Nutrient And Antinutrient Content In Leaves Of Selected Coastal Kenya Cassava Varieties As Affected By Maturity Stage, Leafage And Preparation Method

Abstract

In Kenya, different cassava varieties have been bred for high root yields and low cyanide content, and plant drought and disease resistance for improved food security. However, despite the high protein, vitamin and mineral contents of cassava leaves, limited information exists on utilization and the level of the nutrients and anti-nutrients in the leaves of different cassava varieties’ at different plant maturity stages and leafages. This study was conducted to determine the current mode of utilization and preparation of cassava leaves, effect of plant maturity stage, leaf age and preparation methods on nutrients (β carotene, Vitamin C, Zinc, Iron and Calcium) and anti-nutrient (Cyanide, Nitrates, Oxalates, Phytates and Tannins ) content in raw and prepared cassava leaves of selected coastal Kenya varieties. A survey was conducted to determine the households’ utilization and preparation of the cassava leaves. The 2nd, 3rd, 4th and 5th leaves of the three popular varieties: - Kibanda Meno, Karembo and Tajirika were harvested at 3, 6 and 9 months after planting and separately analyzed for nutrients and anti-nutrients. The survey indicated that cassava leaves are popular vegetables in coastal region and all the types of cassava varieties are used. There were no significant differences (p> 0.05) in Crude protein, Zinc, Iron, Cyanide, Oxalates and Nitrate content of raw cassava leaves at different leafages; however there were significant differences (P<0.05) in protein content among the three cassava varieties. The Crude protein, Zinc and Iron content were higher at 3 months plant maturity stage; while Vitamin C and Calcium contents were higher (P<0.001) at 9 months. The Crude protein, β carotene, Zinc, Iron, Vitamin C and Calcium content ranged from 20% to 35%, 9.07 to 22.09, 11.7 to 135.2, 21.8 to 203.8, 27 to 1087 and 124 to1545mg/100g, respectively. The Cyanide, Oxalates, Tannins and Nitrates content ranged from 324.6 to 1849 mg/kg, 29.54 to 49.04g/100g, 1208 to 3474, 21.2 to 72.7 mg/100g, respectively for all the three varieties and leaf ages. xv | P a g e The Crude protein, β carotene, Zinc and Iron in the leaves decreased as cassava plants matured while the cyanide, tannins, oxalates and nitrates increased with plant maturity. Tajirika and Kibanda Meno varieties exhibited high levels of nutrients and low levels of anti-nutrients, hence most preferred. The most appropriate harvesting stage was at 6 months compared to 3 and 9 months. The raw cassava leaves traditional preparation methods of pounding, fermentation and blanching/solar drying significantly (p<0.05) lowered the nutrient and anti nutrient content. The Cyanide content ranged 170-380 for blanched/solar dried/boiled, 260-410 for fermented/boiled and 150-320 mg/kg for pounded/boiled. The average losses of the anti-nutrients Cyanide, Tannins, Nitrates, Oxalates and Phytates were: 83, 76, 46, 16 and 88 % through pounding-boiling and 72, 85, 66, 48 and 54% through solar drying/boiling, respectively while the losses were 63, 86, 26, 59 and 23% through fermentation/boiling. Average Vitamin C and β carotene retention were 18% and 61% in blanched/solar drying, respectively while retention of Vitamin C and β carotene in pounded leaves were 52 and 63%, respectively. Iron and Calcium levels slightly increased to 109 and 159%, 112 and 114% with fermentation and solar drying, respectively. The best preparation method was pounding which reduced the Cyanide, Tannins and Phytate content followed by solar drying. Therefore, reducing the anti-nutrient toxicity is thus essential to encourage consumption of cassava leaves for their nutritional value.