Biochemical Pathway

The biochemical conversion of lignocellulosic material involves its transformation into various products as a result of direct or indirect action of microorganisms. The main biochemical conversion products generated from olive stones are ethanol and xylitol. The interest of ethanol is in its use as renewable motor fuel [77], while xylitol is a low-calorie sweetener (its sweetener power is similar to that of sucrose and its caloric content is equivalent to 2.4 cal/g) that can be consumed by diabetics [78]. The conversion of biomass to ethanol or xylitol generally includes the following four steps: pre-treatment, hydrolysis of polysaccharides and oligosaccharides into monomer sugars, fermentation of sugars and, finally, separation of bioproducts.

Olive Stones Pretreatment

Lignocellulosic biomass is a complex mixture of carbohydrate polymers from plant cell walls known as cellulose and hemicellulose, plus lignin, ash and a smaller amount of other compounds generally known as extractives. Pretreatment is intended to change the structure of the biomass to improve subsequent hydrolysis of polysaccharides, mainly of cellulose [79]. This can be achieved by physical, chemical or physico-chemical transformations of the material. Physical pretreatment is, for example, the particle size reduction, which brings about no changes in the composition of the biomass but increases its specific surface, thus enhancing the subsequent hydrolysis.

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