English EN
What is degree of hydrolysis (DH) and why does it matter?
Beyond Biopharma | Plant Protein Peptide FAQ
Short answer: Degree of hydrolysis (DH) is the percentage of the peptide bonds in a protein that have been broken during hydrolysis. It is the most useful single process figure on a peptide specification because it records how far the reaction was taken, and it moves with solubility, molecular weight distribution, osmolality and - through a well known bell-shaped relationship - bitterness. It says nothing on its own about which bonds were cut, so the method used to measure it has to be stated.
How DH is calculated and measured
DH is the number of hydrolysed peptide bonds divided by the total number of peptide bonds in the starting protein, expressed as a percentage. The total is estimated from the amino acid composition and the protein content of the feedstock, which means DH is a calculated value rather than a directly measured one. In practice it is obtained by measuring the new terminal groups or the protons released as bonds are cut: colorimetric methods with reagents such as OPA or TNBS on a withdrawn sample, pH-stat titration during the reaction, or titration-based methods after the fact. Because each method counts slightly different things, DH values are only comparable when they come from the same method and the same calculation basis.
What a higher DH changes in practice
- Solubility - more bonds cut means smaller, more polar fragments and better cold water solubility across a wider pH range.
- Clarity - fewer large fragments reduce the tendency to haze or sediment in clear drinks.
- Osmolality - smaller fragments and free amino acids raise the osmotic load, which matters in clinical and sports beverages.
- Taste - bitterness and savoury notes generally become harder to manage as hydrolysis proceeds, unless the enzyme system and a debittering step are designed for it.
- Residual intact protein - the share of larger protein material falls, which is relevant when a product is designed around reduced residual protein; the extent must be verified by analysis for the specific grade.
The bitterness bell curve
Bitterness in hydrolysates is classically described as a bell-shaped function of DH. At low DH only a few bonds are cut, so relatively few hydrophobic regions are exposed and the product tastes mild. Bitterness rises towards a maximum in the middle of the range, where many short hydrophobic peptides are present. At high DH the material is dominated by very small peptides and free amino acids, and bitterness often falls again, although the taste is then characterised by savoury and broth-like notes rather than true bitterness. The position of the maximum depends on the protein and the enzyme, so the curve is a guide to behaviour rather than a fixed rule.
DH is not the same as molecular weight distribution
DH counts broken bonds; molecular weight distribution measures how large the resulting chains are. Enzyme specificity and any fractionation step mean that two plant peptides can reach the same DH with different distributions, so a product with the same DH can still differ in the share of material above 3,000 Da, which is exactly the fraction that causes haze in a clear beverage. Specify both, and ask for the method behind each.
Indicative DH bands in commercial use
| Band | General character | Where it is used |
|---|---|---|
| Low, roughly 5-10 percent | Mild taste, modest solubility gain, larger fragments retained | Products where taste is critical and full clarity is not required |
| Medium, roughly 10-20 percent | Good solubility with manageable bitterness when the enzyme system is chosen well | Beverages, powders and bars; the most common commercial band |
| High, above roughly 20 percent | Highest solubility, smallest fragments, taste management is the main challenge | Clear high protein drinks and formats needing maximum solubility |
These bands overlap in practice and are indicative only. The appropriate target depends on the source, the enzyme system, the format and the taste budget, so it should be fixed with the supplier against your own application trials and confirmed on the specification.
How to write DH into a specification
State a target range rather than a single value, name the analytical method and the calculation basis, and include the accompanying molecular weight distribution and taste requirement so that the three are read together. Never compare a DH from one supplier with a DH from another without checking that both used the same method. Confirm limits and methods against the supplier certificate of analysis and the rules that apply in your market.
Related reading
See molecular weight ranges for plant peptides, what a plant peptide COA should show and how the hydrolysis process is controlled.
