The research team, led by Nisa Alfilasari, Dania Cheaha, and Santad Wichienchot of Prince of Songkla University, obtained Kapi-pla from a commercial producer in Phatthalung Province with more than a decade of manufacturing experience. Kapi-pla is made by fermenting freshwater fish with salt, a process in which endogenous fish proteases first degrade muscle proteins and are then joined by halotolerant and halophilic microbes, including species of Tetragenococcus, Halanaerobium, and Lactobacillus. This sequential proteolysis releases a rich mixture of free amino acids, short peptides, and ammonia, making the paste a dense substrate for anyone curious about what happens when complex protein fragments meet the microbial ecosystem of the gut.

Before any animals were involved, the team asked what parts of the paste could survive the journey to the colon. Using a simulated upper gastrointestinal digestion model followed by liquid chromatography–tandem mass spectrometry, they identified ten peptide sequences that resisted digestion and were retained by a 1 kilodalton dialysis membrane, meaning they could plausibly reach the large intestine intact. Several of these peptides, including ALWQFR, FPKFLR, NMVWFR, and WNSLLRL, scored highly on the PeptideRanker bioactivity prediction tool and were annotated as possible ACE inhibitors, antioxidants, and even neuroprotective agents. Arginine-rich motifs such as FPKFLR resemble cationic arginine-rich peptides, a class known for membrane penetration and anti-inflammatory actions, while the peptide LPGSLLLR carried a predicted antiamnestic annotation. The authors are careful to note that peptides are only one of several potentially active constituents in this complex, salty matrix, alongside free amino acids, fatty acids, and salt itself.

For the animal experiment, fifty male C57BL/6 mice were divided into five groups of ten. An Alzheimer’s-like state was induced over 63 days using daily intraperitoneal injections of D-galactose combined with oral aluminum chloride, a widely used non-transgenic paradigm that reproduces cholinergic deficits, oxidative stress, and progressive learning and memory impairment. Starting in week five, mice received daily oral gavage for 35 days of either distilled water, the standard Alzheimer’s drug donepezil at 1 milligram per kilogram, or Kapi-pla at 150 or 300 milligrams per kilogram. The two Kapi-pla doses correspond to human equivalent doses of roughly 0.75 and 1.5 grams per day for a 60 kilogram adult, and the associated salinity levels were well tolerated, with no adverse effects seen in serum biochemical or hematological screens.

The microbiome results, obtained by 16S rRNA gene sequencing of fecal samples at baseline, after disease induction, and after treatment, told a story of dysbiosis and partial restoration. Induction with D-galactose and aluminum chloride significantly disrupted microbial diversity and community structure, depleting members of the families Muribaculaceae, Lachnospiraceae, Ruminococcaceae, and Akkermansiaceae. After treatment, mice receiving the high 300 milligram per kilogram dose of Kapi-pla showed enrichment of beneficial Bacillota members, including the butyrate-producing Lachnospiraceae_NK4A136 group and Ruminococcus, together with a rise in Akkermansia, a genus famed for maintaining mucus-layer integrity and exerting anti-inflammatory effects. Akkermansia abundance reached its highest normalized value in the high-dose treatment group, second only to healthy controls, and the high-dose group also showed the smallest reduction in total microbial counts across the experiment.

Metabolic readouts reinforced the microbial picture. Gas chromatography analysis of fecal samples showed that acetic acid, the dominant short-chain fatty acid, was significantly higher in the low-dose Kapi-pla group than in untreated disease mice, while the high-dose group recorded the highest propionate and butyrate concentrations. Spearman correlations linked Akkermansia with propionic acid, Ruminococcus with butyric acid, and Lachnospiraceae_NK4A136 with isovaleric acid, each at a correlation coefficient of 0.90. Elevated branched-chain fatty acids such as isovalerate and valerate in the high-dose group fit neatly with the paste’s protein-rich character, since branched-chain amino acids like valine, leucine, and isoleucine are the classic substrates for proteolytic microbial fermentation.

Untargeted metabolomics using ultra-high-performance liquid chromatography with high-resolution mass spectrometry detected nearly 4,500 metabolite features and revealed that high-dose Kapi-pla shifted hundreds of fecal metabolites relative to both healthy and disease controls. Pathway enrichment pointed squarely at amino acid metabolism: alanine, aspartate, and glutamate metabolism, thiamine metabolism, arginine biosynthesis, beta-alanine metabolism, and aminoacyl-tRNA biosynthesis were all significantly affected. These pathways are not metabolic trivia. Alanine, aspartate, and glutamate metabolism feeds directly into glutamatergic neurotransmission, synaptic plasticity, and hippocampal memory consolidation, all of which deteriorate in Alzheimer’s disease, while thiamine is an essential cofactor for the energy-metabolism enzymes that falter when neuronal mitochondria are under oxidative stress. Beta-alanine, meanwhile, has been reported to support carnosine synthesis and to attenuate anxiety and amyloid-beta neurotoxicity in rodents.

The behavioral tests brought these molecular shifts into the realm of function. In the open field test, untreated disease mice moved less and avoided the center of the arena, a classic signature of anxiety-like behavior, whereas high-dose Kapi-pla mice spent more time in the center zone. In the Y-maze, the untreated group explored the novel arm far less than controls, but both donepezil and Kapi-pla partially restored novel-arm exploration, with the strongest improvement at the high dose. The novel object recognition test showed the same pattern through a discrimination index normalized to each animal’s total exploration time: high-dose Kapi-pla mice recognized the novel object significantly better than untreated disease mice, indicating improved long-term memory rather than mere hyperactivity.

Histology provided the final layer of evidence. Hematoxylin and eosin staining of the hippocampus revealed that untreated disease mice suffered pronounced neuronal loss and pyknotic, irregularly shaped neurons, particularly in the vulnerable CA3 and dentate gyrus regions. The high-dose Kapi-pla group retained significantly more healthy neurons in the dentate gyrus than both the untreated and low-dose groups, and in the CA3 region its healthy cell counts were statistically indistinguishable from those of normal controls. The authors suggest this neuroprotection may flow from the cascade upstream of it: a better-balanced microbiome, more short-chain fatty acids, and amino-acid-derived metabolites that temper neuroinflammatory signaling along the gut–brain axis.

Cautions remain, and the researchers enumerate them candidly. Fecal microbiota samples were pooled rather than individually tracked, the metabolomic p-values were nominal rather than multiple-testing corrected, and the correlations between taxa, metabolites, and behavior do not establish causation. Kapi-pla is also a high-salt food, so some microbial effects may reflect salt or free amino acids rather than bioactive peptides, and the study lacked a healthy-mice-plus-Kapi-pla control to separate disease-specific restoration from a generalized dietary effect. No amyloid plaques or tau tangles were measured directly. Still, the framework is compelling: a traditional fermented food, consumed for centuries in southern Thailand, appears capable of steering microbial ecology, microbial metabolism, and possibly brain health in the same direction. As fermented foods draw increasing scrutiny as accessible, diet-based allies against neurodegeneration, Kapi-pla’s peptides and microbes have earned a closer look.

Subject of Research: Effects of fermented fish paste (Kapi-pla) on gut microbiota, metabolomics, and cognitive function in an Alzheimer's disease-like mouse model

Article Title: Fermented fish paste (Kapi-pla) modulates gut microbiota and metabolic profiles to improve cognitive function in an Alzheimer's disease (AD)-like mouse model

Article References: Alfilasari, N., Cheaha, D., & Wichienchot, S. (2026). Fermented fish paste (Kapi-pla) modulates gut microbiota and metabolic profiles to improve cognitive function in an Alzheimer's disease (AD)-like mouse model. Journal of Agriculture and Food Research, 31, Article 103305. https://doi.org/10.1016/j.jafr.2026.103305

Image Credits: AI Generated

DOI: 10.1016/j.jafr.2026.103305

Keywords: Alzheimer's disease, Kapi-pla, fermented fish paste, gut microbiota, microbiota-gut-brain axis, short-chain fatty acids, bioactive peptides, metabolomics, Akkermansia, hippocampus, neuroprotection, mouse model