The importance of molecular weight is not trivial. The bioactivity of collagen and elastin peptides, their absorption in the gut, and ultimately their claimed effects on skin hydration, elasticity and photoaging all depend heavily on the size of the peptide fractions. Smaller peptides, particularly those below 1 kilodalton, are generally considered the most bioavailable and biologically active. Previous work by the same research group had already shown that a collagen peptide beverage maintained a stable distribution during three months of accelerated storage, with more than 65 percent of peptides below 1 kDa and antioxidant activity, measured by ABTS radical scavenging, preserved at 80 to 90 percent. But existing national and industry standards for molecular weight determination were written for simple peptide powders, not for multi-ingredient beverages.

Leading the study, researchers from China compared three mainstream gel permeation chromatography methods drawn from Chinese national and enterprise standards, designated Methods A, B and C, each using a different acetonitrile-water-trifluoroacetic acid mobile phase composition. All three relied on the same TSK-GEL G2000 SWXL size-exclusion column, UV detection at 220 nanometers, and calibration with a suite of peptide standards ranging from cytochrome C at 12,384 daltons down to glycylglycylglycine at just 189 daltons. The team tested the methods on a pure collagen and elastin peptide powder and on two commercial beverages, one fortified with vitamin C and one with epigallocatechin gallate, both made from the same production batches of peptide raw material, allowing a rigorous like-for-like comparison.

The first major finding concerned calibration curve fitting, a detail with outsized consequences. Gel permeation chromatography estimates molecular weight from retention time via a calibration curve, and the researchers showed that the relationship between the logarithm of molecular weight and retention time is inherently sigmoidal rather than linear, consistent with established theory in size-exclusion chromatography. Linear fits produced coefficients of determination between 0.9898 and 0.9925 but left systematic U-shaped residual patterns, revealing hidden bias. Refitting with cubic polynomials raised the R-squared values to between 0.9970 and 0.9999 and slashed the root mean square error, with Method B achieving an extraordinary R-squared of 0.9999 and residuals within ±0.01. In short, the mathematical model used to process the data mattered as much as the chromatography itself.

Repeatability was another pillar of validation. Standard samples re-injected before and after each batch showed retention time relative standard deviations below 0.1 percent, and theoretical plate numbers for the smallest standard exceeded system suitability requirements across all methods, confirming that the column remained in good condition. When the researchers calculated the distribution across five molecular weight ranges and three average molecular weight parameters, the RSD values for all samples stayed below 3 percent under both fitting models, demonstrating that each of the three methods is internally precise and suitable for the comparative analysis that followed.

The most commercially significant breakthrough, however, was the solution to matrix interference. In principle, any peak eluting after the smallest peptide standard, around 20.5 minutes, must represent compounds smaller than 189 daltons. The team hypothesized that this late-eluting region might instead contain aromatic beverage excipients absorbing UV light. Testing pure vitamin C and EGCG under identical conditions confirmed it: both additives eluted after the 20.5-minute cutoff, and the apparent sub-189 dalton fraction swelled to as much as 20 percent of the total distribution in the beverages. By simply excluding peaks after 20.5 minutes, the researchers eliminated the interference entirely. After the cutoff was applied, chromatographic profiles of powder and beverages overlapped almost perfectly, all relative deviations fell below 10 percent, and chromatographic fingerprint similarity analysis using the system recommended by the Chinese Pharmacopeia Commission returned correlation coefficients above 0.99 between each beverage and the pure peptide reference.

With interference removed, the study turned to the question of whether different laboratories using different official methods could ever agree on a number. Under linear fitting, significant differences appeared among the methods, particularly in the high molecular weight range above 3 kDa and in key parameters such as the weight-average molecular weight, whose ranking even flipped depending on the fitting model. Under cubic fitting, those systematic discrepancies largely vanished. In the critical sub-1 kDa region, where bioactive small peptides concentrate, all three methods became statistically consistent, with inter-method RSD values below 5 percent. The authors propose that if the industry adopts cubic polynomial fitting as a shared data-processing convention, results from different platforms become directly comparable; failing that, Method A, which proved most robust across both fitting modes, could serve as an interim reference method.

Perhaps the most reassuring result for product developers is that formulation freedom and analytical rigor can coexist. The two beverages deliberately contained ingredients chosen to adjust pH, viscosity, flavor and stability, including sodium hyaluronate, chitosan oligosaccharide and broccoli seed extract in the EGCG formulation. Electronic nose and electronic tongue profiling confirmed that the drinks delivered noticeably richer, more balanced flavor profiles than the plain peptide powder, with more harmonious distributions of umami, saltiness, sweetness and sourness. Crucially, none of this sensory engineering disturbed the measured molecular weight profile of the peptides. Manufacturers can therefore optimize taste, mouthfeel and shelf life without compromising the verifiable quality of the functional ingredient, provided the 20.5-minute exclusion rule and appropriate fitting model are applied.

The authors are candid about limitations. All experiments ran on a single HPLC platform, so cross-instrument validation remains to be done, and the exclusion rule has so far been tested only in these two matrices, with spiking recovery or blank matrix runs recommended for unknown formulations. The TSK-GEL G2000 SWXL column also has limited resolution below 500 daltons, where a difference of one or two amino acid residues barely changes hydrodynamic volume; the authors suggest LC-MS/MS or dedicated small-molecule columns such as Superdex 30 Increase for fine characterization in that range, and point toward future work linking precise peptide spectra to in vitro bioactivity and clinical endpoints. Even so, the framework delivers three concrete contributions: a validated chromatographic cutoff to strip away non-peptide interference, clear evidence that cubic fitting slashes inter-method variability, and demonstration that the approach survives contact with real, commercially formulated products. For an industry racing to capitalize on collagen’s popularity, that combination of rigor and practicality may prove as valuable as the peptides themselves.

Subject of Research: Molecular weight analysis of fish-derived collagen peptides in beverages by comparative gel permeation chromatography

Article Title: Developing an Analytical Framework for the Molecular Weight Analysis of Fish‐Derived Collagen Peptides in Beverages: A Multi‐Method Comparative Study

Article References: Feng, M., Li, Y., Luo, Y., Jiang, Y., & Zhao, C. (2026). Developing an Analytical Framework for the Molecular Weight Analysis of Fish‐Derived Collagen Peptides in Beverages: A Multi‐Method Comparative Study. Food Science & Nutrition, 14(9), Article e72386. https://doi.org/10.1002/fsn3.72386

Image Credits: AI Generated

DOI: 10.1002/fsn3.72386

Keywords: collagen peptides, gel permeation chromatography, molecular weight distribution, functional beverages, fish-derived peptides, matrix interference, calibration curve fitting, quality control, elastin peptides, food analysis, skin health, HPLC