Protein Gel Formation Research Articles

Effect of NaCl replacement by other salt mixtures on myofibrillar proteins: Underlining protein structure, gel formation, and chewing properties.

The protein structure, gel changes, and chewing properties of low-sodium myofibrillar protein (MP) prepared by compound chloride salts (KCl/MgCl2, KCl/CaCl2, and KCl/MgCl2/CaCl2) and different substitution degrees (10%, 25%, and 40%) at same ionic strength (0.6M) were investigated. The results revealed that the low-sodium MP gels containing CaCl2 manifested more liquid loss and less moisture content accompanied by obvious morphological shrinkage, while KCl/MgCl2 contributed to the gel juiciness. At high substitution degree of 40%, KCl/CaCl2 substitution rendered the gel with dense structure and highest strength, but worse water retention capacity. Using other compound chloride salts influenced the chewing efficiency, and CaCl2 substitution made the gel relatively hard to chew. The inhomogeneous structure accompanied by cluster blocks in KCl/CaCl2-substituted MP gel accelerated the overall fracture rate. During heating process, more proteins in CaCl2-substituted MP did not participate in gel formation, intervening the final gel properties. The chloride salt mixtures containing MgCl2, rather than CaCl2, avoided or alleviated the liquid loss and shrinkage of low-sodium MP gel within the substitution degree of 10%-40%, and substitution degree not exceeding 25% was more reasonable for the controlled qualities.

Soft Ca2+-induced pea protein gels through mild heating: Controlling elasticity and fracturing behavior

With the rising demand for plant-based protein, understanding the formation of pea protein gels induced by calcium is important for manufacturing of food products with appealing textural properties. Moreover, the moderate temperature processing is becoming of greater and greater interest, based on conditions used for food fermentation. The objective of this study is to understand the structural and rheology behaviour of calcium-induced pea protein aggregates at moderate plateau temperatures i.e. in the range 30–45 °C with holding times from 0 to 60,000s. Based on the combination of confocal fluorescence microscopy (CLSM) imaging, rheology and IR spectroscopy, our results show that despite the relatively low temperature range, thermal agitation not only allows for partial protein particle dissolution, but also induces interactions leading to soft gel formation. Within a shorter holding time (0–600s) range, higher Gʹ/Gʹ0 (t) were observed at 40 °C and 45 °C, the end elastic modulus reaching for any parameters tested at least 1000 Pa. As the holding time was extended to 60,000s, the effect of temperature became less pronounced, i.e., all gels reached similar high values of Gʹ even for the low temperature of 30 °C, which is nearly 3–4 times higher than that formed at 600s holding time (at the temperature plateau). IR spectroscopy measurements showed that the protein secondary structure remained stable within the holding time ranging from 0s to 6,000s, while significant but moderate changes were monitored when extending the holding time to 60,000s, which correlated with a more progressive yielding observed in rheology, pointing to the formation of apparently more fragile physical gels. The combination of the techniques shows that the gel formation and strengthening mainly originated from rearrangements at the colloidal level leading to a denser network, while molecular rearrangements only intervened at the longest holding times (i.e, 60,000s).

Formation and characterization of cold-set whey protein gels induced by L-ascorbic acid/calcium for their encapsulation and release

Protein cold-set gels are potential carriers for the encapsulation of bioactive compounds. Meanwhile, bioactive compounds have also been used as cross-linkers or accessories for protein gelation, but their encapsulation has not been investigated during gelation for potential nutritional value. In this study, cold-set gels of whey protein isolate (WPI) were induced by L-ascorbic acid (L-AA) at pH 4.0–6.0, L-ascorbic acid plus CaCl2 at pH 3.8, or L-ascorbic calcium at pH 7.0. The range of pH for WPI gelation induced by L-AA narrowed with the decrease of WPI content from 10% to 6% (w/v). The gel networks were stabilized by non-covalent and covalent interactions, which difference was dependent on the use of cross-linkers. L-Ascorbic recoveries were above 76% in WPI hydrogels, where the highest recovery reached 98%. L-Ascorbic encapsulation efficiency ranged from 69% to 100%. Hydrogels and cyrogels varied from a smooth and dense structure to a coarse structure. L-ACa at 16 mM induced uniform and compact structure of both gels and the highest hardness and storage modulus of hydrogel. L-Ascorbic groups were effectively immobilized into WPI gels via their interaction with whey protein and calcium. L-Ascorbic loading capacity in WPI hydrogels and gel powder increased as the pH decreased and its calcium concentration increased. The release of free L-ascorbic acid from gel powder was independent on protein re-hydration. These results suggest the potential use of protein cold-set gels for the encapsulation and delivery of bioactive compounds with themselves or their combination with calcium as cross-linkers.

Optimizing gelation properties of mixed meat myofibrillar proteins: investigating the effects of different proportions of beef, pork and chicken on physicochemical, structural and gelation properties.

The gelation properties of myofibrillar protein (MP) directly affect the texture, taste and water-holding capacity (WHC) of meat products. To enhance the gelation properties of single-species meat MP, the present study investigated the influence of different proportions of beef, pork and chicken MP on the physicochemical properties, structure and gelation properties of the MP. The results revealed that, when the proportion reached 5:2:3, the particle size decreases, leading to the maximum decomposition and unfolding of MPs, which exposes a greater number of hydrophobic amino acid residues. These changes promote interactions between protein molecules, especially the unfolding of α-helices and the formation of β-sheets during the heating process, which provides favorable conditions for the formation of protein gels and improves the gel strength and WHC of MP gels. Additionally, scanning electron microscopy revealed that the mixed MP gels are more compact and have more uniform gel networks and pores compared to single-species MP gels. Based on these results, the synergistic effect is induced by the interactions between proteins from different. This research provides a method for the subsequent development of new meat products and improvement of meat product quality, and also lays a theoretical foundation for composite research of proteins from different sources. © 2024 Society of Chemical Industry.

Tracking protein aggregation behavior and molecular interactions induced by conformational alterations in the formation of myofibrillar protein-Abelmoschus manihot gum mixed gels during heating process

The present study aimed to systematically investigate the effects of different Abelmoschus manihot gum (AMG) concentrations (0–0.5%, w/w) on the formation of myofibrillar protein (MP) gels during heating process (30–80 °C) based on conformational alterations, protein aggregation behavior and molecular interactions. With the increase of temperature, the fluorescence intensity and α-helix content significantly decreased, revealing conformational transition of MP molecular. Dynamic rheological results indicated that MP had completely denatured and formed temporary gel at 50 °C, and completely formed irreversible cross-linked three-dimensional network structure at 80 °C. Moreover, the addition of AMG decreased the fluorescence intensity, as well as induced the transition of MP from α-helix to β-sheet during the whole heating process. Furthermore, AMG addition significantly decreased the turbidity and improved solubility of MP (P < 0.05), especially for at 0.3% AMG concentration, indicating that AMG accelerated the early unfolding and aggregation of MP during heating process. This was verified by the dynamic rheological results. Additionally, hydrophobic interactions and disulfide bonds were the main molecular forces to induce the formation of MP-AMG mixed gel. Therefore, our present results provided the new insights into the formation of MP-AMG mixed thermal-induced gel, and also contributed to the practical application of AMG in meat processing.

Development and Characterization of Hybrid Meat Analogs from Whey Protein-Mushroom Composite Hydrogels.

There is a need to reduce the proportion of animal-derived food products in the human diet for sustainability and environmental reasons. However, it is also important that a transition away from animal-derived foods does not lead to any adverse nutritional effects. In this study, the potential of blending whey protein isolate (WPI) with either shiitake mushroom (SM) or oyster mushroom (OM) to create hybrid foods with enhanced nutritional and physicochemical properties was investigated. The impact of OM or SM addition on the formation, microstructure, and physicochemical attributes of heat-set whey protein gels was therefore examined. The mushroom powders were used because they have relatively high levels of vitamins, minerals, phytochemicals, and dietary fibers, which may provide nutritional benefits, whereas the WPI was used to provide protein and good thermal gelation properties. A variety of analytical methods were used to characterize the structural and physicochemical properties of the WPI-mushroom hybrids, including confocal microscopy, particle electrophoresis, light scattering, proximate analysis, differential scanning calorimetry, thermogravimetric analysis, dynamic shear rheology, textural profile analysis, and colorimetry. The charge on whey proteins and mushroom particles went from positive to negative when the pH was raised from 3 to 9, but whey protein had a higher isoelectric point and charge magnitude. OM slightly increased the thermal stability of WPI, but SM had little effect. Both mushroom types decreased the lightness and increased the brownness of the whey protein gels. The addition of the mushroom powders also decreased the hardness and Young's modulus of the whey protein gels, which may be because the mushroom particles acted as soft fillers. This study provides valuable insights into the formation of hybrid whey protein-mushroom products that have desirable physiochemical and nutritional attributes.

Insight into the mechanism of the aggregation behavior of wheat protein modulated by l-lysine under microwave irradiation.

This study explored the mechanism of l-lysine intervention in wheat gluten protein (WG) gel formation under a microwave (MW) field. The results showed that the MW treatment had higher ζ-potential values at the same heating rate. After adding l-lysine, the solution conductivity and dielectric loss were significantly increased. Moreover, the WG gel strength enhanced 4.40% under the MW treatment. The Fourier spectra showed that the α-helix content was decreased 13.78% with the addition of lysine. The ultraviolet absorption spectra and fluorescence spectra indicated that MW irradiation impacted the interactions between WG molecules more effectively than the water bath heating, promoting the denaturation and unfolding of the protein structure. In addition, scanning electron microscopy analysis showed that the incorporation of lysine promoted an ordered network structure formation of the protein, which enhanced the gel properties. This indicated that the zwitterion of l-lysine played a regulatory role in the aggregation of proteins in the MW field.

Underlying the mechanisms of incorporation of κ-carrageenan on the formation of low-salt myofibrillar protein gels during heating process: Perspective on the dynamic changes of protein structures and molecular interactions

This study aimed to systematacially investigate the effects of κ-carrageenan (KC) concentration on the formation of myofibrillar protein (MP) gels under low-salt condition based on the dynamic changes of protein structures and molecular interactions during heating process. The results indicated that incorporating KC markedly improved the water holding capacity (WHC) and gel strength of MP gels (P < 0.05). Those properties were most improved by adding 0.4% KC with WHC of 71.44% and gel strength of 1.62 N. During the heating process, when the temperature was above 50 °C, KC addition significantly increased the turbidity and particle size and decreased solubility of MP in a concentration-dependent manner, as well as exhibiting higher surface hydrophobicity at 0.2% KC concentration (P < 0.05), indicating that KC accelerated the rate of aggregation of MP during heating process. The dynamic rheological behaviors indicated that the addition of KC promoted the early unfolding and aggregation of MP at a relatively lower temperature, which was verified by the fluorescence denaturation mechanism results. Moreover, the addition of KC significantly promoted the heat-induced conformational transition of MP from α-helix companied with β-sheet and β-turn, which was due to the interaction between MP and KC accelerating the formation of MP gels during the heating process. Intermolecular forces results revealed that the aggregation of myosin head and cross-linking of myosin tail of MP added KC was enhanced by ionic bonds, hydrophobic interactions, and disulfide bonds, which facilitated the better gel performance. Our present results provided a comprehensive understanding of gelation mechanism of MP-KC mixed gels under low-salt condition, with implications for the practical application of KC in meat processing.

Preparation of soy protein isolate-naringin-chitosan protein gel: Synergistic effect of ohmic heating pre-treatment and chitosan addition

Soybean protein isolate (SPI)-Naringin (Nar) complex pre-aggregates were prepared by ohmic heating (OH) and protein gels were formed by adding chitosan (CS). The properties of the pre-aggregate, gel rheological properties, texture, and water holding capacity (WHC) were evaluated. For the properties of the SPI-Nar pre-aggregate, under an OH treatment of 6 V/cm, the α-helix and β-turn structures of the SPI-Nar pre-aggregate were found to be 17.72% and 15.30%, respectively, with a uniform particle size distribution. The surface hydrophobicity, total free sulfhydryl, and turbidity were measured to be 794, 6.54 μmol SH/g, and 0.364, respectively. Atomic force microscopy images showed an Rq value of 3.63 and a height of 14.5 nm. Regarding the properties of the SPI-Nar-CS protein gel, when the CS addition level was 3%, the gel (SPI-Nar-CS 3) exhibited the best rheological properties, with hardness, springiness, and cohesiveness values of 10.17 g, 0.79 mm, and 0.31, respectively. The WHC and LF-NMR analysis of the protein gel revealed that SPI-Nar-CS 3 exhibited a WHC of 90.67% and optimal LF-NMR imaging and apparent state. SEM images showed the best microstructure at this CS addition level. In addition, the synergistic mechanism between the OH treatment and CS addition in protein gel formation was discussed, providing a theoretical foundation for future applications in the food industry.

Heat-induced agglomeration of water-soluble cod proteins toward gelled structures

Cod proteins (CPs) have potential applications in designing desirable gel-based products, and this study aimed to unravel their heat-induced aggregation pattern and further probe the roles in protein gels. SDS-PAGE analysis indicated that high-precipitation-coefficient aggregates (HPCAs) of CPs aggregates were composed of considerable polymers of myosin heavy chains and actin, and their low-precipitation-coefficient aggregates (LPCAs) contained myosin light chains and tropomyosin. Studies from correlation analysis between the structure and aggregation kinetics revealed that the generation of β-sheet and SS bonds were responsible for their spontaneous thermal aggregation induced by heating temperature and protein concentration, respectively. Additionally, as protein denaturation ratio increased, more and larger HPCAs were formed, which was evidenced driving the network formation of protein gels and resulting in higher storage modulus (G') values. These novel findings may be applicable to other animal proteins for better tailoring the manufacturing of muscle gel-based products.

From amino acid analysis to improved gel properties: The role of dl-valine in Landaise goose myofibrillar protein

The impact of exogenous limiting amino acids on protein gel formation was investigated to enhance the gelation properties of Landaise goose myofibrillar protein (MP). Amino acid composition and gel properties were analyzed, and homologous protein modeling and molecular docking techniques were used to simulate binding sites. Valine was identified as the first limiting amino acid. The addition of 0.075 % dl-valine proved optimal to enhance the gel strength (59.5 g) and water retention (76.76 %) of MP gels. Hydrophobic interactions and disulfide bonds were found to be the main forces maintaining conformational stability of the MP-dl-valine gels. The propyl group of dl-valine can form hydrophobic interactions with protein, contributing to stable complexes. DL valine could also strengthen chemical bonds and secondary structure, convert free water to immobile water, and improve the microstructure of the gel. Therefore, valine can be utilized as a nutritional and gel enhancer in Landaise goose meat products.

Viscosity, mixing regime and power consumption analysis during enzymatic hydrolysis of fish (Sardina pilchardus) processing by-products, through development of power number and Reynolds number correlations

The influence of processing conditions on fluid rheology and mixing regime is of considerable importance during enzymatic hydrolysis of fish processing by-products. Solids concentration ranging from 30 to 70 % (wet basis) and mixing speed from 100 to 400 rpm were investigated, with apparent viscosity, power consumption, power number (Np) and Reynolds number (Re) as response variables of interest. The fish processing by-products at different solids concentration showed power-law pseudoplastic behaviour. Apparent viscosity ranged from 4.35 to 8.51 mPa·s, and power consumption ranged from 53.0 to 492 W/m3. Np―Re curves showed the typical relationship where Np decreased from 20.4 to 1.99 when Re increased from 425 to 3 317. Poor mixing was observed at high solids concentration and low mixing speed, with cavern formation in the early stages of mixing. Liquefaction of solids led to the disappearance of caverns, resulting in good degree of mixing during the hydrolysis process. Contrary to expectations, our study indicated that liquefaction of solids and reduction in molecular weight of proteins had a significant effect on power consumption more than increase in soluble protein concentration, gel formation and/or emulsion. Liquefaction and molecular weight reduction caused a decrease in fluid viscosity while increase in protein concentration, gel formation and/or emulsion contributed to an increase in viscosity. The net result was a decrease in power consumption from 0 to 60 min of enzymatic hydrolysis. The practical implications of the results presented in this study are that one Np―Re curve can be used for any solids concentration between 30 and 50 %. Beyond 50 %, low degree of hydrolysis, protein recovery and significantly high power consumption are experienced.

Regulation of Protein Flexibility and Promoting the Cod Protein Gel Formation Using Ultrasound Treatment.

In order to obtain a soft-textured protein gel suitable for the elderly, the cod protein gel was prepared by improving the protein flexibility under ultrasound treatment. It has been found that the increase in ultrasonic power, protein flexibility, particle size, ζ-potential, surface hydrophobicity, and α-helix content of preheated cod protein exhibited an increasing trend. The improvement of protein flexibility promoted uniformity and density of the gel network, water retention, and texture properties. The flexibility of preheated cod protein increased to 0.189, the water holding capacity of the gel reached up to 99.41%, and the hardness increased to 49.12 g, as the ultrasonic power level increased to 400 W. Protein flexibility was correlated well with the cohesiveness of the gel. The storage modulus (G') initially decreased and then increased during the heating-cooling process. The attractive forces forming between the flexible protein molecules during cooling in the ultrasound treatment groups promoted protein self-assembly aggregation and formed the cod protein gel. The gel obtained at 100-400 W could be categorized as Level 6─soft and bite-sized according to the International Dysphagia Diet Standardization Initiative (IDDSI) framework, indicating that the cod protein gel has potential as an easy-to-swallow diet for the elderly.

The mechanism of alkali-induced rice protein gel formation: Effect of alkali concentration and temperature

Rice protein (RP) is a high-quality hypoallergenic plant protein, but its extremely poor water solubility makes it difficult to be applied in liquid food systems. Therefore, in-depth exploration of its gel properties is an effective way to broaden the application scenarios of RP. In this work, it was first found that the rate and strength of gel formation by RP at 25 °C strongly depended on the increase in alkali concentration (from 0.05 M to 0.125 M), i.e., alkali concentrations above 0.075 M were sufficient to induce the formation of a stable gel by 10% (w/v) of RP in 0.5 h. Increasing the temperature during alkali-induced RP gel formation (50 °C, 80 °C) greatly increased the rate of gel formation, whereas prolonged (>30 min) heat treatment resulted in liquefaction of the gel. A more in-depth analysis revealed that the alkali was able to depolymerize glutelin within the agglomerates in its native state, thereby forming a gel network among glutelin molecules at lower alkali concentrations (CNaOH = 0.075 M) mainly through hydrophobic interactions. Whereas, higher alkali concentration (CNaOH = 0.125 M) resulted in the rapid transformation of exposed free sulfhydryl groups into disulfide bonds, thus exerting a major contribution to the gel network, followed by hydrogen bonding. Furthermore, the phenomenon of heat-induced gel liquefaction was mainly attributed to the dissociation of glutelin subunits and was accompanied by an increase in the disordered structure of proteins in the amide III region. These findings may provide a scientific basis for the development of rice protein gel foods.

Fabrication of pea protein gels with modulated rheological properties using high pressure processing

High pressure processing (HPP) as a non-thermal food preservation technology has recently received growing interest in protein processing. In the present study, the impact of high-pressure level, treatment time, protein concentration, and sample pH on the pea protein gel microstructure and strength were systematically investigated, as well as the protein conformation study, and the gel rheological and dissolution tests. A minimum of 10% and 15% (w/v) protein concentration was required for self-standing pea protein gel formation under 600 MPa and 300 MPa, respectively, at ambient temperature. The pH played an important role in affecting the gel microstructures and properties using HPP treatment. Particulate gels with compact structures and high mechanical strength up to 130 kPa were obtained at pH 5 mainly stabilized by hydrophobic interactions. Whereas fine-stranded gels mainly stabilized by hydrogen bonding with good elasticity and high water-holding capacity were formed at pH 7. The pH, HPP pressure level, and duration have been modulated to prepare a series of pea protein gels to mimic the texture of jelly, pudding, and tofu products. The tunable capacity using HPP makes pea protein a potential gelling ingredient in a wide range of food applications as a substitute for animal or soy protein. Furthermore, the gels treated with pH-shifting followed by HPP showed high freeze-thaw stability with a minimum syneresis level of 15% after two freeze-thaw cycles, demonstrating their potential to be used in frozen food products. Considering the advantages such as improved nutritional quality and extended shelf life compared to thermal technologies, HPP could be a promising non-thermal technique for the fabrication of pea protein gels with tunable rheological and mechanical properties to meet consumer needs for diversified texture and sensory quality.

Changes in advanced protein structure during dense phase carbon dioxide induced gel formation in golden pompano surimi correlate with gel strength

Changes in protein structure are closely related to gel strength. Dense phase carbon dioxide (DPCD) treatment is an excellent non-thermal food processing method that can be used to induce gel formation in surimi. The sensory, water holding capacity and gel strength of DPCD induced gels are superior to heat-induced gels. Fourier-transform infrared spectroscopy was used to investigate the role of DPCD in the quality of golden pompano surimi gels and changes in protein structure. The intermolecular forces of surimi gels were analyzed in terms of ionic and hydrogen bonds, disulfide covalent and non-disulfide covalent bonds, as well as hydrophobic interactions. Correlation analysis was used to investigate the relationship between the changes in advanced protein structure and gel strength during DPCD-induced gel formation in golden pompano surimi. The results showed that the α-helix and random coil levels of surimi gel were significantly decreased (p &amp;lt; 0.05), while the β-sheet and β-turn content was significantly increased (p &amp;lt; 0.05). The number of ionic and hydrogen bonds in gel proteins decreased significantly (p &amp;lt; 0.05), while the hydrophobic interactions, and disulfide and non-disulfide covalent bonds increased significantly (p &amp;lt; 0.05) after DPCD treatment. Correlation analysis showed that β-sheets, β-turns, hydrophobic interactions, and disulfide and non-disulfide covalent bonds were strongly positively correlated with gel strength, whereas α-helices, random coils, and ionic and hydrogen bonds were strongly negatively correlated with gel strength. Therefore, the α-helix and random coil structures of surimi gels were transformed into β-sheet and β-turn structures after DPCD treatment. Hydrophobic interactions, and disulfide and non-disulfide covalent bonds were the main intermolecular forces during the DPCD-induced gel formation of surimi. Ionic and hydrogen bonds were not the main intermolecular forces. The results provide fundamental data for elucidating the mechanism of DPCD-induced protein gel formation.

Effect of high-pressure homogenization on Ca2+ -induced gel formation of soybean 11 S globulin.

High-pressure homogenization (HPH) is commonly used as a non-thermal processing technique for soybean and soy protein products, and the preparation of soy protein gel products often requires the synergistic effect of HPH and heat treatment. The dissociative association behavior of 11 S is the key to the protein gel formation state. In this study, therefore, 11 S thermal gels were prepared by high-pressure homogenization and co-induction (90 °C, 30 min) (adding Ca2+ to promote gel formation before heat treatment), and the effects of different high-pressure homogenization pressures (0-100 MPa) and co-treatment on the dissociative association behavior of 11 S protein, gel properties, and microstructure of 11 S gels were investigated. The results showed that HPH at higher pressures led to the breaking of disulfide bonds of aggregates and disrupted non-covalent interactions in protein aggregates, leading to collisions between protein aggregates and the reduction of large protein aggregates. High-pressure homogenization treatment at 60 MPa improved the gel properties of 11 S more. The HPH combined with heating changed the binary and tertiary structure of 11 S soy globulin and enhanced the hydrophobic interaction between 11 S molecules, thus improving the gel properties of 11 S. The change in intermolecular forces reflected the positive effect of HPH treatment on the formation of denser and more homogeneous protein gels. In conclusion, high-pressure homogenization combined with heating can improve the properties of 11 S gels by changing the structure of 11 S protein, providing data and theoretical support for soy protein processing and its further applications. © 2022 Society of Chemical Industry.

Functional properties of soybean isolate protein as influenced by its critical overlap concentration

The critical overlap concentration (c*) of soy protein isolate (SPI) was studied at a wide range of temperatures (10–90 °C). Results obtained indicate that temperature and c* were directly proportional. The c* determined experimentally was similar to the theoretical value that was calculated by the inverse of the intrinsic viscosity, [η]. At c*, SPI solutions can be divided into the dilute and semi-dilute regimes. The [η] values were estimated by four semi-empirical equations: the Huggins equation, the Kraemer equation, the Tanglertaibul-Rao equation, and the Oliver-Ward equation, of which the Oliver-Ward equation was found to be the most suitable. The aggregation behavior of the SPI was confirmed by association with the start of molecular entanglement at c*. Turbidity, foam capacity (FC) and foam stability (FS) increased significantly when solutions concentration reached c* at all experimental temperatures. The rheology measurement results indicated onset of gel formation when protein concentration reached c* at 90 °C, which can be considered as the gel formation concentration at that temperature. At concentrations below c*, the SPI solutions were unable to form gels and had much lower water holding capacities (WHC) than gels prepared at c*. These findings suggested that c* was related to a number of functional characteristics of SPI, including FC, FS and WHC, and can be used to estimate the concentration required for protein gel formation.

Effect of reverse osmosis and ultra-high-pressure homogenization on the composition and microstructure of sweet buttermilk

Buttermilk (BM), the by-product of butter making, is similar to skim milk (SM) composition. However, it is currently undervalued in dairy processing because it is responsible for texture defects (e.g., crumbliness, decreased firmness) in cheese and yogurt. One possible way of improving the incorporation of BM into dairy products is by the use of technological pretreatments such as membrane filtration and homogenization. The study aimed at characterizing the effect of preconcentration by reverse osmosis (RO) and single-pass ultra-high-pressure homogenization (UHPH) on the composition and microstructure of sweet BM to modify its techno-functional properties (e.g., protein gel formation, syneresis, firmness). The BM and RO BM were treated at 0, 15, 150, and 300 MPa. Pressure-treated and control BM and RO BM were ultracentrifuged to fractionate them into the following 3 fractions: a supernatant soluble fraction (top layer), a colloidal fraction consisting of a cloudy layer (middle layer), and a high-density pellet (bottom layer). Compositional changes in the soluble fraction [lipid, phospholipid (PL), protein, and salt], as well as its protein profile by PAGE analysis, were determined. Modifications in particle size distribution upon UHPH were monitored by laser diffraction in the presence and absence of sodium citrate to dissociate the casein (CN) micelles. Microstructural changes in pressure-treated and non-pressure-treated BM and RO BM particles were monitored by confocal laser scanning microscopy. Particle size analysis showed that UHPH treatment significantly decreased the size of the milk fat globule membrane fragments in BM and RO BM. Also, pressure treatment at 300 MPa led to a significant increase in the recovery of total lipids, CN, calcium, and phosphate in the BM soluble fraction (top layer) following ultracentrifugation. However, PL were primarily concentrated in the pellet cloud (middle layer), located above the pellet in BM concentrated by RO. In contrast, PL were evenly distributed between soluble and colloidal phases of BM. This study provides insight into the modifications of sweet BM constituents induced by RO and UHPH from a compositional and structural perspective.

Spirulina platensis protein isolate nanoparticle stabilized O/W Pickering emulsions: Interfacial adsorption and bulk aggregation

In this paper, novel food-grade Spirulina platensis protein (SPP) Pickering nanoparticles were obtained using a facile top-down approach of heat-set protein gel formation followed by controlled shearing and high-pressure homogenization. Results showed that nanoparticles not only adsorbed on the surface of oil droplets but also formed aggregation networks in continuous phases by varying nanoparticle concentration (c, 0.5–2 wt%) and oil phase fraction (φ, 30–65 wt%), which had a positive effect on the stability. Supported interfaces and regular polygonal shape deformations were observed in the micromorphology of emulsions when φ exceeded 50 wt%, becoming the more decisive factor of emulsion stability. And there was a significant positive correlation between φ and the recovery rate. Pickering emulsion with 30 wt% φ, stabilized by nanoparticle adsorption and aggregation network without the shared interface, had a recovery rate of 6.57–39.77% for the destroyed aggregation network after suffering 100% strain. While φ increased to 50 wt% or more, emulsions behaved recoverable at a rate of 56.69–73.86% for supported interfaces regardless of broken nanoparticle aggregation networks. Findings from this study on SPP nanoparticles and emulsions were of great significance for the utilization of sustainable microalgae protein in the food industry and would open avenues for rational designing of novel plant-based products in the future.