The study, published in Food Chemistry: X, combined an advanced mass spectrometry technique called in-depth analysis of molecular networking (IDAMN) with untargeted metabolomics and functional validation in zebrafish and intestinal cells. Led by Yuhao Zhang and Wanshu Li, the researchers set out to answer a question that has puzzled pharmaceutical scientists for years: what is the chemical basis for the well-documented clinical observation that bran-processed Fructus Aurantii (BS-FA) causes fewer side effects and delivers greater therapeutic benefit than the raw fruit (Raw-FA)?

Fructus Aurantii, derived from the dried immature fruit of Citrus aurantium L., occupies a unique position as both a medicine and a food in Chinese pharmacopeia. It is traditionally used to promote gastrointestinal motility and relieve indigestion, and modern research has confirmed its extensive applications in functional food development. Yet the raw fruit carries a potent, drying nature that can irritate the gastrointestinal tract when used directly. Bran stir-frying — the most classical and widely used processing method — was believed to moderate these harsh properties, but the underlying chemistry remained largely unexplained.

Previous studies had compared major flavonoids between raw and processed samples using high-performance liquid chromatography, revealing that the bran process partially converts flavonoid glycosides into their corresponding aglycones, potentially enhancing bioavailability. But these investigations were largely limited to quantitative comparisons of a handful of primary compounds and had yet to comprehensively characterize the dynamic transformation of the overall chemical profile. Moreover, systematic functional validation of the altered components was lacking.

To overcome these limitations, the team deployed IDAMN, a strategy designed to improve the reliability of molecular networking (MN) by recognizing and removing redundant nodes — false-positive signals arising from other adducts, isotopes, and in-source fragments that plague conventional molecular networks. Before IDAMN processing, more than half of the nodes in the Fructus Aurantii molecular network were redundant, with false-positive rates of 63.5 percent in positive ionization mode and 62.8 percent in negative mode. After IDAMN refinement, no nodes meeting the predefined criteria for redundancy remained, producing a dramatically cleaner network for compound classification and transformation analysis.

Using this refined approach, the researchers identified a total of 110 compounds from Fructus Aurantii, including 16 flavonoid aglycones, 49 flavonoid glycosides, 7 limonoids, and 38 phosphoglycerides. According to the Metabolomics Standards Initiative criteria, 14 compounds confirmed by comparison with authentic standards were classified as level 1, while the remaining 96 were putatively annotated at level 2 based on accurate mass, isotope patterns, MS/MS fragmentation, database matching, and literature evidence.

Untargeted metabolomics then revealed the dramatic chemical shifts induced by bran stir-frying. Eight components increased significantly, while 34 decreased. Among the upregulated compounds were several flavonoid aglycones — naringenin, hesperetin, kaempferol, sinensetin, and natsudaidain — while downregulated compounds included flavonoid glycosides such as naringin, hesperidin, diosmin, and neodiosmin, along with multiple limonoids and phosphoglycerides. Targeted quantitative validation confirmed these trends: hesperidin dropped from 6.34 to 4.23 micrograms per milliliter, naringin fell from 4.55 to 3.41, and limonin declined from 12.38 to 7.99. In contrast, hesperetin rose from 0.50 to 0.93 and naringenin climbed from 1.46 to 2.59 micrograms per milliliter.

The critical insight came when the researchers mapped these differential components onto the molecular network. They discovered that in-source fragment (ISF) nodes of flavonoid glycosides appeared within the molecular network clusters of flavonoid aglycones — a previously unrecognized connection. By transmitting these ISF nodes between networks, the team merged the glycoside and aglycone clusters into an integrated network where downregulated glycosides and upregulated aglycones coexisted, revealing that bran stir-frying primarily drives the transformation of flavonoid glycosides into flavonoid aglycones.

Validation experiments confirmed the mechanism. Six consecutive extraction rounds showed that the cumulative peak areas of naringenin and hesperetin in BS-FA reached 170.4 K and 240.8 K respectively, compared with 85.2 K and 129.9 K in Raw-FA — and the contribution of the first extraction was comparable between groups, ruling out improved extraction efficiency as the cause. Simulated heating experiments provided direct evidence: when naringin and hesperidin standards were heated at 220°C for 8 minutes under processing-simulated conditions, their signals diminished while distinct signals corresponding to naringenin and hesperetin emerged, confirming that heat promotes cleavage of glycosidic bonds.

For limonoids, the story was different. No chemical conversion products were detected. Instead, the researchers hypothesized that these hydrophobic triterpenoids might be transferred to and retained by wheat bran — rich in dietary fiber, starch, and protein — during processing. Time-course analysis using paired FA and wheat bran samples collected at 0, 2, 4, 6, and 8 minutes from six independent batches showed that desoxylimonin, limonin, nomilin, and nomilinic acid gradually decreased in FA while progressively increasing in wheat bran. An apparent mass-balance analysis for limonin showed that the estimated losses from FA were 22.8, 49.5, 54.1, and 58.6 milligrams at 2, 4, 6, and 8 minutes respectively, while the corresponding amounts recovered in wheat bran were 5.3, 10.9, 11.6, and 13.8 milligrams. Across the 2–8 minute window, limonin recovered in wheat bran accounted for approximately 21.4–23.5 percent of the corresponding decrease in FA, indicating that transfer to wheat bran contributed to limonoid reduction but explained only part of the total loss.

The functional consequences were then evaluated in zebrafish models. Using Nile red staining combined with gastrointestinal fluorescence imaging, the team demonstrated that both Raw-FA and BS-FA promoted gastrointestinal emptying in a dose-dependent manner. At intermediate doses, BS-FA produced a slightly higher emptying rate than Raw-FA, and at high doses, BS-FA elicited the strongest promotility effect with a markedly higher emptying rate. Anti-inflammatory activities were assessed using a CuSO₄-induced inflammation model in Tg(lyz:EGFP) transgenic zebrafish, where both preparations attenuated neutrophil recruitment dose-dependently, with BS-FA generally resulting in fewer recruited neutrophils than Raw-FA at equivalent concentrations. Notably, all larvae in the 200 micrograms per milliliter Raw-FA group died before imaging, while 18 of 30 larvae survived in the corresponding BS-FA group — a striking difference suggesting that bran processing alleviates the adverse effects of Fructus Aurantii at high concentrations.

Three representative compounds — naringin (flavonoid glycoside), naringenin (flavonoid aglycone), and limonin (limonoid) — were selected for further functional characterization. In zebrafish, naringenin consistently produced a greater gastrointestinal promotility effect than naringin at equivalent concentrations, particularly at 50 and 100 micromolar. All three compounds significantly inhibited CuSO₄-induced neutrophil recruitment, with naringenin exhibiting dose-dependent anti-inflammatory activity across 25–100 micromolar and consistently stronger effects than naringin. In IEC-6 intestinal epithelial cells exposed to LPS, naringenin significantly suppressed all three inflammatory markers — TNF-α, IL-6, and COX-2 — at both 10 and 100 micromolar, producing lower expression levels than naringin at 100 micromolar and suggesting a broader inhibitory effect on inflammatory gene expression.

Limonin showed a distinct concentration-response profile. It significantly promoted gastrointestinal emptying at 25 micromolar, but this effect diminished at 50 micromolar and became undetectable at 100 micromolar, suggesting biphasic regulation. Similarly, limonin significantly reduced neutrophil recruitment at 25 and 50 micromolar, but the inhibitory effect was attenuated at 100 micromolar. In IEC-6 cells, limonin reduced LPS-induced IL-6 and COX-2 expression at both concentrations, although its inhibitory effect on TNF-α was observed only at 10 micromolar. These findings align with previous reports that limonoids are the major bitter constituents of Fructus Aurantii, suggesting that excessive limonoid levels may contribute to gastrointestinal irritation.

The physicochemical basis for the superior activity of naringenin over naringin is consistent with previous reports that flavonoid aglycones generally exhibit greater lipophilicity, membrane permeability, absorption, and bioavailability than their corresponding glycosides. These properties provide a plausible explanation for the association between aglycone enrichment and the greater functional effects of BS-FA. However, the researchers caution that the comparison of naringenin and naringin alone cannot establish that glycoside-to-aglycone conversion caused the effects of the whole extract, because other constituents altered during processing may also have contributed.

Beyond flavonoids and limonoids, bran stir-frying also markedly decreased glycerophospholipid levels, suggesting that processing affects structural lipids as well as the characteristic constituents. As ubiquitous components of cellular membranes, glycerophospholipids may undergo hydrolysis or oxidation during thermal processing, potentially explaining their decline. Although these changes provide additional evidence of broader compositional alterations, they were not investigated further because the study focused primarily on flavonoids and limonoids as characteristic constituents of Fructus Aurantii.

The researchers propose that flavonoid aglycones such as naringenin may serve as efficacy-related quality markers, while limonoids such as limonin and nomilin may serve as potential bitterness or irritation-related markers. Monitoring these two compound classes under different processing conditions may facilitate optimization of bran stir-frying toward increased flavonoid aglycones, controlled limonoid levels, enhanced gastrointestinal regulatory activity, and improved sensory quality. However, validation of these compounds as definitive quality markers requires further studies across diverse batches and processing conditions.

Several limitations frame the interpretation of these findings. Most compound annotations without authentic standard confirmation should be regarded as putative according to Metabolomics Standards Initiative criteria. All samples were obtained from a single manufacturer, so variability associated with different manufacturers, production conditions, and geographical origins was not evaluated. The zebrafish experiments provided comparative evidence for bran-induced functional changes but did not fully capture the complexity of mammalian or clinical pharmacological systems, and CuSO₄-induced inflammation is a controlled aquatic model whose biological responses may be influenced by exposure conditions and water-quality variables. Formal dose-response modeling was not performed, and only part of the decrease in limonin was recovered in wheat bran, suggesting that additional mechanisms underlying the remaining loss require further investigation.

Collectively, these findings suggest that bran stir-frying enhances certain quality-related characteristics of Fructus Aurantii through coordinated chemical remodeling — enriching potentially efficacy-related flavonoid aglycones while depleting bitterness-related limonoids. The integrated strategy of combining IDAMN, untargeted metabolomics, and functional validation may provide a useful framework for exploring processing-induced chemical changes and their potential functional relevance in traditional Chinese medicine, moving the field beyond simple abundance measurements toward biologically informed processing optimization.

Subject of Research: Bran stir-frying remodels Fructus Aurantii through flavonoid Deglycosylation and Limonoid reduction

Article Title: Bran stir-frying remodels Fructus Aurantii through flavonoid Deglycosylation and Limonoid reduction

Article References: Zhang, Y., Li, W., Li, Q., Chen, L., Zhao, B., Chen, Q., Zhu, X., & Lin, H. (2026). Bran stir-frying remodels Fructus Aurantii through flavonoid Deglycosylation and Limonoid reduction. Food Chemistry: X, Article 104646. https://doi.org/10.1016/j.fochx.2026.104646

Image Credits: AI Generated

DOI: 10.1016/j.fochx.2026.104646

Keywords: Fructus Aurantii, bran stir-frying, flavonoid deglycosylation, limonoid reduction, molecular networking, IDAMN, traditional Chinese medicine, zebrafish validation, Food Chemistry X, Bran, stir-frying, remodels