[en] This study highlights the possibility of using brewers' grains (BSGs) for the successive extraction of the main lignocellulosic biopolymers, namely cellulose, hemicelluloses and lignin. An exhaustive chemical characterization revealed a variability of composition in distinct batches of BSGs, depending on their origin and the brewing process used. In particular, the protein content can vary from 13 to 23 wt.%, which is accompanied by a change in the hemicelluloses content from 9 to 23% (in the samples of our study). By applying a two-step aqueous treatment, involving an acid (1.25% v/v aq. H2SO4) and a base (3% w/v aq. NaOH) at a temperature of 120°C and fixed reaction time of a few tens of minutes (15 to 90 min), more than 80% of hemicelluloses could be recovered. Cellulose could be isolated at more than 68%, while a high purity lignin could be recovered from a lignin-rich fraction (70wt.%). Our work also suggests that the variability of the chemical composition of these brewers' grains is a hindrance to achieving process standardization and large-scale exploitation. The pooling of various materials is therefore not a recommended option, and the preliminary chemical analysis of the composition is therefore a prerequisite for an efficient extraction process. [fr] Cette étude met en évidence la possibilité d'utiliser les drêches de brasserie pour l'extraction successive des principaux biopolymères lignocellulosiques, à savoir la cellulose, les hémicelluloses et la lignine. Une caractérisation chimique exhaustive a révélé une variabilité de la composition de lots distincts de drêches de brasserie, en fonction de leur origine et du procédé de brassage utilisé. En particulier, la teneur en protéines peut varier de 13 à 23 % en poids, ce qui s'accompagne d'une variation de la teneur en hémicelluloses de 9 à 23 % (dans les échantillons de notre étude). En appliquant un traitement aqueux en deux étapes, impliquant un acide (1,25% v/v aq. H2SO4) et une base (3% p/v aq. NaOH) à une température de 120°C et un temps de réaction fixe de quelques dizaines de minutes (15 à 90 min), plus de 80% des hémicelluloses ont pu être récupérées. La cellulose a pu être isolée à plus de 68%, tandis qu'une lignine de haute pureté a pu être récupérée à partir d'une fraction riche en lignine (70wt.%). Nos travaux suggèrent également que la variabilité de la composition chimique de ces drêches de brasserie est un frein à la standardisation des procédés et à leur exploitation à grande échelle. La mise en commun de diverses matières n'est donc pas une option recommandée, et l'analyse chimique préliminaire de la composition est donc une condition préalable à un processus d'extraction efficace.
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