Influence de la variété et de l’environnement sur l’aptitude à la transformation des racines de manioc (Manihot esculenta Crantz) par rouissage

Abstract

The suitability for processing by retting being one of the major criteria taken into account by farmers in choosing to adopt a new variety of cassava, the major objective of this work is to contribute to the increase the adoption rate of improved cassava varieties through a better understanding of the physiology of cassava roots during retting. In this study, eight varieties of cassava (including four varieties with white pulp: LMR, 92/0326, I090616 and one local variety; four varieties with yellow pulp: 01/0040-27, 01/1797, I071026 and I090593) were characterized during retting in two agro-ecological zones of Cameroon: zone V (Mbalmayo) and zone III (Foumbot). The cassava roots were soaked in water for three days during which the roots and soaking waters were sampled. These samples were characterized at the physical and biochemical levels. Overall, the variables studied were influenced either by the genotype or by the duration of retting in the two production zones. The softening of cassava roots during retting was generally faster in Mbalmayo (with an overall average softening rate of 63.03% after 24 hours of retting compared to 12.48% in Foumbot) with a significant variety effect. The histological sections revealed a more or less significant degradation of the cell walls during retting depending on the varieties and climatic zones. Retting also significantly reduced the maltose and glucose contents both in the roots and in the soaking water, the contents of total phenolic compounds and total pectins (from 592.27 to 486.58 mg/100g and 758.6 at 456.97 mg/100g for Mbalmayo and Foumbot respectively) of the roots in the two production zones. The variety 01/0040-27 was richer in total pectin while the varieties with yellow pulp (01/0040 27 and 01/1797) were richer in free polyphenols in the two production areas. Retting reduced the overall viscosity of flour starches depending on the variety and production area. The present study showed that major histological and biochemical changes occur during cassava root retting, some of them associated with the process. Although this process is characterized by root softening and breakdown of cell wall structure, the present study strongly suggests that pectin is not the only cell wall component involved in these changes. Retting affects the starching properties of starch more than its physical appearance.