How does industry separate glucose from fructose using liquid chromatography when producing high-fructose corn syrup?

Question

Can someone explain how the separation of glucose and fructose is achieved using liquid chromatography in the industrial production of high-fructose corn syrup?

I've seen references to ion-exchange chromatography, but both glucose and fructose are primarily neutral molecules, so I am not sure how that would work. Other have stated size-exclusion, which makes even less sense.

I've also come across mentions of simulated moving bed chromatography being used. I'm interested in understanding what the stationary phase is and the exact separation method employed in this process.

Answer 1

I am glad that you realized that ion-chromatography is not an effective chromatographic mode for separating neutral molecules. However, we should not forget the backbone of cation or anion exchange resins. It is an aromatic group backbone of ethylene divinyl benzene polymers (among other possibilities). In general these resins can interact strongly with organic compounds. Coming back to sugars. Sugars can be ionized in a special way- if you use an strongly alkaline solution like dilute NaOH. Once ionized by losing the protons of the hydroxyl groups, these sugar anions are amenable to ion chromatography, so the organic backbone, plus their ionized state contributes to retention and infact pretty good peak shapes in alkaline medium.

Search Thermo Fisher's website for separating sugars via ion chromatography. They have dedicated columns This is a general answer which should be good enough to let you search deeper.

Answer 2

I was surprised, I got feedback so quickly, I thought I was asking into the void.

The production of HFCS-55 goes through this process:

• Corn kernels are ground into corn starch
• α-Amylase enzyme hydrolyzes α-bonds in starch, producing oligosaccharides
• Glucoamylase breaks down oligosaccharides into glucose
• Xylose isomerase converts glucose to ~42% fructose and ~50% glucose
• Liquid chromatography purifies fructose to ~90% concentration
• 90% fructose solution mixed with 42% fructose to create 55% fructose "High Fructose Corn Syrup"

I was really curious about the "liquid chromatography"

I think I finally found the answer when I ran across this PDF document, entitled: AmberLiteTM Uniform Particle Size Ion Exchange Resins - Chromatographic Separation of Fructose and Glucose with AmberLiteTM CR99 Ion Exchange Resins - Technical Manual and the section on "3.1 The Chromatographic Mechanism"

[...] Inside the bead, the dissolved sugars interact with the calcium ions held by the resin. Fructose, glucose and water form weak ligand complexes with the calcium ion. A stronger interaction in the fructose/calcium ion complex than in the glucose/calcium ion complex is the basis of the mechanism of separation of fructose from glucose¹. This mechanism of separation is called ligand exchange chromatography.

While technically it is a cation exchange column using Ca2+, the interaction between fructose/glucose and the Ca ions, is an affinity relationship. The footnote from the DuPont technical manual clears this up:

¹ Chromatographic separation resins do not “exchange” ions as do the resins used in deashing and mixed bed polishing. They function by adsorbing and “slowing” fructose as it moves down the column. The syrup doesn’t exchange ions in the process.

I also found a nice webpage from PuroLite, that goes through the process.

This sweetener is produced by passing a 42% fructose solution through a calcium form strong acid cation resin to effect a separation and create a 75-90% fructose solution which can be blended back with additional 42% fructose to produce a 55% fructose purity.

and

Owing to a greater number of sites available for hydrogen bonding, the fructose molecule will form a coordination complex with calcium ions fixed onto a strong acid cation resin. This results in a preferential affinity of the resin for the fructose molecule over the glucose molecule and hence a chromatographic separation of the two sweeteners as they pass through the resin bed. From a feed solution containing a purity of 42% fructose by weight, the fructose in the product fraction can reach in excess of 99% purity.

When producing 55% fructose, the optimum productivity and efficiency of the system is achieved by enriching to an 85-90% fructose concentration.

some other highlights:

In the 1970s, the technology was developed for continuous chromatographic separation of fructose utilizing a simulated moving bed (SMB) separation system.

let me know if I missed anything.