Industrial enzymes for sweeteners: Which enzyme mainly performs the conversion step that turns glucose syrups into high fructose corn syrup (HFCS) in starch processing?

Introduction:
High fructose corn syrup production involves a cascade of enzymatic steps: liquefaction, saccharification, and isomerization. This question checks whether you know which specific enzyme is mainly responsible for the glucose to fructose conversion that defines HFCS.

Given Data / Assumptions:

• Feedstock: starch from corn or other cereals.
• Process: liquefaction to dextrins, saccharification to glucose, then isomerization to fructose.
• Target: fructose enrichment characteristic of HFCS.

Concept / Approach:
α-amylase hydrolyzes internal α-1,4 bonds to liquefy starch into shorter dextrins. Glucoamylase hydrolyzes α-1,4 (and some α-1,6) bonds from non-reducing ends to produce glucose. The pivotal step that differentiates HFCS is the isomerization of glucose to fructose, catalyzed by glucose isomerase (also called gluco-isomerase or xylose isomerase variants for immobilized systems).

Step-by-Step Solution:
Liquefaction: starch --(α-amylase)--> dextrins.Saccharification: dextrins --(glucoamylase)--> glucose syrup.Isomerization: glucose syrup --(glucose isomerase)--> fructose-rich syrup (HFCS).Therefore, the enzyme mainly responsible for the HFCS conversion step is glucose isomerase.

Verification / Alternative check:
Industrial HFCS specifications (HFCS-42, HFCS-55) are achieved by controlling glucose isomerase reaction conditions and subsequent chromatographic enrichment if needed.

Why Other Options Are Wrong:
α-amylase: necessary for liquefaction but does not create fructose.

Glucoamylase: produces glucose but does not isomerize it to fructose.

All of these: incorrect because only glucose isomerase performs the defining step to fructose.

Common Pitfalls:

• Confusing saccharification with isomerization.
• Assuming any carbohydrate hydrolase can generate fructose directly.

Final Answer:
Glucose isomerase (gluco-isomerase)