Erythorbic acid is produced through a 5-step manufacturing process involving the fermentation of food-grade starch by Pseudomonas fluorescens to produce calcium 2-keto-D-gluconate, which is then acidified to form 2-keto-D-gluconic acid. This is esterified with methanol to yield methyl 2-keto-D-gluconate, which reacts with sodium bicarbonate or sodium carbonate to form sodium erythorbate. The final step is the reaction of sodium erythorbate with sulphuric acid to produce erythorbic acid.

1. How is Erythorbic Acid made?
It can be produced by a reaction between methyl 2-keto-D-gluconate and sulphuric acid.
Generally, the manufacturing process has 5 steps:
Producing calcium 2-keto-D-gluconate: food-grade starch hydrolysate fermentation by
Pseudomonas fluorescens with calcium carbonate.
Acidify the above fermentation broth to obtain 2-keto-D-gluconic acid (2-KG).
Esterification 2-KG with methanol under acid conditions to yield methyl 2-keto-D-gluconate.
The synthesis of sodium erythorbate: heating the above suspension with sodium bicarbonate
or sodium carbonate.
The reaction between sodium erythorbate and sulphuric acid.
Structure
Erythorbic acid chemical structure
Properties
Appearance White to slightly yellow crystalline solid which darkens gradually on exposure
to light.
Other names D-Isoascorbic acid; D-Araboascorbic acid
CAS number 89-65-6
Chemical formula C6H8O6
Molecular weight 176.13
PKa It is a diprotic acid having pKa’s 11.34 and 4.04.
Solubility
In water: 40 g in 100 mL water at 25 °C.
In organic solvents: Soluble in alcohol, pyridine; moderately soluble in acetone; slightly soluble
in glycerol