The invention relates to a process for the preparation of a sugar product from lignocellulosic material, comprising pretreatment of the lignocellulosic material with heat, mechanical and/or chemical modification or any combination of such methods and enzymatic hydrolysis of the pretreated lignocellulosic material using an enzyme composition comprising at least two cellulases and whereby the enzyme composition at least comprises a lytic polysaccharide monooxygenase, wherein the amount of the formed gluconic acid at the end of the enzymatic hydrolysis by the oxidation of the lignocellulosic material containing cellulose and/or cello-oligosaccharides is kept between 3 to 10 g/kg glucan present in the lignocellulosic material by adding a suitable amount of oxygen after the pre-treatment and before and/ or during the enzymatic hydrolysis to the lignocellulosic material.
