Sugar and Rice Flour Reshape the Flavor Chemistry of Low-Salt Shrimp Paste

Shrimp paste is one of the oldest fermented condiments in coastal Asia, prized for the deep umami character it lends to everything from simple rice dishes to elaborate stir-fries. But the traditional version carries a heavy salt load of 25 to 30 percent, a level that clashes with modern dietary guidance and creates its own quality-control headaches during spontaneous fermentation. A research team in China has now shown that a surprisingly simple intervention—adding a small amount of glucose or glutinous rice flour to the fermenting mash—can transform the chemistry, safety, and sensory appeal of low-salt shrimp paste, and they have mapped the molecular consequences in unprecedented detail.

The study, published in Food Chemistry: X, was led by Ping Hong, Meiqi Gu, and colleagues at Zhejiang Ocean University working with Soottawat Benjakul, a prominent seafood fermentation scientist. The team prepared fresh red shrimp (Solenocera crassicornis) into a homogeneous paste and divided it into three fermentation groups, each receiving 12 percent edible salt. One group served as a control. A second received 6 percent food-grade glucose, and a third received 6 percent glutinous rice flour. All three batches fermented at 25 degrees Celsius for 12 days, with samples drawn at days 0, 3, 6, 9, and 12 and frozen at minus 80 degrees until analysis. Three independent fermentation batches per group provided biological replicates.

The choice of additives was deliberate. Shrimp paste is a fundamentally different fermentation matrix from bread dough or soy-based condiments: it is rich in protein and almost devoid of endogenous sugars. While glucose and sucrose additions are well established in carbohydrate-rich systems, where they boost organic acid production and steer microbial communities, nobody had systematically traced the metabolic fate of added carbon sources in a protein-dominated, low-salt seafood ferment. The researchers combined non-targeted metabolomics by liquid chromatography-tandem mass spectrometry with headspace solid-phase microextraction gas chromatography-mass spectrometry (HS-SPME-GC-MS) to capture both the non-volatile and volatile halves of the flavor story.

The physicochemical results revealed a clear pattern. Total viable counts rose in all three groups, but the control group reached 9.55 log CFU per gram by day 12, compared with 9.11 in the glucose group and 9.05 in the rice flour group. The authors attribute this suppression to lactic acid bacteria rapidly consuming the added sugars and producing lactic and acetic acids, which lower the pH and slow the aerobic spoilage bacteria such as Pseudomonas and Enterobacteriaceae that typically dominate shrimp paste. Lower water activity from the sugar additions likely contributed as well. Meanwhile, protein degradation accelerated dramatically in the supplemented groups: total protein fell from 119.27 to 70.24 milligrams per gram in the glucose group and from 112.52 to 60.72 in the rice flour group, versus a drop from 127.09 to 83.80 in the control. SDS-PAGE confirmed that bands for actin, troponin T, and other myofibrillar proteins faded far faster when carbon sources were present, indicating more extensive hydrolysis into peptides and free amino acids—the raw material of flavor.

Safety is the perennial concern with salt reduction, because biogenic amines formed by microbial decarboxylation of amino acids can trigger foodborne illness. The team tracked six amines by high-performance liquid chromatography and found that both additives restrained the most problematic ones. Tyramine, the most prevalent and harmful amine in fermented foods, accumulated least in the rice flour group, apparently because branched starch adsorbs free tyrosine through hydrogen bonding and hydrophobic interactions, starving the decarboxylation reaction of its precursor. Cadaverine and tryptamine also stayed consistently lower in both supplemented groups, likely because glucose competes with free amino acids in early Maillard reactions, forming reversible Schiff bases that reduce the substrate pool available for decarboxylase enzymes. Spermine levels declined in all groups, while spermidine rose most in the rice flour group, suggesting the carbon additions shifted microbial metabolism away from protein degradation and toward glycolysis.

The metabolomics layer of the study was vast. Database searching against HMDB and METLIN putatively annotated 2,089 non-volatile compounds, dominated by organic acids and derivatives (29.09 percent), lipids and lipid-like molecules (26.86 percent), and organoheterocyclic compounds. Principal component analysis separated day-0 from day-12 samples cleanly along the first principal component, and partial least squares discriminant analysis split the three groups into distinct clusters at day 12, with permutation tests confirming the models were stable and free of overfitting. Every group showed more upregulated than downregulated metabolites over the fermentation, a net-synthetic profile the authors note is characteristic of low-salt fermented foods, which favor accumulation of flavor- and nutrition-oriented small molecules.

Among the differential metabolites, the downregulated set was rich in glycerophospholipids, including phosphatidylcholine and its lysophospholipid derivatives, with the extent of decline following the order glucose greater than rice flour greater than control. The authors suggest this means carbon supplementation is more effective than traditional fermentation at reducing potentially inflammatory lipids. On the upregulated side, lotaustralin and glutarylcarnitine rose most in the glucose group. Lotaustralin, a cyanogenic glucoside known to release hydrogen cyanide in plant-insect systems, may contribute broad-spectrum antimicrobial activity to the paste, though the authors caution this remains speculative pending in vitro and in vivo validation. Glutarylcarnitine, an intermediate in mitochondrial beta-oxidation, has been linked in mammalian studies to CoA pool homeostasis and Nrf2-mediated antioxidant capacity, hinting that glucose addition may indirectly help maintain antioxidant balance during fermentation.

Pathway enrichment against the KEGG database identified seven metabolic pathways shared by all three groups—linoleic acid metabolism, glycerophospholipid metabolism, D-amino acid metabolism, nucleotide metabolism, pyrimidine metabolism, arachidonic acid metabolism, and tryptophan metabolism—forming what the authors describe as the core framework for material transformation and energy supply during fermentation. Notably, the glucose group lacked the arginine and proline metabolism and lysine degradation pathways that appeared in the control, a difference consistent with its reduced biogenic amine content. The rice flour group uniquely activated the biosynthesis of cutin, suberine, and waxes, hydrophobic biopolyesters that may limit water evaporation and lipid oxidation in late fermentation, preserving flavor precursors.

The volatile analysis identified 709 compounds by HS-SPME-GC-MS, and the differences between groups were striking. Isobutylmethoxypyrazine, associated with roasted and nutty notes, reached 10.80 micrograms per gram in the rice flour group at day 12, significantly higher than in the other two groups. Methyl alpha-ionone, which contributes floral and fruity aromas, rose in all groups but peaked at 0.54 micrograms per gram with rice flour. Ethyl benzoate and other esters, which impart fruity and creamy notes and mask the pungency of fatty acids, also climbed over time. Odor activity values confirmed that key aroma compounds such as linalool, beta-ionone, nonanal, and 2-methoxy-3-(2-methylpropyl)pyrazine exceeded their odor thresholds by more than a hundredfold in every group, with cucumber-like (E,Z)-3,6-nonadien-1-ol and coconut-like dodecanoic acid most abundant in the supplemented pastes.

The sensory panel of ten trained assessors delivered the verdict that matters most to consumers. Overall scores rose with fermentation in all groups, but the supplemented pastes pulled decisively ahead: by day 12, the glucose group scored 88.30 and the rice flour group 90.60 on the 100-point composite scale, against 71.90 for the control, whose aroma and flavor scores actually declined late in fermentation. Descriptive analysis tied glucose to enhanced sweet, minty, fruity, honey, and caramel notes, while rice flour produced stronger sweet, fruity, herbal, and coconut character. The authors conclude that exogenous carbon sources lower relative salt content, deepen protein hydrolysis, curb major biogenic amines, and lift both aromatic complexity and sensory acceptability. They caution that the underlying mechanisms and the effects of varying addition ratios on flavor development and storage stability still need to be worked out, but the message for producers is already clear: a modest scoop of sugar or rice flour may be the cheapest tool yet for making healthier shrimp paste that actually tastes better.

Subject of Research: Effects of glucose and glutinous rice flour supplementation on the metabolome, biogenic amines, volatile compounds, and sensory quality of low-salt fermented shrimp paste

Article Title: Metabolomics reveals the effects of different carbon sources on the quality and flavor profile of low-salt shrimp paste

Article References: Hong, P., Gu, M., Tu, C., Zheng, W., Shui, S., Li, J., Benjakul, S., & Zhang, B. (2026). Metabolomics reveals the effects of different carbon sources on the quality and flavor profile of low-salt shrimp paste. Food Chemistry: X, 39, Article 104593. https://doi.org/10.1016/j.fochx.2026.104593

Image Credits: AI Generated

DOI: 10.1016/j.fochx.2026.104593

Keywords: shrimp paste, fermentation, low-salt foods, metabolomics, flavor chemistry, biogenic amines, volatile compounds, glucose, glutinous rice flour, food safety, umami, HS-SPME-GC-MS