Multiproduct biorefinery from defatted olive mill waste: preparation of hemicellulose-based biodegradable films and instant controlled pressure drop (DIC)-assisted isolation of value-added products

Abstract

The olive oil extraction industry generates huge amounts of olive mill waste (OMW) which is an excellent source of several biocompounds. The aim of this study is to investigate the viability of a multiproduct biorefinery approach to valorize OMW as a source of hemicelluloses for the production of biodegradable films and extraction of other valuable compounds by taking advantage of the instant controlled pressure drop (DIC) technique. Glycerol, sorbitol, and xylitol at a concentration of 30% (w/w) were found as suitable plasticizers for biodegradable film preparation. Films with glycerol showed the lowest solubility in water (73.25 & PLUSMN; 0.83%) and the lowest biodegradability in soil, while showing the highest water vapor permeability (1.82 & PLUSMN; 0.1 g mm m(-2) h(-1) kPa(-1)), and lowest solubility in different media at pH of 3-12. Xylitol-plasticized films exhibited the highest tensile strain (10.17 & PLUSMN; 0.85 MPa) which is 43% higher than that of unplasticized film. Overall, the glycerol-plasticized films showed a potential for food packaging applications where low solubility and high water vapor permeability are required. Xylitol-plasticized films could be advantageous where higher solubility and mechanical strength are expected. DIC pretreatment performed at 5 bar steam pressure for 10 min resulted in a destructured OMW with lower crystallinity providing higher extraction yields of value-added products. An increase of 37.5% in total phenolics content and 22.1% in hemicellulose extraction yield were obtained after DIC pretreatment, respectively. In addition, app. 3-fold antioxidant activity and 2.2-fold reducing sugar concentration were reached, as compared to unpretreated OMW.