Effect of ultrasound pre-treatment on formation of transglutaminase-catalysed soy protein hydrogel as a riboflavin vehicle for functional foods

Effect of transglutaminase cross-linking on the structure and emulsification performance of heated black bean protein isolate

BACKGROUND

Transglutaminase (TGase) is a heat-resistant biocatalyst with strong catalytic activity, which functions effectively under moderate temperature and pH conditions, and is used widely in protein cross-linking and recombination. Transglutaminase cross-linking is a novel and specific modification method for black bean protein isolate (BBPI). This article investigates the effect of transglutaminase cross-linking on the structure and emulsification performance of heated BBPI.

RESULTS

Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) analysis showed that heated BBPI with TGase had a higher molecular weight than heated BBPI without TGase, and the protein bands widened with increasing enzyme activity, indicating that TGase cross-linking promoted protein molecule aggregation. A high molecular weight polymer can better stabilize the oil-water interface, preventing the emulsion from layering. Fourier transform infrared (FTIR) spectroscopy showed that the α-helix content decreased from 15.64% to 13.75%, and the β-sheet content increased from 48.13% to 54.08%. The decrease in α-helix content and increase in β-sheet content could make the structure more stable and improve the emulsifying properties of heated BBPI. When TGase was 20 U g-1, the protein emulsification activity index (EAI) reached its highest value of 1.87 m2 g-1, and the emulsification stability index (ESI) value was 0.27 min (P < 0.05); these figures were 0.19 m2 g-1, and 0.07 min higher, respectively, than in the sample without added TGase.

CONCLUSION

In summary, transglutaminase cross-linking has a positive effect on the structure and emulsification performance of heated BBPI and can be used as an effective method for BBPI modification. © 2024 Society of Chemical Industry.

Development and characterization of bigel systems as carriers for thyme essential oil utilizing hydrogel from chicken processing by-products for food applications

A chicken protein hydrogel (HG) was enzymatically prepared and blended with a carnauba wax-based oleogel (OG) to form bigels (BG) in ratios of 50:50 to 90:10. These systems were infused with thyme essential oil (TEO) at 0.5 %, 1 %, and 2 % v/v to harness its antioxidant properties. Polarized light microscopy revealed that carnauba wax crystals were tightly arranged in thin, plate-like structures, while the HG exhibited a completely amorphous form. FT-IR analysis indicated that OH bonds in the HG and CH bonds in cycloalkanes from the OG contributed to the stability and strength of the gels. Unlike the biphasic gels, both the OG and HG samples experienced structural disintegration when the applied strain reached approximately 30 %. HG samples, with an onset melting temperature of 59.18 °C, were particularly susceptible to thermal deformation, leading to coalescence and destabilization of the BG due to the HG phase in the composite matrix. Regardless of the TEO concentrations, the BG (50:50) demonstrated the highest water-holding capacity (60.83 %), and oil-binding capacity (99.23 %) compared to the single biopolymer gels. The lightness of the BG increased as the HG ratio increased. Additionally, the antioxidant capacity increased with higher TEO concentrations, demonstrating the gels' potential for food applications.

Vanillin strengthened complex coacervation behavior between gelatin and sodium carboxymethyl cellulose endowed improved mechanical properties of microcapsules

The inherent heterogeneous structure of biomass molecules usually makes the formed interfacial film prone to defects such as core material mass transfer loss, while chemical modification may be an effective means to improve the performance of biobased interfacial films. In this study, gelatin‑sodium carboxymethyl cellulose (CMC-Na) complex coacervation microcapsules were used as models and the typical aroma molecule vanillin as modifier to explore the differences in mechanical properties and other physicochemical properties of microcapsules before and after modification, as well as the potential mechanism of the differences. Results showed that the aldehyde group of vanillin formed covalent imine bond with the amino group on gelatin protein through Schiff base reaction, and the hydroxyl group on the benzene ring of vanillin formed hydrogen bonds with CMC-Na and gelatin simultaneously; these two effects were synergistically enhanced cross-linking between wall materials, thereby strengthening the mechanical properties of the microcapsules. The rupture force of microcapsules with 0.5 % vanillin was 36.60 % higher than that of blank microcapsules. In summary, this study used aroma compounds to modify biomass macromolecules, which provided a new idea for strengthening the physicochemical properties of bio-based microcapsules.

Development of soybean protein-based bioactive substances delivery systems: A systematic overview based on recent researches

Some bioactive substances in food have problems such as poor solubility, unstable chemical properties and low bioavailability, which limit their application in functional foods. In recent years, in order to improve the above problems of bioactive substances, soybean protein-based drug delivery systems have been developed. This article reviewed the structure and properties of several major soybean protein commonly used to construct bioactive substance delivery systems. Several common carrier types based on soybean protein were then introduced. The biological functions and limitations of several common soybean protein delivery bioactive substances and the role of soybean protein-based delivery systems were discussed. At present, soybean protein is the most widely used in drug delivery systems. Soybean protein-based nano-particles are currently the most commonly used delivery carriers. Soybean protein-based hydrogels, emulsions, microcapsules and electrospinning are also widely used. Polyphenols, carotenoids, vitamins, functional oils and probiotics are bioactive substances that are frequently delivered. However, in order to promote the application of soybean protein-based delivery systems in food, soybean protein peptidyl delivery vectors and collaborative delivery are the future development trends. In addition, a number of challenges must be addressed, including the sensitization of soybean protein, intolerance to environmental conditions, and the limitations of processing technologies.

Hydrogel delivery systems of functional substances for precision nutrition

Hydrogel delivery systems based on polysaccharides and proteins have the ability to protect functional substances from chemical degradation, control/target release, and increase bioavailability. This chapter summarizes the recent progress in the utilization of hydrogel delivery systems for nutritional interventions. Various hydrogel delivery systems as well as their preparation, structure, and properties are given. The applications for the encapsulation, protection, and controlled delivery of functional substances are described. We also discuss their potential and challenges in managing chronic diseases such as inflammatory bowel disease, obesity, liver disease, and cancer, aiming at providing theoretical references for exploring novel hydrogel delivery systems and their practical prospects in precise nutritional interventions.

Integrated ultrasonic-transglutaminase modification of lesser mealworm protein isolate: A pioneering cobalamin delivery vehicle in gluten-free breads

A combined approach of microbial transglutaminase (MTGase) crosslinking and high-intensity ultrasound (HIU) was implemented to improve the physicochemical, rheological, structural, and thermal properties, as well as the targeted release of vitamin B12 of lesser mealworm protein isolate (LMPI)-based gels. Prolonging HIU to 60 min significantly reduced LMPIs' size, polydispersity, zeta-potential, and fluorescence intensity while increasing surface hydrophobicity, free amino (FAGs), and sulfhydryl (FSGs) groups. The MTGase-catalyzed LMPI gels effectively decreased the content of FAGs and FSGs. LMPI gels from 60 and 75 min HIU and MTGase catalysis exhibited a shear-thinning flow behavior, superior thermal stability, and improved water retention and gel strength with the most controlled release of vitamin B12 during in vitro simulated gastrointestinal digestion. Incorporating freeze-dried gel powders from 60 min HIU-treated MTGase-catalyzed LMPI and pea protein isolate into the dough of a new gluten-free bread improved physicochemical, textural, and sensory properties, with notable vitamin B12 retention rate.

Preparation of Transglutaminase-Catalyzed Rice Bran Protein Emulsion Gels as a Curcumin Vehicle

Protein-based emulsion gels have tunable viscoelasticity that can be applied to improve the stability of bioactive ingredients. As the by-product of rice processing, rice bran protein (RBP) has high nutritional value and good digestibility, exhibiting unique value in the development of hypoallergenic formula. In this study, the effect of transglutaminase (TGase) cross-linking on the physicochemical properties of RBP emulsion gels was investigated. To improve the stability of curcumin against environmental stress, the entrapment efficiency and stability of curcumin in the emulsion gel systems were also evaluated. The results indicated that TGase increased the viscoelastic modulus of RBP emulsion gels, resulting in a solid-like structure. Moreover, the entrapment efficiency of curcumin was increased to 93.73% after adding TGase. The thermal stability and photo-stability of curcumin were enhanced to 79.54% and 85.87%, respectively, compared with the sample without TGase addition. The FTIR results showed that TGase induced the cross-linking of protein molecules and the secondary structure change in RBP. Additionally, SEM observation confirmed that the incorporation of TGase promoted the formation of a compact network structure. This study demonstrated the potential of RBP emulsion gels in protecting curcumin and might provide an alternative strategy to stabilize functional ingredients.

Research progress of protein complex systems and their application in food: A review

Among the common natural biomolecules, the excellent properties of proteins have attracted extensive attention from researchers for functional applications, however, in native form proteins have many limitations in the performance of their functional attribute. However, with the deepening of research, it has been found that the combination of natural active substances such as polyphenols, polysaccharides, etc. with protein molecules will make the composite system have stronger functional properties, while the utilization of pH-driven method, ultrasonic treatment, heat treatment, etc. not only provides a guarantee for the overall protein-based composite system, but also gives more possibilities to the protein-composite system. Protein composite systems are emerging in the fields of novel active packaging, functional factor delivery systems and gel systems with high medical value. The products of these protein composite systems usually have high functional properties, mainly due to the interaction of the remaining natural active substances with protein molecules, which can be broadly categorized into covalent interactions and non-covalent interactions, and which, despite the differences in these interactions, together constitute the cornerstone for the stability of protein composite systems and for in-depth research.

Water in water emulsion stabilized by liposomes developed from whey protein isolate and xanthan gum: Environmental stability and photoprotection effect for riboflavin

The purpose of this work is to explore the feasibility of water in water (W/W) emulsion stabilized with liposomes as a water-soluble nutraceutical carrier. A W/W emulsion system composed of xanthan gum (XG) and whey protein isolate (WPI) with different amount (0.2 %, 0.4 %, and 0.6 %) of liposomes as stabilizer was constructed. Fast green staining observation showed that XG was the internal phase and WPI was the continuous phase respectively. Confocal laser scanning microscopy revealed that with the increase of liposomes concentration from 0.4 % to 0.6 %, the interface thickness of the W/W emulsions was approximately twice that of the 0.2 % liposome-stabilized emulsion.The emulsions remained stable under neutral and weakly alkaline conditions. The droplet sizes of the emulsions were little affected by ionic strength. The binding constant (Ka) for XG to riboflavin (12.22) was approximately 5 times that for WPI to riboflavin (2.46), suggesting that riboflavin had a stronger binding affinity for the XG molecule compared to WPI. The fluorescence spectra of riboflavin showed that 0.4 % and 0.6 % liposome stabilized emulsions could effectively retard the photodegradation of riboflavin under ultraviolet irradiation. The successful construction of liposomes stabilized W/W emulsion provides a novel strategy for delivering water-soluble bioactive substances.

Enhancing the Gelation Behavior of Transglutaminase-Induced Soy Protein Isolate(SPI) through Ultrasound-Assisted Extraction

Gelation, as an important functional property of soy protein isolate (SPI), can be improved by some green technologies in food manufacturing, including ultrasound, ultrahigh pressure and microwave treatments. This work investigated the effect of an alkaline solubilisation step in SPI extraction combined with sonication on protein properties. The TGase-induced gel of the modified SPI was prepared to explore the effect of ultrasound on gel properties, including structures, strength, water-holding capacity and rheological properties. Additionally, the differences between traditional ultrasound modification of SPI and current modification methods were analyzed. The results showed that the ultrasonication-assisted extraction method could result in a significant increase in extraction rate from 24.68% to 42.25%. Moreover, ultrasound-assisted modification of SPI gels induced with transglutaminase (TGase) exhibited significant improvement in mechanical properties, such as texture, water-holding capacity and rheological properties, In particular, SPI extracted at 400 W ultrasound intensity for 180 s showed the best overall performance in terms of gel properties. Our method efficiently uniformizes gel structure, enhancing mechanical properties compared to conventional ultrasound methods, which reduced energy consumption and costs. These findings provide insights into the production of high-gelation SPI in food manufacturing.

Riboflavin-loaded soy protein isolate cold gel treated with combination of high intensity ultrasound and high hydrostatic pressure: Gel structure, physicochemical properties and gastrointestinal digestion fate

Transglutaminase (TGase) was added to soy protein isolate (SPI) dispersion after the combination treatment of high intensity ultrasound (HIU) and high hydrostatic pressure (HHP) to catalyze the formation of cold gel, which was used to encapsulate riboflavin. The structure, physicochemical properties and in vitro digestion characteristics of riboflavin-loaded SPI cold gel were investigated. HIU-HHP combined treatment enhanced the strength, water retention, elastic property, thermal stability and protein denaturation degree of riboflavin-loaded SPI cold gels, and improved the gel network structure, resulting in a higher encapsulation efficiency of riboflavin and its chemical stability under heat and light treatment. HIU-HHP combined treatment reduced the erosion and swelling of SPI cold gel in simulated gastrointestinal fluid, and improved the sustained release effect of SPI gel on riboflavin by changing the digestion mode and rate of gel. In addition, HIU-HHP combined treated gels promoted the directional release of riboflavin in the simulated intestinal fluid, thereby improving its bioaccessibility, which was related to the secondary structure orderliness, tertiary conformation tightness and aggregation degree of protein during the gastrointestinal digestion. Therefore, HIU-HHP combined treatment technology had potential application value in improving the protection, sustained/controlled release and delivery of SPI cold gels for sensitive bioactive compounds.

Inclusion of konjac glucomannan in pea protein hydrogels improved the rheological and in vitro release properties of the composite hydrogels

In this study, a composite hydrogel consisting of pea protein and konjac glucomannan (KG) was fabricated using three approaches, namely neutral, salt-set, and alkaline gelation. Hydrogels made from pea protein were brittle and weak. The addition of KG improved the elasticity and water holding capacity of the pea protein hydrogels. Concomitantly, a decrease in syneresis rate and swelling of the composite hydrogels was observed. The alkaline-set hydrogels exhibited the highest resilience to strain. Thixotropicity was found to be less pronounced for salt-set hydrogels. Sulphate had a greater positive effect on the structural recovery and negative effect on hysteresis area than chloride due to the greater salting-out effect of the sulphates. The addition of KG facilitated the formation of an interconnected structure with limited mobility of biopolymer chains. A sharp increase in G' and G" during the temperature ramp indicated the predominance of hydrophobic interactions towards the aggregation of biopolymers. The infrared spectra of the hydrogels revealed a change in secondary structure of proteins on addition of KG. A controlled in vitro release of riboflavin was observed in neutral and salt-set hydrogels. The alkaline-set hydrogels exhibited a prolonged gastric retention time, thereby establishing in vitro antacid activity in the gastric environment.

Transglutaminase-induced soybean protein isolate cold-set gels treated with combination of ultrasound and high pressure: Physicochemical properties and structural characterization

Soybean protein isolate (SPI) was treated by the combined exposure to ultrasound and high pressure and then subjected to transglutaminase (TGase)-catalyzed cross-linking to prepare SPI cold-set gels. The effects of combined treatments on physicochemical and structural properties of TGase-induced SPI cold-set gels were investigated. The combination of ultrasound and high pressure promoted the covalent disulfide bonds and ε-(γ-glutaminyl) lysine isopeptide bonds as well as non-covalent hydrophobic interactions, which further improved the gelation properties of SPI compared to ultrasound or high pressure alone. In particular, the 480 W ultrasound followed by high pressure treatment of gels led to higher strength (120.53 g), water holding capacity (95.39 %), immobilized water (93.92 %), lightness (42.18), whiteness (51.03), and elasticity (G' = 407 Pa), as well as more uniform and compact microstructure, thus resulting in the improved gel network structure. The combination of two treatments produced more flexible secondary structure, tighter tertiary conformation and higher denaturation degree of protein in the gels, leading to more stable gel structure. The structural modifications of SPI contributed to the improvement of its gelation properties. Therefore, the combined application of ultrasound and high pressure can be an effective method for improving the structure and properties of TGase-induced SPI cold-set gels.

Mechanism of ultrasonic combined with different fields on protein complex system and its effect on its functional characteristics and application: A review

In recent years, new food processing technologies (such as ultrasound, high-pressure homogenization, and pulsed electric fields) have gradually appeared in the public 's field of vision. These technologies have made outstanding contributions to changing the structure and function of protein complexes. As a relatively mature physical field, ultrasound has been widely used in food-related fields. However, with the gradual deepening of related research, it is found that the combination of different fields often makes some characteristics of the product better than the product under the action of a single field, which will not only lead to a broader application prospect of the product, but also make the product a better solution in some special fields. There are usually synergistic and antagonistic effects when multiple fields are combined, and these effects will also gradually enlarge the interaction between different components of the protein complex system. In this paper, while explaining the mechanism of ultrasonic combined with other fields affecting the steric hindrance and shielding site of protein complex system, we will further explain the effect of this effect on the function and application of protein complex system.

Application of ultrasound and its real-time monitoring of the acoustic field during processing of tofu: Parameter optimization, protein modification, and potential mechanism

Tofu is nutritious, easy to make, and popular among consumers. At present, traditional tofu production has gradually become perfect, but there are still shortcomings, such as long soaking time, serious waste of water resources, and the inability to realize orders for production at any time. Moreover, tofu production standards have not yet been clearly defined, with large differences in quality between them, which is not conducive to industrialized and large-scale production. Ultrasound has become a promising green processing technology with advantages, such as high extraction rate, short processing time, and ease of operation. This review focused on the challenges associated with traditional tofu production during soaking, grinding, and boiling soybeans. Moreover, the advantages of ultrasonic processing over traditional processing like increasing nutrient content, improving gel properties, and inhibiting the activity of microorganisms were explained. Furthermore, the quantification of acoustic fields by real-time monitoring technology was introduced to construct the theoretical correlation between ultrasonic treatments and tofu processing. It was concluded that ultrasonic treatment improved the functional properties of soybean protein, such as solubility, emulsifying properties, foamability, rheological properties, gel strength, and thermal stability. Therefore, the application of ultrasonic technology to traditional tofu processing to optimize industrial parameters is promising.

Effect of High-Intensity Ultrasound Pretreatment on the Properties of the Transglutaminase (TGase)-Induced β-Conglycinin (7S) Gel

In this study, we investigated the effects of different high-intensity ultrasound (HIU) pretreatment times (0-60 min) on the structure of β-conglycinin (7S) and the structural and functional properties of 7S gels induced by transglutaminase (TGase). Analysis of 7S conformation revealed that 30 min HIU pretreatment significantly induced the unfolding of the 7S structure, with the smallest particle size (97.59 nm), the highest surface hydrophobicity (51.42), and the lowering and raising of the content of the α-helix and β-sheet, respectively. Gel solubility showed that HIU facilitated the formation of ε-(γ-glutamyl)lysine isopeptide bonds, which maintain the stability and integrity of the gel network. The SEM revealed that the three-dimensional network structure of the gel at 30 min exhibited filamentous and homogeneous properties. Among them, the gel strength and water-holding capacity were approximately 1.54 and 1.23 times higher than those of the untreated 7S gels, respectively. The 7S gel obtained the highest thermal denaturation temperature (89.39 °C), G', and G″, and the lowest tan δ. Correlation analysis demonstrated that the gel functional properties were negatively correlated with particle size and the α-helix, while positively with Ho and β-sheet. By contrast, gels without sonication or with excessive pretreatment showed a large pore size and inhomogeneous gel network, and poor properties. These results will provide a theoretical basis for the optimization of HIU pretreatment conditions during TGase-induced 7S gel formation, to improve gelling properties.

Construction of transglutaminase covalently cross-linked hydrogel and high internal phase emulsion gel from pea protein modified by high-intensity ultrasound

BACKGROUND

The poor gelling and emulsification properties of pea protein (PeaP) limit its application in gel-based products. In this study, a strong hydrogel and a high internal phase emulsion (HPLE) gel of PeaP were constructed by covalent cross-linking of transglutaminase (TGase) assisted by high-intensity ultrasound.

RESULTS

Ultrasound promoted the catalytic efficiency of TGase, with the gel-point temperature dropping from 44 °C to 28 °C after 10 min of ultrasound. As the ultrasound time increased from 1 min to 10 min, the microstructure of the hydrogel also changed from an irregular macropore structure to a relatively homogeneous honeycomb structure. This was accompanied by an improvement in gel strength, water holding capacity, and ultimate stress. Ultrasound enhanced the binding of water to PeaP, but had little effect on the water-locking ability of the network structure. Ultrasonication improved the self-supporting ability of the HPIE gels. The oil droplets within the HPIE gels were closely aligned to form a hexagonal structure. The PeaP layer was further cross-linked by TGase, strengthening the network structure. High internal phase emulsion gel displayed a higher gel strength, viscosity, and good self-healing ability under 1 min ultrasound. Meanwhile, HPIE gel at 1 min of ultrasound could be printed with the highest clarity.

CONCLUSION

This work provided some insights into improving the functional properties of PeaP, which is helpful for the design and development of PeaP-based gel products. © 2022 Society of Chemical Industry.

Effect of multiple-frequency ultrasound-assisted transglutaminase dual modification on the structural, functional characteristics and application of Qingke protein

Qingke protein rich in restricted amino acids such as lysine, while the uncoordination of ratio of glutenin and gliadin in Qingke protein has a negative impact on its processing properties. In this study, the effect of multiple-frequency ultrasound combined with transglutaminase treatment on the functional and structural properties of Qingke protein and its application in noodle manufacture were investigated. The results showed that compared with the control, ultrasound-assisted transglutaminase dual modification significantly increased the water and oil holding capacity, apparent viscosity, foaming ability, and emulsifying activity index of Qingke protein, which exhibited a higher storage modulus G' (P < 0.05). Meanwhile, ultrasound combined with transglutaminase treatment enhanced the cross-linking degree of Qingke protein (P < 0.05), as shown by decreased free amino group and free sulfhydryl group contents, and increased disulfide bond content. Moreover, after the ultrasound-assisted transglutaminase dual modification treatment, the fluorescence intensity, the contents of α-helix and random coil in the secondary structure of Qingke protein significantly decreased, while the β-sheet content increased (P < 0.05) compared with control. SDS-PAGE results showed that the bands of Qingke protein treated by ultrasound combined with transglutaminase became unclear. Furthermore, the quality of Qingke noodles made with Qingke powder (140 g/kg dual modified Qingke protein mixed with 860 g/kg extracted Qingke starch) and wheat gluten 60-70 g/kg was similar to that of wheat noodles. In summary, multiple-frequency ultrasound combined with transglutaminase dual modification can significantly improve the physicochemical properties of Qingke protein and the modified Qingke proteins can be used as novel ingredients for Qingke noodles.

Walnut Protein Isolate-κ-Carrageenan Composite Gels Improved with Synergetic Ultrasound-Transglutaminase: Gelation Properties and Structure

Walnut protein is a kind of natural, high-quality plant protein resource. However, its high content of gluten, strong hydrophobicity and poor gelation ability have greatly limited its development and utilization in gel products. It was found in this experiment that ultrasonic power combined with transglutaminase (TGase) had a significant effect on the gel properties of the walnut protein isolate (WNPI)-κ-carrageenan (KC) complex. The results showed that the gel strength of the WNPI-KC complex first increased and then decreased with the increase in ultrasonic power (0-400 W). WNPI-KC composite gel had the best texture properties, rheological properties, water-holding capacity (99.41 ± 0.76%), swelling ratio (2.31 ± 0.29%) and thermal stability (83.22 °C) following 200 W ultrasonic pretreatment. At this time, the gel network was more uniform and much denser, and the water molecules were more tightly bound. Further, 200 W ultrasonic pretreatment could promote the transformation of α-helices to β-folds in protein molecules, improve the fluorescence intensity, increase the content of free sulfhydryl groups and enhance the intermolecular forces. The experimental results could provide technical support for the development of walnut protein gel food.

Effect of ultrasonic pretreatment on the rheology and structure of grass pea (Lathyrus sativus L.) protein emulsion gels induced by transglutaminase

In this study, emulsion gels were prepared by sonicated grass pea protein isolates (GPPI) at different ultrasonic amplitudes (25, 50 and 75 %) and times (5, 10 and 20 min). Formation of emulsion gels was induced by transglutaminase. Enzymatic gelation of emulsions stabilized by sonicated GPPI occurred in two stages. A relatively fast stage led to the formation of a weak gel which was followed by a slow stage that strongly reinforced the gel structure. Emulsion gels fabricated by sonicated GPPIs showed a homogeneous and uniform droplet distribution with higher elastic modulus compared to the native protein. A stiffer emulsion gel with a higher G' was formed after the protein was treated at 75 % amplitude for 10 min. After sonication of GPPI, the water holding capacity (WHC) of emulsion gels increased in accordance with the mechanical properties. Higher intermolecular cross-linking within the gel network increased the thermal stability of emulsion gels fabricated by sonicated GPPI. Although sonicated-GPPI emulsion gels clearly displayed homogenous microstructure in comparison to that made with native GPPI, the microstructures of these gels were nearly identical for all sonication amplitudes and times.

Gelation profile of laccase-crosslinked Bambara groundnut (Vigna subterranea) protein isolate

Enzymatic crosslinking has gained attention in improving plant protein heat-induced gels, which are composed of weak network structures. The aim of the study was to investigate the effect of laccase crosslinking on the rheological and microstructural properties of heat-induced Bambara groundnut protein gels. The rheological properties of laccase-modified Bambara groundnut protein isolate (BPI¹) gel formed in situ were investigated. Changes in viscoelastic properties were monitored during heating and cooling ramps and gel structure fingerprints were analyzed by frequency sweep. Laccase addition induced an initial protein structure breakdown (G″>G') at an enzyme dose-dependent (1-3 U/g) before gel formation and stabilization. Gel point temperatures were significantly decreased from 85°C to 29°C (∼3 folds) with increasing laccase activity (0 to 3 U/g protein, respectively). For laccase crosslinked gels, G' was substantially greater than G" (>1 log) with no dependency on angular frequency, which suggests the formation of relatively well-structured gels. The highest gel strength (tan δ of 0.09, G* of 555.51 kPa & An of 468.04 kPa) was recorded at a laccase activity of 2 U/g protein and the gels formed at this activity appeared homogeneous with compact lath sheet-like structure. The crosslinking effects of laccase were corroborated by the decrease in thiol and phenolic contents as well as the crosslinking of amino acids in model reactions. Overall, the use of laccase improved gel properties and significantly altered the gelation profile of BPI. Laccase-modified Bambara groundnut protein gels have potential to be used in food texture improvement and development of new food products. For instance, they can be used in plant-based milk products such as yoghurt and cheese.

Fabrication of icariin-soymilk nanoparticles with ultrasound-assisted treatment

Ultrasound is effective to fabricate nanocomplex. Soymilk is a natural nanocarrier with good compatibility. However, information about soymilk-nutraceuticals nanocomplex is limited. In this work, soymilk was used to encapsulate icariin, a well known nutraceutical with poor bioavailability. The effect of ultrasound on the quality of icariin-soymilk nanocomplexes (ISNCs) was investigated. Ultrasound could reduce the particle size, improve the surface hydrophobicity and change the microstructure of soymilk. With increasing ultrasound treatment time, an increased surface hydrophobicity was observed. The highest encapsulation efficiency (89.67 %) and loading capacity (28.92 µg/mg) were found for USI-20, whereas the smallest particle size (132.47 nm) was observed for USI-120. USI-60 showed the lowest ζ-potential (-31.33 mV) and the highest bioaccessibility (76.08 %). Ultrasound could enhance the storage stability of ISNCs. The data of NMR and fluorescence indicated that ISNCs were mainly stabilized by hydrophobic interaction.

Quality Assessment of the Protein Ingredients Recovered by Ultrasound-Assisted Extraction from the Press Cakes of Coconut and Almond Beverage Preparation

The manufacture of vegetal beverages has the drawback of producing large amounts of press cakes that are generally used as feed components. This work had the objective of valorizing the press cakes deriving from almond and coconut drinks production by using ultrasound-assisted extraction (UAE) to obtain protein ingredients for human use. Starting from coconut and almond press cakes, whose initial protein contents were 19.7% and 18.6%, respectively, the UAE treatment allowed liquid fractions to be obtained that were then freeze-dried: the extraction yields were 24.4 g dry extract/100 g press cake in case of coconut and 49.3 g dry extract/100 g press cake in case of almond. The protein contents of these dried materials were 30.10% and 22.88%, respectively. The quality of the extracted protein ingredients was assessed in term of phytic acid content, protein profile, techno-functional features, and antioxidant properties. The sonication had also a favorable effect on digestibility.

Legume Seed Protein Digestibility as Influenced by Traditional and Emerging Physical Processing Technologies

The increased consumption of legume seeds as a strategy for enhancing food security, reducing malnutrition, and improving health outcomes on a global scale remains an ongoing subject of profound research interest. Legume seed proteins are rich in their dietary protein contents. However, coexisting with these proteins in the seed matrix are other components that inhibit protein digestibility. Thus, improving access to legume proteins often depends on the neutralisation of these inhibitors, which are collectively described as antinutrients or antinutritional factors. The determination of protein quality, which typically involves evaluating protein digestibility and essential amino acid content, is assessed using various methods, such as in vitro simulated gastrointestinal digestibility, protein digestibility-corrected amino acid score (IV-PDCAAS), and digestible indispensable amino acid score (DIAAS). Since most edible legumes are mainly available in their processed forms, an interrogation of these processing methods, which could be traditional (e.g., cooking, milling, extrusion, germination, and fermentation) or based on emerging technologies (e.g., high-pressure processing (HPP), ultrasound, irradiation, pulsed electric field (PEF), and microwave), is not only critical but also necessary given the capacity of processing methods to influence protein digestibility. Therefore, this timely and important review discusses how each of these processing methods affects legume seed digestibility, examines the potential for improvements, highlights the challenges posed by antinutritional factors, and suggests areas of focus for future research.

Influence of ultrasound and enzymatic cross-linking on freeze-thaw stability and release properties of whey protein isolate hydrogel

This study investigated the effect of ultrasound and enzymatic cross-linking on the freeze-thaw (FT) stability and release properties of whey protein isolate hydrogels. We evaluated the FT stability by the changes in the microstructure, riboflavin retention, syneresis, water holding capacity (WHC), and texture of gels subjected to 3 FT cycles. High-intensity ultrasound (HUS) and transglutaminase (TGase)-mediated cross-linking improved the FT stability of whey protein isolate hydrogels loaded with riboflavin (WPISAR), as demonstrated by a more uniform and denser porous structure, significantly higher riboflavin retention, WHC, and textural properties, and lower syneresis after 3 FT cycles than those of untreated hydrogels. Furthermore, HUS- and TGase-mediated cross-linking decreased protein erosion and swelling ratio of WPISAR in simulated gastrointestinal fluids (SGIF) and reduced the riboflavin release rate in SGIF both with and without the addition of digestive enzymes. After 3 FT cycles, faster riboflavin release occurred due to a more porous structure induced by ice crystal formation compared with their unfrozen counterparts as detected by confocal laser scanning microscopy. High-intensity ultrasound- and TGase-mediated cross-linking alleviated the FT-induced faster riboflavin release rate in SGIF. High-intensity ultrasound- and TGase-treated gel samples showed that both diffusion and network erosion were responsible for riboflavin release regardless of FT. These results suggest that HUS- and TGase-mediated cross-linking improved the FT stability of WPISAR with a high riboflavin retention, and might be a good candidate as a controlled-release vehicle for riboflavin delivery to overcome undesired FT processing.

New Perspective on Natural Plant Protein-Based Nanocarriers for Bioactive Ingredients Delivery

The health effects of bioactive substances in the human body are affected by several factors, including food processing conditions, storage conditions, light and heat, among others. These factors greatly limit the stability and bioavailability of bioactive substances. These problems can be solved by a novel protein-based nanocarrier technology, which has the excellent potential to enhance solubility, bioavailability, and the controlled release of bioactive substances. In addition, plant protein has the advantages of economy, environmental protection, and high nutrition compared to animal protein. In this review, the preparation, characterization, and application of plant protein-based nanocarriers are summarized. The research deficiency and future prospects of plant protein nanocarriers are emphasized.

Application of emerging technologies to obtain legume protein isolates with improved techno-functional properties and health effects

Current demand of consumers for healthy and sustainable food products has led the industry to search for different sources of plant protein isolates and concentrates. Legumes represent an excellent nonanimal protein source with high-protein content. Legume species are distributed in a wide range of ecological conditions, including regions with drought conditions, making them a sustainable crop in a context of global warming. However, their use as human food is limited by the presence of antinutritional factors, such as protease inhibitors, lectins, phytates, and alkaloids, which have adverse nutritional effects. Antitechnological factors, such as fiber, tannins, and lipids, can affect the purity and protein extraction yield. Although most are removed or reduced during alkaline solubilization and isoelectric precipitation processes, some remain in the resulting protein isolates. Selection of appropriate legume genotypes and different emerging and sustainable facilitating technologies, such as high-power ultrasound, pulsed electric fields, high hydrostatic pressure, microwave, and supercritical fluids, can be applied to increase the removal of unwanted compounds. Some technologies can be used to increase protein yield. The technologies can also modify protein structure to improve digestibility, reduce allergenicity, and tune technological properties. This review summarizes recent findings regarding the use of emerging technologies to obtain high-purity protein isolates and the effects on techno-functional properties and health.

Role of Food Hydrocolloids as Antioxidants along with Modern Processing Techniques on the Surimi Protein Gel Textural Properties, Developments, Limitation and Future Perspectives

Texture is an important parameter in determining the quality characteristics and consumer acceptability of seafood and fish protein-based products. The addition of food-based additives as antioxidants (monosaccharides, oilgosaccharides, polysaccharides and protein hydrolysates) in surimi and other seafood products has become a promising trend at an industrial scale. Improvement in gelling, textural and structural attributes of surimi gel could be attained by inhibiting the oxidative changes, protein denaturation and aggregation with these additives along with new emerging processing techniques. Moreover, the intermolecular crosslinking of surimi gel can be improved with the addition of different food hydrocolloid-based antioxidants in combination with modern processing techniques. The high-pressure processing (HPP) technique with polysaccharides can develop surimi gel with better physicochemical, antioxidative, textural attributes and increase the gel matrix than conventional processing methods. The increase in protein oxidation, denaturation, decline in water holding capacity, gel strength and viscoelastic properties of surimi gel can be substantially improved by microwave (MW) processing. The MW, ultrasonication and ultraviolet (UV) treatments can significantly increase the textural properties (hardness, gumminess and cohesiveness) and improve the antioxidative properties of surimi gel produced by different additives. This study will review potential opportunities and primary areas of future exploration for high-quality surimi gel products. Moreover, it also focuses on the influence of different antioxidants as additives and some new production strategies, such as HPP, ultrasonication, UV and MW and ohmic processing. The effects of additives in combination with different modern processing technologies on surimi gel texture are also compared.

Effects of ultrasound synergized with microwave on structure and functional properties of transglutaminase-crosslinked whey protein isolate

In the present study, ultrasound (400 W, U), microwave heating (75 ℃ for 15 min, M) and ultrasound synergized with microwave heating (UM) pretreatments of whey protein isolate (WPI) were applied to investigate and compare their influence on structure, physicochemical and functional characteristic of transglutaminase (TGase)-induced WPI. From the results of size exclusion chromatography, it could be seen that all three physical pretreatments could promote the formation of polymers in TGase cross-linked WPI, whose polymer amounts were increased by the order of U, UM and M pretreatment. Among three physical methods, M pretreatment had the strongest effect on structure and functional characteristics of TGase-induced WPI. Furthermore, compared with TGase-induced WPI, α-helix and β-turn of M-treated TGase-induced WPI (M-WPI-TGase) were reduced by 7.86% and 2.93%, whereas its β-sheet and irregular curl were increased by 15.37% and 7.23%. Zeta potential, emulsion stability and foaming stability of M-WPI-TGase were increased by 7.8%, 59.27% and 28.95%, respectively. This experiment exhibited that M was a more effective pretreatment method than U, UM for WPI, which could promote its reaction with TGase and improve its functional properties.

Independent and combined effects of ultrasound and transglutaminase on the gel properties and in vitro digestion characteristics of bay scallop (Argopecten irradians) adductormuscle

The effects of transglutaminase (TGase) addition (0.4–1.2 g/100g), ultrasound (120–720 W, 20 min), and their combination on the gel properties and in vitro digestion characteristics of bay scallop adductor muscle were studied. The gel strength of the gel sample with TGase content of 0.8 g/100g (TG-0.8) was 58.2% higher than that of the control sample (CON). The gel sample treated with ultrasound at 480 W (UT-480) had the highest gel strength. The strength of the gel prepared by combination of 0.8 g/100g TGase and 360 W ultrasound (UT-TG) was 82.3% higher than that of CON. The whiteness and water holding capacity of the gel increased regardless of the addition of TGase or ultrasound treatment. SDS-PAGE patterns showed that the myosin heavy chain of the treated samples became thinner, and the changes of actin and tropomyosin were not significant. The scanning electron microscopy results of gel samples prepared by ultrasound combined with TGase showed a denser structure, which was related to the lowest total sulfhydryl content and TCA-soluble peptide content. The results of dynamic rheology show that the UT-TG sample had the highest G′ value, followed by TG-0.8. The in vitro digestion characteristics of the selected gel samples were also discussed. The degree of protein hydrolysis and the content of free amino acids in TG-0.8 samples were the lowest, which improved after ultrasound treatment. Overall, the combination of appropriate ultrasound treatment and TGase addition provides an effective means for improving gel properties and digestibility of scallop surimi product.

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Ultrasound and TGase enhanced gel properties of bay scallop adductor muscle (BSM).

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Ultrasound-assisted treatment promoted the cross-linking of BSM myosin by TGase.

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A denser gel network structure was formed when ultrasound combined with TGase.

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Ultrasound combined with TGase can improve the digestibility of the gel in vitro.

Recent advancements in enzyme-mediated crosslinkable hydrogels: In vivo-mimicking strategies

Enzymes play a central role in fundamental biological processes and have been traditionally used to trigger various processes. In recent years, enzymes have been used to tune biomaterial responses and modify the chemical structures at desired sites. These chemical modifications have allowed the fabrication of various hydrogels for tissue engineering and therapeutic applications. This review provides a comprehensive overview of recent advancements in the use of enzymes for hydrogel fabrication. Strategies to enhance the enzyme function and improve biocompatibility are described. In addition, we describe future opportunities and challenges for the production of enzyme-mediated crosslinkable hydrogels.

Effect of ultrasound pretreatment on structural, physicochemical, rheological and gelation properties of transglutaminase cross-linked whey protein soluble aggregates

A solution (10%, w/v) of whey protein soluble aggregates (WPISA) was pretreated with high-intensity ultrasound (HUS, 20 kHz) for different durations (10-40 min) before incubation with transglutaminase (TGase) to investigate the effect of HUS on the structural, physicochemical, rheological, and gelation properties of TGase cross-linked WPISA. Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) results showed that HUS increased the amounts of high-molecular-weight polymers/aggregates in WPISA after incubation with TGase. HUS significantly increased (P < 0.05) the degree of TGase-mediated cross-linking in WPISA, as demonstrated by a reduction in free amino group contents. HUS significantly increased (P < 0.05) the particle size, intrinsic fluorescence intensity, and surface hydrophobicity of TGase cross-linked WPISA, but had no significant impact (P > 0.05) on the zeta-potential or total free sulfhydryl group content of TGase cross-linked WPISA. The apparent viscosity and the consistency index of TGase cross-linked WPISA were significantly increased by HUS (P < 0.05), which indicated that HUS facilitated the formation of more high-molecular-weight polymers. HUS significantly increased (P < 0.05) the water holding capacity and gel strength of glucono-δ-lactone (GDL)-induced TGase cross-linked WPISA gels. The results indicated that HUS could be an efficient tool for modifying WPISA to improve its degree of TGase-mediated cross-linking, which would lead to improved rheological and gelation properties.