Search

This method seeks to describe the preparation of samples for cell wall polysaccharides analysis in order to assess the amount of the different types of sugars contained in the cell walls of raw and boiled yam and plantain. The extraction of cell wall polysaccharides (CWP) involves several steps. Yam and plantain are rich in starch polysaccharides (>80% d.b.) in order to obtain reliable and measurable data on cell wall polysaccharides, starch removal is mandatory before cell wall analysis. This step has been particularly optimized. This SOP has been developed on commercial yam and green plantain, as they are particularly high in starch. It was then applied to various yam and banana samples at different ripening stages (fresh fruits, cold powders or freeze-dried). The preparation of CWP samples from amylaceous products requires 4 steps: (i) extraction of alcohol insoluble solids (AIS) to remove all the soluble sugars and polyphenols, (ii) starch removal in aqueous solution thanks to enzymatic reactions, (iii) quenching by 96% EtOH, followed by new extraction of destarched AIS, to remove the soluble sugars and polypeptides produced by the starch removal process, and finally (iv) starch assay to assess the efficiency of the starch removal process.

Amylose-free and wild-type cassava starches were fermented for up to 30 days and oven- or sun-dried. The specific volume (ν) after baking was measured in native and fermented starches. The average ν (across treatments) for waxy starch was 3.5 times higher than that in wild-type starches (17.6 vs. 4.8 cm3 g−1). The best wild-type starch (obtained after fermentation and sun-drying) had considerably poorer breadmaking potential than native waxy cassava (8.4 vs. 16.4 cm3 g−1, respectively). The best results were generally obtained through the synergistic combination of fermentation (for about 10–14 days) and sun-drying. Fermentation reduced viscosities and the weight average molar mass led to denser macromolecules and increased branching degree, which are linked to a high loaf volume. The absence of amylose, however, was shown to be a main determinant as well. Native waxy starch (neutral in taste, gluten-free, and considerably less expensive than the current alternatives to cassava) could become a new ingredient for the formulation of clean label-baked or fried expanded products.

International audience; Roots, tubers and bananas (RTB) products such as yam are staple food in Africa and the some countries of the Caribbean. Developers and breeders have worked for years to improve their yield and/or composition. However, they did not take into account consumer preferences such as cooking ability. Even ancient varieties highly appreciated by producers and consumers 1 have been evaluated for their yield and not for their quality traits including cooking ability.. Among the sensory criteria, texture is a primary quality factor for yam products, and it depends on both the initial characteristics of raw material and processing techniques 2,3. In highly amylaceous products such as yam, the impact of starch on textural properties has been heavily explored. However, it cannot fully explain the texture and the cooking behaviour of these crops. Non-starch polysaccharides are known to be involved in the texture of non-starchy products such as apples 4. Yam tuber hardness or mealiness after boiling has been hypothesized to be due to cell wall (CW) thickening, permeability changes and cell adhesion 2,3. However there is little knowledge on the link between the texture of raw and boiled yam, and the relationship with cell wall structure and composition still remains to be detailed. The aim of this work was to determine the CW polysaccharides (CWP) composition of yam tubers to evaluate the relationship between CWP, cooking ability and textural properties. To do so, cultivars and pedoclimatic conditions were varied to obtain yams with different tissue structure. Their cooking ability was evaluated (cooking time, texture). CWP were then extracted from five cultivars of Dioscorea spp. raw and steamed tubers, chosen for their highlycontrasted cooking behavior. A specific CW extraction procedure, involving an alcohol insoluble solids (AIS) extraction followed by an enzymatic starch removal procedure, was developed. Starch, lignin, CWP and pectin composition, acetylation and methylation degree were then determined by means of chromatographic and spectroscopic techniques (GC-FID, GC-MS). AIS content in fresh tubers varies from 24% to 33%. The AIS contains 66% to 85% starch, representing 50 to 70% of the dry matter whereas cell walls weigh about 2%. Raw yam CWP contain 15 to 20% galacturonic acid and 20 to 25% galactose, which correlates with data reported previously for cassava roots 5. Composition varies according to genotype, soil and cooking process. Steamed yam CWP show a decrease in galacturonic acid content (8 to 12%), which is consistent with β-elimination induced by the cooking process. This characterization of yam CWP in regard to cooking ability is the first of its kind. It gives an overview of West Indies yam composition and opens the way to a better understanding of yam quality traits for ancient varieties but also for the development of new hybrids. Many new varieties of yams, although resistant to diseases and pests have serious problems of acceptability and adoption by the targeted consumers. It is therefore important to provide breeders and developers with tools for the creation and selection of hybrids based on the expected sensory quality.

International audience

International audience

International audience