MICROSTRUCTURE OF BOILED YAM (DIOSCOREA SPP.) AND ITS IMPLICATION FOR ASSESSMENT OF TEXTURAL QUALITY

The effects of boiling on the microstructure of yams and their association with the textural quality of “boiled yam,” arguably the most common food product from yams, were studied using six varieties with variable cooking qualities from each of the two species, Dioscorea alata L. and D. rotundata Poir. Histological studies on raw yams showed parenchyma cells of both species to be three‐dimensional and polyhedral in shape, with starch granules loosely arranged in D. rotundata but densely packed in D. alata. Generally, there was cell separation and rounding off of cells in cooked yams of D. rotundata varieties, whereas cell separation was only partial with no rounding off in D. alata. Mealy boiled yams showed complete cell separation and the “rounding off” phenomenon, whereas the waxy ones showed partial retention of textural cell integrity. These relative changes in microstructure of yam when boiled could serve as indicators of textural quality in boiled yam.     

THE EFFECT OF PROCESSING ON THE NUTRIENT CONTENT OF CASSAVA (MANIHOT ESCULENTA CRANTZ) LEAVES

Leaves of two varieties of cassava ( Manihot esculenta Crantz) – TME1 (local) and TMS30572 (improved) – were subjected to African household processing (heat-treated, pounded and cooked and crushed, ground and cooked) and compared for proximate composition, minerals, vitamins and antinutritional factors. The processing methods had no effect on ash, lipids, protein, fiber, total carbohydrate, carotene, calcium, magnesium, potassium, sodium, phosphorus, copper, zinc and manganese but produced diminution in free sugars (23.2% reduction), ascorbic acid (77.7% reduction), thiamine (37.1% reduction), cyanogenic potential ( > 99% reduction) and tannin (55.2% reduction;) levels. On the contrary, iron level increased three- to fivefold with grinding but not with the pounding process. This study showed that adequate processing practically detoxifies cassava leaves with considerable nutrient retention, thus enhancing utilization of cassava leaves for human consumption.

PRACTICAL APPLICATIONS

This study has clearly shown that cassava leaves are very nutritious. However, they also have anti-nutrients which can render them toxic. This is responsible for the fear exhibited in the consumption of cassava leaves because of anticipated poisoning. This study shows that African processing methods tremendously reduce the ant-nutrients with minimal loss in the nutrients. There should therefore be no fear in the utilization of cassava leaves either for animal feed formulation or man's own direct consumption as a good source of leafy vegetables. The food quality of processed cassava leaves renders them a potential source of raw material for the animal feed industry as well as for the formulation of weaning foods especially for the underdeveloped world.