Effect of synergism of sucrose ester and xanthan gum on the stability of walnut milk.

BACKGROUND: Single emulsifiers have an effect on the stability of plant protein drinks, giving some improvement. Emulsifiers are more effective in maintaining emulsion stability when combined with polysaccharides such as xanthan gum. In this paper, we studied the food-grade emulsifier sucrose ester and measured the average particle size, polydispersity value, zeta potential, microrheological properties, microstructure and creaming index related to walnut protein emulsion by constructing a walnut protein emulsion simulation system. SDS-PAGE and low-field NMR were used to analyze the relative molecular masses of emulsions and the water distribution of emulsions, respectively, to further investigate the synergistic effects of sucrose esters and xanthan gum on the ease of emulsification and intrinsic mechanisms of different molecular weight proteins of walnut protein emulsions. RESULTS: The results indicate that the synergistic effect of sucrose esters and xanthan gum was to stabilize emulsions better than single emulsifiers. Xanthan gum and protein may form protein-polysaccharide complexes, as well as the hydrophobic interaction between sucrose ester and xanthan gum. The properties of xanthan gum can improve the stability of the emulsion by affecting the mechanical properties of walnut protein emulsion, and the combination of sucrose ester and xanthan gum can better stabilize large protein molecules. CONCLUSION: The results not only provide a theoretical basis for the stability of plant protein emulsion systems, but also provide technical support for the production and processing of large-molecule plant proteins into emulsions in this field for improving their stability, and also provide more possibilities for other types of emulsions. © 2023 Society of Chemical Industry.

Polyphenol removal with ultrasound-assisted ethanol extraction from defatted walnut powder: optimization of conditions and effect on functional properties of protein isolates.

BACKGROUND: Walnut kernels are high in polyphenols (PPs), which cause low protein solubility, limiting the use of walnut protein in the food industry. To obtain the best technical parameters of the dephenolization treatment, the defatted walnut powder was dephenolized using ultrasound-assisted ethanol extraction (UAE), and the response surface optimization was performed on the basis of single factor. On this basis, the effects of dephenolization on the solubility, emulsifying properties and foaming properties of walnut protein isolates (WPIs) were compared to those of defatted walnut powder without dephenolization. RESULTS: The results showed that PP extraction in the UAE could significantly increase PP yield. The optimal process parameters were as follows: 51% (v/v) ethanol concentration, 140 W ultrasound power, 10 min extraction time, 30 °C ultrasound temperature, and a material-liquid ratio of 1:30 (w/v). The results revealed that the UAE dephenolization treatment significantly improved the functionality of WPI and that the functionality of the dephenolized WPI by UAE was superior to that of the protein without dephenolization, and that the functionality of both walnut proteins was the worst at pH 5, with solubility of 5.31% and 4.86%, emulsifying activity index (EAI) of 24.95 and 19.91 m2 /g, and foaming capacity (FC) of 3.66% and 2.94%, respectively; and the best at pH 11, with solubility of 82.35% and 73.55%, EAI of 46.35 and 37.28 m2 /g, and FC of 35.85% and 18.87%, respectively. CONCLUSION: The study found that dephenolization by UAE can significantly improve the functionality of WPI, and this method should be promoted and used in walnut and walnut protein processing industries. © 2023 Society of Chemical Industry.

Purification, Identification and Molecular Docking of Novel Antioxidant Peptides from Walnut (Juglans regia L.) Protein Hydrolysates.

Walnut protein isolate (WPI) was hydrolyzed using Alcalase for 0, 30, 60, 90, 120 and 150 min to investigate the effect of different hydrolysis times on the structure and antioxidant properties of walnut proteins. The identified peptides HADMVFY, NHCQYYL, NLFHKRP and PSYQPTP were used to investigate the structure-activity relationship by using LC-MS/MS and molecular docking. The kinetic equations DH = 3.72ln [1 + (6.68 E0/S0 + 0.08) t] were developed and validated to explore the mechanism of WIP hydrolysis by Alcalase. Structural characteristics showed that the UV fluorescence intensity and endogenous fluorescence intensity of the hydrolysates were significantly higher than those of the control. FTIR results suggested that the secondary structure gradually shifted from an ordered to a disordered structure. Enzymatic hydrolysis containing much smaller molecule peptides than WPI was observed by molecular weight distribution. In vitro, an antioxidant test indicated that Alcalase protease hydrolysis at 120 min showed more potent antioxidant activity than hydrolysates at other hydrolysis times. In addition, four new antioxidant peptides were identified by LC-MS/MS. Molecular docking indicated that these peptides could interact with ABTS through interactions such as hydrogen bonding and hydrophobic interactions. Thus, WPI hydrolysates could be used as potential antioxidants in the food and pharmaceutical industries.

Effect of Chlorogenic Acid on the Physicochemical and Functional Properties of Coregonus Peled Myofibrillar Protein through Hydroxyl Radical Oxidation.

The effects of chlorogenic acid (CA) (6, 30, and 150 µM/g protein) on the physicochemical and functional properties of Coregonus peled myofibrillar protein (MP) through oxidation using a hydroxyl radical oxidation system (0.01 mM FeCl3, 0.01 mM Asc, and 1 mM H2O2) were investigated. The result showed that CA inhibited the increase in protein carbonyl content but did not prevent losses in sulfhydryl and free amine contents caused by oxidation. The presence of CA also increased conformational changes in the secondary and tertiary structures of oxidized MP. Oxidized MP containing 6 µM/g CA had superior functional properties (solubility, emulsifying, foaming, and gel properties), while oxidized MP containing 150 µM/g CA aggregated, resulting in insolubility and a poor gel network.

Amino acid composition, molecular weight distribution and gel electrophoresis of walnut (Juglans regia L.) proteins and protein fractionations.

As a by-product of oil production, walnut proteins are considered as an additional source of plant protein for human food. To make full use of the protein resource, a comprehensive understanding of composition and characteristics of walnut proteins are required. Walnut proteins have been fractionated and characterized in this study. Amino acid composition, molecular weight distribution and gel electrophoresis of walnut proteins and protein fractionations were analyzed. The proteins were sequentially separated into four fractions according to their solubility. Glutelin was the main component of the protein extract. The content of glutelin, albumin, globulin and prolamin was about 72.06%, 7.54%, 15.67% and 4.73% respectively. Glutelin, albumin and globulin have a balanced content of essential amino acids, except for methionine, with respect to the FAO pattern recommended for adults. SDS-PAGE patterns of albumin, globulin and glutelin showed several polypeptides with molecular weights 14.4 to 66.2 kDa. The pattern of walnut proteins in two-dimension electrophoresis (2-DE) showed that the isoelectric point was mainly in the range of 4.8-6.8. The results of size exclusion chromatogram indicated molecular weight of the major components of walnut proteins were between 3.54 and 81.76 kDa.

Chemical composition, molecular weight distribution, secondary structure and effect of NaCl on functional properties of walnut (Juglans regia L) protein isolates and concentrates.

Chemical composition, molecular weight distribution, secondary structure and effect of sodium chloride concentration on functional properties of walnut protein isolates, concentrates and defatted walnut flour were study. Compared with walnut protein concentrates (75.6%) and defatted walnut flour (52.5%), walnut protein isolates contain a relatively high amount of protein (90.5%). The yield of walnut protein isolates and concentrates was 43.2% and 76.6%, respectively. In molecular weight distribution study, Walnut protein isolates showed one peak with molecular weight of 106.33 KDa (100%) and walnut protein concentrates showed four peaks with molecular weight of 16,725 KDa (0.8%),104.943 KDa(63.9%), 7.3 KDa (11.4%), 2.6 KDa (23.9%). The secondary structure of walnut protein isolates was similar to that of walnut protein concentrates, but was differ from that of defatted walnut flour. The addition of sodium chloride (0 ~ 1 M) could improve the functionality of walnut protein concentrates, isolates and defatted walnut flour. The maximum solubility, water absorption capacity, emulsifying properties and foaming properties of walnut protein isolates, concentrates and defatted walnut flour were at sodium chloride solutions of 1.0 M, 0.6 M, 0.4 M, 0.6 M, respectively. The solubility of walnut protein concentrates (32.5%) in distilled water with 0 M sodium chloride was lower than that of walnut protein isolates (35.2%). The maximum solubility of walnut protein isolates, concentrates and defatted walnut flour in solution were 36.8%, 33.7% and 9.6% at 1.0 M sodium chloride solutions, respectively. As compared with other vegetable proteins, walnut protein isolates and concentrates exhibited better emulsifying properties and foam stability.

Effect of different amphiphilic emulsifiers complexed with xanthan gum on the stability of walnut milk and structural characterization of their complexes.

The kind of compounding emulsifier used and the amount of compounding have a significant impact on the emulsion's stability. In this study, the average particle size, Zeta potential, emulsification index, laser confocal microstructure, and rheological properties shows that the ratio of monoglyceride-xanthan gum and sucrose ester-xanthan gum could maintain the good stability of the emulsion in a certain range, and the monoglyceride and sucrose ester compounding could effectively improve the stability of the emulsion in a specific ratio (7:3). The results of fluorescence spectroscopy, Fourier transform infrared spectroscopy and sodium dodecyl sulfate polyacrylamide gel electrophoresis indicated that the simultaneous complexation of three substances was more likely to produce hydrophobic interactions with walnut proteins than the simultaneous complexation of two substances. Also confirmed were the hydrogen bonding connections between the proteins and the monoglyceride, sucrose ester, and xanthan gum. Monoglyceride and xanthan gum complexes were also found to stabilize more proteins.

Effect of Alkyl Peroxyl Radical Oxidation on the Oxidative Stability of Walnut Protein Emulsions and Their Adsorbed Proteins.

Walnuts are high in protein content and rich in nutrients and are susceptible to oxidation during production and processing, leading to a decrease in the stability of walnut protein emulsions. In this paper, the effect of alkyl peroxyl radical oxidation on the stability of walnut protein emulsions is investigated. With the increase of 2,2-azobis (2-methylpropionamidine) dihydrochloride (AAPH) concentration, both its protein and fat were oxidized to different degrees, and the droplets of the emulsion were first dispersed and then aggregated as seen from the laser confocal, and the stability of walnut protein emulsion was best at the AAPH concentration of 0.2 mmol/L. In addition to this, the adsorption rate of adsorbed proteins showed a decreasing and then an increasing trend with the increase in the oxidized concentration. The results showed that moderate oxidation (AAPH concentration: 0-0.2 mmol/L) promoted an increase in protein flexibility and a decrease in the protein interfacial tension, leading to the decrease in emulsion droplet size and the increase of walnut protein emulsion stability, and excessive oxidation (AAPH concentration: 1-25 mmmol/L) weakened protein flexibility and electrostatic repulsion, making the walnut protein emulsion less stable. The results of this study provide theoretical references for the quality control of walnut protein emulsions.

Food emulsions stabilized by proteins and emulsifiers: A review of the mechanistic explorations.

The stability of food emulsions is the basis for other properties. During their production and processing, emulsions tend to become unstable due to their thermodynamic instability, and it is usually necessary to add emulsifiers and proteins to stabilize emulsions. It becomes crucial to study the intrinsic mechanisms of emulsifiers and proteins and their joint stabilization of food emulsions. This paper summarizes the research on intrinsic mechanisms of food emulsions stabilized by emulsifiers and proteins in recent years. The destabilization and stabilization of emulsions are related to the added surfactants. The properties, type, and concentration of emulsifiers determine the stability of emulsions, and the emulsifiers can be classified into different types (e.g., ionic or nonionic, solid or liquid) according to their properties and sources. The physicochemical properties of proteins (e.g., spatial conformation, hydrophobicity) and the composition of proteins can also determine the stability of emulsions, and emulsions stabilized by emulsifiers and proteins together not only depend on these factors but also have a great relationship with the mutual combination and competition between the two. The instability and stability of emulsions are related to factors such as interfacial interaction forces, the rheological nature of the interface, and the added surfactant.

Effects of Packaging Materials on Structural and Simulated Digestive Characteristics of Walnut Protein during Accelerated Storage.

Walnuts are rich in fat and proteins that become oxidized during the processing and storage conditions of their kernels. In this study, the effect of three packaging materials (e.g., polyethylene sealed packaging, polyamide/polyethylene vacuum packaging, and polyethylene terephthalate/aluminum foil/polyethylene vacuum packaging) were investigated on the oxidation, structural and digestive properties of walnut kernel proteins. Results showed that the amino acid content gradually decreased and carbonyl derivatives and dityrosine were formed during storage. The protein molecule structure became disordered as the α-helix decreased and the random coil increased. The endogenous fluorescence intensity decreased and the maximum fluorescence value was blue-shifted. After 15 days of storage, surface hydrophobicity decreased, while SDS-PAGE and HPLC indicated the formation of large protein aggregates, leading to a reduction in solubility. By simulating gastrointestinal digestion, we found that oxidation adversely affected the digestive properties of walnut protein isolate and protein digestibility was best for polyethylene terephthalate/aluminum foil/polyethylene vacuum packaging. The degree of protein oxidation in walnuts increased during storage, which showed that except for fat oxidation, the effect of protein oxidation on quality should be considered. The results of the study provided new ideas and methods for walnut quality control.

The influence of social alienation on maintenance hemodialysis patients' coping styles: chain mediating effects of family resilience and caregiver burden.

Objective: Research on the possible impact of social alienation, family resilience, and caregiver burden on the coping styles of Chinese patients on maintenance hemodialysis (MHD) is scarce. We explore the influence of social alienation, family resilience, and caregiver burden on the coping styles of MHD patients, both directly and indirectly. Methods: We invited 173 MHD patients and their primary caregivers for a cross-sectional study; the study using convenience sampling method at the hemodialysis center of the First People's Hospital of Foshan. The Chinese version of the generalized social of alienation scale, the Chinese version of the simplified coping style questionnaire, and a sociodemographic questionnaire were completed by the MHD patients, while their primary caregivers had filled out the Chinese family resilience assessment scale, the Chinese version of the Zarit caregiver burden interview, and provided socio-demographic information. SPSS macro program PROCESS v3.3 Model 6 were used for analyses of chain-mediated effects. Results: In the mediating effects model, the direct influence of social alienation upon coping styles was significant (95% CI -0.050, -0.014), and social alienation indirectly impacted coping style by family resilience in a significant way (95% CI -0.012, -0.001) or caregiver burden (95% CI -0.013, -0.001). In addition, social alienation significantly impacted coping style by both family resilience and caregiver burden (95% CI -0.008, -0.001). Conclusion: Social alienation can exert both a direct and indirect influence on coping styles through the mediating factors of family resilience and caregiver burden. Clinicians can take interventions to strengthen family resilience and reduce caregiver burden, which may be useful in improving socially isolated behaviors and coping skills in MHD patients.

Immunogenicity and safety of concomitant administration of the sabin-strain-based inactivated poliovirus vaccine, the diphtheria-tetanus-acellular pertussis vaccine, and measles-mumps-rubella vaccine to healthy infants aged 18 months in China.

OBJECTIVES: During the COVID-19 pandemic, there was a decline in vaccine coverage, and the implementation of combined vaccines and co-administration strategies emerged as potential solutions to alleviate this predicament. Our objective is to delve into the concurrent administration of the sabin-strain-based inactivated poliovirus vaccine (sIPV), the diphtheria-tetanus-acellular pertussis vaccine (DTaP), and measles-mumps-rubella vaccine (MMR), with the intention of bridging the evidentiary gap pertaining to vaccine co-administration in Chinese infants, and to ensure a safe and effective vaccination strategy, ultimately leading to an augmentation in immunization coverage. METHODS: This study was a follow-up trial of the "Immunogenicity and safety of concomitant administration of the sIPV with the DTaP vaccine in children: a multicenter, randomized, non-inferiority, controlled trial." Blood samples were collected on day 0 and day 30, and serum antibody levels were detected to measure antibody responses to each of the antigens. Local and systemic adverse events were monitored and compared among groups. This study is the first to fill the knowledge gap in China regarding the safe and effective combined vaccination of sIPV, DTaP, and MMR vaccines. RESULTS: The geometric mean titer of the poliovirus types I, II, and III neutralizing antibodies were 1060.22 (95% CI: 865.73-1298.39), 1537.06 (95% CI: 1324.27-1784.05), and 1539.10 (95% CI: 1296.37-1827.29) in group I on day 30; geometric mean titer of antibodies against DTaP and MMR in the simultaneous vaccination group was non-inferior to those in the DTaP alone and MMR alone group. Reporting rates of local and systemic adverse reactions were similar between groups and no serious adverse events were reported throughout the clinical study period. CONCLUSION: Co-administration of the sIPV, DTaP, and MMR was safe and did not impact immunogenicity, which would help to mitigate administrative costs and enhance vaccine coverage rates.

Composition, structure and functional properties of protein concentrates and isolates produced from walnut (Juglans regia L.).

In this study, composition, structure and the functional properties of protein concentrate (WPC) and protein isolate (WPI) produced from defatted walnut flour (DFWF) were investigated. The results showed that the composition and structure of walnut protein concentrate (WPC) and walnut protein isolate (WPI) were significantly different. The molecular weight distribution of WPI was uniform and the protein composition of DFWF and WPC was complex with the protein aggregation. H(0) of WPC was significantly higher (p < 0.05) than those of DFWF and WPI, whilst WPI had a higher H(0) compared to DFWF. The secondary structure of WPI was similar to WPC. WPI showed big flaky plate like structures; whereas WPC appeared as a small flaky and more compact structure. The most functional properties of WPI were better than WPC. In comparing most functional properties of WPI and WPC with soybean protein concentrate and isolate, WPI and WPC showed higher fat absorption capacity (FAC). Emulsifying properties and foam properties of WPC and WPI in alkaline pH were comparable with that of soybean protein concentrate and isolate. Walnut protein concentrates and isolates can be considered as potential functional food ingredients.

Effects of Oxidation Modification by Malondialdehyde on the Structure and Functional Properties of Walnut Protein.

(1) Background: The effects of protein oxidization induced by malondialdehyde (MDA), which was selected as a representative of lipid peroxidation products, on the structure and functional properties of walnut protein were investigated. (2) Methods: Walnut protein isolate was produced by alkali-soluble acid precipitation. The modification of walnut protein isolate was conducted by MDA solutions (0, 0.01, 0.1, 1, and 10 Mm), which were incubated in the dark for 24 h. (3) Results: Increased carbonyl content and the degradation of sulfhydryl groups indicated MDA-induced protein oxidization. The circular dichroism spectra revealed disruption of the ordered protein secondary structure. The change in the tertiary conformation of the MDA-treated protein was observed through intrinsic fluorescence. Small polypeptide chain scission was observed at low MDA concentrations (≤0.1 mM) and protein aggregation was observed at high MDA concentrations (>0.1 mM) using high-performance size exclusion chromatography. Oxidized protein solubility was reduced. Furthermore, the emulsification stability index, foam capacity, and foam stability of walnut proteins were increased after treatment with 0.1 mM of MDA. An excessive concentration of MDA (>0.1 mM) decreased emulsification and foaming properties. (4) Conclusions: These results show that MDA oxidation modified the structure of walnut protein and further affected its function, which should be taken into account in processing walnut protein products.

Effect of Oxidative Modification by Peroxyl Radical on the Characterization and Identification of Oxidative Aggregates and In Vitro Digestion Products of Walnut (Juglans regia L.) Protein Isolates.

Walnut protein is a key plant protein resource due to its high nutritional value, but walnuts are prone to oxidation during storage and processing. This article explored the oxidative modification and digestion mechanism of walnut protein isolates by peroxyl radical and obtained new findings. SDS-PAGE and spectral analysis were used to identify structural changes in the protein after oxidative modification, and LC-MS/MS was used to identify the digestion products. The findings demonstrated that as the AAPH concentration increased, protein carbonyl content increased from 2.36 to 5.12 nmol/mg, while free sulfhydryl content, free amino content, and surface hydrophobicity decreased from 4.30 nmol/mg, 1.47 µmol/mg, and 167.92 to 1.72 nmol/mg, 1.13 µmol/mg, and 40.93 nmol/mg, respectively. Furthermore, the result of Tricine-SDS-PAGE in vitro digestion revealed that protein oxidation could cause gastric digestion resistance and a tendency for intestinal digestion promotion. Carbonyl content increased dramatically during the early stages of gastric digestion and again after 90 min of intestine digestion, and LC-MS/MS identified the last digestive products of the stomach and intestine as essential seed storage proteins. Oxidation causes walnut proteins to form aggregates, which are then re-oxidized during digestion, and proper oxidative modification may benefit intestinal digestion.

Application of Imaging Indicators Based on 18F-Fluorodeoxyglucose Positron Emission Tomography/Computed Tomography in Colorectal Peritoneal Carcinomatosis.

Objective: The imaging features of peritoneal carcinomatosis (PC) with different locations and pathological types of colorectal cancer (CRC) on 18F-fluorodeoxyglucose positron emission tomography/computed tomography (18F-FDG PET/CT) were analyzed and discussed. Methods: The PET/CT data of 132 patients with colorectal peritoneal carcinomatosis (CRPC) who met the inclusion and exclusion criteria between May 30, 2016, and December 31, 2019, were collected and analyzed. Observations included the location and pathological type of CRC, the peritoneal cancer index (PCI), standardized uptake maximum value (SUVmax), and retention index (RI) of the CRPC. Statistical analysis was performed using SPSS 20.0 software, and P < 0.05 was considered statistically significant. Results: (1) The range of the PCI in the 132 patients studied was 2-30, with a mean value of 7.40 ± 8.14. The maximum long diameter of the CRPC lesions ranged from 0.6 to 12.1 cm, with an average of 3.23 ± 1.94 cm. The SUVmax ranged from 1.2 to 31.0, with a mean value of 9.65 ± 6.01. The SUVmax and size correlation coefficient for maximal CRPC lesions was r = 0.47 (P < 0.001). The RI range of the 72 patients who underwent time-lapse scanning was -10.0-112.2%, with RI quartiles of 13.5-48.9%; RI was ≥5% in 65 cases and <5% in seven cases. (2) The patients were grouped by the location of their CRC: the right-sided colon cancer (RCC, n = 37), left-sided colon cancer (LCC, n = 44), and rectal cancer groups (RC, n = 51). There were significant differences in the CRC pathological types (P = 0.009) and PCI scores (P = 0.02) between the RCC and RC groups and the RI between the RCC group and the other two groups (P < 0.001). (3) There were 88 patients organized into three groups by the pathology of their CRC: the moderately well-differentiated adenocarcinoma (group A, n = 57), poorly differentiated adenocarcinoma (group B, n = 16), and mucinous adenocarcinoma groups (group C, n = 15 cases, including one case of signet-ring cell carcinoma). There were significant differences in the CRC position (P = 0.003) and SUVmax (P = 0.03) between groups A and C. Conclusion: The PCI, SUVmax, and RI of peritoneal metastatic carcinoma caused by CRC in different locations and pathological types vary. Mucinous adenocarcinoma and poorly differentiated adenocarcinoma are relatively common in the right colon, and the PCI of peritoneal metastatic carcinoma is fairly high, but the SUVmax and RI are somewhat low.

Distribution Characteristics of Colorectal Peritoneal Carcinomatosis Based on the Positron Emission Tomography/Peritoneal Cancer Index.

Background: Colorectal peritoneal carcinomatosis (CRPC) is a primary cause of death in colorectal cancer (CRC) patients. In the past, computed tomography (CT) has been the primary method used to evaluate the distribution of CRPC. This study uses 18F-FDG positron emission tomography/computed tomography (PET/CT) to investigate the distribution characteristics of CRPC. Materials and Methods: The distribution characteristics of 46 patients with CRC who were treated in the authors' hospital were retrospectively analyzed using the peritoneal cancer index (PCI). Results: The 46 patients in the study showed CRPC involvement in 203 of the 598 abdominal and pelvic regions studied (33.9%, 203/598). The regional proportions of CRPC involvement, from high to low, were as follows: region 6 (13.8%), region 0 (10.3%), region 1 (9.9%), region 5 (8.9%), region 7 (8.4%), region 3 (8.4%), region 2 (7.4%), region 4 (7.4%), region 11 (6.9%), region 8 (6.4%), region 12 (5.4%), region 9 (3.4%), and region 10 (3.4%). Thirty-three patients had a PCI of <20, and 13 patients had a PCI of ≥20. Those 13 were among the 17 (37% 17/46) who had CRPC involvement in all three regions. According to the location of the primary CRC focus, the 46 patients were divided into three groups: right hemicolon, left hemicolon, and rectum. The frequency of CRPC was greater in the rectum group than in the left hemicolon group, and the SUVmax of CRPC was greater in the right hemicolon group than in the left hemicolon group; these differences were statistically significant (p < 0.05). Conclusions: The distribution of CRPC has certain characteristics in the abdominal and pelvic cavities. The PET-PCI scores can provide a basis for the diagnosis and clinical treatment strategies in patients with CRC.

Effects of oxidative modification of peroxyl radicals on the structure and foamability of chickpea protein isolates.

A chickpea protein isolate (CPI) was oxidized using peroxyl radicals derived from 2,2'-azobis (2-amidopropane) dihydrochloride (AAPH), and the structural and foaming properties of the oxidized CPI were evaluated. The oxidation degree of protein was determined by measuring carbonyl content, dimer tyrosine content, free thiol content, and total thiol content. The structural changes of oxidized protein were evaluated by surface hydrophobicity, endogenous fluorescence intensity, Fourier transform infrared spectroscopy, SDS-PAGE, and amino acid content changes. Compared with the control group (0 mmol/L AAPH), moderate oxidation (0.04 mmol/L AAPH) led to the formation of a soluble protein with flexibility, which could improve the foaming properties of the protein (foaming capacity and stability increased by 25.50% and 6.38%, respectively). Over-oxidized (25 mmol/L AAPH) protein exhibited improved foaming capability, but its foam stability was reduced owing to the formation of insoluble aggregates. The results indicate that oxidation can change protein conformation, and the protein structure can affect the foamability of the CPI. PRACTICAL APPLICATION: CPI is a protein supplement food. Protein oxidation can occur during processing and storage, thereby affecting protein function. In this study, we evaluated how peroxy free radicals affect the structure, solubility and foaming properties of CPI, and clarified the mechanism between them. It has been found that peroxy free radicals can accelerate the oxidation of proteins and have a significant effect on foaming. Therefore, the degree of oxidation should be controlled to improve the quality of CPI.

µ-Calpain oxidation and proteolytic changes on myofibrillar proteins from Coregonus Peled in vitro.

The purpose of this study was to investigate the structural properties of µ-calpain induced by hydroxyl radical oxidation and its effect on the degradation of myofibrillar protein (MP) from the dorsal muscles of Coregonus peled. The carbonyl and sulfhydryl content of µ-calpain changed significantly after oxidation. The content of α-helix in the secondary structure decreased from 0.825 to 0.232 and the changes in intrinsic fluorescence and ultraviolet (UV) absorption spectra indicated that oxidation could cause the expansion and aggregation of µ-calpain molecules. Changes in µ-calpain structure could improve the activity of µ-calpain, reaching the highest value at 0.5 mM H2O2. The highest µ-calpain activity facilitate the degradation of unoxidized MP, while the degradation of oxidized MP was facilitated at the 1 mM H2O2. Thus, our results provide a scientific basis for the interaction mechanism among hydroxyl radical oxidation, µ-calpain, and MP degradation.

The influence of endogenous cathepsin in different subcellular fractions on the quality deterioration of Northern pike (Esox lucius) fillets during refrigeration and partial freezing storage.

The purpose of this study was to investigate the endogenous cathepsin activity in each subcellular fraction and the effect of this activity on myofibrillar protein and texture during refrigeration and partial freezing storage of northern pike (Esox lucius) fillets. The results showed that fillets stored under the refrigerated condition were more susceptible to oxidation than partial freezing. Endogenous cathepsin activity indicated that partial freezing destroys the integrity of lysosomes more effectively than refrigeration and inhibits the increase in cathepsin B and B + L in lysosomes. The activity of cathepsin B and B + L in lysosomes, mitochondria and myofibrils under the partial freezing conditions was always lower than that under refrigeration. Texture analysis showed that refrigeration had a negative impact on hardness and springiness. In conclusion, the cathepsin activity in each subcellular fraction was effectively inhibited and better textural characteristics were obtained with partial freezing than refrigeration.