Casein Concentration Research Articles

Study on Single Nucleotide Polymorphism of LAP3 Gene and Its Correlation with Dairy Quality Traits of Gannan Yak.

This study explored the polymorphism of the leucine aminopeptidase (LAP3) gene and its relationship with milk quality characteristics in Gannan yak. A cohort of 162 Gannan yak was genotyped utilizing the Illumina Yak cGPS 7K BeadChip, and the identified single nucleotide polymorphisms (SNPs) were evaluated for their association with milk protein, casein, lactose, and fat concentrations. The results showed that four SNPs (g.4494G > A, g.5919A > G, g.8033G > C, and g.15,615A > G) in the LAP3 gene exhibited polymorphism with information content values of 0.267, 0.267, 0.293, and 0.114, respectively. All four SNPs were in Hardy-Weinberg equilibrium (p > 0.05). The g.4494G > A and g.5919A > G SNPs were significantly associated with protein content (p < 0.05), with homozygous genotypes showing significantly higher protein content than heterozygous genotypes (p < 0.05). The g.8033G > C SNP was significantly associated with casein content, protein content, non-fat solids, and acidity (p < 0.05), with the CC genotype having significantly higher casein, protein, and non-fat solids content than the GG and GC genotypes (p < 0.05). The g.15,615A > G SNP was significantly associated with average fat globule diameter (p < 0.05). In general, the mutations within the LAP3 gene demonstrated a positive impact on milk quality traits in Gannan yak, with mutated genotypes correlating with enhanced milk quality. These results indicate that the LAP3 gene could be a significant or candidate gene affecting milk quality traits in Gannan yak and offer potential genetic markers for molecular breeding programs in this species.

Modulation of Poultry Cecal Microbiota by a Phytogenic Blend and High Concentrations of Casein in a Validated In Vitro Cecal Chicken Alimentary Tract Model.

Phytogenic blends (PBs) consist of various bioactive plant-derived compounds that are used as growth promoters for farm animals. Feed additives based on PBs have beneficial effects on farm animals' production performance, health, and overall well-being, as well as positive modulating effects on gut microbiota. In this study, we used a validated in vitro cecal chicken alimentary tract model (CALIMERO-2) to evaluate the effects of a PB (a mix of components found in rosemary, cinnamon, curcuma, oregano oil, and red pepper), alone or in combination with casein (control), on poultry cecal microbiota. Supplementation with the PB significantly increased the abundance of bacteria associated with energy metabolism (Monoglobus) and growth performance in poultry (Lachnospiraceae UCG-010). The PB also decreased the abundance of opportunistic pathogens (Escherichia-Shigella) and, most importantly, did not promote other opportunistic pathogens, which indicates the safety of this blend for poultry. In conclusion, the results of this study show promising perspectives on using PBs as feed additives for poultry, although further in vivo studies need to prove these data.

Influence of thermophilic and mesophilic cultures blended with buffalo milk on camel milk cheese quality and proteolysis

SummaryCamel milk and its products are gaining higher demand due to their attractive nutritional and therapeutic profile. However, manufacturing of camel milk cheese (CMC) is a challenging task. This study aimed to compare the quality of camel milk cheese made using different starter cultures. Four groups CM (camel milk + mesophilic cultures), CT (camel milk + thermophilic cultures), CBM (camel milk + 10% buffalo milk using mesophilic cultures), and CBT (camel milk + 10% buffalo milk using thermophilic cultures) were created. The cheeses were stored for 60 days at 4 °C to assess their physicochemical, sensory, and proteolytic properties. Results indicated highest moisture content in CM (70.19%) as opposed to the lowest moisture in CBT (55.19%). In addition, CM and CBM revealed lower acidity (0.63% and 0.66%) in contrast with CT and CBT (0.78% and 0.83%, respectively). On the other hand, CBM and CBT exhibited higher contents of protein (21.04, 21.57%) and fat (17.65, 17.70%) during storage. All quality indices of cheese samples significantly declined (P &lt; 0.01) during storage excluding acidity. Sensory analyses revealed that panellists highly preferred CBT treatment followed by CBM and CT. Furthermore, urea‐PAGE and RP‐HPLC were performed for the proteolytic study of cheese samples. The study revealed that the presence of buffalo milk and thermophilic cultures in cheese resulted in a decrease concentration of intact caseins (αs1, β‐, and κ‐caseins) as storage days passed. The degree of proteolysis was found to be higher in CBT compared to CBM, CT, and CM. Based on the results, it was concluded that the use of pasteurisation at 65 °C for 30 min, pH of 5.5, 0.06% CaCl2, and the incorporation of 10% buffalo milk using thermophilic cultures (Lactobaccilus bulgaricus and Streptococcus thermophilus) resulted in desirable quality characteristics.

Comparative detection of goat's milk casein through various enzyme‐linked immunosorbent assay (ELISA) approaches using caprine alpha‐S1 casein peptides and bovine casein polyclonal antibodies

SummaryCasein causes allergic reactions in cow's milk protein allergy (CMPA) individuals. Casein can cross‐react with cows and goats. Hence, a rapid and highly specific technique is required for its detection. The study aims to evaluate and optimise multiple Enzyme‐Linked Immunosorbent Assay (ELISA) approaches for the detection of casein isolated from goat's milk. The study utilised and optimised various ELISA approaches, including direct, indirect and sandwich with various antibodies. Several parameters of ELISA including pre‐treatments of casein, blocking reagent, concentrations of antibodies and background signal were evaluated. The results showed that sandwich ELISA revealed a good signal‐to‐noise ratio at 1 mg mL−1. Indirect ELISA showed a higher signal‐to‐noise ratio without any heat treatment in comparison to the direct ELISA despite utilising an equivalent concentration (i.e., 10 μg mL−1) of goat's milk casein. The findings provide a theoretical foundation for obtaining a high signal‐to‐noise ratio for antigenicity studies of goat's milk casein to minimise its immunological response.

Influence of Heating Temperature and pH on Acid Gelation of Micellar Calcium Phosphate-Adjusted Skim Milk.

Micellar calcium phosphate (MCP) plays an important role in maintaining the structure and stability of the casein micelle and its properties during processing. The objective of this study was to investigate how heating (10 min at 80 or 90 °C) at different pH levels (6.3, 6.6, 6.9, or 7.2) impacted the acid-induced gelation of MCP-adjusted milk, containing 67 (MCP67), 100 (MCP100), or 113 (MCP113) % of the original MCP content. The unheated sample MCP100 at pH 6.6 was considered the control. pH acidification to pH 4.5 at 30 °C was achieved with glucono delta-lactone while monitoring viscoelastic behaviour by small-amplitude oscillatory rheology. The partitioning of calcium and proteins between colloidal and soluble phases was also examined. In MCP-depleted skim milk samples, the concentrations of non-sedimentable caseins and whey proteins were higher compared to the control and MCP-enriched skim milk samples. The influence of MCP adjustment on gelation was dependent on pH. Acid gels from sample MCP67 exhibited the highest storage modulus (G'). At other pH levels, MCP100 resulted in the greatest G'. The pH of MCP-adjusted skim milk also impacted the gel properties after heating. Overall, this study highlights the substantial impact of MCP content on the acid gelation of milk, with a pronounced dependency of the MCP adjustment effect on pH variations.

Process optimization for the production of fibrinolytic enzyme by a novel marine fungus – Penicillium steckii KU1

The demand for microbial thrombolytic agents is alarmingly increasing, and the discovery of novel microbial species with significant level of fibrinolytic enzyme production are required to cope up with the current circumstances. Surprisingly, marine fungi remain largely unexplored in this regard, presenting an untapped potential for the production of fibrinolytic enzymes.A novel marine fungal strain (Penicillium steckii KU1) was isolated successfully from Kappil beach, Kerala. At the beginning Czapek-dox media was used for the production of fibrinolytic enzyme. Statistical optimization of the enzyme production was achieved initially by Plackett-Burman design (PB). Interactive effect of various process parameters was further scrutinized by Central Composite Design (CCD). Incubation time, inoculum size and concentration of casein were shown significant contribution towards production. Statistical optimization, resulted in a tenfold increment (454.49 ± 14.66 U/mL) [optimized conditions - 30 °C, pH 7, casein 2.7 % (w/v), inoculum 5.75 million spores/mL and 115 h incubation], against the predicted value 441.42 U/mL.

New generation of functional yogurts fermented with probiotic lactic acid bacteria isolated from human milk

Background: The cultures used in the production of "bio-yoghurts" typically consist of a blend of traditional yogurt starters, such as S. thermophilus and L. delbrueckii subsp. bulgaricus, along with probiotics like L. acidophilus, L. casei, L. reuteri, and Bifidobacterium spp. These probiotics, although beneficial, face challenges thriving in milk due to its short fermentation time (4–5 hours). The rapid acidification caused by the starter’s results in probiotic levels dropping below the "therapeutic minimum" during the intended refrigerated shelf life of the product. A potential solution to this issue lies in leveraging lactic acid bacteria isolated from the human milk which possess both robust probiotic characteristics and starter properties. Incorporating such strains in yogurt starter could address the acidity imbalance and contribute to maintaining optimal probiotic levels throughout the refrigerated shelf life of the product. Objective: This research aims to develop a new generation of sustainable functional yoghurts suitable for consumers of all ages using as starters predominant probiotic lactic acid bacteria isolated from the breast milk of healthy women. Results: This study marks the first implementation of the critical dilution culture method in sterile cow milk for the selection of predominant lactic acid bacteria (LABs) from women's breast milk. Remarkably, all samples yielded LAB capable of independently fermenting milk. Although breast milk is a good medium for the growth of residential lactic acid bacteria, it never coagulates due to low concentration of caseins. The isolated strains, identified as belonging to the species L. delbrueckii subsp. lactis, L. fermentum, L. casei subsp. sakei, Streptococcus thermophiles and Lactococcus lactis, exhibited probiotic and adaptive properties essential for gut colonization in humans. Utilizing symbiotic LAB starters were created functional yogurts with heightened technological, physicochemical, and sensory characteristics. Conclusions: Yogurts fermented using human milk LABs are safe and can be recommended as a functional dairy food, for pregnant women as well as for pre-term and full-term infants as a substitute/supplement for mother's milk. Moreover, these LABs can be included in infant formulas or used in pre-treatment of infant formula milk to improve its nutritional value and safety. Keywords: Breast milk, lactic acid bacteria, probiotic, milk fermentation, functional yogurt

Structural Properties of Casein Micelles with Adjusted Micellar Calcium Phosphate Content.

Micellar calcium phosphate (MCP) content of skim milk was modified by pH adjustment followed by dialysis. Turbidity, casein micelle size and partitioning of Ca and caseins between the colloidal and soluble phases of milk were determined. Protein structure was characterised by Fourier transform infrared (FTIR) spectroscopy and proton nuclear magnetic resonance (1H NMR), whereas organic and inorganic phosphorus were studied by phosphorus-31 nuclear magnetic resonance (31P NMR). The sample with the lowest MCP content (MCP7) exhibited the smallest particle size and turbidity, measuring 83 ± 8 nm and 0.08 ± 0.01 cm-1, respectively. Concentrations of soluble caseins increased with decreasing MCP levels. At ~60% MCP removal, FTIR analysis indicated a critical stage of structural rearrangement and 31P NMR analysis showed an increase in signal intensity for Ca-free Ser-P, which further increased as MCP concentration was further reduced. In conclusion, this study highlighted the importance of MCP in maintaining micellar structure and its impact on the integrity of casein micelle.

Casein micelle formation as a calcium phosphate phase separation process: Preparation of artificial casein micelles through vacuum evaporation and membrane processes

Industrial-scale production of artificial casein micelles (ACM) is required to produce dairy alternatives from recombinant casein. However, the currently common micelle preparation method of dropwise mixing casein and salt solutions is inefficient and may prove difficult to scale up. Here, we view casein micelle formation as a process driven by calcium phosphate phase separation in the presence of casein. On this basis, we developed novel routes to prepare ACM through vacuum evaporation, forward osmosis, or reverse osmosis. ACM prepared through these methods have similar properties and improved coagulation behaviour compared to those prepared through the currently common method and natural bovine casein micelles. The properties and functionality of the micelles depend on the preparation time and surface area available for micelle formation, with longer times and larger surfaces (i.e. lower fluxes) yielding smaller ACM that form firmer curds. These novel processes enable fast, efficient, and continuous production of ACM for application in future dairy alternatives. Industrial relevanceArtificial casein micelles can be used as a building block in the production of animal-free milk and cheese based on precision fermentation. The herein described novel processes to prepare artificial casein micelles are based on vacuum evaporation, forward osmosis, and reverse osmosis, which are mild, resource-efficient, and easily scalable processes. The processes require a dilute feed stream (e.g. caseins after precision fermentation), provide an elegant way to minimise local differences in the concentration of caseins and ions during micelle production, and offer the opportunity to design continuous micelle formation processes. These are all advantages over the existing methods to prepare artificial casein micelles with regard to industrial application.

The Biocompatibility and Self-Healing Effect of a Biopolymer’s Coating on Zn Alloy for Biomedical Applications

The objective of this study was to formulate dip coatings, incorporating casein, NaOH, and nanocrystalline hydroxyapatite (nanoHAp), with self-healing properties for application on ZnMg3.2 wt.% alloy in the field of biomedical applications. This study hypothesizes that the self-healing mechanism within the layer will impede substrate degradation by progressively filling defects where chlorides from simulated body fluids intervene. Furthermore, it aims to mitigate potential damage effects during the implantation process by the layer’s self-healing capabilities. The research focused on the dip-coating process parameters and chemical composition of baths for producing casein coatings on Zn alloy surfaces. This study investigated the impact of casein and NaOH concentration, along with the immersion time of ZnMg3.2 wt.% samples in the coating bath, on the self-healing capability of the coating under simulated human body fluid conditions (Ringer’s solution, temperature: 37 °C). Effective technology was developed by selecting specific chemical compositions and immersion times in the coating bath, enhancing the self-healing progress against coating damage in Ringer’s solution at 37 °C. The most significant self-healing effect was observed when the ZnMg3.2 wt.% substrate underwent a 1 h immersion in a coating bath containing 2 g of casein, 4 g of NaOH, and 0.1 g of nanoHAp powder. Electrochemical tests were instrumental in determining the optimal casein concentration and immersion time of the Zn alloy in the coating bath.

Modulation of Swine Gut Microbiota by Phytogenic Blends and High Concentrations of Casein in a Validated Swine Large Intestinal In Vitro Model.

Phytogenic feed additives are gaining popularity in livestock as a replacement for antibiotic growth promotors. Some phytogenic blends (PB) positively affect the production performance, inhibit pathogens within the gut microbiota, and improve the overall health of farm animals. In this study, a swine large intestine in vitro model was used to evaluate the effect of two PBs, alone or in combination with casein, on swine gut microbiota. As a result, the combination of casein with PB1 had the most beneficial effects on swine gut microbiota, as it increased the relative abundance of some commensal bacteria and two genera (Lactobacillus and Oscillospiraceae UCG-002), which are associated with greater production performance in pigs. At the same time, supplementation with PBs did not lead to an increase in opportunistic pathogens, indicating their safety for pigs. Both PBs showed fewer changes in swine gut microbiota compared to interventions with added casein. In contrast, casein supplementation significantly increased beta diversity and the relative abundance of commensal as well as potentially beneficial bacteria. In conclusion, the combination of casein with PBs, in particular PB1, had the most beneficial effects among the studied supplements in vitro, with respect to microbiota modulation and metabolite production, although this data should be proven in further in vivo studies.

Ethanol-mediated electrospinning of casein-only bead-free nanofibers

Fabrication of electrospun nanofibers by blending casein with electrospinnable polymers and/or additives is well reported. However, the electrospinnablility of pure casein has not been described due to the tendency of casein proteins to self-aggregate and form large colloidal structures. Here we analyze the influence of pH, ethanol content, ionic environment, and casein concentration on the solubility, solution viscosity, surface tension, and conductivity of casein-based spinning dopes. Further, the influence of casein dope characteristics on our ability to electrospin bead-free nanofibers was evaluated. A homogenous dispersion of casein was observed for mixtures with 20 wt % casein prepared using 60 % ethanol/water mixture at pHeth 10. A minimum number of bead defects (BN, 6 × 10−3/μm2) and bead area (BA, 8.7 × 10−2) with minimum average fiber diameter (FD, 424 nm) and porosity (52 %) were observed for casein fibers fabricated using dopes containing 2 wt % of tetrasodium pyrophosphate (TSPP) on a casein basis. Further, the viscosity dependence on casein concentration at constant relative TSPP content was like that expected for a polyelectrolyte, and bead-free nanofibers were obtained at a concentration ∼2.5 times the entanglement concentration (Ce). Our results indicate that micellar dissociation is a necessary condition for the electrospinning of casein-only fibers free of beads and other polymers to fabricate novel biodegradable, and biocompatible, casein-based nanostructured mats, with the potential for food, cosmetic, packaging, and biomedical applications.

Experimental study on the mechanical behavior of EICP-casein-treated calcareous sand

In order to protect and develop marine resources, it is essential to reinforce the calcareous sand foundation on coral reefs during engineering construction. This study proposes a novel approach that combines enzyme-induced carbonate precipitation (EICP) with casein to solidify calcareous sand, which overcomes the issues of low calcium carbonate crystallization and insufficient cementation strength encountered in the pure EICP method. This study investigated the reinforcement effects and mechanisms of the combined method across various scales. Sonic time testing revealed an initial decline in sample density followed by a gradual increase, with the lowest density observed at 10% casein content. Sample strength depends on casein dosage and curing time. Overall, the trend in sample strength showed an initial decrease followed by a gradual increase, with 10% casein content again resulting in the lowest strength. The measured experimental groups achieved a minimum strength of approximately 1.17 MPa and a maximum strength of around 6.34 MPa. As casein concentration rises, the optimal curing time increases from 12–48 h. Microscopic experiments reveal casein expansion and dissolution in the EICP liquid, explaining UCS value changes with casein dosage and curing time. Combining scanning electron microscopy and microscopic experiments highlights the cementitious material’s vital role in strengthening samples. In conclusion, combining EICP and casein for solidifying calcareous sand is technically feasible and highly effective with significant reinforcement effects.

Quantitative Determination of Casein and Lactose in Processed and Unprocessed Milk Samples from Ogwashi-Uku, Delta State

Milk is one of the most important nutritional constituent of our diet because it is largely composed of proteins and along with vitamins and minerals. This present study was based on determining the amount of casein and lactose present in processed (Dano cool cow and Peak milk) and unprocessed milk (Cow and Goat milk) samples collected from Ogwashi-uku, Delta State. The casein content was analyzed using Kjeldahl method and lactose content was analyzed using Benedict’s Method. Results from this study shows that cow milk sample; an unprocessed form of milk has more lactose content (40.298%) than other forms of milk while Dano cool cow milk, a processed milk has more casein (23.93%) as compared to all other milk. High concentration of casein is more beneficial to health and high percentage of lactose do not poses no threat as it can be digested easily.

The effect of calcium removal from skim milk by ion exchange on the properties of the ultrafiltration retentate

New processes are needed to produce concentrated milk feedstocks with tailored calcium content, due to the direct link between calcium concentration and final product texture and functionality. Skim milk treatment with cation exchange resin 1% (w/v) or 2% (w/v) prior to ultrafiltration to a volumetric concentration factor (VCF) of 2.5 or 5 successfully decreased the calcium concentration by 20–30% and produced concentrates with solids content at ∼22–24 g 100 g−1 at a VCF of 5. Calcium reduction partially solubilized the casein micelles, increasing the concentration of soluble protein and individual caseins, leading to decreased turbidity but increased protein hydration and hydrophobicity. Decalcification (2% (w/v) resin treatment) reduced thermal stability, significantly decreasing the denaturation temperature of α-lactalbumin and β-lactoglobulin in the milk by ∼3 °C and ∼1 °C respectively. Filtration was also altered, reducing permeation flux and the gel concentration and increased filtration time. When combined, calcium reduction and filtration altered functional properties including soluble calcium, soluble protein and sedimentable solids, with increased milk protein hydration also contributing to increased viscosity. This study provides a route to produce calcium-reduced milk concentrates with potential for use in retentate-based dairy products with tailored functionality.

Purification Scheme and Biochemical Profile of Metallo-alkaline Protease Produced by B.t. Dendrolimus IP 4A/4B

Objective: Purify and classify alkaline protease (AP), produced by Bacillus thuringiensis (B.t.) dendrolimus 4A/4B. Methods: Inoculum preparation, production media, enzymes assays, protein determination, ammonium sulfate precipitation, acetone fractionation, Sephadex Gel chromatography filtration. Results: The purification scheme, (a) ammonium sulfate fractionation, the most active fraction with 1.93 purification fold was at 60-75% saturation; (b) acetone precipitation, where the most active fraction was at 30-45% with purification fold of about 3.92 times; (c) Column chromatography on G-100 Sephadex with final purification folds 5.36 times of the crude enzyme with final yield recovery 1.9%. Purified AP showed stability against H2O2 1%, 5% and 10% (v/v), and retained 111%, 101% and 66% of its activity, respectively. AP retained 82%, 87% and 101% of its activity with 10, 5 and 1mM PMSF, respectively. Enzyme activity was completely inhibited by 10mM EDTA, while the enzyme retained about 125% of its activity with 10mM Mercapto-ethanol. CaCl2 and MgCl2 (10mM) showed activation effect, increasing the activity to 136% and 147% compared to the control, respectively. The optimum pH are 8.0 and 10.0. AP activity was increased through 30ºC to 50ºC. At 60˚C, the enzyme retained ~48% of its original activity. AP concentration 0.014mg protein/mL has maximum activity (6.750U/mL/min). The highest maximum velocity (Vmax) was 31.821μg tyrosine/mL/min. Km value 0.833%, w/v casein concentration. Conclusion: Thus, this inhibition profile suggested that the AP produced belongs to the class of metalo-proteases.

Polymorphism at the CSN1S1 Locus and Energy Intake Level Affect Milk Traits and Casein Profiles in Rossa Mediterranea Goats.

A total of twenty-seven Rossa Mediterranea lactating goats, consisting of nine homozygous for strong alleles (AA), twelve heterozygous (AF) and six homozygous for weak alleles (FF) at the CSN1S1 locus, were used to evaluate the effect of genotype, diet and genotype × diet interaction on goat milk traits and casein profile. The goats were used in a 3 × 3 factorial arrangement of treatments, with three genotypes (AA, AF and FF) and three different energy intake levels: high (H), medium (M) and low (L). The diets supplied a complete pelleted feed containing 65% of alfalfa hay, respectively, at 150%, 100% and 70% of the total energy requirements. Milk yield was significantly affected by the genotype and diet: Lower levels were found in FF goats than in AA and AF genotypes (673.7 vs. 934.5 and 879.8 d/g, respectively; p = 0.002) as well as in goats fed with the L diet (651.5 vs. 1041 and 852.9 g/d for H and M diet, respectively, p < 0.001). The genotype influenced the casein profile. Specifically, AA goat milk exhibited higher concentrations of total casein and αs1-casein compared to AF and FF genotypes (for total casein and αs1-casein, respectively: 24.9 vs. 20.4 and 19.8 g/kg, p = 0.001; 7.2 vs. 3.7 and 0.7 g/kg, p < 0.001), while the FF genotype showed higher values for αs2-casein concentrations compared to homozygous AA and heterozygous AF goats (3.1 vs. 2.4 and 2.5 g/kg, respectively, p < 0.001). A significant genotype x diet interaction occurred for αs2-casein levels (g/kg) (p = 0.034) and αs1-casein yields (p = 0.027): The αs2-casein level was not affected by the diet in AA goats, whereas it increased with energy intake in AF and FF genotypes. Conversely, the αs1-casein yield gradually increased with energy intake in AA and AF groups, whereas the diet in FF goats did not modify it. The results demonstrated that high energy input, as well as the strong allele at the CSN1S1 locus, enhanced milk production and casein concentrations. Furthermore, they confirmed the existence of an interaction between αs1-casein polymorphism and diets, influencing the milk casein composition and yield.

Acid gelation functionality of casein micelles in concentrated state: Influence of calcium supplementation or chelation combined with enzymatic stabilization

The main structure-building component in gelled dairy products is the casein micelle (CM). It was previously shown that in concentrated state of CMs, the changes of their compositional and colloidal properties in response to the addition or chelation of calcium divers from the reactions at milk-like casein concentration. This study aimed to evaluate the relationship between these specifically induced properties of CMs and the acid gelation functionality of a micellar casein concentrate (MCC). A covalent stabilization of the structures of pre-modified and native CMs by treatment with transglutaminase (Tgase) prior to acidification with glucono-δ-lactone was additionally tested. During acidification, structure formation was monitored in a rheometer to gain insights on mechanistic changes in the course of structural changes during acidification compared to gelation of unmodified MCC. Gelation pH, gel firmness, and serum binding capacity were analyzed to characterize gel structures at a final pH of 4.6. The structure formation process was highly affected by prior changes in composition, integrity, and structural stabilization of CMs. Gelation pH and acid gel firmness were reduced by ionic strength. Thermal and Tgase treatment induced opposing effects, leading to compensation when combined with prior salt supplementation. A synergistic increasing effect on serum binding capacity was found for trisodium-citrate supplementation and subsequent Tgase treatment. New mechanistic insights on acid gel structure formation progression were gained. This study provides a better insight into the relationship between structural CM properties prior to acid gelation and the resulting acidification progress, as well as the final acid gel properties.

Effect of microbial transglutaminase on functional, rheological, and structural properties of lentil protein-casein binary gels

In recent years, various strategies have been introduced to partially substitute animal proteins with plant proteins. This study applied microbial transglutaminase (MTGase) to crosslink lentil protein isolate (LPI) and casein. The gel mixtures prepared using different LPI-casein ratios (4:0, 3:1, 2:2, 1:3, 0:4), and the structural, gelation characteristics of these hetero-mixtures were investigated. SDS-PAGE showed the bands of vicilins (∼50 kDa), and 11S acidic subunit (∼40 kDa) almost disappeared and partly 11S basic subunit (20 kDa) involved in the polymerization, whereas almost all the bonds of casein were involved in the MTGase-induced gelation process. With the increasing concentration of casein, LPI-casein binary gels presented enhanced mechanical textural properties (increased from 284.83 to 1128.33g of hardness), rheological properties (increased from 105.8 to 4405 Pa of storage modulus), water holding capacity (increased from 63.86 to 98.82%) and more homogeneous and compact microstructural properties (CLSM, SEM) as a result of homologous and heterologous crosslinking mediated by MTGase. Interestingly, gels prepared by partial casein replacement (by 25% LPI) had similar textural, water holding capacity, and microstructural properties to those prepared by casein-alone gels, demonstrating the possibility of successfully replacing casein with 25% LPI in MTGase induced system. This study presents a new interaction strategy mediated by MTGase for LPI and casein binary system to greatly enhance their gelation performance, as well as the potential of LPI in substitute dairy to formulate diversified food products.

Hybrid metasurface using graphene/graphitic carbon nitride heterojunctions for ultrasensitive terahertz biosensors with tunable energy band structure

Integrating novel materials is critical for the ultrasensitive, multi-dimensional detection of biomolecules in the terahertz (THz) range. Few studies on THz biosensors have used semiconductive active layers with tunable energy band structures. In this study, we demonstrate three THz biosensors for detecting casein molecules based on the hybridization of the metasurface with graphitic carbon nitride, graphene, and heterojunction. We achieved low-concentration detection of casein molecules with a 3.54 ng/mL limit and multi-dimensional sensing by observing three degrees of variations (frequency shift, transmission difference, and phase difference). The favorable effect of casein on the conductivity of the semiconductive active layer can be used to explain the internal sensing mechanism. The incorporation of protein molecules changes the carrier concentration on the surface of the semiconductor active layer via the electrostatic doping effect as the concentration of positively charged casein grows, which alters the energy band structure and the conductivity of the active layer. The measured results indicate that any casein concentration can be distinguished directly by observing variations in resonance frequency, transmission value, and phase difference. With the heterojunction, the biosensor showed the highest response to the protein among the three biosensors. The Silvaco Atlas package was used to simulate the three samples’ energy band structure and carrier transport to demonstrate the benefits of the heterojunction for the sensor. The simulation results validated our proposed theoretical mechanism model. Our proposed biosensors could provide a novel approach for THz metasurface-based ultrasensitive biosensing technologies.