Enzymes and Acids: What is used for making glucose from starch?

December 11, 2025 •

3 min read

For over a century, the primary methods for converting starch into glucose on an industrial scale have centered around either powerful acids or specialized enzymes. While acid hydrolysis was historically significant, modern industrial processes predominantly use a two-step enzymatic method involving amylase and glucoamylase for higher purity and efficiency.

Quick Summary

Starch is converted into glucose via enzymatic hydrolysis using alpha-amylase and glucoamylase, or through an older method of acid hydrolysis with sulfuric acid.

Key Points

Enzymatic Hydrolysis: Modern industrial production of glucose from starch uses a two-step enzymatic process involving alpha-amylase and glucoamylase.
Alpha-Amylase for Liquefaction: This enzyme breaks down long starch polymers into shorter dextrin chains at high temperatures.
Glucoamylase for Saccharification: This enzyme completes the process by converting dextrins into individual glucose molecules.
Acid Hydrolysis: A traditional method that uses a strong, dilute acid like sulfuric acid under high heat and pressure to break down starch.
Superiority of Enzymes: Enzymatic methods offer higher specificity, greater purity, and more controlled reaction conditions compared to harsh acid hydrolysis.
Industrial Process Flow: The complete process involves preparation, liquefaction, saccharification, and purification steps like filtration and ion exchange.

The Dominant Method: Enzymatic Hydrolysis

Modern food and beverage production primarily uses enzymatic hydrolysis to create glucose syrup from starch due to its efficiency, control, and milder conditions. This process typically involves multiple steps, enzymes, and controlled temperature and pH.

Stage 1: Liquefaction with Alpha-Amylase

Liquefaction is the initial enzymatic step where starch is broken into smaller dextrins using heat-stable alpha-amylase in a gelatinized starch slurry. The slurry is first heated in a 'jet cooker' to prepare the starch for enzymatic action. Alpha-amylase hydrolyzes $\alpha$-1,4 glycosidic bonds, reducing viscosity and preparing for the next stage.

Stage 2: Saccharification with Glucoamylase

After cooling, glucoamylase is added to convert dextrins into glucose. Glucoamylase cleaves glucose units from the ends of chains, breaking both $\alpha$-1,4 and $\alpha$-1,6 linkages to achieve high glucose conversion. The duration and conditions influence the dextrose equivalent (DE) value, indicating glucose content.

Key Enzymes Used for Starch Conversion

Alpha-Amylase: Breaks starch into dextrins, often from Bacillus bacteria.
Glucoamylase: Converts dextrins to glucose, typically from fungi like Aspergillus niger.
Pullulanase: A debranching enzyme improving efficiency by targeting $\alpha$-1,6 bonds.

The Traditional Method: Acid Hydrolysis

Historically, glucose was produced by boiling starch with dilute acid under pressure and heat, a method known as acid hydrolysis.

Using Sulfuric Acid

Dilute sulfuric acid ($H_2SO_4$) is a common acid used, breaking glycosidic bonds at high temperatures and pressure. Neutralization and purification follow the hydrolysis.

The Drawbacks of Acid Hydrolysis

Acid hydrolysis is less favored industrially due to drawbacks compared to enzymatic methods.

Byproduct Formation: Harsh conditions create unwanted colored byproducts.
Equipment Corrosion: Strong acids require expensive, corrosion-resistant equipment.
Lower Yield and Purity: It is difficult to achieve high glucose purity, with potential destruction of glucose and formation of side compounds.

Comparison of Starch Hydrolysis Methods


Feature	Enzymatic Hydrolysis	Acid Hydrolysis
Catalyst	Enzymes (e.g., alpha-amylase, glucoamylase)	Strong acid (e.g., dilute $H_2SO_4$)
Temperature	Multi-step process with varying temperatures (e.g., 90-110°C for liquefaction, 55-65°C for saccharification)	High, sustained temperature (e.g., 393 K)
pH Conditions	Varies by enzyme stage (e.g., 5-7 for liquefaction, 3.5-5 for saccharification)	Very low (acidic), requires neutralization
Specificity	High, enzymes target specific bonds for higher purity	Low, acid randomly breaks bonds, leading to byproducts
Yield & Purity	Higher glucose purity and conversion efficiency	Lower glucose purity and overall yield
Equipment	Standard industrial equipment, not corrosion-resistant	Requires expensive, corrosion-resistant equipment
Environmental Impact	More sustainable, milder conditions, less waste	Higher waste from neutralization, harsher chemicals

Conclusion

Modern industrial glucose production from starch primarily relies on a two-stage enzymatic hydrolysis process using alpha-amylase and glucoamylase, offering better control, higher purity, and efficiency compared to older acid hydrolysis with agents like sulfuric acid. While acid hydrolysis is still viable for certain applications, enzymatic conversion is generally the industry standard due to advantages in product quality, environmental impact, and equipment longevity. The choice of method depends on factors like desired purity and cost, but enzymes represent a more advanced and sustainable option.

For additional detail on the biological effects of salivary amylase, see this National Institutes of Health (NIH) article.

Frequently Asked Questions

The two primary methods used for converting starch into glucose are enzymatic hydrolysis and acid hydrolysis. Enzymatic hydrolysis is the modern, more efficient method, while acid hydrolysis is a traditional, older technique.

Specific enzymes used in the conversion process include alpha-amylase, which breaks down starch into shorter dextrin chains, and glucoamylase, which then converts the dextrins into individual glucose units.

The acid commonly used for making glucose from starch, particularly in older industrial processes, is dilute sulfuric acid ($H_2SO_4$). Hydrochloric acid ($HCl$) can also be used.

Enzymatic hydrolysis is preferred because it is more specific, operates under milder conditions, and results in a higher-purity glucose product with fewer unwanted byproducts. Acid hydrolysis is less flexible and can corrode equipment.

Liquefaction is the first step in the enzymatic process where the enzyme alpha-amylase is used to break down long starch molecules into shorter, soluble dextrin chains, which lowers the viscosity of the slurry.

Enzymes like alpha-amylase and glucoamylase are typically sourced from microorganisms, including thermophilic bacteria (e.g., Bacillus licheniformis) and fungi (e.g., Aspergillus niger).

The glucose solution is purified through several steps after saccharification, including filtration to remove solids, decolorization using activated carbon, and ion exchange to remove impurities and adjust pH.