tubers. Generally the cassava peel contains higher cyanide content than the pulp. Removal of the peels therefore reduces the cyanogenic glucoside content considerably. In studies carried out by the author, the peel of the “bitter” cassava variety was shown to contain on average 650 ppm and the pulp to contain 310 ppm total cyanide; the corresponding values for “sweet” varieties were 200 ppm and 38 ppm respectively. The above classification is conveniently based on the cyanide content; with the sweet varieties having most cyanide in the cortex and skin and little or no cyanide in the pulp, whereas the bitter varieties, more or less, have an even distribution of cyanide throughout the tuber. For these reasons the former can be eaten boiled while the latter has to be processed before it can be consumed.
Peeling, therefore, can be an effective way to reduce the cyanide content by at least 50% in cassava tubers.

2.Grating

This process takes place after peeling and is sometimes applied to whole tubers. Grating of the whole tuber ensures the even distribution of the cyanide in the product, and will also make the nutrients contained in the peel available for use. In the grated product, the concentration of cyanide depends on the time during which the glucoside and the glucosidase interact in an aqueous medium.
Grating also, obviously, provides a greater surface area for fermentation to take place.

3.Soaking
Soaking of cassava roots normally precedes cooking or fermentation. It provides a suitably larger medium for fermentation and allows for greater extraction of the soluble cyanide into the soaking water. The process removes about 20% of the free cyanide in fresh root chips after 4 hours, although bound cyanide is only negligibly reduced. Bound cyanide begins to decrease only after the onset of fermentation. A very significant reduction in total cyanide is achieved if the soaking water is routinely changed over a period of 3–5 days.

4.Boiling/Cooking
As with soaking, the free cyanide of cassava chips is rapidly lost in boiling water. About 90% of free cyanide is removed within 15 minutes of boiling fresh cassava chips, compared to a 55% reduction in bound cyanide after 25 minutes.

5.Fermentation
Microbial fermentations have traditionally played important roles in food processing for thousands of years. The importance of fermentation in cassava processing is based on its ability to reduce the cyanogenic glucosides to relatively insignificant levels.
It has been shown that the higher the retention of starch in grated cassava the better the detoxification process. This could be attributed to the fermentative substrate provided by the starch. Also, the longer the fermentaion process the lower the residual cyanide content.



6.Ensiling
Ensiling is to turn (green fodder) into silage by causing it to ferment in a closed pit or silo.
The ensiling process causes the disintegration of the intact glucoside via marked cell disruption, drop in pH of ensiled medium and intense heat generation.
Ensiled cassava roots have been used for livestock feeding. Ensiling cassava chips reduced the cyanide content to 36% of the initial value after an ensiling period of 26 weeks.

7.Drying
Since cassava root contains about 61% water, coupled with the solubility of its cyanogenic glucoside component, the dehydration (dewatering) process results in a substantial reduction in the content of this toxin in the pressed pulp. Drying is carried out using solar radiation (sundrying) or Driers (electric or fuel) depending on economic viability. The process is achieved at varying temperature.

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Titany answered the question on April 25, 2022 at 05:47