Storage Modulus Research Articles

Chemical analysis and performance evaluation of ClearCorrect® aligners as received and after intraoral use: Implications for durability, aesthetics, and patient safety

BackgroundOrthodontic treatment with transparent aligners is popular with patients. Any alteration of the plastic material, as subjected to the oral environment, could influence the treatment's durability, the aligner's aesthetic appearance, and the patient's safety. PurposeThis study concerns the physicochemical properties of ClearCorrect® aligners before and after intraoral use, focusing on transparency, surface topography, leachable, polymer glass transition temperature, and viscoelastic properties. MethodsAligners were collected after two weeks of intraoral use. Unused samples were obtained from the manufacturers. Transparency was measured by UV–visible spectroscopy. Chemical modifications were studied using infrared and Raman spectroscopies. Thermal degradation, glass transition (Tg), and storage modulus (E') were characterized by thermal analysis (DSC, TGA, DMA). Surface morphology and roughness were studied thanks to SEM and AFM. Aligners were immersed in water-based solutions to identify and quantify organic leachable by HPLC chromatography and trace elements by atomic absorption spectroscopy. ResultsClearCorrect® aligners have a three-layer structure (outer PETG/inner PU layers). Slight chemical alterations occurred after aging. There was also no significant evolution in Tg and thermal degradation temperatures and only a minimal evolution of E'. Surface and transparency alterations occurred. A difference in organic compound and trace element release levels between new and used aligners was evidenced, suggesting an intraoral release during use. SignificanceIntra-oral aging mainly impacts the aligner transparency and surface. The leachable study suggests significant ingestion of organic and non-organic compounds by the patient: investigations are needed to assess the impact of the long-term use of trays on patient health.

Role and influence mechanism of different concentration of hyaluronic acid on physicochemical and organoleptic properties of yogurt

Hyaluronic acid (HA) has been approved to be added to milk and other dairy products, it has highly water-binding ability which can combine with a large number of water molecules through intramolecular hydrogen bonding to form high viscous gels. In addition, HA is one of the prebiotics, can provide health benefits like anti-aging, anti-inflammatory, angiogenic, is a potential additive for enhancing the quality of yogurt. Therefore, the aim of this study was to evaluate the effect of 0%, 0.02%, 0.05%, 0.1%, 0.25% and 0.5% HA on rheological properties, functional properties, thermal stability, protein stability, protein structure and protein fractions of yogurt. The addition of HA, storage modulus (G') is always larger than loss modulus (G'') in all the samples, which is a typical characteristic of gel networks, and the microstructures of the yogurt samples showed a continuous and more homogeneous spatial network structure. Overall, the higher concentration (0.5%) had positive effect on the yogurt characteristics, like higher WHC, foam stability, microstructure, and texture. In contrast, the 0.1% concentration HA lead to a very abnormal results, it had a negative effect on yogurt including water-holding capacity, texture, and protein stability, suggesting structural destabilization and disruption of inter-aggregation before protein. These findings provide a valuable fundamental data for commercialized HA adding yogurt development and quality control processes.

Pasting, structural properties, and in vitro digestibility of water chestnut (Eleocharis dulcis Burm. f., Cyperaceae) starch co-gelatinized with different hydrocolloids

Hydrocolloids have been widely used to modulate the processing properties of native starch, this study aimed to investigate the effects of carrageenan (KC), tamarind seed polysaccharide (TSP), and xanthan gum (XG) on the pasting, rheology, structural properties, and in vitro digestibility of water chestnut starch (WCS). The pasting results showed that XG increased the peak viscosity (PV), trough viscosity (TV), final viscosity (FV) and breakdown viscosity (BD) of WCS gel, but decreased the setback (SB), TSP significantly increased SB. The rheological data found that KC, TSP and XG increased the apparent viscosity and storage modulus (G') and loss modulus (G'') of WCS, which gradually increased by the concentration gradient of hydrocolloids. The hardness of starch with KC increased from 171.52g to 323.36g, and the addition of 0.3% KC and 0.5% KC enhanced the thermal stability. Furthermore, XG significantly increased the resistant starch (RS) content and decreased the hydrolysis rate of starch. These results will provide theoretical references for expanding the application range of WCS.

Surface-engineered caterpillar-like silica nanocomposites for enhanced interparticle friction and interlock in shear thickening suspension

This study presents a novel method for fabricating surface-engineered caterpillar-like silica nanocomposites by combining rod-like nanorods with spherical nanoparticles to control aspect ratios and surface functionalization. This unique design facilitates functional assembly at the nanoscale. Additionally, we developed an innovative composite by encapsulating polyurethane elastomers within shear thickening fluid (STF)-impregnated Kevlar, significantly enhancing the flexibility and durability of the resulting STF/Kevlar/PU composite. Microstructural and chemical modifications were characterized, and detailed rheological analysis revealed a 165 % increase in viscosity and a substantial rise in storage modulus from 91.56 to 18,640 Pa, indicating improved surface morphology and roughness. These enhancements promoted stronger interparticle friction and rotational motion during flow. Impact resistance tests further demonstrated a 314 % increase in peak impact force, driven by frictional interactions between the dispersed caterpillar-like particles. The results confirmed that surface roughness and adhesive forces play a critical role in activating stress-dependent frictional contacts, a key mechanism behind the improved performance. These findings highlight the potential of these composites for mitigating penetration injuries and offer precise control over the shear-thickening transition in engineering applications, making them promising candidates for lightweight protective materials.

Engineering Microgel Packing to Tailor the Physical and Biological Properties of Gelatin Methacryloyl Granular Hydrogel Scaffolds.

Granular hydrogel scaffolds (GHS) are fabricated via placing hydrogel microparticles (HMP) in close contact (packing), followed by physical and/or chemical interparticle bond formation. Gelatin methacryloyl (GelMA) GHS have recently emerged as a promising platform for biomedical applications; however, little is known about how the packing of building blocks, physically crosslinked soft GelMA HMP, affects the physical (pore microarchitecture and mechanical/rheological properties) and biological (in vitro and in vivo) attributes of GHS. Here, the GHS pore microarchitecture is engineered via the external (centrifugal) force-induced packing and deformation of GelMA HMP to regulate GHS mechanical and rheological properties, as well as biological responses in vitro and in vivo. Increasing the magnitude and duration of centrifugal force increases the HMP deformation/packing, decreases GHS void fraction and median pore diameter, and increases GHS compressive and storage moduli. MDA-MB-231 human triple negative breast adenocarcinoma cells spread and flatten on the GelMA HMP surface in loosely packed GHS, whereas they adopt an elongated morphology in highly packed GHS as a result of spatial confinement. Via culturing untreated or blebbistatin-treated cells in GHS, the effect of non-muscle myosin II-driven contractility on cell morphology is shown. In vivo subcutaneous implantation in mice confirms a significantly higher endothelial, fibroblast, and macrophage cell infiltration within the GHS with a lower packing density, which is in accordance with the in vitro cell migration outcome. These results indicate that the packing state of GelMA GHS may enable the engineering of cell response in vitro and tissue response in vivo. This research is a fundamental step forward in standardizing and engineering GelMA GHS microarchitecture for tissue engineering and regeneration.

Texture, swallowing and digestibility characteristics of a low-GI dysphagia food as affected by addition of dietary fiber and anthocyanins

Dysphagia is a common problem in the elderly population, thus texture modifications in foods suitable for dysphagic patients aroused a lot of interest. In the study, low glycemic index (GI) dysphagia foods were designed with adding dietary fiber (DF) and anthocyanins (AS), and their in vitro enzymatic digestion and predicted GI values were investigated by first-order kinetic model and slope log model. Results showed that all samples belonged to dysphagia foods at level 4 (pureed) in the International Dysphagia Diet Standardization Initiative (IDDSI) framework, and exhibited shear thinning behavior. AS reduced the apparent viscosity and storage modulus, increased redness, while DF decreased the hardness and gumminess of dysphagia food masses. DF and AS significantly increased the slowly digestible starch and resistant starch content in food system. With the increased addition of 5 % DF and 3 % AS, the predicted GI value of dysphagia food masses could be decreased to 51.08 ± 2.48, which belonged to the low-GI food, and showed the best water holding capacity and the highest total sensory evaluation score. In addition, a strong correlation was also found between the slow digestion indicators, rheological properties and swallowing ease. This study provides a theoretical foundation for the design of dysphagia food products with slow digestibility and low GI values.

Repeated Mechanical Recycling of Biodegradable Polymers: PLA Exhibits Less Deterioration than PBAT/PLA Blend.

Biodegradable polymers have been extensively researched as alternatives to non-biodegradable fossil-based polymers. Although they reduce environmental impact, their production competes with land needed for food crops. Therefore, exploring their reuse and recycling is essential for enhancing their circular economy and sustainability. This study evaluated the recyclability of commercially available biodegradable polymers, poly (lactic acid) (PLA) and its blend with poly (butylene adipate co-terephthalate) (PBAT), across three cycles of mechanical recycling. Each cycle simulates plastic production, shelf-life, washing, and reprocessing stages. Samples were analysed after molding, ageing, and washing for each cycle using Differential Scanning Calorimetry (DSC), Fourier-transform infrared spectroscopy (FTIR), tensile testing, and rheological analysis to track changes in crystallization, chemical structure, viscosity, and mechanical behaviors. Results indicated that both PLA and PBAT/PLA (55/45wt.%) blend showed a rise in crystallinity () due to the annealing effect of the ageing and washing. No changes in FTIR spectra and were detected after one recycling cycle, indicating stability. After three reprocessing cycles, second heating crystallinity rose from 2% to 13% for PLA and from 2% to 12% for PBAT/PLA (45 wt% PLA), indicating morphological changes from degradation and molecular weight reduction. Despite higher crystallinity and a more moderate decline in complex viscosity and storage modulus than PLA, PBAT/PLA showed reduced mechanical properties, with a 90% drop in elongation at break and nearly 50% in stress at break, highlighting the need for interventions to control PBAT degradation. PLA maintained strong mechanical properties, demonstrating its potential as a compostable recyclable material.

Optimizing Tilapia-based surimi ink for 3D printing: Enhancing physicochemical properties and printability with Ulva powder

The elderly face malnutrition and dysphagia. 3D printing with high-protein surimi offers an innovative way to customize nutrition and texture of foods for the elderly. This study explored whether tilapia-based surimi ink (TBSI) with Ulva powder (UP, 0–3 %) could improve physicochemical properties and printability as an alternative to traditional pollock-based surimi ink (PBSI). TBSI showed a more uniform microstructure, greater water-holding capacity (WHC), and better printability with consistent extrusion than PBSI. Adding UP to TBSI promoted cross-linking and enhanced microstructure and WHC. Rheological analysis revealed that all inks exhibited shear-thinning behavior. UP increased complex viscosity, storage modulus, and loss modulus. Notably, UP above 2 % improved protein matrix uniformity, structural integrity, and printability, as confirmed by FT-IR and 3D printing tests. The hardness of steamed TBSI fish cake increased when infill density increased. This study highlights the potential of TBSI with UP for 3D printing to prepare personalized and elderly-friendly food.

Bulk and Interfacial Behavior of Potato Protein-Based Microgels.

This study aims to understand the bulk and interfacial performance of potato protein microgels. Potato protein (PoP) was used to produce microgels of submicrometer diameter via a top-down approach of thermal cross-linking followed by high-shear homogenization of the bulk gel. Bulk "parent" gels were formed at protein concentrations [PoP] = 5-18 wt %, which subsequently varied in their bulk shear elastic modulus (G') by several orders of magnitude (1-100 kPa), G' increasing with increasing [PoP]. The PoP microgels (PoPM) formed from these parent gels had diameters varying between 100 and 300 nm (size increasing with increasing G' and [PoP]), as observed via dynamic light scattering and atomic force microscopy (AFM) of PoPM adsorbed onto silicon. Interfacial rheology (interfacial shear storage and loss moduli, Gi' and Gi″) and interfacial tension (γ) of adsorbed films of PoP (i.e., nonheated PoP) and PoPM (both at tetradecane-water interfaces) were also studied, as well as the bulk rheology of the PoPM dispersions. The results showed that PoPM dispersions (at 50 vol %) had significantly higher bulk viscosity and shear thinning properties compared to the nonmicrogelled PoP at the same overall [PoP], but the bulk rheological behavior was in sharp contrast to the interfacial rheological performance, where Gi' and Gi″ of PoP were higher than for any of the PoPM. This suggests that the deformability and size of the microgels were key in determining the interfacial rheology of the PoPM. These findings may be attributed to the limited capacity for "unfolding" and lateral interactions of the larger PoPM at the interface, which are presumed to be stiffer due to their production from the strongest PoP gels. Our study further confirmed that heating and cooling the adsorbed films of PoPM after their adsorption showed little change, highlighting that hydrogen bonding was limited between the microgel particles.

Intelligent Monitoring of Post-Processing Characteristics in 3D-Printed Food Products: A Focus on Fermentation Process of Starch-gluten Mixture Using NIR and Multivariate Analysis

The production of three-dimensional (3D)-printed food products requires not only optimal 3D-printing adaptability but also appropriate post-processing characteristics. This study aimed to use near infrared (NIR) spectroscopy to predict the rheological properties of 3D-printed dough, enabling intelligent monitoring of the dough’s fermentation process. Utilizing support vector machine (SVM) classification model, the fermentation stages can be classified as under-fermentation, complete fermentation, and over-fermentation. Employing preprocessing methods with Synergy Interval Partial Least Square-Competitive Adaptive Reweighted Sampling (SIPLS-CARS) algorithm, 27, 39, 23, and 27 key wavelengths were filtered from the raw NIR spectral data, corresponding to the prediction of storage modulus (G'), loss modulus (G''), complex viscosity (η*), and loss factor (tan δ), respectively. Quantitatively, SVM (Support Vector Machine) regression outperformed Partial Least Squares (PLS) with Rc2 values (0.95, 0.94, 0.94) and Rp2 values (0.93, 0.93, 0.94) for G', G'', and η*. NIR spectra-based predictive models demonstrated superior performance compared to rheo-fermentation properties models. In summary, these findings show the potential of NIR spectroscopy as a rapid tool for predicting the fermentation progress of 3D-printed doughs.

Strain hardening of acid-induced sodium caseinate gels as a function of pH and temperature

Strain hardening is a type of rheological behaviour that can be observed in large deformation tests of various materials. In oscillatory shear rheometry, it is characterised by an increase in storage and loss modulus ( and ) with increasing oscillation amplitude (i.e, shear strain) until the material fractures and the moduli drop again. Acid-induced caseinate gels were previously shown to exhibit such a strain hardening behaviour. However, it has not been studied in much detailed how the extent of strain hardening is affected by pH and acidification temperature. In this work, the strain hardening of acid-induced caseinate gels was characterised as a function of pH by starting strain sweeps at various time points during acidification with glucono-delta-lactone, and the experiments were conducted at either 20, 30 or 40 °C to investigate the impact of temperature. The results demonstrate that the strain at fracture and the extent by which increases with the strain amplitude change throughout acid-induced gelation of sodium caseinate in a complex manner with characteristic minima and maxima being barely related to the parameters observed in small strain experiments. The findings demonstrate the importance of considering the pH and temperature when characterising the strain hardening of caseinate gels as previous work showed that the strain hardening properties are related to water expression in forced syneresis experiments.

Regulation of tapioca starch 3D printability by yeast protein: Rheological, textural evaluation, and machine learning prediction

This article investigated the effects of yeast protein (YP) on gel rheology, texture, and 3D printability of tapioca starch and the feasibility of Principal component analysis (PCA) and support vector machine (SVM) algorithms for classification and prediction of printability. The results indicated that increasing YP content enhanced the viscosity, storage and loss moduli, and hardness, thereby improving extrudability and supportability of 3D printing. The addition of 15% YP exhibited the best 3D printing performance, but excessively high YP addition hindered ink extrusion. PCA analysis based on rheological and texture indices categorized the ink's 3D printing performance into four classes: poor support and low printing accuracy; good support but low printing accuracy; good support and high printing accuracy; and non-smooth extrusion. Furthermore, SVM algorithm used texture data to predict printability classification, with the highest prediction accuracy (91.67%) achieved at polynomial kernel among four different kernel functions. These results confirm that YP can serve as a potential ink for 3D printing and underscore SVM's efficacy in predicting ink's 3D printing performance.

Dielectric relaxation and electrical conduction mechanism via hopping of polarons in (Pb0.3Bi0.7)(Zn0.1Nb0.2Fe0.7)O3 perovskite compound: A study based on CBH model

This work analyses the dielectric and conducting properties of the PZN-modified BF solid solution (0.3PZN-0.7BF) synthesized at 850 °C by solid-state reaction. The Rietveld refinement of 0.3PZN-0.7BF solid solution displays three phases: tetragonal Pb(Fe0.5Nb0.5)O3 (76.68 %), α-BZN (21 %), and Bi2Fe4O9 (2.32 %). Dielectric parameter frequency dispersion implies normal ferroelectricity. Thermal relaxation shifts dielectric loss, imaginary impedance (Z''), and loss modulus (M'') peaks to higher frequencies. Electrical investigation indicates electrode polarization, dipole orientation, charge ordering, oxygen vacancies, and defects. Investigations suggest p-type polarons dominate conductivity. At room temperature and 1 MHz, the compound has 117 dielectric constant and 0.009 tangent loss. Conductivity and impedance testing show semi-conductivity. UV–Vis spectrum investigation shows a 1.97 eV energy band gap, supporting its semiconductor properties. Photovoltaic and optoelectronic device applications benefit from 0.3PZN-0.7BF solid solution optical and electrical property studies.

Impact of fiber diameter and surface substituents on the mechanical and flow properties of sonicated cellulose dispersions.

This study investigates how sonication amplitude and time affect 2wt% cationic nanofibrils (CCNF) and microfibrils (CCMF) dispersions, focusing on mechanical properties and flow behavior. Sonication reduces fiber diameter and increases the concentration of substituent groups available for hydrogen bonding. This effect becomes significant when diameters fall below 100nm, leading to enhanced storage and loss moduli. CCNF achieves a maximum shear modulus of 600Pa, whereas CCMF fibers do not undergo similar size reductions. CCNF's viscosity and critical stress follow a square root relationship with sonication amplitude, due to minimal fiber size reduction at high sonication levels (smaller than 20nm), unlike CCMF (diameter reduction up to 50nm), which exhibits a linear increase due to more pronounced fiber fragmentation. At high sonication levels, CCNF shows an exponential rise in critical stress (up to 800Pa), suggesting tiny fibers infiltrate the hydrogel network, thereby improving its integrity and resistance to shear stresses. By integrating theoretical models with experimental findings, this work presents a unified view of sonication's essential role in fine-tuning the mechanical and flow properties of cellulose-based materials. This research enhances understanding of cellulose dispersion behavior under sonication and provides a foundation for designing optimized cellulose-based materials.

Rock failure mechanisms based on rheological dynamics

This paper investigates the mechanisms of rock failure related to axial splitting and shear failure due to hoop stresses in cylindrical specimens. The hoop stresses are caused by normal viscous stress. The rheological dynamics theory (RDT) is used, with the mechanical parameters being determined by P- and S-wave velocities. The angle of internal friction is determined by the ratio of Young's modulus and the dynamic modulus, while dynamic viscosity defines cohesion and normal viscous stress. The effect of frequency on cohesion is considered. The initial stress state is defined by the minimum cohesion at the elastic limit when axial splitting can occur. However, as radial cracks grow, the stress state becomes oblique and moves towards the shear plane. The maximum and nonlinear cohesions are defined by the rock parameters under compressive strength when the radial crack depth reaches a critical value. The efficacy and precision of RDT are validated through the presentation of ultrasonic measurements on sandstone and rock specimens sourced from the literature. The results presented in dimensionless diagrams can be utilized in microcrack zones in the absence of lateral pressure in rock masses that have undergone disintegration due to excavation.

Constructing stable emulsion gel from gelatin and sodium alginate as pork fat substitute: Emphasis on lipid digestion in vitro

This study aimed to develop a gelatin-sodium alginate (G-SA) emulsion gel that can efficiently hold corn oil, as a substitute for pork fat while controlling the digestive behaviors of lipids in vitro. UV, fluorescence, and circular dichroism spectra and surface hydrophobicity measurements of the G-SA mixtures indicated that gelatin and sodium alginate primarily form aggregates through hydrogen bonds and hydrophobic interactions, and the optimum gelatin-to-sodium alginate w/w ratio was identified as 1.9. The final emulsion gel contained 3.15% gelatin and 1.65% sodium alginate (w/w) with a corn oil content of 40% (w/w). G-SA emulsion gel had a higher proportion of polyunsaturated fatty acids (PUFAs, 53.95 g/100 g) than pork fat (15.17 g/100 g). In addition, the G-SA emulsion gel exhibited stable viscoelastic properties without storage and loss moduli changes at increasing shear rates. The G-SA emulsion gel had a higher melting temperature (42.63 °C) than pork fat (35.07 °C). In vitro digestion studies showed that corn oil had a higher free fatty acid release (40.32%) compared to the G-SA emulsion gel (12.66%) and pork fat (8.53%) (P<0.05), indicating that the digestibility of corn oil was reduced in the G-SA emulsion gel. Calcein release experiments revealed that G-SA emulsion gel released the least amount of calcein (P<0.05) during digestion at a slow rate. The G-SA emulsion gel, similar to pork fat, contained evenly distributed digestive particles encapsulating corn oil after in vitro gastric digestion, with the smallest particle size among the treatments. After the in vitro small intestinal digestion phase, the G-SA emulsion gel maintained small droplet sizes with bridging flocculation. The in vitro digesta of the G-SA emulsion gel contained a significantly higher proportion of PUFAs compared to pork fat (P<0.05). Consequently, the G-SA emulsion gel can be a potential substitute for pork fat, offering higher proportions of PUFAs, lower fat content, and controlled lipid digestion with reduced lipid digestibility.

Influence of loading rate on the mode II fracture characteristics of SCC samples: Experiments and numerical simulations

This paper explores the influence of loading rate on mode II fracture failure in rock. Impact experiments were performed on samples of SCC at five different impact pressures via an SHPB system. This study reveals the correlations among the peak load, fracture toughness, and dynamic elastic modulus of rock mode II fractures under diverse loading rates, as well as the alterations in fracture trajectories. Simultaneously, PFC3D discrete element software has been adopted to numerically simulate the experiments and analysis of the fracture process of rocks and the variations in crack quantity and energy from a microscopic perspective. The results suggest that dynamic mode II fracture tends to increase as the loading rate increases and that the loading rate affects the fracture failure trajectory of a sample. Concurrently, as loading increased, the percentage of shear cracks in the samples gradually decreased, whereas the proportion of tensile cracks gradually increased, indicating that the samples experienced compressive stress after mode II fracture occurred at high loading rates. The proportion of energy absorbed by the samples for crack initiation and development, as well as the kinetic energy of the particles, initially tends to decrease but then increases with increasing loading rate, which is related to whether the loading rate generates secondary cracks. It is hypothesized that there exists a critical loading rate that triggers secondary cracks in SCC samples.

Microstructure and characteristics of phase-separated gels of Type-A gelatin and hydroxypropyl starch: pH responsiveness

The impact of phase separation behavior on the performance of hydrogels has always been the research focus. This study explored the relationship of “pH-microstructure-hydrogel properties” of phase-separated hydrogels composed of type-A gelatin (GE, 5 wt%) and hydroxypropyl starch (HPS, 3 wt%). The results revealed that changes in the microstructure of the hydrogel at different pHs significantly impacted the gel properties. At pH 4.00 and 11.00, phase separation occurred in the GE/HPS gel with a microstructure of HPS-in-GE. In particular, at pH 5.00, 6.00, 7.00, and 9.00, severe phase separation resulted in the separation of substantial aggregates of HPS and GE, resulting in a continuous phase structure. At pH 2.00 and 3.00, phase separation was suppressed, resulting in a homogeneous microstructure. Compared to the phase-separated gels at pH 4.00–11.00, the homogeneous systems at pH 2.00 and 3.00 displayed a synergistic effect with higher gel strength. Analysis of intermolecular forces in the GE/HPS gel indicated that hydrogen bonding was the primary interaction force. Furthermore, the addition of GE/HPS into hawthorn jelly at about pH 3.00 effectively preserved the structural appearance and exhibited higher levels of hardness, thus improving the sensory properties of hawthorn jelly. In summary, phase separation decreased the storage modulus of GE/HPS gel, but the compatibility of GE/HPS macromolecules exhibited synergistic effects at 2.00 and 3.00 and improved the hydrogel mechanical properties. This work provides some new insights for GE/HPS-based gel foods.

Impact of preacidification on the functionality and insoluble calcium levels of Low-Moisture Part-Skim Mozzarella made from high-casein milk

The use of low-concentration factor ultrafiltered (LCF-UF) milk for cheesemaking has become popular in recent years. Research on using LCF-UF milk to make low-moisture part-skim (LMPS) Mozzarella manufacture is limited due to concerns about the negative impact of the higher casein content on functional properties, such as melt and stretch. Pre-acidification (PA) (reflects acid added to milk before the addition of the starter culture) has been used in low-fat and nonfat Mozzarella cheeses to lower calcium levels and improve their texture and melting properties. We explored the use of PA to reduce the insoluble calcium content of cheese (calcium that is a crosslinking material for the casein proteins) and its impact on the functionality of LMPS Mozzarella made from high casein (4.2%) milk. Seven vats of LMPS Mozzarella, with a control (no PA), 2 pH values for PA (6.40 and 6.00) and 3 different acidification methods (use of acetic, citric, or carbonic acid from carbon dioxide) were evaluated for their impact on solubilization of colloidal calcium phosphate during LMPS manufacture. Composition, proteolysis, microstructural and functional changes in the LMPS cheeses were monitored during 90 d of refrigerated storage. All cheeses had similar composition except for the cheese made with milk PA with carbonic acid, which had a lower fat-in-dry matter probably due to foaming observed in this sample during the gas sparging. The cheese made with milk PA with citric acid to pH 6.00 had the lowest amount of total and insoluble calcium compared with other cheeses at all steps during cheese manufacture and storage, likely due to the calcium chelating ability of citric acid. The cheese that was made with milk PA with citric acid to pH 6.40 had a trend of slightly lower (not significant) total and insoluble calcium during cheese manufacture compared with other cheeses that were made with milk PA to pH 6.40. The pH value in all the cheeses remained similar throughout 90 d of storage, whereas the cheese that was made with milk PA with citric acid to pH 6.00 had the lowest pH values during storage. Treatment significantly (P < 0.05) impacted instrumental hardness, the maximum loss tangent during heating, the melting temperature and the storage modulus values measured at 70°C. Proteolysis was not impacted by treatment suggesting that typical aging should occur. Cheese that was PA with citric acid to pH 6.00 initially had lower maximum loss tangent values and higher hardness, possibly due to the lower pH value of this cheese. The performance of cheeses on pizza was assessed using Sensory Spectrum® method and quantitative descriptive analysis. The PA of cheese milk with citric acid helped to reduce the insoluble Ca level and at 30 and 90 d of storage, these cheeses had lower first chew hardness, lower chewiness, and lower strand thickness values compared with other cheeses. The use of PA could help improve the functionality of LMPS Mozzarella made from milk high in casein with citric acid being the most efficient in dissolving the insoluble calcium from casein.

Development of a Human Recombinant Collagen for Vat Polymerization-Based Bioprinting.

In light-based 3D-bioprinting, gelatin methacrylate (GelMA) is one of the most widely used materials, as it supports cell attachment, and shows good biocompatibility and degradability in vivo. However, as an animal-derived material, it also causes safety concerns when used in medical applications. Gelatin is a partial hydrolysate of collagen, containing high amounts of hydroxyproline. This causes the material to form a thermally induced gel at ambient temperatures, a behavior also observed in GelMA. This temperature-dependent gelation requires precise temperature control during the bioprinting process to prevent the gelation of the material. To avoid safety concerns associated with animal-derived materials and reduce potential issues caused by thermal gelation, a recombinant human alpha-1 collagen I fragment was expressed in Komagataella phaffii without hydroxylation. The resulting protein was successfully modified with methacryloyl groups and underwent rapid photopolymerization upon ultraviolet light exposure. The developed material exhibited slightly slower polymerization and lower storage modulus compared to GelMA, while it showed higher stretchability. However, unlike the latter, the material did not undergo physical gelation at ambient temperatures, but only when cooled down to below 10°C, a characteristic that has not been described for comparable materials so far. This gelation was not caused by the formation of triple-helical structures, as shown by the absence of the characteristic peak at 220nm in CD spectra. Moreover, the developed recombinant material facilitated cell adherence with high cell viability after crosslinking via light to a 3D structure. Furthermore, desired geometries could be easily printed on a stereolithographic bioprinter.