The invention relates to a method for the preparation of fried vegetable products. In particular, it relates to a method for the preparation of fried vegetable products which have been subjected to an asparagine-reducing enzyme. The method comprises reducing the amount of enzyme product formed on the surface of the enzyme-treated vegetable material due to the action of the asparagine-reducing enzyme. If the amount of enzyme product is reduced before frying, this will contribute to the colour and the quality of the frying oil and of products subsequently fried in the oil and, thus, will minimize the loss of quality of the frying oil. The invention also relates to use of an asparagine-reducing enzyme preparation for preserving the colour of the frying oil.