Analytical chemists evaluating the molecular composition of East Asian distilled spirits have established a sensitive liquid chromatography mass spectrometry profiling workflow revealing distinct dipeptide signatures across commercial liquors from China, Japan, and South Korea. Using chemical derivatization targeted to trace short-chain peptides, the investigative team detected a total of 112 unique dipeptides across 15 commercial brands, identifying substantial divergence in peptide abundance, variety, and compositional overlap. Across the tested market inventory, Korean soju demonstrated significantly higher overall dipeptide diversity and profile consistency than Chinese baijiu and Japanese shochu. Six distinct dipeptides were detected exclusively in all three Korean soju varieties, pointing to potential discriminatory compositional markers that differentiate traditional fermented and distilled regional spirits without relying on standard volatile compound screening.
East Asian brewing traditions encompass millennia of fermented and distilled beverage production, extending from ancient Neolithic fermented beverages to modern industrialized spirits. While volatile flavor components like esters, aldehydes, ketones, and organic acids have been extensively cataloged, non-volatile short peptides are increasingly recognized as active regulators of food flavor and biological properties. In fermented beverages such as beer, sake, and traditional rice wines, dipeptides occur in relatively substantial quantities. Conversely, the thermal distillation process required to produce distilled spirits dramatically reduces dipeptide concentrations through thermal degradation and selective vapor partitioning. Because short-chain peptides in distilled liquors persist at minute trace concentrations, evaluating their occurrence across diverse production methodologies has historically faced significant analytical challenges requiring highly sensitive chromatographic separation and targeted spectral acquisition.
To overcome the challenge of trace-level quantification in distilled spirits, the researchers designed a shotgun-like screening and verification protocol using dansylation combined with liquid chromatography multiple reaction monitoring mass spectrometry. Chemical derivatization with dansyl chloride introduces hydrophobic, ionizable tags onto the amino groups of peptides, markedly enhancing chromatographic retention, electrospray ionization efficiency, and characteristic fragmentation behavior during mass spectrometry. To build a comprehensive reference framework, the team utilized a panel of 44 synthesized authentic dipeptide standards alongside complex peptide extracts derived from three fermented soybean matrices, including Japanese natto, Dalian miso, and Chinese soybean paste. This preliminary library construction enabled the team to screen 361 theoretical dansylated dipeptide candidates, establishing targeted transition sets and collision energy values across the molecular weight spectrum.
The experimental setup coupled ultra-high performance liquid chromatography with tandem mass spectrometry platforms, utilizing a C8 reversed-phase column operated at fifty degrees Celsius under a water and acetonitrile gradient acidified with zero-point-one percent formic acid. Target dipeptide screening relied on a triple quadrupole mass spectrometer operating in multiple reaction monitoring mode, configured to monitor peptide-specific product ions alongside the characteristic dansyl fragment at mass-to-charge ratio 170. Validation of candidate chromatographic peaks was simultaneously performed using a high-resolution time-of-flight mass spectrometer operated in positive ion electrospray ionization mode. Candidate features had to satisfy strict screening criteria, requiring retention time matching within zero-point-one minutes across multiple reaction transitions and accurate mass errors of less than five parts per million on the high-resolution instrument.
Sample preparation and derivatization conditions were systematically refined using response surface methodology to ensure maximum recovery of low-abundance peptides without introducing analytical artifacts. Freeze-dried liquor residues required a minimum reconstitution volume of 50 microliters of buffer to maintain a resuspension volume coefficient of variation below ten percent, which also yielded significantly higher total peptide responses compared to 100 or 200 microliter systems. Optimization through a Box-Behnken experimental design evaluated buffer concentration, incubation time, and temperature using a larger-the-better signal-to-noise ratio index designed to penalize interspecies variability among low-recovery peptides. The response surface model demonstrated that sodium bicarbonate and sodium carbonate buffer concentration was the sole statistically significant parameter, leading researchers to establish a 45 millimolar buffer concentration paired with incubation at 45 degrees Celsius for 40 minutes as a robust operational baseline.
Rigorous analytical performance evaluations demonstrated the high sensitivity, dynamic range, and reproducibility of the optimized procedure across 34 representative synthetic standards. Limits of detection spanned from 1 picogram per milliliter to 500 picograms per milliliter, achieving a median detection limit of 1.5 picograms per milliliter, while limits of quantification defined linear calibration curves extending across two to three orders of magnitude with regression determination coefficients exceeding 0.99. Both intraday and interday precision metrics remained below fifteen percent relative standard deviation at both low and high concentration levels. Matrix-matched recovery assessments conducted at 5 and 50 nanograms per milliliter in pooled liquor matrix demonstrated recovery rates between 75 and 101 percent at low spike levels and 80 to 103 percent at high spike levels, with 96 percent of evaluated spikes falling strictly within the accepted 80 to 120 percent range.
Applying this validated analytical workflow to commercial market samples, the researchers examined fifteen distilled spirits spanning three major East Asian regional classes. The sample set comprised nine Chinese baijiu across three distinct aroma types—including sauce aroma varieties Xi-Jiu, Hong-Hua-Lang, and Bei-Da-Cang; strong aroma varieties Wu-Liang-Ye, Guo-Jiao, and Jian-Nan-Chun; and light aroma varieties Fen-Jiu, Niu-Lan-Shan, and Bao-Feng-Jiu—alongside three Korean soju brands (Jinro, Chum-churum, Good Day) and three Japanese shochu varieties (iichiko, Asahi, Kuro Kirishima). Five independent technical replicates were prepared and analyzed for each commercial sample, interspersed with pooled quality control injections after every ten analytical runs to monitor instrument stability and exclude features exhibiting relative standard deviations exceeding thirty percent in quality controls or fifteen percent across sample replicates.
The quantitative comparative profiling revealed marked compositional divergence across national categories, with individual liquor varieties containing between 21 and 108 detectable dipeptides. Korean soju brands displayed the greatest peptide richness, with Jinro, Chum-churum, and Good Day containing 108, 86, and 83 dipeptides, respectively. Korean soju also exhibited the highest intragroup profile consistency, sharing 69 common dipeptides among the three brands and yielding a Jaccard index of 0.62 and an overlap coefficient of 0.83. By contrast, Chinese baijiu aroma categories and Japanese shochu varieties shared only 18 to 22 dipeptides within their respective groups, presenting Jaccard indices between 0.30 and 0.35 despite overlap coefficients between 0.75 and 0.95. When comparing Chinese baijiu as an aggregated group against Korean and Japanese spirits, the cross-regional Jaccard index fell to 0.06, underscoring pronounced regional divergence.
Across the entire multi-regional dataset, only four specific dipeptides—prolyl-leucine, valyl-alanine, valyl-isoleucine, and asparaginyl-arginine—were universally detected in all fifteen evaluated liquor products. Relative abundance levels for prolyl-leucine, valyl-alanine, and valyl-isoleucine were consistently elevated in Korean soju relative to Chinese light-aroma baijiu and Japanese shochu. Furthermore, circos heatmap cluster analysis indicated that dipeptides possessing hydrophobic N-terminal amino acid residues, specifically valine, proline, isoleucine, or leucine, exhibited significantly higher overall detection frequencies across distilled liquors.
A critical outcome of the comparative analysis was the discovery of six specific dipeptides—isoleucyl-tyrosine, glycyl-isoleucine, phenylalanyl-glycine, alanyl-glycine, valyl-tyrosine, and threonyl-alanine—that were present across all three Korean soju varieties but completely absent from all twelve Chinese baijiu and Japanese shochu samples. The authors hypothesized that distinct traditional manufacturing techniques account for this pattern.
The research team emphasized several methodological and structural boundaries that frame the interpretation of their findings. Because synthetic reference standards were available for only 44 peptides, the study reported relative abundances normalized to isotope-labeled internal standards across the broader panel rather than absolute concentrations, although matrix-matched spike recoveries confirmed internal measurement consistency. Furthermore, the cross-country survey sampled a single commercial unit per brand, providing a product-level comparison rather than evaluating inter-batch industrial variation across production lots. Sensory associations also remain preliminary; while hydrophobic residues such as isoleucine, valine, phenylalanine, and tyrosine are linked to bitter tastes in model peptide systems, the sensory thresholds and direct perceptual contributions of the six soju-specific markers in commercial beverage matrices require dedicated human sensory evaluation.
Subject of Research: Comparative dipeptide profiling of East Asian distilled liquors
Article Title: Comparative profiling of dipeptides in East Asian distilled liquors via dansylation-labeled LC–MRM/MS
Article References: Wang, H., Li, S., Huang, D., Yang, L., Xu, T., Wang, Y., Li, R., Lu, X., & Zhou, Y. (2026). Comparative profiling of dipeptides in East Asian distilled liquors via dansylation-labeled LC–MRM/MS. Food Chemistry: X, 40, Article 104763. https://doi.org/10.1016/j.fochx.2026.104763
Image Credits: AI Generated
DOI: 10.1016/j.fochx.2026.104763
Keywords: Distilled spirits, Korean soju, Chinese baijiu, Japanese shochu, Dipeptides, Liquid chromatography, Tandem mass spectrometry, Multiple reaction monitoring, Dansylation derivatization, High-resolution mass spectrometry, Food metabolomics, Trace analysis, Fermentation starters, Nuruk, Aroma profiles, Food chemistry