Why is bulk vitamin C production so dependent on sorbitol feedstock, and how does that affect sorbitol demand in China?

Why is bulk vitamin C production so dependent on sorbitol feedstock, and how does that affect sorbitol demand in China?
China's vitamin C industry is the single largest domestic consumer of sorbitol, using a two-step fermentation route that starts with glucose hydrogenation to D-sorbitol, then bacterial oxidation to L-sorbose and onward to 2-keto-L-gulonic acid. This process, which avoids acetone protection steps used in the classic Reichstein method, is standard among Chinese producers and directly ties sorbitol demand to vitamin C output. Since vitamin C is a high-volume, price-sensitive commodity, any swing in its export margins or capacity utilization quickly feeds back to sorbitol procurement volumes. For sorbitol suppliers, this means monitoring vitamin C plant operating rates and export prices is essential for anticipating domestic demand shifts. The linkage also explains why China's sorbitol market is more exposed to pharmaceutical raw material cycles than to food or oral care trends.