Valorization of Olive-Oil Industry Solid Waste: Statistical Optimization of Alkaline Extraction Conditions for Light-Coloured Hemicelluloses

Abstract

Olive solid waste (OSW), the by-product of olive oil production process, is a lignocellulosic material with very low economic value. The hemicellulose fraction of OSW has a potential to be used as a raw material for several industrial applications. The main objective of the present work was to statistically develop an alkaline hemicellulose extraction procedure to achieve the highest possible crude hemicellulose extraction yield from OSW with concurrent efforts to lighten the colour of black hemicelluloses. Box-Behnken Design based response surface methodology was employed for optimization. The optimum hemicellulose extraction conditions were found as 19.3% (w/v) alkaline (KOH) concentration, 1.3 mm particle size, 25.3 h extraction time, 1% (w/v) MgSO 4 concentration, 6.4% (v/v) H 2 O 2 concentration and 60°C temperature. The maximum experimental hemicelluloses yield at this condition was 35.6±0.5% which is in agreement with the predicted yield value of 31.2%. As a result, the extraction yield has been increased from 21.7% to 35.6% (w/w). The colour values (L*,a*,b*) of hemicelluloses extracted at optimum conditions were predicted as 31.69±0.28, -2.90±0.04 and 5.49±0.04, sequentially. The findings of this study demonstrated the route for isolation of light-coloured OSW hemicelluloses that have potential for conversion into industrially important value-added products such as biodegradable plastics for food packaging applications and xylooligosaccharides.