Influence of Crop Age on Nutritional Quality and Hydrogen Cyanide Levels of Roots from Popular Coastal Kenyan Cassava Varieties

Abstract

Cassava is an important crop in coastal Kenya commonly harvested at 12 months after planting but earlier during food shortages. There is limited information that addresses the effect of early harvesting on root quality especially for newly released varieties. Varieties Tajirika, Karembo and Kibanda Meno (roots) were harvested at different ages from Research Centres, studied for nutritional quality and hydrogen cyanide levels for safe utilization. Results showed significant (p < 0.05) interaction effect of varieties and crop age on studied nutrients. Karembo and Tajirika had peak dry matter of 43.42% and 41.42% respectively at 12 months while the peak for Kibanda Meno was 44.99% at 9 months. Mean starch content varied with variety; Karembo (91.3%), Kibanda Meno (93.4%), and Tajirika (85.5%). Karembo and Tajirika had peak carbohydrates at 12 months while the peak for Kibanda Meno was at 9 months. Vitamin C was highest at 6 months for Karembo (6.4 mg/100g) and Kibanda Meno (66 mg/100g). Tajirika had highest vitamin C (7.0 mg/100g) at 9 months. Iron was peak at 3 months for Karembo (3.63 mg/100g) and Tajirika (5.33 mg/100g) but at 9 months for Kibanda Meno (7.12 mg/100g). Peak Zinc was 2.1 mg/100g for Karembo at 6 months while for Kibanda Meno (1.94 mg/ 100g) and Tajirika (1.75mg /100g) at 12 months. Hydrogen cyanide increased from 8.6 to 9.3 mg/kg in Karembo between 9 and 12 months, it decreased from 7.8 to 5.2 mg/kg and from 5.1 to 4.5 mg/kg in Tajirika and Kibanda Meno, respectively. Harvesting of cassava roots should be staggered across crop ages to maximize on peaks of different root nutrients and processing is important. 33 1. 2 Proximate compositionThere was significant (p < 0.05) difference in carbohydrate content accumulation for the improved varieties and Kibandameno -the local variety. The improved varieties had peak accumulation of carbohydrates at 12 months while Kibanda Meno had its peak at 9 months after planting. Crop age 6 to 9 months had significant (p < 0.05) effect on carbohydrate content of Kibanda Meno and Tajirika. Tajirika had the highest increase in this age range at 31.8%. The carbohydrate content of Karembo was 37.6% at 9 months and 40.5% (dwd) at 12 months after planting (Table 1). These results are within the range of carbohydrates contents that was reported by Richardson, (2013) who tested six mature improved varieties harvested at between 12 and 13 months after planting. The six varieties evaluated by Richardson, (2013) had carbohydrates content of between 26.3 % and 39.6 % (dwb). However, the nutritional content of cassava depends on geographic location, variety, age of the plant and the specific plant part (root or leaves) and environmental conditions Salvador et al. (2014); Bechoff et al. (2018); Burns et al. (2012)Crop age had significant (p < 0.05) effect that resulted to change in energy content of cassava roots between 3 and 12 months after planting. There was 17.9 %, 41.3% and 40.1% increase in energy (kcal/100 g dry weight) content, for Karembo, Kibanda Meno and Tajirika, respe...