The motivation behind the work is a genuine public health problem. Raw meat-based diets, particularly those fed to pets, retain their natural nutritional profile and palatability but carry inherent zoonotic risks in the shared living environments of animals and their owners. Regulatory bodies including the U.S. Food and Drug Administration and the American Veterinary Medical Association have warned about pathogen-contaminated raw pet food, yet conventional thermal sterilization destroys the very qualities that make raw diets appealing. High hydrostatic pressure offers an alternative: it transmits pressure uniformly through a product regardless of shape or size, works on sealed packages to prevent recontamination, has regulatory approval in major markets, and preserves heat-sensitive nutrients and flavors.

The study’s experimental design was deliberately broader than most previous work. Earlier investigations typically tested a narrow pressure range of 200 to 400 megapascals and examined either microbial safety or physicochemical quality in isolation. Here, pork samples were artificially contaminated with multiple strains of Escherichia coli, Bacillus cereus, Salmonella Typhimurium, Listeria monocytogenes, and Staphylococcus aureus, reaching initial populations of roughly 10^5 to 10^8 colony-forming units per gram. Vacuum-sealed samples were then treated in an industrial high-pressure sterilizer maintained at 21 degrees Celsius internally, creating a graduated pressure-time matrix that had never been systematically evaluated for raw pork intended for pet food.

The microbial results were striking and strongly pressure-dependent. Treatment at 500 megapascals for fifteen minutes produced the most pronounced inactivation across all organisms, and Salmonella Typhimurium and Listeria monocytogenes were reduced to below the detection limit during subsequent refrigerated storage. The mechanism is physical rather than chemical: compressive forces deform cell membranes and walls, increase membrane permeability, disrupt intracellular ion balance, dissociate ribosomes, and inactivate enzymes, ultimately collapsing cellular homeostasis. Pressures above 100 megapascals alter the phospholipid bilayer itself, impairing nutrient transport and energy metabolism.

Not every pathogen surrendered equally easily, however, and the species-specific patterns proved scientifically revealing. Although gram-positive bacteria are generally considered more pressure-resistant thanks to their thicker peptidoglycan layers, Listeria monocytogenes, despite being gram-positive, was completely eliminated under the harshest conditions, while Staphylococcus aureus showed the highest resistance of all organisms tested. Staphylococcus possesses a thick, highly cross-linked peptidoglycan layer of roughly 20 to 40 nanometers, and in the most intense treatment group its counts actually increased during storage, suggesting recovery and regrowth from sublethal injury. Bacillus cereus and E. coli also remained detectable under most conditions, with Bacillus spores protected by a multilayered structure that distributes pressure and maintains a dehydrated core stabilized by calcium-dipicolinic acid complexes.

The physicochemical consequences of pressure treatment were equally systematic. As pressure and holding time increased, water-holding capacity, shear force, and pH all rose above control values, while moisture and protein contents increased and fat and ash decreased. The researchers attribute these shifts to pressure-induced denaturation and reorganization of myofibrillar proteins. The non-covalent bonds that maintain protein structure, including ionic bonds, hydrogen bonds, and hydrophobic interactions, are voluminous and unstable under pressure, so when secondary and tertiary structures collapse, myosin partially unravels and exposes polar and charged groups that bind water. The resulting compact protein network traps moisture in a gel-like matrix but also cross-links myosin aggregates, making crack propagation difficult and increasing mechanical strength, which explains the higher shear force.

Color changes followed a nuanced pattern tied to the pigment myoglobin and to light-scattering physics. Lightness increased with pressure and time, redness peaked in the 300 megapascal groups before falling again at 500 megapascals, and yellowness was highest in the 500 megapascal, five-minute group. Previous research has shown that dramatic pressure-induced color changes in meat generally appear only above roughly 400 to 600 megapascals, leaving color largely preserved at lower intensities. The observed paleness here is attributed more to protein denaturation and microstructural changes that enhance light scattering than to straightforward myoglobin oxidation, a combined effect rather than a single pigment transformation.

Oxidation and spoilage chemistry told a two-sided story. Thiobarbituric acid reactive substances, a marker of lipid oxidation, rose with pressure and time, reaching their highest values in the 500 megapascal, fifteen-minute group and climbing further during storage. Pressures between 300 and 700 megapascals disrupt phospholipid membranes and expose lipids to oxygen and pro-oxidants, while structural changes in heme proteins can release iron ions that catalyze oxidative chain reactions. In contrast, volatile basic nitrogen, an indicator of protein decomposition and spoilage, was suppressed by treatment, with the 500 megapascal, five-minute group showing the lowest increase rate during storage at just 13.24 percent compared with 111.72 percent in the mildest group. Microbial inactivation and pressure-induced enzyme inactivation both limit the production of ammonia and volatile amines.

Correlation analysis tied the whole picture together. Pressure and holding time correlated negatively with all tested microorganisms, redness, and volatile basic nitrogen, while water-holding capacity, shear force, pH, lightness, yellowness, and lipid oxidation correlated positively, all consistent with cumulative pressure-induced effects on membranes, myofibrils, myoglobin, and enzymes. The authors conclude that while high hydrostatic pressure effectively inactivated Salmonella and Listeria, enhanced water retention, and suppressed spoilage markers, it also produced a paler appearance, increased lipid oxidation, and failed to achieve complete microbial elimination, with pressure-tolerant organisms surviving or recovering.

The practical takeaway is that pressure treatment should not be deployed as a stand-alone solution. The researchers recommend integrated hurdle strategies, combining pressure with salt addition, antimicrobial agents, optimized packaging, and strict refrigerated storage management, to push microbial safety further while preserving quality. For a food industry increasingly interested in minimally processed products, the study provides something rare: a complete pressure-time map showing exactly where pathogen reduction ends and quality degradation begins, at least for raw pork. As demand for raw pet food and clean-label meats grows, that map may prove one of the most useful tools yet for producers navigating the delicate balance between safety and freshness.

Subject of Research: Effects of high hydrostatic pressure processing on microbial inactivation and physicochemical quality of raw pork

Article Title: Application of high hydrostatic pressure on the microbial and physicochemical characteristics of pork

Article References: Baek, U.-B., & Kim, H.-Y. (2026). Application of high hydrostatic pressure on the microbial and physicochemical characteristics of pork. Food Science of Animal Resources, 46(1), Article 73. https://doi.org/10.1007/s44463-026-00091-8

Image Credits: AI Generated

DOI: 10.1007/s44463-026-00091-8

Keywords: high hydrostatic pressure, food safety, pork, microbial inactivation, non-thermal processing, Salmonella, Listeria monocytogenes, lipid oxidation, myofibrillar protein, water-holding capacity, raw pet food, food science

The research team set out to answer a question that has practical consequences for the pet food industry: how much pressure is enough to kill dangerous microbes, and how much is too much before the meat itself begins to suffer? They treated raw beef loin, a primary ingredient in raw pet food formulations, at pressures of 0.1, 100, 300, and 500 megapascals for holding times of 5 to 15 minutes, then tracked both microbial survival and a battery of physicochemical properties over two weeks of refrigerated storage. Five pathogens were inoculated onto the meat: Salmonella Typhimurium, Escherichia coli, Staphylococcus aureus, Listeria monocytogenes, and Bacillus cereus. The samples were vacuum-packed and processed within two hours of inoculation to minimize any changes in microbial populations before treatment.

The microbial results followed a clear pressure-time hierarchy. At 100 megapascals, the inactivation effect was limited, consistent with reversible cellular responses rather than irreversible damage; membranes may become permeabilized without sufficient disruption of intracellular structures, allowing microorganisms to recover. As pressure increased, structural disruption of cell membranes and protein denaturation progressed, leading to irreversible cellular damage. The most striking result came at 500 megapascals for 15 minutes, where Salmonella Typhimurium was reduced to below the detection limit of one log colony-forming unit per gram and was never re-detected during the entire two-week storage period. The other pathogens were not completely eliminated, but they showed substantial reductions with limited regrowth.

The differential survival of the pathogens tells a fascinating story about cell architecture. Gram-positive bacteria such as Listeria monocytogenes and Staphylococcus aureus possess thicker peptidoglycan layers than their gram-negative counterparts, conferring greater pressure resistance. Among all the organisms tested, Staphylococcus aureus proved the toughest, and the authors attribute this to a suite of defensive features: the antioxidant pigment staphyloxanthin, a high content of branched-chain fatty acids in the cell membrane, extensive secondary cross-linking of peptidoglycan, and teichoic acids that stabilize the cell wall against deformation. Immediately after the 500-megapascal, 15-minute treatment, E. coli, Listeria, Staphylococcus, and Bacillus were reduced by 77.47, 77.58, 48.77, and 71.83 percent respectively compared with the control, and over the storage period the reductions reached 59.46, 68.35, 53.39, and 92.08 percent.

Bacillus cereus added another layer of complexity because of its spore-forming ability. Rather than being killed directly, pressures above 50 megapascals stimulate germinant receptors and SpoVA channels within the spores, triggering the release of calcium and calcium-dipicolinic acid and raising the water content of the spore core. Once germinated, the spores convert into vegetative cells, losing their pressure resistance and becoming more susceptible to oxidative stress and DNA damage. This supports what the authors describe as a germination-inactivation sequence rather than direct spore lethality, a nuance that matters greatly for shelf-stable product design.

On the quality side, the picture was more mixed. Proximate composition, meaning moisture, protein, fat, and ash content, remained unchanged across all treatments, largely because vacuum packaging prevented drip loss, the main route by which pressure treatment can alter bulk nutritional composition. pH was similarly stable throughout processing and storage, which the researchers link to the suppression of microbial metabolism and endogenous enzymatic activity, the two main drivers of postmortem biochemical change. However, higher pressures and longer holding times increased lightness, yellowness, shear force, water-holding capacity, and thiobarbituric acid reactive substances, a marker of lipid oxidation, while redness declined. The 500-megapascal, 15-minute treatment raised lightness by 36.95 percent compared with the control, producing a visibly paler product.

One of the most intriguing findings is a paradox in texture. The highest pressure-time combination produced both the greatest water-holding capacity and the highest shear force, meaning the meat held more water yet became tougher. The authors explain this through pressure-induced protein aggregation: dissociated myofibrillar proteins interact through exposed sulfhydryl groups and hydrophobic residues, forming gel-like networks that immobilize water within a mechanically rigid matrix. Water retention, in other words, does not equal tenderness under high pressure. Meanwhile, color changes were governed by non-linear interactions between structural light scattering and myoglobin redox chemistry; at an intermediate 300 megapascals, metmyoglobin-reducing enzymes remain active enough to partially preserve redness, whereas 500 megapascals inactivates those enzymatic defenses.

Oxidation and spoilage chemistry also responded to pressure in opposing directions. Lipid oxidation, measured as TBARS, increased with both pressure intensity and storage time, driven by the release of non-heme iron when myoglobin’s porphyrin structure is destroyed; that iron reacts with hydrogen peroxide to generate hydroxyl radicals that attack lipids. Volatile basic nitrogen, an indicator of protein deterioration, moved the opposite way, falling significantly at 500 megapascals because high pressure suppresses both the microbes and the proteolytic enzymes, including calpains and cathepsins, that would otherwise degrade muscle proteins. Yet even here, storage mattered: VBN values climbed in all groups by week two, suggesting residual enzymatic activity persists after treatment.

The study’s practical conclusion is that processing intensity must be optimized rather than maximized. The 500-megapascal, 15-minute condition delivered the strongest antimicrobial effect but also the worst quality outcomes, including tougher texture, more lipid oxidation, and color deterioration. Moderate conditions around 300 megapascals for 15 minutes achieved substantial microbial reduction while better preserving the attributes that determine palatability, which matters because companion animals are sensitive to texture and appearance as well as to microbial hazards. The authors acknowledge limitations, notably the absence of sensory evaluation, and propose that future work employ electronic nose and tongue instruments and gas chromatography-based volatile analysis, along with digestibility trials, to establish biologically relevant processing windows. For an industry racing to make raw diets safe without making them sterile and unappetizing, this study provides exactly the kind of pressure-time framework needed to find that balance.

Subject of Research: Effects of high-pressure processing on microbial safety and physicochemical quality of raw beef loin for pet food

Article Title: Analyses of the microbial safety and physicochemical characteristics of beef loin treated with high-pressure

Article References: Baek, U.-B., & Kim, H.-Y. (2026). Analyses of the microbial safety and physicochemical characteristics of beef loin treated with high-pressure. Food Science of Animal Resources, 46(1), Article 74. https://doi.org/10.1007/s44463-026-00081-w

Image Credits: AI Generated

DOI: 10.1007/s44463-026-00081-w

Keywords: high-pressure processing, raw pet food, beef loin, foodborne pathogens, Salmonella, Listeria monocytogenes, Staphylococcus aureus, microbial inactivation, lipid oxidation, meat quality, non-thermal sterilization, food safety