Some questiones about Malic acid

Malic acid is a kind of colorless, crystalline compounds, the molecule formula is COOHCH2CHOHCOOH, that occurs naturally in a wide variety of unripe fruit, including apples, cherries, and tomatoes, and is used as a flavoring and in the aging of wine.

In winemaking, when certain bacteria convert Malic acid(CAS NO:636-61-3) to lactic acid (which is much less strong and sour), a process called "malolactic fermentation" occurs. This reduces the wine's tartness, adds complexity to the flavor and sometimes contributes a slight sparkle.Malic acid is used as an acidulant as well as a flavoring agent in the processing of some foods.

What is differnece in D(+)-Malic acid and L-malic acid?

There are two different structures of malic acid(CAS NO:636-61-3), L-Malic acid and D(+)-Malic acid. The only difference between the two is that they rotate the light shining on them in two different directions. L-Malic acid is produced naturally in fruits. 90% of the acid in apples is malic acid. When malic acid is produced synthetically, a mixture of the two isomers is obtained which is called DL-malic acid (because it contains both D(+)- and L-malic acid). When you eat DL-malic acid, your body digests it in just the same way as it does for L-malic acid. It is part of the Krebs cycle. 

Is malic acid a natural product?

There are two forms of malic acid; the L-Malic acid is found naturally in most fruits and many vegetables in varying amounts. Of the total acid content in apples, 90-98% is L-malic acid. Malic acid can also be produced synthetically from maleic anhydride. It is impossible to choose whether natural L-malic acid or the unnatural D(+)-Malic acid is formed during synthesis so a mixture of the two is formed, often called DL-malic acid. It is most likely that if malic acid is used as an additive, it is the synthetic DL-malic acid. The body metabolises the two forms in exactly the same way.

How is malic acid purified?

Malic acid can be produced in a pure form by crystallising it out of water when it has been made synthetically from maleic anhydride, which in turn is made simply from butane gas. This reaction process leads to a mixture of the two malic acid isomers. To purify the natural form of L-malic acid, it is necessary to remove it from apples or other fruits where malic acid is present in a high concentration. This can be done by fractionated distillation. Green apples are best for this since 90% of the acid present in them is malic acid.

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