Catalyzes the irreversible reduction of the cytotoxic compound methylglyoxal (MG, 2-oxopropanal) to (S)-lactaldehyde. MG is synthesized via a bypath of glycolysis from dihydroxyacetone phosphate and is believed to play a role in cell cycle regulation and stress adaptation. (S)-lactaldehyde + NADP(+) = H(+) + methylglyoxal + NADPH Has antigenic properties. Elicits a specific immune response in systemic candidiasis human patients undergoing malignant hematological disorders. Belongs to the NAD(P)-dependent epimerase/dehydratase family. Dihydroflavonol-4-reductase subfamily.