Microplate reader and application of microplate reader in determination of L-malic acid content

The invention discloses a microplate reader and application of the microplate reader in determination of the content of L-malic acid. When the content of the L-malic acid is measured by using a microplate reader, the L-malic acid in a to-be-measured sample solution is oxidized into oxaloacetic acid by nicotine adenine dinucleotide in the presence of L-malic dehydrogenase, the oxaloacetic acid is converted into L-aspartic acid under the catalysis of glutamic acid oxaloacetic acid transaminase in the presence of L-glutamic acid, and the L-aspartic acid is converted into the L-malic acid. The continuous conversion of oxaloacetic acid promotes the continuous proceeding of the L-malic acid conversion reaction, the total amount of NADH in one of the products of the L-malic acid conversion reaction can be regarded as the total amount of L-malic acid, and then the content of NADH under the wavelength of 340 nm is measured through a microplate reader, namely the content of L-malic acid. By applying the microplate read