Biological Activities of Soy Protein Hydrolysates Conjugated with Mannose and Allulose

If you formulate with soy protein, you already know the trade-off. Hydrolysates digest well and carry bioactivity, but they taste bitter and can be unstable in finished products. A new study in Foods suggests Maillard conjugation with rare sugars could solve part of that equation.

This is not another hypothetical. The researchers took soy protein hydrolysate, bound it with mannose and allulose through the Maillard reaction, and measured what the conjugates actually do in lab assays. The results are worth your attention if you develop functional foods, sports nutrition, or weight-management products.

Background

Peptide conjugation through the Maillard reaction has moved from flavor chemistry into the functional ingredients space. The reaction, when run under controlled conditions, attaches reducing sugars to free amino groups on peptides. That changes solubility, heat stability, and often bioactivity.

Soy protein hydrolysates already show antioxidant, ACE-inhibitory, and lipase-inhibiting potential. But the raw hydrolysate has limits. Conjugation with sugars can amplify those effects. This study chose mannose and allulose because both are rare sugars with interesting metabolic profiles. Allulose, in particular, is nearly zero-calorie and does not spike blood glucose.

What the study did

The team formed conjugates of soy protein hydrolysate with mannose and allulose using non-enzymatic Maillard reactions. Then they ran three sets of tests. They measured radical scavenging activity with the DPPH assay. They measured ferric reducing antioxidant power, or FRAP. And they checked pancreatic lipase inhibition. They also looked at ACE inhibition, an indicator of blood-pressure-regulating potential.

Not every result was reported in the same detail. The mannose conjugate appears in the study design, but the available data center on SPHA, the allulose conjugate. That is the material with the most complete evidence here.

Key findings

The allulose conjugate performed well across the board. Its DPPH radical scavenging activity reached 280.87 ± 16.39 µg Trolox/mL. That is a meaningful number in antioxidant screening. Its FRAP value was 38.91 ± 0.02 mg Trolox/mL. In plain terms, the conjugate can reduce ferric ions effectively, which is a standard marker of electron-donating ability.

The lipase inhibition result stood out, too. SPHA inhibited pancreatic lipase at 29.43 ± 1.94%. That is not pharmaceutical-strength, but for a food-derived ingredient, it is competitive. It suggests the conjugate could support fat digestion modulation when used at the right dose.

ACE inhibition was present in the conjugated mixtures. The rare sugars themselves also showed ACE-inhibitory properties. That means part of the bioactivity may come from the sugar component, not just the peptide.

Here is the quick picture:

Assay	SPHA result
DPPH radical scavenging	280.87 ± 16.39 µg Trolox/mL
FRAP	38.91 ± 0.02 mg Trolox/mL
Pancreatic lipase inhibition	29.43 ± 1.94%
ACE inhibition	Positive, in conjugates and in rare sugars

What it means for manufacturers

There are two practical reads on this data.

First, allulose is not just a bulk sweetener. It can participate in the Maillard reaction and improve peptide functionality. That gives formulators a clean-label route to enhanced antioxidant and enzyme-inhibiting activity without adding a long chemical name to the label.

Second, the ACE inhibition found in both conjugates and rare sugars opens an angle for blood-pressure-oriented products. If a rare sugar itself contributes ACE-inhibitory activity, then even a simple co-formulation might carry benefits. The conjugated version could go further, though more data is needed.

The lipase inhibition figure of 29.43% is moderate. Do not treat it as a magic bullet. Treat it as evidence that an allulose-conjugated soy hydrolysate could fit into a weight-management matrix alongside other ingredients. You would likely need to combine it with proven carriers or dose it carefully to achieve a meaningful physiological effect.

One more thing to consider: bitter taste. Soy protein hydrolysates are notoriously bitter. Maillard conjugation often masks bitterness through new flavor compound formation. This study does not report sensory data, so do not assume the conjugate tastes good. But the bioactivity results justify taking a sample into your own bench trials.

FAQ

What is SPHA in this study? SPHA appears to be the allulose-conjugated soy protein hydrolysate. It was the test material with the most reported data in the evidence.

Are rare sugars alone bioactive? Yes. In this study, the rare sugars themselves showed ACE-inhibitory properties. That is a useful finding for formulators who want benefits even before conjugation.

Should I replace my current antioxidant ingredient with this? Not yet. The antioxidant numbers are strong in vitro, but cell and human data are missing. Treat this as a validation for further development, not a finished claim.

Closing thought: Maillard conjugation is not just for color and aroma. This study shows it can turn a commodity soy hydrolysate into a more functional protein ingredient. Allulose, already valued for its low calorie profile, may now do double duty as a peptide modifier. Ask your supplier for samples and run your own activity assays. That is the only way to know if SPHA fits your formulation.