Tryptophan Fluorescence Intensity Research Articles

Inhibitory effect of chlorogenic acid and vanillic acid on fluorescent advanced glycation end products formation in low-temperature-processed pork meat

This work aimed to investigate the effects of chlorogenic acid (CA) and vanillic acid (VA) on structural changes in myofibrillar protein (MP) and fluorescent advanced glycation end products (fAGEs) formation in low-temperature-processed pork meat. Raw pork was prepared, different concentrations (0, 0.005%, 0.010%, 0.020%, 0.040%) of CA or VA were added, and then heated at 50 °C for 12 h. The results suggested that the degree of lipid oxidation significantly declined with increase in amounts of CA (from 12.166 ± 0.469 to 4.661 ± 0.333) or VA (from 11.771 ± 0.355 to 5.451 ± 0.362), and carbonyls, surface hydrophobicity, tryptophan fluorescence intensity, and protein oxidation products also showed a significant downward trend (p < 0.05). Compared with the control (498.183 ± 10.849), there were marked decrease of fAGEs intensity in samples containing CA (70.958 ± 4.114) or VA (76.667 ± 3.882). Besides, mitigating capacity of CA on fAGEs accumulation was just greater than that of VA. Therefore, CA and VA can impede MP and lipid oxidation of raw pork, which further reduce fAGEs formation in low-temperature-processed pork meat. This study is expected to provide a new strategy to prevent the oxidation of MP and reduce fAGEs contents in the meat industry.

Ultrasound as Green Technology for the Valorization of Pumpkin Leaves: Intensification of Protein Recovery.

The recovery of valuable nutritional compounds, like proteins, from waste streams and by-products is a key strategy for enhancing production sustainability and opening up new market potential. This research aimed to use high-intensity ultrasound as an innovative technique to extract the soluble proteins from the pumpkin leaves. The impact of various sonication amplitudes and duration periods on protein yield, functional properties, antioxidant qualities, and structural characteristics, were studied. Utilization of ultrasound technology significantly increased the yield of pumpkin leaf protein by up to 40%-six times higher than maceration. The ultrasound extraction provided a RuBisCO-rich protein fraction with high radical scavenging and chelating activities, especially at 40% amplitude. Cavitation modified the tertiary and secondary structures of leaf proteins: the amount of α-helix changed based on amplitude (12.3-37.7%), the amount of random coil increased to 20.4%, and the amount of β-turn reduced from 31 to 18.6%. The alteration of the protein fluorescence spectrum (blue shift in spectrum) provides further evidence that ultrasound alters the proteins' molecular structure in comparation with maceration; the maximum tryptophan fluorescence intensity decreased from 22.000 to 17.096. The hydrophobicity values of 76.8-101.5 were substantially higher than the maceration value of 53.4, indicating that ultrasound improved the hydrophobicity of protein surfaces. Ultrasound resulted in a significant increase in solubility in an acidic environment with the increase in sonication amplitude. A 2.4-fold increase in solubility at pH 2 becomes apparent (20% amplitude; 43.1%) versus maceration (18.2%). The emulsifying ability decreases from 6.62 to 5.13 m2/g once the sonication amplitude increases by 20-70%. By combining the ultrasound periods and amplitudes, it is possible to create high-value protein leaf extracts with improved properties which can find real application as food additives and dietary supplements.

Fluctuation of flavor quality in roasted duck: The consequences of raw duck preform’s repetitive freeze-thawing

This study aimed to investigate the changes in flavor quality of roasted duck during repetitive freeze-thawing (FT, −20 ℃ for 24 h, then at 4 ℃ for 24 h for five cycles) of raw duck preforms. HS-SPME/GC–MS analysis showed that more than thirty volatile flavor compounds identified in roasted ducks fluctuated with freeze-thawing of raw duck preforms, while hexanal, nonanal, 1-octen-3-ol, and acetone could as potential flavor markers. Compared with the unfrozen raw duck preforms (FT-0), repetitive freeze-thawing increased the protein/lipid oxidation and cross-linking of raw duck preforms by maintaining the higher carbonyl contents (1.40 ∼ 3.30 nmol/mg), 2-thiobarbituric acid reactive substances (0.25 ∼ 0.51 mg/kg), schiff bases and disulfide bond (19.65 ∼ 30.65 μmol/g), but lower total sulfhydryl (73.37 ∼ 88.94 μmol/g) and tryptophan fluorescence intensity. Moreover, A lower protein band intensity and a transformation from α-helixes to β-sheets and random coils were observed in FT-3 ∼ FT-5. The obtained results indicated that multiple freeze-thawing (more than two cycles) of raw duck preforms could be detrimental to the flavor quality of the roasted duck due to excessive oxidation and degradation.

Investigation of the potential mechanisms of α-amylase and glucoamylase through ultrasound intensification

The aim of this study is to enhance the efficiency of enzymes, reduce operational costs, and increase production output. Experimental research shows that ultrasound positively impacted the activity of α-amylase and glucoamylase, with the peak α-amylase activity observed at 30 W for 5 min and the highest glucoamylase activity at 60 W for 3 min. Ultrasonication extended the optimal temperature of both enzymes, but had no effect on the optimal pH. According to the kinetic experiments, ultrasonic treatment could improve the catalytic efficiency of α-amylase and glucoamylase. Furthermore, the SDS-PAGE results revealed that ultrasound treatment did not alter the molecular weights of the enzymes and their primary structures; The circular dichroism and fluorescence spectroscopy analysis indicated the secondary structural components, especially the α-sheet and the tryptophan fluorescence intensity, were notably affected by ultrasound. The changes in the secondary and tertiary structure of α-amylase and glucoamylase suggest that ultrasonic treatment may enhance their activities. Our findings provide a theoretical basis for the efficient utilization of α-amylase and glucoamylase through understanding the enzyme structure changes after ultrasound.

Characterization of the Effects of Low-Sodium Salt Substitution on Sensory Quality, Protein Oxidation, and Hydrolysis of Air-Dried Chicken Meat and Its Molecular Mechanisms Based on Tandem Mass Tagging-Labeled Quantitative Proteomics.

The effects of low-sodium salt mixture substitution on the sensory quality, protein oxidation, and hydrolysis of air-dried chicken and its molecular mechanisms were investigated based on tandem mass tagging (TMT) quantitative proteomics. The composite salt formulated with 1.6% KCl, 0.8% MgCl2, and 5.6% NaCl was found to improve the freshness and texture quality scores. Low-sodium salt mixture substitution significantly decreased the carbonyl content (1.52 nmol/mg), surface hydrophobicity (102.58 μg), and dimeric tyrosine content (2.69 A.U.), and significantly increased the sulfhydryl content (74.46 nmol/mg) and tryptophan fluorescence intensity, suggesting that protein oxidation was inhibited. Furthermore, low-sodium salt mixture substitution significantly increased the protein hydrolysis index (0.067), and cathepsin B and L activities (102.13 U/g and 349.25 U/g), suggesting that protein hydrolysis was facilitated. The correlation results showed that changes in the degree of protein hydrolysis and protein oxidation were closely related to sensory quality. TMT quantitative proteomics indicated that the degradation of myosin and titin as well as changes in the activities of the enzymes, CNDP2, DPP7, ABHD12B, FADH2A, and AASS, were responsible for the changes in the taste quality. In addition, CNDP2, ALDH1A1, and NMNAT1 are key enzymes that reduce protein oxidation. Overall, KCl and MgCl2 composite salt substitution is an effective method for producing low-sodium air-dried chicken.

Heat-induced gelation of egg white proteins depending on heating temperature: Insights into protein structure and digestive behaviors in the elderly in vitro digestion model

This study investigated the effects of heating temperature of egg white gels (EWGs) on the digestive characteristics by heating egg white (EW) to reach 75 °C (EWG-75) and 95 °C (EWG-95). The gel protein structure showed a decrease in the maximum tryptophan fluorescence intensity and a significant increase in the surface hydrophobicity of EWGs compared to EW (P < 0.05). The total and reactive free sulfhydryl groups were higher in the EWGs than in the EW (P < 0.05). While the proportions of α-helical and β-sheet structures remained similar in EW and EWG-75 (P > 0.05), EWG-95 exhibited a notable decrease in α-helix content (P < 0.05) and an increase in β-sheet content (P < 0.05). Furthermore, EWG-95 displayed higher hardness and cohesiveness than EWG-75 (P < 0.05). In the adult and elderly in vitro digestion models, EWG-95 exhibited the highest protein digestibility (50.44 % and 54.65 % in the models of elderly and adult subjects, respectively) after GI digestion (P < 0.05), followed by EWG-75 and EW. The electrophoretogram of the digesta revealed more intense protein bands in the elderly digestion model, particularly in the gastric digesta of EW, indicating slower digestion compared to the adult model. Therefore, EW should be appropriately heated before consumption, especially for elderly individuals, to facilitate efficient protein digestion and absorption.

Insights into the Mechanism of Tryptophan Fluorescence Quenching due to Synthetic Crowding Agents: A Combined Experimental and Computational Study.

Intrinsic tryptophan fluorescence spectroscopy is an important tool for examining the effects of molecular crowding and confinement on the structure, dynamics, and function of proteins. Synthetic crowders such as dextran, ficoll, polyethylene glycols, polyvinylpyrrolidone, and their respective monomers are used to mimic crowded intracellular environments. Interactions of these synthetic crowders with tryptophan and the subsequent impact on its fluorescence properties are therefore critically important for understanding the possible interference created by these crowders. In the present study, the effects of polymer and monomer crowders on tryptophan fluorescence were assessed by using experimental and computational approaches. The results of this study demonstrated that both polymer and monomer crowders have an impact on the tryptophan fluorescence intensity; however, the molecular mechanisms of quenching were different. Using Stern-Volmer plots and a temperature variation study, a physical basis for the quenching mechanism of commonly used synthetic crowders was established. The quenching of free tryptophan was found to involve static, dynamic, and sphere-of-action mechanisms. In parallel, computational studies employing Kohn-Sham density functional theory provided a deeper insight into the effects of intermolecular interactions and solvation, resulting in differing quenching modes for these crowders. Taken together, the study offers new physical insights into the quenching mechanisms of some commonly used monomer and polymer synthetic crowders.

In Vitro Study of the Interaction between Ochratoxin A and Human Serum Albumin by Spectroscopic and Molecular Docking Methods

AbstractOchratoxin A (OA) is a mycotoxin that has a potential risk to human health due to its nephrotoxic, immunotoxic and carcinogenic effects. For these reasons the interaction of ochratoxin A with human serum albumin (HSA) was investigated in physiological media by various techniques such as UV‐Vis, fluorescence (FL), circular dichroism (CD), attenuated total reflection (ATR), differential scanning calorimetry (DSC), atomic force microscopy (AFM) and molecular docking study via Auto Dock‐vina software. The fluorescence intensity of tryptophan in HSA was strongly quenched in the present of OA and the quenching constants and binding constant were valued 108 M−1 and 1.04 M−1, respectively. The CD spectra showed alteration in the secondary structure of HSA in the presence of ochratoxin by reducing the regular alpha helical structure and increasing the beta‐sheet structure. By increasing the concentration of OA to 1.25 μM, the intensity of absorption spectrum at 282 nm was increased, indicating the strong interaction of OA and HSA. The enthalpies of these molecular interaction calculated from DSC analysis indicate OA interaction with HAS is exothermic. The docking calculations showed that the amino acids of Lys190, ASP187, LYS519, ARG186 and ARG428 were interacted with OA by hydrogen bonding.

Production of freeze-dried beef powder for complementary food: Effect of temperature control in retaining protein digestibility

This study investigated the effect of temperature control during freeze-drying of beef on the in vitro protein digestibility. Frozen (at − 50 °C for 2 days)-then-aged (at 4 °C for 26 days) beef was freeze-dried at 25 °C (FD1) and 2 °C (FD2) to obtain freeze-dried beef powder. Tryptophan fluorescence intensity and total free sulfhydryl groups of beef myofibrillar proteins decreased (P < 0.05) and increased (P < 0.05) after freeze-drying, respectively. In the myosin fraction of FD2, α-helix increased and β-sheet decreased (P < 0.05) compared to raw beef. In contrast, the actin fraction of FD1 showed a decrease in α-helix and increase in β-sheet (P < 0.05) compared to raw beef. The contents of α-amino group and proteins digested to<3 kDa in the in vitro digesta of beef were retained in FD2 while the α-amino group of FD1 decreased (P < 0.05). Therefore, freeze-drying at 2 °C can efficiently retain in vitro protein digestibility of beef.

Improved tenderness and water retention of pork pieces and its underlying molecular mechanism through the combination of low-temperature preheating and traditional cooking.

The effects of two-stage heating with different preheating combinations on the shear force and water status of pork-pieces were explored. The results showed that the combined preheating at 50 ℃ for 35min or at 60 ℃ for 5 or 20min with traditional high temperature heating reduced the shear force and improved the water retention of meat, which was attributed to uniformly separation of myofibers and smaller myofiber space. Visible dissociation of actomyosin in heating groups of 50 ℃-35min, and 60 ℃-5, 20min was related to the tenderization of meat. The higher surface hydrophobicity, tryptophan fluorescence intensity, and lower α-helices of actomyosin at 60 ℃ contributed to the liberation of actin. However, severe oxidation of sulfhydryl groups at 70 ℃ and 80 ℃ promoted the aggregation of actomyosin. This study presents the advantage of two-stage heating in improving meat tenderness and juiciness and its underlying mechanisms.

High-pressure processing of beef increased the in vitro protein digestibility in an infant digestion model

Beef is an ideal protein source for use as a complementary food in infants. Considering the limited protein-digesting capacity of infants, it is required to enhance protein digestibility while minimizing the deterioration of beef quality. Thus, this study aimed to determine the effects of high-pressure processing (HPP) on the physicochemical properties and in vitro digestibility of beef proteins in an infant digestion model. HPP at 200 and 300 MPa decreased the tryptophan fluorescence intensity of the myosin and actin fractions relative to that at 0.1 MPa (P < 0.05). Compared to treatment at 0.1 and 100 MPa, HPP at 300 MPa decreased α-helix and β-turn contents in the myosin and actin fractions (P < 0.05), whilst increasing the β-sheet content (P < 0.05). Beef actomyosin content decreased (P < 0.05) during HPP at 200 and 300 MPa (c.f., 0.1 and 100 MPa). After in vitro digestion of beef, HPP at 200 and 300 MPa increased the α-amino group content and the abundance of proteins below 3 kDa in the digesta (P < 0.05). However, due to the considerable lipid oxidation at 300 MPa, HPP at 200 MPa is ideal for improving the protein digestibility of beef when incorporated into complementary foods for infants.

C14-HSL limits the mycelial morphology of pathogen Trichosporon cells but enhances their aggregation: Mechanisms and implications

The biosecurity hazards caused by pathogenic fungus have been widely concerned. Given the long-term coexistence of eukaryotic pathogens and quorum sensing bacteria in different habitats in environments, we hypothesized that they have social interactions via signal molecules. In this work, we firstly discovered the well-known bacterial signal molecules play an adverse role in the cell morphology and metabolism in a model pathogen Trichosporon asahii. N-Tetradecanoyl-l-homoserine lactone (C14-HSL) was discovered to increase pathogen hazards of T. asahii, which limited mycelium by 52%, but enhanced cell aggregation by 93%. Higher fluorescence intensity of tryptophan (59%) and aromatic protein (2-fold) contents after the treatment of C14-HSL, indicating that aromatic proteins helped aggregate Trichosporon and showed hydrophobicity. Transcriptome analysis revealed that C14-HSL upregulated the shikimate pathway (above 1-fold) located in downstream of tricarboxylic acid cycle, which contributed to the synthesis of more aromatic proteins and the formation of larger flocs. The limited mycelial growth of T. asahii attributed to the up-regulated expressions of cell cycle process. The fungal transboundary response to bacterial C14-HSL was controlled by signal transduction pathways. This study provides new insights into the co-evolution of bacterial and pathogenic fungi in microecosystems.

Concentration-dependent effect of eugenol on porcine myofibrillar protein gel formation

The effects of different concentrations of eugenol (EG = 0, 5, 10, 20, 50, and 100 mg/g protein) on the structural properties and gelling behavior of myofibrillar proteins (MPs) were investigated. The interaction of EG and MPs decreased free thiol and amine content, and reduced tryptophan fluorescence intensity and thermal stability, but enhanced surface hydrophobicity and aggregation of MPs. Compared with the control (EG free), the MPs' gels treated with 5 and 10 mg/g of EG had a higher storage modulus, compressive strength, and less cooking loss. A high microscopic density was observed in these EG-treated gels. However, EG at 100 mg/g was detrimental to the gelling properties of the MPs. The results indicate that an EG concentration of 20 mg/g is a turning point, i.e., below 20 mg/g, EG promoted MPs gelation, but above 20 mg/g, it impeded gelation by interfering with protein network formation. The EG modification of MPs could provide a novel ingredient strategy to improve the texture of comminuted meat products.

The influence of piperine on oxidation-induced porcine myofibrillar protein gelation behavior and fluorescent advanced glycation end products formation in model systems

This study investigated the effects of piperine on oxidation-induced porcine myofibrillar protein (MP) gelation behavior and fluorescent advanced glycation end products (fAGEs) formation. Model systems were prepared, lipid oxidation, MP gelling behavior, and fAGEs content were determined daily. The results indicated that lipid oxidation, carbonyl content, S0, cooking loss, and tryptophan fluorescence intensity of MP significantly decreased, whereas gel strength, WHC, and whiteness markedly increased as the concentration of piperine increased (from 0 to 30 μM/g protein), indicating that piperine could reduce lipid oxidation and oxidative damage to MP. The fluorescence intensity of fAGEs markedly decreased (P < 0.05), from 93.1 ± 4.4 to 61.2 ± 3.0, as the concentration of piperine increased from 0 μM/g protein to 30 μM/g protein after 5 days of incubation. These results in model systems suggest that the presence of piperine has an important role in the inhibition of MP oxidation and fAGEs formation.

Effects of quercetin on the gel properties of pork myofibrillar proteins and related changes in protein conformation.

To study the effects of quercetin on the functionality of myofibrillar proteins (MPs), various levels of quercetin (0, 10, 50, 100 and 200 μmol g-1 protein) were added to MP solution and the structure and gel properties of MPs were determined. Compared with the control MPs not treated with quercetin, adding 10, 50 and 100 μmol g-1 quercetin caused a significant (P < 0.05) loss of sulfhydryls; 10 and 50 μmol g-1 quercetin enhanced the surface hydrophobicity significantly (P < 0.05), and 50, 100 and 200 μmol g-1 quercetin reduced the fluorescence intensity of tryptophan. Additions of 50, 100 and 200 μmol g-1 quercetin resulted in a significant (P < 0.05) reduction in MP solubility. Adding 10, 50 and 100 μmol g-1 quercetin did not significantly (P > 0.05) change the gel strength and water-holding ability of MPs than control, but 200 μmol g-1 quercetin declined the gel properties significantly (P < 0.05). The microstructure and dynamic rheological properties confirmed the results of the gel properties of MPs affected by various levels of quercetin. The results obtained in the present study show that mildly high levels of quercetin can maintain the gel properties of MPs, which may be a result of the moderate MP cross-linkage and aggregation caused by the covalent and non-covalent interactions of MPs. © 2023 Society of Chemical Industry.

Hybrid Sausages Using Pork and Cricket Flour: Texture and Oxidative Storage Stability.

This study aimed to study the functionalities of cricket flour (CF) and the effects of the addition of CF on the texture and oxidative stability of hybrid sausages made from lean pork and CF. Functional properties of CF, including protein solubility, water-holding capacity, and gelling capacity, were examined at different pHs, NaCl concentrations, and CF contents in laboratory tests. The protein solubility of CF was significantly affected by pH, being at its lowest at pH 5 (within the range 2-10), and the highest protein solubility toward NaCl concentrations was found at 1.0 M (at pH 6.8). A gel was formed when the CF content was ≥10%. A control sausage was made from lean pork, pork fat, salt, phosphate, and ice water. Three different hybrid sausages were formulated by adding CF at 1%, 2.5%, and 5.0% levels on top of the base (control) recipe. In comparison to control sausage, the textural properties of the CF sausages in terms of hardness, springiness, cohesiveness, chewiness, resilience, and fracturability decreased significantly, which corresponded to the rheological results of the raw sausage batter when heated at a higher temperature range (~45-80 °C). The addition of CF to the base recipe accelerated both lipid and protein oxidation during 14 days of storage, as indicated by the changes in TBARS and carbonyls and the loss of free thiols and tryptophan fluorescence intensity. These results suggest that the addition of CF, even at low levels (≤5%), had negative effects on the texture and oxidative stability of the hybrid sausages.

The effect of lactose and its isomerization product lactulose on functional and structural properties of glycated casein

Lactulose is an isomer of lactose, formed under thermal processing of milk. Alkaline conditions favor the isomerization of lactose. As reducing sugar, lactose and lactulose could participate in the Maillard reaction and cause protein glycation in milk products. In this study, the influence of lactose and lactulose on the functional and structural properties of glycated casein was investigated. The results demonstrated that compared with lactose, lactulose led to severer changes in molecular weight, more disordered spatial structure and decrease of tryptophan fluorescence intensity of casein. Besides, the glycation degree and advanced glycation end products (AGEs) results suggested that lactulose exhibited stronger glycation ability than lactose due to the higher proportion of open chain in solution. Furthermore, higher glycation degree induced by lactulose resulted in lower solubility, surface hydrophobicity, digestibility and emulsifying capacity of casein-glycoconjugates compared with lactose. The results of this study are essential for tracking the effects of harmful Maillard reaction products on the quality of milk and dairy products.

Higher Protein Digestibility of Chicken Thigh than Breast Muscle in an In Vitro Elderly Digestion Model.

This study investigated the protein digestibility of chicken breast and thigh in an in vitro digestion model to determine the better protein sources for the elderly in terms of bioavailability. For this purpose, the biochemical traits of raw muscles and the structural properties of myofibrillar proteins were monitored. The thigh had higher pH, 10% trichloroacetic acid-soluble α-amino groups, and protein carbonyl content than the breast (p<0.05). In the proximate composition, the thigh had higher crude fat and lower crude protein content than the breast (p<0.05). Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) of myofibrillar proteins showed noticeable differences in the band intensities of tropomyosin α-chain and myosin light chain-3 between the thigh and breast. The intrinsic tryptophan fluorescence intensity of myosin was lower in the thigh than in the breast (p<0.05). Moreover, circular dichroism spectroscopy of myosin revealed that the thigh had higher α-helical and lower β-sheet structures than the breast (p<0.05). The cooked muscles were then chopped and digested in the elderly digestion model. The thigh had more α-amino groups than the breast after both gastric and gastrointestinal digestion (p<0.05). SDS-PAGE analysis of the gastric digesta showed that more bands remained in the digesta of the breast than that of the thigh. The content of proteins less than 3 kDa in the gastrointestinal digesta was also higher in the thigh than in the breast (p<0.05). These results reveal that chicken thigh with higher in vitro protein digestibility is a more appropriate protein source for the elderly than chicken breast.

Separating the effects of confinement and interfacial interactions for the model protein Cytochrome C using reverse micelle encapsulation.

Bulk aqueous solution has been the standard condition for studying protein stability. Inside the cell, however, large molecules are packed tightly, resulting in a highly crowded environment with limited space that may cause changes in protein thermodynamics. This crowded condition presents a wide range of spatial restriction, but it also presents opportunities for nonspecific interactions between proteins and their environment that may further alter stability. We are using reverse micelles to mimic the conditions presented by intracellular confinement. Reverse micelles are spontaneously organizing complexes with an aqueous core surrounded by a layer of surfactant dissolved in a nonpolar solvent. By encapsulating cytochrome c in the reverse micelle interior, we are using this system to examine the effects on protein stability. Cytochrome c denaturation is monitored by observing the intensity of the intrinsic tryptophan fluorescence which is quenched by the heme in the native state. By adjusting the pH of the system without affecting the composition of the reverse micelle shell, we can compare the influence of histidine protonation on stability as a function of the protein's environment. We examine this property using two surfactant mixtures of varying chemistry to extract the effects of nonspecific interactions with the interface on the thermodynamic stability of the protein. The results of our analysis will be presented and will show the differential effects of these important aspects of the protein's environment.

Effects of κ-carrageenan addition and chlorogenic acid covalent crosslinking on protein conformation and gelling properties of soy protein hydrogels

This paper reports the effects of κ-carrageenan (KC) additions (0.6% w/v) and covalent crosslinking by chlorogenic acid (CA) on the protein conformation and gelling properties of soybean protein isolate (SPI) hydrogels. Treatment with KC and CA changed the conformation of the SPI and improved the antioxidant capacity and gel properties, as confirmed by fluorescence spectroscopy, Fourier-transform infrared spectroscopy, antioxidant capacity analysis, and rheology measurements. The addition of CA (0.01 g/g-SPI) decreased the number of free amino groups, free sulfhydryl content, tryptophan fluorescence intensity, and surface hydrophobicity of SPI by 44.22%, 10.05%, 30.47%, and 44.61%, respectively, and increased the DPPH and ABTS radical scavenging activities by 30.29% and 40.69%, respectively. The addition of KC (0.6% w/v) enhanced the DPPH radical scavenging activities of the SPI-CA (0.002 and 0.01 g/g-SPI) conjugates by 11.29–16.50%, and improved the viscoelasticity, water immobilization, density, and thermal stability of the SPI–CA gels.