Involved in F420 biosynthesis through the oxidation of lactaldehyde to lactate. The substrate preference order is propionaldehyde > DL-lactaldehyde, DL-glyceraldehyde > crotonaldehyde > glycolaldehyde > acetaldehyde, acrolein > formaldehyde. No activity was observed towards methylglyoxal or glyceraldehyde-3-phosphate. Has a preference for NAD over NADP. (S)-lactaldehyde + H2O + NAD(+) = (S)-lactate + 2 H(+) + NADH As the lactaldehyde used was a mixture of D and L isomers, the kinetic parameters do not reflect the possible stereospecificity of the enzyme. Optimum pH is 9. The activity remained constant to pH 10.0. Below pH 9, the activity gradually declined, and the enzyme was inactive at pH 6 or below. Cofactor biosynthesis; coenzyme F420 biosynthesis. Homotetramer. Belongs to the aldehyde dehydrogenase family.