Tuesday, May 3, 2011
The valorisation of waste products constitutes an important challenge of economically sustainable industrial processes. Agricultural wastes are an attractive renewable feedstock for the production of liquid fuels and high-value products (e.g. antioxidants, mono- and oligosaccharides). Chestnut fruits (Castanea sativa) are used in the food industry for production of marron-glacè, purée, etc.. The main by-product generated from the peeling process of the fruit, the shells, accounts for 10% of the whole weight. Chestnut shells are currently used as fuel nevertheless their extracts contain high amounts of sugars and antioxidants. In fact they contain 36% polysaccharides but their exploitation has not been taken into account until now. Xylo- and cellooligosaccharides are emerging classes of non-digestible oligosaccharides provided with prebiotic properties, while fermentable sugars can be used for bioethanol, xylitol or syrups production. Therefore, the enzymatic hydrolysis of the polysaccharidic fractions has been considered by using novel or commercial enzymes. Here, we report on the production of oligosaccharides with mesophilic or thermophilic cellulases and xylanases. Preliminary experiments with mesophilic enzymes on raw residues showed a low conversion yield of the xylan fraction into xylooligosaccharides. To increase the hemicellulose recovery from the residue by enzyme, different pretreatments were investigated, namely steam explosion (180-190°C, 10 min, 3 % sulphuric acid) and alkaline soaking (ammonium and sodium hydroxide). The results obtained confirmed the efficiency of pretreatments to destroy the lignin matrix which hinders both solubility and the enzyme action. Extraction and analysis of the polyphenolic fraction containing useful molecules (e.g. ellagic acid) have also been performed.