Current challenges facing one-step production of l-ascorbic acid.

l-ascorbic acid (L-AA, vitamin C) is an essential vitamin that is widely used as a nutrient or medicine in the pharmaceuticals, cosmetics, food, beverage and feed additive industries, and accounts for the largest share of the global vitamins market. L-AA is mainly produced by a classic two-step fermentation process that suffers from the use of a multi-step mixed culture system and two rounds of sterilisation, which significantly increases the cost of the final product. One-step fermentation has been attempted, but a method rivalling the efficiency of the two-step process has not yet been achieved on an industrial scale. In this review, based on the current classical two-step fermentation processes and other potential routes for L-AA production, the challenges and pitfalls of a one-step fermentation process are summarised. The prospects for one-step fermentation production of L-AA and how this might be achieved are also discussed.