Valorization of chestnut (Castanea sativa) residues: Characterization of different materials and optimization of the acid-hydrolysis of chestnut burrs for the elaboration of culture broths.

Four kinds of waste from the industrial processing of chestnuts (Castanea sativa), namely leaves, pruned material and burrs from chestnut tree plus chestnut shells, were characterized to determine their content in polymers and thus their potential use in biorefinery processes. Results revealed that chestnut burrs have the highest polysaccharide content being the most promising for carrying out the subsequent stages of acid hydrolysis. Treatment with diluted sulfuric acid (prehydrolysis) allowed the solubilization of xylose, glucose and arabinose, but also some toxic compounds such as furan derivatives, aliphatic acids and phenolic constituents. Xylose, the main component released in the hemicellulosic hydrolyzates, was maximized by using a 3**(2-0) full factorial design combined with desirability function. At optimum conditions set at 130 °C and 3% (w/v) H2SO4, this value was 22.6 g L-1 xylose. Three concentrations of activated charcoal (1, 2.5 and 5% w/v) were evaluated to remove certain unwanted byproducts, and it was found that under the highest dosage, 95.27 ± 0.03% of the color was removed with an almost total reduction of furan derivatives, making this liquor an appropriate basis for the development of suitable culture media for lactic acid bacteria. To validate this hypothesis three lactic acid bacteria, namely Lactobacillus plantarum, Lactobacillus pentosus and Lactococcus lactis were positively tested finding lactic acid yields of 0.89, 0.92 and 0.83 g/L·h respectively.