Degradation of non-structural carbohydrates in grape cane: enzymatic hydrolysis of starch by a novel halophilic alpha-amylase.

The grape and wine production system produces huge amounts of solid waste whose management and disposal gives environmental problems. These residues are rich in organic matter and pose severe pollution problems. One of this waste is represented by grape cane, which derive from the pruning process. Grape cane can contain up to 15% of dry weight of non-structural carbohydrates (NSC) in addition to cellulose and hemicellulose and, consequently, the exploitation of NSC represents a potential additional source of sugars for bioethanol production. Grape cane of the CV Sangiovese, with the following NSC composition, was chosen for the present work (average NSC composition expressed as % of the dry weight ± SE: glucose 0.36 ± 0.01, fructose 0.55 ± 0.02, sucrose 2.02 ± 0.07 starch 7.35 ± 0.19). The material was pretreated by steam explosion in a 10 l batch reactor under different severities (180 and 200°C, 10 min) and pH, and then submitted to hydrolysis of starch by alpha-amylase from the halophilic Archaea Haloterrigena turkmenica at 55°C for 72h. The aim was to establish if a pretreatment has influence on the starch hydrolysis yield as for cellulose and xylan hydrolysis, in order to set-up a saccharification process yielding to the hydrolysis of all polysaccharides contained in the biomass by a single-step. Our preliminary data showed that acid-catalyzed steam exploded biomass gave the highest sugar release in comparison to steam exploded and untreated grape cane.