Commercial production of vitamin C for fortification and dietary supplements

In most mammals, vitamin C is made in the liver from blood sugar using a four-step enzymatic process. Humans and about 20 other mammalian species lack one of these enzymes, requiring us to both obtain vitamin C from our diet and to sustain internal levels of vitamin C using a variety of other food antioxidants.

But rather than extracting vitamin C from foods, the modern way to manufacture it is to start with dextrose, a sugar identical to blood glucose, and manipulate it into ascorbic acid, which is vitamin C; mimicking the biological production technique to some extent. The result is a nature-identical vitamin indistinguishable from the form in foods.

The primary method of biosynthesizing vitamin C starts with the conversion of glucose into sorbitol. Dextrose is converted to sorbitol by adding hydrogen to the molecule; that is typically done with a catalyst (defined as an easily recoverable material that facilitates a chemical reaction but is not used up in the reaction nor added to the molecule). The only added element is hydrogen, which is applied in a pressure tank.

Converting the sorbitol into sorbose and then into an intermediate known as 2-KLG is done using a two-step fermentation process

Then a final lactonization step (reacting 2-KLG with acid and/or dehydration is used to produce the lactone known as l-ascorbic acid/vitamin C; chemical form C₆H₈O₆).