The raw material at the center of the study is porcine liver, a protein-rich co-product of pork processing that contains roughly 22 percent protein and accounts for about 1.35 percent of a pig’s live body weight. Because animal by-products are already mainstays of the pet food industry, prized as sustainable and economical protein sources, liver represents an attractive substrate for producing bioactive peptides. The researchers freeze-dried fresh livers collected from three-way crossbred pigs at a commercial slaughterhouse, ground them into a powder containing approximately 81 grams of crude protein per 100 grams, and then subjected the powder to enzymatic hydrolysis using Alcalase 2.4 L, a bacterial protease, at 50 degrees Celsius for two hours with the enzyme dosed at one percent by weight relative to protein.

From that hydrolysate the team generated three distinct treatments, each representing a step along a processing gradient. The untreated control, designated PLH, was simply the alcalase hydrolysate. A second sample, PLH-H, was heated at 120 degrees Celsius for 90 minutes in an oil bath without any added sugar, isolating the effects of heat alone. The third, PLH-HX, received the same thermal treatment but in the presence of 2.5 percent D(+)-xylose, a five-carbon reducing sugar noted in the literature for its relatively high reactivity in Maillard chemistry. Xylose’s aldehyde group attacks the free epsilon-amino groups of lysine residues on the peptides, forming Schiff bases that rearrange into Amadori products and eventually cascade into a complex family of Maillard reaction products, including brown, polymeric melanoidins.

Three structural assays confirmed that the intended chemistry had, in fact, occurred, and also revealed what had not. Sulfhydryl content, measured with Ellman’s reagent, fell by 20 to 25 percent in both heated samples relative to the unheated control, which started at 18.14 micromoles per gram of protein, but the xylose-treated sample was statistically indistinguishable from the heat-only sample. That pattern indicates the thiol loss stemmed from thermal oxidation and thiol-disulfide exchange rather than from glycation itself; xylose apparently targeted lysine side chains, not cysteine residues. Meanwhile, the browning index, read as absorbance at 420 nanometers, rose sharply only in the xylose-treated material, signaling the formation of chromophoric melanoidin-type compounds, and the o-phthaldialdehyde assay showed that free amino groups dropped most steeply in that same sample, the inverse of the browning trend and a classic fingerprint of advanced Maillard progression.

Electrophoresis added a molecular-resolution view of the transformation. Conventional SDS-PAGE of the untreated hydrolysate showed distinct bands near 70 kilodaltons, likely residual albumin-like serum proteins resistant to the enzymatic conditions, alongside a population of low-molecular-weight fragments between 10 and 20 kilodaltons. After heating, higher-molecular-weight bands intensified, consistent with heat-induced aggregation. The xylose-treated sample displayed the strongest bands in the 70 to 100 kilodalton region, plausibly reflecting sugar attachment or peptide cross-linking that altered charge and mobility. Tricine SDS-PAGE, which resolves small peptides, told a complementary story: the 10 to 15 kilodalton bands that were prominent in the control faded markedly after glycation, reinforcing the conclusion that xylose had covalently decorated the low-molecular-weight peptide fraction.

Those structural gains came at a digestive cost. When the samples were pushed through a simulated canine gastrointestinal model, two hours of pepsin digestion at pH 2.0 and 39 degrees Celsius, the normal body temperature of dogs, followed by four hours with pancreatin at pH 7.5, apparent digestibility, calculated from the mass of undigested residue, ranked the treatments in the exact order of their structural modification. The untreated hydrolysate achieved 49 percent digestibility, the heat-treated sample slipped to 46 percent, and the xylose-glycated sample fell to just 40 percent. The authors attribute the decline to the modification of epsilon-amino groups and potential cross-linking between peptide chains, which can interfere with protease recognition and reduce substrate flexibility. In other words, the sugar tags that create antioxidant activity also act as steric shields against the very enzymes meant to break the protein down.

The antioxidant results before digestion were, on the surface, a triumph for the Maillard approach. In the DPPH radical-scavenging assay, the glycated hydrolysate posted a remarkable 94.81 percent scavenging activity, well above the untreated control at 88.61 percent and the heat-treated sample at 64.89 percent. Hydroxyl radical scavenging followed the same hierarchy, with the glycated sample reaching 10.11 percent compared with 2.49 percent for the control, an outcome the authors link to enhanced metal-chelating capacity and redox-active intermediates generated during the reaction. Reducing power, a measure of electron-donating capability, also peaked in the glycated sample, consistent with the formation of melanoidin-like structures that donate electrons through stable redox cycling. Curiously, the ABTS assay broke the pattern: before digestion the glycated sample actually recorded the lowest ABTS activity of the three, suggesting that Maillard-derived structures do not uniformly enhance every electron-transfer chemistry.

Digestion then rewrote the scoreboard, and in an assay-dependent way. DPPH activity declined in all samples after simulated digestion, but the drop was dramatic for the glycated material, which lost 36.95 percent of its activity, compared with a modest 4.88 percent loss for the heat-treated sample. The Maillard-derived radical-scavenging structures, it appears, are themselves vulnerable to enzymatic degradation. Hydroxyl radical scavenging showed a similar vulnerability: the glycated sample fell from 10.11 to 5.92 percent after digestion, while the untreated hydrolysate actually rose from 2.49 to 6.13 percent, likely because gastrointestinal proteolysis released fresh low-molecular-weight peptides with metal-chelating or radical-quenching properties. Yet the ABTS assay flipped in the opposite direction, with all treatments increasing after digestion and the glycated sample posting the highest post-digestion value at 4.51 percent, up from 2.81 percent. This suggests the glycated proteins may function as latent antioxidant reservoirs that release hydrophilic, electron-donating peptides upon proteolytic attack, a form of activity the ABTS assay is particularly sensitive to detecting.

Reducing power, meanwhile, proved remarkably indifferent to digestion: simulated gastrointestinal processing did not substantially alter it, while treatment effects persisted, with the glycated sample retaining the highest value at 0.017 versus 0.014 for the control. The authors interpret this as evidence that Maillard-derived redox-active structures possess greater digestive resilience than the radical-scavenging structures detected by DPPH or hydroxyl radical assays. Taken together, the four assays paint a picture in which the antioxidant benefit of glycation is real but selectively preserved: electron-transfer capacity survives the digestive gauntlet, while bulky radical-scavenging structures are partially dismantled. For formulators, the practical lesson is that no single chemical assay can predict how a functional ingredient will behave inside an animal; the choice of assay fundamentally changes the conclusion.

The study’s framing within the booming pet wellness economy gives its findings added weight. As the population of aging dogs grows, the industry has chased ingredients that combat oxidative stress, chronic inflammation, and immune dysfunction, and protein-derived antioxidant peptides have been leading candidates. This work demonstrates, with careful replication across three independent production batches and two-way statistical analysis of treatment and digestion-stage effects, that a combined hydrolysis and Maillard strategy can modulate the structural and redox characteristics of porcine liver without elaborate processing. But it also demonstrates that the enhancement is fragile and conditional, and that glycation measurably reduces digestibility, a critical parameter for any feed ingredient. The authors are explicit that their in vitro model serves only as a preliminary screening tool; previous studies suggest in vitro and in vivo antioxidant behavior of Maillard products tends to align broadly, but the metabolic handling of advanced Maillard reaction structures in companion animals remains under discussion. In vivo validation, along with peptide-level characterization of the digesta, will be needed before sugar-grafted liver hydrolysates earn a place in a senior dog’s bowl. Until then, the study stands as an elegant caution: in functional nutrition, what a molecule does in a test tube is only the first chapter of its story.

Subject of Research: Xylose-mediated Maillard reaction effects on antioxidant capacity and digestibility of enzymatically hydrolyzed porcine liver during simulated canine gastrointestinal digestion

Article Title: Impact of xylose-mediated Maillard reaction on antioxidant capacity and digestibility of alcalase-hydrolyzed porcine liver during simulated canine digestion

Article References: Impact of xylose-mediated Maillard reaction on antioxidant capacity and digestibility of alcalase-hydrolyzed porcine liver during simulated canine digestion. (n.d.). https://doi.org/10.1007/s44463-026-00090-9

Image Credits: AI Generated

DOI: 10.1007/s44463-026-00090-9

Keywords: Maillard reaction, xylose, porcine liver hydrolysate, alcalase, antioxidant activity, in vitro digestion, canine digestion, pet food, digestibility, bioactive peptides, melanoidins, animal by-products

The research team, led by Hee Jin Chung of the Mammalian Ecology and Conservation Unit at UC Davis’s Veterinary Genetics Laboratory, recruited owners of indoor–outdoor cats in Davis and Sacramento, California. Participants were given simple kits containing ethanol-filled tubes, nitrile gloves, and a printed log, and were asked to collect five of their cat’s fecal samples over several weeks, along with a sample of whatever food the cat was being fed. Between November 8 and December 21, 2023, the team received 38 scats from eight neutered house cats—three males and five females—whose samples were, for anonymity, labeled Cat A through Cat H. Most samples came straight from litter boxes and were collected within hours of defecation, making them unusually fresh for molecular work.

The technical core of the study was DNA metabarcoding, a sequencing approach that identifies the mixture of DNA left behind in feces. The researchers amplified two mitochondrial markers: the 12S rRNA gene to detect vertebrate prey and the 16S rRNA gene to detect invertebrates. Because cat DNA overwhelmingly dominates cat feces, the team designed a custom blocking oligonucleotide—a short synthetic molecule carrying a three-carbon spacer—that binds to domestic cat sequences and stalls their amplification, allowing dietary DNA to be recovered more easily. Sequencing was performed on an Illumina platform, and the resulting reads were processed with cutadapt and DADA2, which identify distinct amplicon sequence variants, before taxa were assigned using BLAST searches against custom and NCBI reference libraries. Samples below strict read-count and identity thresholds were discarded to guard against contamination.

The results were striking, and somewhat humbling for anyone who assumes their cat is quietly devastating the neighborhood. Of 32 analyzable scat samples, roughly a third contained no vertebrate DNA at all except that of the cat itself. Most of the remainder revealed only anthropogenic food items—chicken, pig, turkey, and fish from the drum, hake, and herring families—matching the provisioned pet foods owners submitted for comparison. In total, only a single scat, produced by Cat H, contained wild vertebrate prey: the California vole, Microtus californicus, a common rodent in the region. The cat that produced it had not been seen with any prey by its owner in the preceding 24 hours.

Even more revealing were the three cases where owners did witness their cats carrying prey—a live house mouse caught indoors, a small unidentified rodent brought to the door, and a lizard caught in front of the home. In every instance the prey was alive and intact, and in every instance the corresponding scat, produced within 24 hours, contained no wild prey DNA whatsoever. The findings suggest that domestic cats frequently hunt without consuming what they catch, consistent with earlier camera-collar studies showing that satiated cats hunt for enrichment, practice, or caching rather than nutrition. They also imply that significant prey consumption is needed before prey DNA becomes detectable in feces, meaning molecular scat analysis and owner reports capture different facets of the same hunting behavior—and should be used together.

The comparison between provisioned food and scat also yielded a methodological surprise. Chicken and pig DNA appeared in all four collected food samples, as expected, but recovery of those ingredients in the corresponding scats varied widely. Chicken, present in nearly every relevant food, showed up in 14 of 15 expected scat samples, making it the most digestible and detectable ingredient. By contrast, the two prescription diets—a hydrolyzed-protein formula and a kidney-care wet food—showed the poorest post-digestion recovery, likely because heavy industrial processing degrades DNA before the food even reaches the bowl. Notably, several scats from cats eating animal-based diets contained no animal DNA other than cat DNA, a finding with implications beyond cats: urban wildlife studies routinely identify pet food as an anthropogenic food source in carnivore scats, and this study suggests such DNA may often be too degraded to detect.

The team also tested a cost-saving shortcut that could matter for future studies: pooling. Because DNA extraction and sequencing are expensive, they homogenized subsamples of three to five scats from each cat into a single pooled sample, then compared pooled results against individually extracted samples. The answer was mixed. Common items such as chicken were recovered reliably regardless of pooling, and for two cats the two approaches matched perfectly. But the study’s only wild prey detection—the California vole—appeared only in the individually extracted sample and vanished in the pooled version. When the target of a study is a rare or rarely consumed prey item, the authors conclude, pooling samples before extraction can erase exactly the signal researchers are looking for.

The invertebrate results illustrate another caution. The 16S data were compromised by heavy contamination in negative controls and poor amplification, and although Orthoptera, flies, true bugs, jumping spiders, and noctuid moths were detected in some scats, the team excluded the invertebrate dataset from formal analysis. Primer bias is a further limitation: the 12S primers used here perform poorly on reptiles and amphibians, so the absence of lizard DNA in the scats—despite one owner reporting a caught lizard—may reflect molecular bias rather than true absence. The authors recommend that future studies pair molecular methods with morphological analysis of scat contents to avoid missing entire taxonomic groups.

Despite its small sample size and short duration—cats were sampled for an average of about 12 days—the study demonstrates that owned cats, paired with their willing owners, can serve as a viable study system for predator diet research. Citizen-science sample collection slashes the cost and effort of fieldwork, while owner logs add behavioral context that scat alone cannot provide. And because neither sterilization nor regular feeding reliably suppresses hunting, even well-fed, neutered cats remain relevant to wildlife conservation, particularly where vulnerable prey such as the endangered Amargosa vole, a California vole subspecies, persist. The broader lesson is that a single tool will never fully capture the ecology of a predator that hunts both out of hunger and out of instinct. DNA metabarcoding catches the meals owners never see; owner questionnaires catch the trophies cats bring home uneaten. Used together, they offer the clearest picture yet of what the world’s most popular pet is really doing to the wildlife in its own backyard.

Subject of Research: DNA metabarcoding of owner-collected scat samples to assess the diet and wild prey consumption of owned domestic cats.

Article Title: Using DNA Metabarcoding and Citizen Science to Assess the Diet of Owned Domestic Cats

Article References: Chung, H. J., Vanderzwan, S. L., & Sacks, B. N. (2026). Using DNA Metabarcoding and Citizen Science to Assess the Diet of Owned Domestic Cats. Ecology and Evolution, 16(9), Article e74404. https://doi.org/10.1002/ece3.74404

Image Credits: AI Generated

DOI: 10.1002/ece3.74404

Keywords: domestic cat, DNA metabarcoding, citizen science, diet analysis, wildlife conservation, California vole, pet food, hunting behavior, scat samples, owned cats, Metabarcoding, Citizen