VALEUR ALIMENTAIRE DE QUELQUES PRODUITS AMYLACÉS D'ORIGINE TROPICALE : ÉTUDE IN VITRO ET IN VIVO DE LA PATATE DOUCE, DE L'IGNAME, DU MALANGA, DU FRUIT A PAIN ET DE LA BANANE

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Abstract
The in vitro susceptibility to .alpha.-amylase of starch from tropical fruits or roots, raw or cooked in boiling water for 30 min, was measured and their feeding value was estimated by determining growth rate, digestibility and N retention in white rats as compared with control receiving a diet based on maize starch. The raw starches, except that of banana, were very resistant to the .alpha.-amylase; when cooked, their susceptibility to the enzyme increased in variable proportions according to the nature of the product. After cooking, the easily hydrolyzable starch fraction of breadfruit, malanga, sweet potato, banana and yam represented 79, 59, 54, 57 and 40%, respectively. The growth performances of rats fed diets based on raw products were significantly lower (20-30%) according to the nature of the basal constituent, than that obtained in animals fed the control diet. The feed efficiency was also lower (P < 0.05). However, when the basal products were cooked, the growth performances of the groups receiving sweet potato, breadfruit and banana did not significantly differ from the control group. In addition, cooking improved significantly (P < 0.05) the apparent digestibility of the organic matter of the diets based on banana (+ 4.3 points) and especially malanga (+ 9.4 points) and breadfruit (+ 12.8 points). Cooking largely enhanced the rate of amylolysis, but did not increase the same proportions the digestibility of the organic matter of the feeds. The crude protein digestibility of the diets based on tropical feeds remained low and always inferior (P < 0.05) to the control diet. It was significantly improved (P < 0.01) by cooking in the case of banana (+ 3.9 points) and especially sweet potato (+ 8.9 points) and breadfruit (+ 9.6 points). Starchy tropical products, provided they are cooked, might constitute a source of energy for monogastric animals, in some cases (sweet potato, breadfruit and banana) similar to that of cereal starch.

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