What does lactic acid fermentation convert into lactic acid?

In lactic acid fermentation, pyruvic acid is directly converted to lactic acid.

Explanation:

The conversion of pyruvic acid to lactic acid is the final reaction (i. e the 11nth stage) in the lactic acid fermentation. The lactic acid fermentation actually begins with the conversion of Glucose to Glucose-6-phosphate with the aid of hexokinase.

The final reaction is catalyzed by an enzyme called lactate dehydrogenase (LDH) in the presence of NADH. Two atoms of hydrogen makes lactic acid different from pyruvic acid. The resulting lactic acid gets its two hydrogen atoms from the reduced Nicotinamide Adenine Dinucleotide (NADH + H+) during the catalytic reduction of the substrate, pyruvic acid, by LDH.

The addition of the two hydrogen atoms occurs on the carbon-2 or the alpha carbon of pyruvic acid.