Study of High Molecular Weight Hemicelluloses Recovered from Black Spruce Mill Waste for Potential Value-Added Applications in Foods

The aim of this study was to characterize the high molecular weight fraction (> 10,000 g/mol) of black spruce sawdust water extracts obtained by controlled auto-hydrolysis and membrane filtration, in order to evaluate its potential as food ingredient (i.e., fiber supplement). The carbohydrate and phenolic content as well as the molecular weight distribution of the filtrated extract (i.e., isolate) were determined by colorimetric, spectrophotometric, and chromatographic methods. Its fermentability was studied during a in vitro batch fermentation experiment, using a chyme-like medium and a standardized eight strains co-culture. Results indicated that the isolate consisted mainly of non-cellulosic polysaccharides (i.e., hemicelluloses) with an average degree of polymerization (DPn) of 63. The galactose:glucose ratio (1:0.29) and the galactose:mannose ratio (1:0.75) indicated a significant amount of galactans among the recovered hemicelluloses. The fermentation profile of the filtrated extract, measured over a period of 30 h, was not significantly different from the fermentation profile of a starch-rich fibre mixture (starch, pectin, mannans, galactans, xylans and fructans at a ratio of 5:2:1:2:2:1). The extract did act as a fiber replacer and was steadily metabolized, inhibiting protein fermentation and the release of free ammonia. Our study suggests that black spruce sawdust may be a valuable source of functional soluble fibers. Further research is however required to assess the full potential of the extract as food ingredient.