Processing Techniques to Reduce Toxicity and Antinutrients of Cassava for Use as a Staple Food
Cassava is a valuable source of food for developing countries, but it contains highly toxic cyanogen compounds and antinutrients. Cyanogens are found in 3 forms in cassava: cyanogenic glucoside (95% linamarin and 5% lotaustratin), cyanohydrins, and free cyanide. Different processing techniques exist to remove cyanogens and their effectiveness depends on the processing steps and the sequence utilized, and it often is time-dependent. Pounding or crushing is the most effective for cyanogenic glucoside removal because it ruptures cell compartments, thus allowing direct contact between linamarin and the enzyme linamarase that catalyzes the hydrolytic breakdown. Crushing and sun-drying cassava roots made into flour removes 96% to 99% of total cyanogens, whereas soaking and sun-drying into lafun or fufu, or soaking and fermenting and roasting into gari or farina, removes about 98% of cyanogens. For cassava leaves, which have 10 times more cyanogens than roots, pounding and boiling in water is an efficient process to remove about 99% of cyanogens. Other strategies to reduce toxicity include development of low-cyanogen cassava varieties and cassava transgenic lines with accelerated cyanogenesis during processing. Although phytate and polyphenols have antioxidant properties, they interfere with digestion and uptake of nutrients. Fermentation and oven-drying are efficient processing methods to remove phytate (85.6%) and polyphenols (52%), respectively, from cassava roots. Sun-drying the leaves, with or without prior steaming or shredding, removes about 60% phytate. Cassava is a nutritionally strategic famine crop for developing countries and, therefore, reducing its toxicity and improving its nutritional value is crucial.