Abstract: A method of synthesizing vitamin C (ascorbic acid) directly from the hydrolysis products of lactose. Lactose, economically obtained from whey, undergoes hydrolysis with a warm aqueous slurry of lactase to produce D-galactose and D-glucose. Preparing the methyl glycosides of these two sugars protects a labile C-O linkage during the oxidation of the sugars to D-galacturonic acid and D-glucuronic acid. The mixture of these acids, after the removal of the methyl group through hydrolysis, undergoes reduction with gaseous hydrogen in the presence of an Adams catalyst or Raney nickel to produce a mixture of L-gulonic acid and L-galactonic acid. Removing the water from these acids forces their conversion into the corresponding lactones. Because of the applicable rate constants, adding water to the lactones does not result in their rapid reconversion to the acids. Accordingly, they can then undergo oxidation, in the presence of an enzyme obtained from pea seeds, to L-ascorbic acid.

Abstract: 2-Keto-L-gulonic acid, an ascorbic acid intermediate, is prepared by cultivating a microorganism of the genus Citrobacter in an aqueous nutrient medium in the presence of 2,5-diketo-D-gluconic acid.

Abstract: 2-Keto-L-gulonic acid is prepared from 2,5-diketo-D-gluconic acid through microbial conversion. The 2-keto-L-gulonic acid producing microorganism used for this microbial conversion includes strains which belong to genera of Brevibacterium, Arthrobacter, Micrococcus, Staphylococcus, Pseudomonas and Bacillus. Both the incubation of the microorganism in a medium containing 2,5-diketo-L-gluconic acid and the direct contact of any products obtained from the cells with a substrate containing said 2,5-diketo-D-gluconic acid may be used in the disclosed process.