How would lactose react toward barford test?

Barfoed's test distinguishes monosaccharides with a free aldehyde group from monosaccharides with a potential aldehyde group or from disaccharides. When heated in the presence of Barfoed's reagent, which is a copper acetate solution made alkaline with acetic acid, monosaccharides with a free aldehyde group will produce a red precipitate of cuprous oxide, indicating a positive reaction. Disaccharides, such as lactose, do not have a free aldehyde group, so they will give a negative reaction and will not produce a red precipitate.