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POTENTIELS NUTRITIONNEL ET TECHNOLOGIQUE DES TUBERCULES DURCIS DE L'IGNAME Dioscorea dumetorum (Kunth) pax : ETUDE DU DURCISSEMENT POST -RECOLTE ET DES CONDITIONS DE TRANSFORMATION DES TUBERCULES DURCIS EN FARINE

Abstract : Dioscorea dumetorum (Kunth) pax tubers constitute a good source of nutrients and
energy. Their storage under tropical ambient conditions renders them susceptible to a
hardening phenomenon characterised by loss of the ability to soften during cooking. This
study was carried out with the aim of determining tuber hardening mechanism, evaluate
physicochemical changes occurring during tuber storage and to find out pre-treatment
conditions of hardened tubers for their processing into flour. Results obtained showed that D. dumetorum tubers hardening follows a multiple mechanism, which includes phytate hydrolysis as a minimal contributor to cooked hardness and total phenols loss via a lignification-like mechanism as a major contributor. Tuber hardening was separated into two factors, reversible and irreversible which were respectively associated with phytate and total phenols. Modeling of the hardening process indicated that the rate of the irreversible reaction was more dependent on storage temperature and relative humidity than the reversible reaction. Storage of D. dumetorum tubers under tropical ambient conditions (19-28°C, RH 60-85%), significantly (P ´ 0.05) decreased antinutritional factors (total phenols, tannin, phytate, oxalates, trypsin and Α-amylase inhibitors) and increased functional properties of flours (water absorption capacity, water solubility index, oil absorption capacity, hydrophilic-lipophilic index, least gelification concentration, swelling capacity). The physicochemical parameters varied with storage in two main phases, from days 2 to 21 and from days 28 to 56. Since sprouting of most tubers was observed after 28 days of storage, the results suggest that post-harvest hardening and sprouting influence the physicochemical properties of D. dumetorum tubers. If steeping of D. dumetorum hardened tubers into NaCl or kanwa solutions significantly increased tubers softening rate during cooking, it did not totally reverse tuber hardness. kanwa pretreatment significantly affected functional properties of D. dumetorum flours and improved on protein quality and sugar bioavailability. Fermentation of hardened tubers as pretreatment method resulted in completely soft tubers after 7 days of natural fermentation and significantly reduced antinutritional factors. Only lignin was not affected by tubers fermentation. Functional properties of the flours were also influenced significantly by tubers fermentation. The least gelatinisation concentration increased with fermentation time and the other properties decreased. More over, fermentation significantly increased protein content, protein quality and sugars bioavailability of D. dumetorum tubers. Studies on gelatinisation showed that gelatinisation temperature of D. dumetorum occurs between 70-75°C. Gelatinisation process of D. dumetorum follows a first order reaction of the general form ln(1- Α) = -kG.t. The gelatinisation rate constant (kG) decreased with cooking temperature and with increase of tuber storage time. Soaking in kanwa solution and natural fermentation significantly affected the gelatinisation rate of D. dumetorum hardened tubers. Partial substitution of wheat flour by hardened-yam flour showed on the basis of multivariate techniques (hierarchical cluster analysis and principal component analysis) that wheat and kanwa-treated-hardened-yam/wheat composite flours, for all substitution levels used in this study constituted the same cluster.
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Contributor : Gabriel Medoua Nama <>
Submitted on : Wednesday, December 28, 2005 - 11:24:57 AM
Last modification on : Tuesday, January 3, 2006 - 5:35:07 PM
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Gabriel Medoua Nama. POTENTIELS NUTRITIONNEL ET TECHNOLOGIQUE DES TUBERCULES DURCIS DE L'IGNAME Dioscorea dumetorum (Kunth) pax : ETUDE DU DURCISSEMENT POST -RECOLTE ET DES CONDITIONS DE TRANSFORMATION DES TUBERCULES DURCIS EN FARINE. Autre. Université de Ngaoundéré, 2005. Français. ⟨tel-00011268⟩

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