Aldose or ketose sugars in alkaline medium isomerize. For example; on heating with conc. solution of NaOH glucose (aldose) first turns yellow and then brown and finally resinifies with dilute solution of NaOH glucose (aldose) undergoes a reversible isomerization and is converted into a mixture of D-glucose, D-maltose and D-fructose. This reaction is known as lobry de Bruyn-van Ekenstein rearrangement.