Nutrients and Anti-Nutrients Levels, and Nutrients Bioaccessibility in Cooked Manihot Esculenta Crantz Varieties Grown in Kilifi and Busia Counties, Kenya
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Date
2025-11
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Kenyatta University
Abstract
Manihot esculenta Crantz (cassava) is a staple crop, with different sweet and bitter varieties
grown in developing nations. Bitter cassava varieties are primarily used for industrial purposes
like making flour, starch, bioethanol, and adhesives after being processed to remove toxic
cyanide. Sweet cassava is used for direct food consumption, where it is boiled, fried, or baked,
and it can also be processed into various food products like flour and snacks. The study areas in
Kenya, Kilifi County, grow Kibandameno and Tajirika varieties while MM96/2480 and Migyera
are cultivated in Busia County. The crop’s roots and leaves are a source of protein, thiamine,
riboflavin, ascorbic acid, niacin, potassium, calcium, zinc, iron, oxalate and phytate. Nutritional
data has shown that Kilifi and Busia Counties have high prevalence of under nutrition, amidst
relying on otherwise nutritious cassava-based diets. For consumption, the general cooking
methods involves roots being boiled or deep-fried, while leaves are pounded then boiled. In view
of malnutrition statistics in communities that otherwise consume cassava, it is unclear whether
the underlying factor would be attributed to impact that cooking has on nutritional levels of both
leaves and roots of cassava, or nutrient bioaccessibility. This was envisaged as a study gap. The
concentrations of specific anti-nutrient and nutrients in cassava leaves and roots with age of the
plant, impact that boiling and deep-frying tubers and boiling leaves of cassava has on nutritional
and anti-nutrient levels, and finally the bioaccessibility of nutrients were determined. Static
gastrointestinal digestion was performed after and prior to determination of protein (by kjeldahl),
vitamins and anti-nutrients (by HPLC) and minerals (by AAS and AES). Nutrient levels (mg/100
g) in raw roots ranged from 17.00 - 114.00 (protein), 1.93 - 12.74 (vitamin C), and from 32.08 -
162.98 (Ca). Levels of anti-nutrients (mg/100 g) ranged from 390.37 - 561.28 (phytate), and
from 4.72 - 613.46 (oxalate). Cooking resulted in a reduction of the levels ranging from 12% (K)
to 98% (vitamin B1) in all nutrients and anti-nutrients studied, with boiling roots recording
higher losses than deep-frying (P<0.001). The bioaccessibility of vitamins and minerals was
lower in raw roots (15 - 72%), but significantly higher (P<0.001) in cooked roots, with deep
fried roots showing bioaccessibility between (20 – 79%) and boiled roots between (27 – 84%). A
trend similar to the one observed in roots was observed in cooked cassava leaves with
bioaccessibility ranges of vitamins in raw leaves (8 – 69%) being significantly lower (P<0.001)
than in boiled leaves (11 – 81%). The study concludes that levels of ascorbic acid, thiamin,
riboflavin, niacin, protein, calcium, zinc, iron and potassium, phytate and oxalate in Manihot
esculenta Crantz varieties depend on the variety, part of the plant (roots or leaves), and
harvesting age. Cooking significantly reduces levels of these nutrients and anti-nutrients with a
higher reduction on boiling than deep-frying. The bioaccessibility of nutrients however
significantly increased with cooking but the levels were lower than the recommended dietary
allowance (RDA) for all the nutrients determined. The study recommends that cooking lowers
anti-nutrients and increases nutrient bioaccessibility. Cassava roots should not be left in the farm
for a longer period after maturity when nutrient levels are high and cooking by deep frying to
retain high levels of the water-soluble nutrients
Description
A Thesis Submitted in Partial Fulfillment of the Requirements for the Award of the Degree of Doctor of Philosophy In Chemistry in the School of Pure and Applied Sciences of Kenyatta University. November, 2025
Supervisor
Mildred Nawiri
Hudson Nyambaka