A method of oxidising carbohydrates and/or carbohydrate derivatives having primary alcohol groups comprising contacting a reaction medium containing said carbohydrates and/or carbohydrate derivatives with a nitroxy radical mediator and a peroxidase enzyme, characterized in that the initial reaction medium contains at least 10% by weight carbohydrates and/or carbohydrate derivatives, in that the peroxidase enzyme is an oilseed peroxidase and in that a hydroperoxide and an alkali compound are gradually added to the reaction medium such that its pH is maintained at between 3.5 and 10.0 (pH-Stat); use of said method in a process for producing gluconic acid, glucaric acid and/or D-glucuronolactone.