Researchers at Yanbian University in China worked with rump steaks from 36-month-old Yanbian Yellow Cattle, cut from the biceps femoris muscle within 24 hours of slaughter. The steaks, vacuum-packed and weighing roughly 250 grams each, were divided into four treatment groups drawn from the same carcass. One control group was held at 4 degrees Celsius. The others were rapidly frozen in a minus 30 degrees Celsius freezer until their core temperatures reached minus 0.5 degrees Celsius, representing supercooling with little or no ice formation; minus 5 degrees Celsius, representing sub-freezing with partial ice formation; or minus 18 degrees Celsius, representing deep-freezing with complete freezing. Each group was then packed with six pre-frozen gel ice packs in alternating layers, wrapped in an insulating bag, sealed inside an EPS box, and placed in an incubator at 25 degrees Celsius for 48 hours to simulate a realistic summer delivery.

Temperature logging confirmed the scenario the team wanted to reproduce. During the first 15 hours, while the ice packs melted, the core temperature of all pre-cooled groups stayed below zero. Thereafter, temperatures gradually rose, reaching between minus 1.7 and 3.3 degrees Celsius at the delivery stage depending on the treatment. Sampling continued through five days of subsequent refrigerated storage at 4 degrees Celsius, but only while total volatile basic nitrogen, a spoilage marker, remained below the strict threshold of 20 milligrams per 100 grams. The deep-frozen and sub-frozen groups crossed that limit prematurely, a first hint that their quality was deteriorating faster than the others.

Color told the most visible part of the story. Surface color is the attribute consumers weigh most heavily when buying meat, and it depends on the balance between bright red oxymyoglobin and brown metmyoglobin. At the frozen stage, the deep-frozen steaks actually looked best, showing the highest redness values and the highest lightness, the latter reflecting ice-crystal damage that pushed free water to the surface and increased light scattering. But appearances deceived. Once the parcels warmed during simulated distribution, redness in the deep-frozen group fell fastest, and its metmyoglobin content climbed to the highest level of any group during refrigerated storage. The supercooled group, by contrast, showed the slowest decline in redness, the smallest rise in lightness and yellowness, and consistently low metmyoglobin accumulation, indicating that avoiding ice formation preserved both pigment stability and the endogenous antioxidant environment that protects it.

Texture measurements reinforced the pattern. Deep-frozen steaks were initially the most tender, with a shear force of about 82.65 newtons compared with 123.56 newtons for the refrigerated control, because ice crystals physically disrupted the muscle fibers. Yet after the temperature rise of distribution, shear force in the deep-frozen and sub-frozen groups spiked sharply to 142.37 and 132.36 newtons respectively, a hardening attributed to drip loss, fiber shrinkage, and protein denaturation. Later, both groups softened excessively as structural degradation took over, with the deep-frozen group falling to roughly 53 newtons by 72 hours after delivery. The myofibril fragmentation index, a measure of proteolytic breakdown, surged in the frozen groups after distribution, consistent with freeze-thaw damage releasing lysosomal enzymes such as cathepsins, while the supercooled group showed a gradual, orderly increase reflecting normal aging.

The molecular core of the study lay in the myofibrillar proteins, the structural scaffold that governs water-holding capacity and tenderness. These proteins are acutely sensitive to reactive oxygen species: oxidation converts amino acid side chains to carbonyls, unfolds the native alpha-helical structure, exposes hydrophobic groups buried inside the molecule, and drives cross-linking and aggregation. Carbonyl content rose in all pre-cooled groups during pre-cooling itself, showing that even the phase transition imposes oxidative stress. But after distribution the groups diverged dramatically. By 72 hours after delivery, carbonyl content in the deep-frozen group had reached 2.610 nanomoles per milligram and the sub-frozen group 2.287, while the supercooled group sat at only 1.357, close to the refrigerated control.

Surface hydrophobicity, measured by bromophenol blue binding, painted the same picture of unfolding and aggregation. Deep-frozen and sub-frozen samples already showed markedly elevated hydrophobicity before shipping, and values climbed steeply for every group once distribution began. Protein solubility, meanwhile, fell fastest in the deep-frozen group, dropping from 14.043 to 8.791 over 72 hours after delivery, a rate of decline roughly 80 percent faster than the supercooled group’s. Fourier transform infrared spectroscopy of the amide I band added a structural dimension: after distribution, alpha-helix content in the deep-frozen group collapsed from 56.21 percent to 11.25 percent while beta-sheet, a conformation associated with intermolecular aggregation, jumped to 50.19 percent. The supercooled group retained far more ordered structure, with 23.34 percent alpha-helix and only 18.55 percent beta-sheet at the same stage.

Sensory panels of ten trained assessors, evaluated against ISO 8586 standards, confirmed what the instruments recorded. Scores for meat color, fat color, wetness, and firmness declined most rapidly in the deep-frozen and sub-frozen groups after distribution, and by 72 hours after delivery those groups offered little remaining quality. The supercooled steaks maintained relatively high appearance scores, stable wetness, and acceptable firmness for the longest period, translating the molecular advantages into a longer window of consumer acceptability. The pH trajectory mirrored the biochemical sequence: stable and mildly acidic early on, rising near 6.8 as endogenous proteases released alkaline nitrogen compounds, then falling again as psychrotrophic spoilage bacteria presumably produced organic acids in the later stages.

The study’s central insight is the causal chain it draws from pre-cooling state to protein stability to final quality. Deep-freezing buys a larger thermal reserve and a briefly better initial appearance, but the ice crystals it creates, followed by melting and recrystallization during the warm ride, rupture cell membranes, release pro-oxidants and proteolytic enzymes, and set off a cascade of moisture exudation, pigment oxidation, carbonylation, unfolding, and aggregation. Supercooling at minus 0.5 degrees Celsius threads a needle: it supplies enough cold reserve to blunt the thermal shock of passive distribution while sidestepping the phase transition and its physical damage entirely. For the EPS box and ice pack systems that dominate fresh meat e-commerce, the authors conclude, supercooled pre-cooling is the strategy most likely to deliver beef that still looks, feels, and tastes the way the shopper expects, and the findings offer cold-chain planners a molecularly grounded rationale for rethinking how far down the thermometer a shipment should go before it leaves the warehouse.

Subject of Research: Effects of supercooling, sub-freezing, and deep-freezing pre-cooling on beef quality and myofibrillar protein stability during EPS-based e-commerce distribution

Article Title: Effects of supercooling, sub−freezing, and deep−freezing pre−cooling on color, pH, shear force, sensory quality, and myofibrillar protein properties of beef during expanded polystyrene−based distribution

Article References: Effects of supercooling, sub−freezing, and deep−freezing pre−cooling on color, pH, shear force, sensory quality, and myofibrillar protein properties of beef during expanded polystyrene−based distribution. (n.d.). https://doi.org/10.1007/s44463-026-00083-8

Image Credits: AI Generated

DOI: 10.1007/s44463-026-00083-8

Keywords: beef, supercooling, sub-freezing, deep-freezing, pre-cooling, cold chain, e-commerce distribution, myofibrillar proteins, protein oxidation, meat color, shear force, sensory quality

The research centers on microencapsulated phase change materials, or mPCMs, tiny core-shell particles in which a substance that melts and freezes at a useful temperature is locked inside a polymer wall. Phase change materials absorb large amounts of latent heat as they melt and release that heat as they solidify, acting as thermal batteries that buffer temperature swings. The catch is that the most common PCMs are solid-liquid paraffins that leak when they melt, which is why encapsulation is essential. Microencapsulation solves the leakage problem, dramatically increases the surface area available for heat transfer, and allows the particles to be blended directly into concrete, coatings, textiles, or packaging without any special handling.

What makes the Turkish team’s work novel is the shell material. Most commercial and laboratory mPCMs rely on formaldehyde-based resins such as melamine-formaldehyde or urea-formaldehyde, which can release harmful substances during synthesis and use, or on polystyrene and PMMA, which are flammable. The researchers instead dissolved waste PVC, sourced from a commercial leather company, together with 1-tetradecane, a paraffin that melts at around 5 degrees Celsius, in tetrahydrofuran and used a solvent evaporation technique to precipitate PVC shells around droplets of the paraffin. It is the first time waste PVC has been used this way for a low-temperature, cold-storage PCM, and the choice is doubly clever because PVC is inherently flame retardant, with a limiting oxygen index between 40 and 45, far above the threshold of 26 that separates flame-retardant polymers from ordinary combustible ones.

The synthesis itself is a piece of practical process chemistry. Solution A contained 26 grams of sodium chloride and 9 grams of gelatin dissolved in deionized water, with the salt raising the ionic strength to keep the water from dissolving the THF and the gelatin acting as a natural, biodegradable surfactant that stabilizes the emulsion. Solution B held the waste PVC powder and 1-tetradecane in THF. When B was dripped into the vigorously stirred A, droplets formed whose size depended on how they were added: a Pasteur pipette produced large particles, a micropipette produced small ones. The emulsion was then heated to 56 degrees Celsius so the THF evaporated, leaving behind hardened capsules that were filtered, washed with water and ethanol, and dried. Remarkably, the final particle diameter tracked the initial droplet size, giving the team a simple dial for tuning capsule dimensions, something conventional in-situ polymerization cannot easily achieve.

Two particle populations emerged. The small-particle capsules, designated mPCM/SP, averaged 145 micrometers, while the large-particle capsules, mPCM/LP, averaged 612 micrometers. Both were unimodally distributed, a sign of a well-controlled process. Fourier transform infrared spectroscopy confirmed that the characteristic C-Cl stretching peak of PVC at 1750 per centimeter persisted in the capsules and that the CH2 stretching bands of the paraffin core remained intact, indicating that core and shell coexist without strong chemical interaction, exactly what a good encapsulation should deliver. Differential scanning calorimetry showed that the capsules behave isothermally like the pure paraffin, with melting temperatures of 5.0 and 4.7 degrees Celsius and latent heats of 126.7 and 136.9 joules per gram for the large and small particles respectively. Encapsulation ratios reached 66.5 percent for the large particles and 71.9 percent for the small ones, squarely within the 60 to 90 percent range typical of the best polymer-shelled paraffin microcapsules in the literature.

One subtlety the authors confront head-on is supercooling. The encapsulated paraffin froze at slightly lower temperatures than the bulk material, a well-documented consequence of the shell adding thermal resistance and constraining nucleation within the confined core. Crucially, however, the capsules still solidified above 1 degree Celsius, comfortably inside the operating window for cold-chain and anti-icing service, and the shift is partly an artifact of the relatively fast 5 degrees per minute DSC scanning rate, which is known to exaggerate apparent supercooling. Repeated cycling showed deviations of less than 1 degree Celsius in transition temperatures and about 1.2 percent in latent heat, confirming that the phase change process remains fully reversible and that encapsulation has not degraded the PCM’s intrinsic properties.

Durability testing was equally convincing. The capsules endured 1,000 accelerated thermal cycles between -20 and 30 degrees Celsius, the equivalent of roughly 15 years of daily freeze-thaw service, with DSC signals reproduced almost perfectly after every 100 cycles and FT-IR spectra after 1,000 cycles showing no chemical change. Leak tests were brutal in their simplicity: samples were frozen at -18 degrees Celsius for 12 hours, then baked at 50 degrees Celsius for another 12 hours on filter paper. No visible PCM leakage appeared, and weight losses were a negligible 0.05 to 0.08 percent. Thermogravimetric analysis showed the capsules degrade at higher temperatures than the free paraffin, meaning the PVC shell genuinely protects the core.

The flame retardancy results may be the study’s most distinctive contribution. Because standard limiting oxygen index tests require rectangular samples that microparticles cannot form, the team built a calibration curve by burning reference plastics of known LOI, including expanded polystyrene, polyacrylonitrile, PET, nylon 66, and ABS, and correlating burning times with literature values. Using the resulting equation, they estimated LOI values of 27.6 percent for mPCM/SP and 28 percent for mPCM/LP, above the flame-retardancy threshold and a dramatic improvement over pure 1-tetradecane, whose LOI of 17 means it burns in ordinary air. The mechanism is intrinsic: when PVC decomposes it releases hydrogen chloride gas, which suppresses combustion and promotes a protective char layer. Unlike conventional flame-retardant PCM systems that rely on added ammonium polyphosphate or expandable graphite, this fire resistance comes free with the recycled shell material itself.

The application vision spans two very different worlds. In the sub-5-degree melting range, the capsules are natural candidates for cold-chain packaging, refrigerated transport containers, and insulated panels, where they would absorb heat whenever temperatures rise and release it back as things cool, smoothing out the fluctuations that spoil food and vaccines. In civil infrastructure, mixed into concrete pavements, bitumen binders, or surface coatings, the latent heat released as the capsules freeze could slow the drop of road surface temperature, delay ice nucleation, and reduce ice adhesion, potentially cutting dependence on corrosive chloride deicers. Earlier work by Farnam and colleagues demonstrated the pavement concept with other PCMs, and the Turkish team’s flame-retardant, waste-derived capsules would bring an added safety margin to exactly that use case.

Beyond the immediate applications, the study is a template for what materials scientists call waste valorization: converting an environmental liability into a high-value functional material. PVC is notoriously difficult to recycle through conventional plastic streams because its chlorine content and rheology make it incompatible with aliphatic polyesters and polyolefins, so it is usually landfilled or incinerated. Here, that same chlorine chemistry becomes an asset, delivering flame retardancy that other shell polymers must buy with additives. The process also avoids the nastier solvents common in encapsulation chemistry, using halogen-free THF whose high vapor pressure makes recovery straightforward. As the authors conclude, the work validates a route from a persistent waste problem to thermally reliable, fire-safe, size-tunable microcapsules, and it broadens the reach of phase change material technology into the low-temperature regime where cold chains, winter roads, and a warming world’s cold-storage demands increasingly intersect.

Subject of Research: Flame-retardant microencapsulated phase change materials synthesized from waste poly(vinyl chloride) for low-temperature thermal energy storage and anti-icing applications

Article Title: Novel flame retardant microencapsulated phase change materials from waste poly(vinyl chloride) for maintaining cold and anti-icing applications

Article References: Alkan, C., & Alakara, E. H. (2026). Novel flame retardant microencapsulated phase change materials from waste poly(vinyl chloride) for maintaining cold and anti-icing applications. Journal of Materials Science: Polymers, 1(1), Article 16. https://doi.org/10.1007/s44493-026-00017-2

Image Credits: AI Generated

DOI: 10.1007/s44493-026-00017-2

Keywords: phase change materials, waste PVC recycling, microencapsulation, thermal energy storage, flame retardancy, 1-tetradecane, anti-icing, cold chain, latent heat, solvent evaporation, supercooling, sustainable materials