L-Malic acid is the predominate acid in pure apple juice and no D-malic acid should be present. Synthetic malic acid contains 50% D-malic acid, is inexpensive, and can be used to create nonauthentic apple juice. L-Malic/total malic ratios of 0.9 or less are indicative of a nonauthentic sample. Fourteen laboratories participated in a collaborative study to determine the L-malic/total malic acid ratio in apple juice. Ten samples of apple juice were sent to each laboratory. Authenticity of the samples varied from 0 to 100%. The coefficients of variation in all cases were acceptable, i.e., ca 5%. The method was adopted first action by AOAC INTERNATIONAL.

A HPLC method using an aqueous mobile phase containing the chiral ligand-exchanger Cu II-L-valine complex at pH 5.5 with a polystyrene divinyl-benzene copolymer column was used to resolve D-malic acid in apple, pear, and Concord grape juices. D-malic acid was detected and quantitated at 330 nm in less than 15 min per sample. The detection limit appeared to be 2 mg/lOO mL D-ialic acid in 12 Brix juice, or 0.33% total malic acid in a typical apple juice containing 0.6 s/l00 mL using the described procedure.