Unlocking the molecular modifications of plasma-activated water-induced oxidation through redox proteomics: In the case of duck myofibrillar protein (Anas platyrhynchos).

Plasma-activated water (PAW) contains multiple active species that alter the structure of myofibrillar protein (MP) to enhance their gel properties. This work investigated the impact of PAW on the oxidation of cysteine in MP by label-free quantitative proteomics. PAW treatment caused the oxidation of 8241 cysteine sites on 2815 proteins, and structural proteins such as nebulin, myosin XVIIIB, myosin XVIIIA, and myosin heavy chain were susceptible to oxidation by PAW. Bioinformatics analysis, including Gene Ontology (GO), Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway, subcellular localization, and STRING analysis, indicated that these proteins with differential oxidation sites were mainly derived from the cytoplasm and membrane, and were involved in multiple GO terms and KEGG pathways. This is one of the first reports of the redox proteomic changes induced by PAW treatment, and the results are useful for understanding the possible mechanism of PAW-induced oxidation of MP.

Goose liver protein emulsion with enhanced interfacial stabilization by facile core-shell curcumin complexation.

The role of facile curcumin dispersion and its hydrophobic complexation onto GLP, in the form of shell (GLPC-E), core (GLPE-C) and with synergy (GLP-ECE), on the protein interfacial and emulsion stabilization was investigated. Turbiscan instability index, microrheological elasticity, viscosity and solid-liquid balance values showed that the O/W emulsion stability was in the order of GLP-E < GLPC-E < GLPE-C < GLP-ECE. GLP-ECE also gave the most reduced D [4, 3] (8.11 ± 0.14 µm) with lowest indexes of flocculation (2.80 ± 0.05 %) and coalescence (2.83 ± 0.10 %) at day 5. Interfacial shear rheology suggested the GLP-curcumin complexation fortified the GLP interfacial gelling and then the efficiency as steric stabilizer, especially of core-shell complexation (14.2 mN/m) that showed the most sufficient in-plane protein interaction against strain. Dilatational elasticity and desorption observation revealed the synergistic curcumin complexation facilitated GLP unfolding and macromolecular association at O/W interface, as was also verified from SEM image and surface hydrophobicity (from 36.23 to 76.04). Overall, this study firstly reported the facile curcumin bi-physic dispersion and GLP complexation in improving the emulsion stabilizing efficiency of the protein by advancing its interfacial stabilization.

Insights into the identification of bitter peptides from Jinhua ham and its taste mechanism by molecular docking and transcriptomics analysis.

In order to identify the peptides responsible for bitter defects and to understand the mechanism of bitterness in dry-cured ham, the peptides were identified by LC-MS/MS, and the interaction between bitter peptides and receptor proteins were evaluated by molecular docking and molecular dynamics simulation; the signal transduction mechanism of bitter peptides was investigated using the model of HEK-293T cells by calcium imaging and transcriptomics analysis. The results of LC-MS/MS showed that 11 peptides were identified from the high bitterness fraction of defective ham; peptides PKAPPAK, VTDTTR and YIIEK derived from titin showed the highest bitterness values compared with other peptides. The results of molecular docking showed that lower CDOCKER energy was observed in the interaction between these peptides and hT2R16 in comparison with these receptors of hT2R1, hT2R4, hT2R5, hT2R8 and hT2R14, and the interaction of hT2R16 and peptides was stabilized by hydrophobic interaction and hydrogen bond. The average RMSF values of VTDTTR were higher than that of YIIEK and PKAPPAK, while EC50 values of VTDTTR were lower compared with PKAPPAK and YIIEK. Transcriptomics analysis showed that 529 differentially expressed genes were identified in HEK-293T cells during the stimulating by VTDTTR and were mainly enriched into neuroactive ligand-receptor interaction, MAPK pathway, cAMP pathway and calcium signaling pathway, which were mainly responsible for the bitter signal transduction of VTDTTR. These results could provide evidence for understanding the bitter defects of dry-cured ham and the taste mechanism of bitter peptide.

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.

Phosphate type dependent phosphorylation on the interfacial and emulsion stabilizing behaviors of goose liver protein: Perspective of protein charging.

Elucidation on the emulsifying behaviors of goose liver protein (GLP) from interfacial perspective was scarce when protein charging was altered. This work aimed to elucidate the role of phosphorylation on the interfacial associative interaction and then emulsion stabilizing properties of GLP using three structurally relevant phosphates of sodium trimetaphosphate (STMP), sodium tripolyphosphate (STPP) and sodium pyrophosphate (TSPP). A monotonic increment of protein charging treated from STMP, STPP to TSPP caused progressively increased particle de-aggregation, surface hydrophobicity and structural flexibility of GLP. Compared with STMP and TSPP, STPP phosphorylation rendered the most strengthened interfacial equilibrium pressure (11.98 ± 0.24 mN/m) due to sufficient unfolding but moderated charging character conveyed. Desorption curve and interfacial protein microstructure indicated that STPP phosphorylation caused the highest interfacial connectivity between proteins adsorbed onto the same droplet, as was also verified by interfacial elastic modulus (10.3 ± 0.21 mN/m). STPP treated GLP also yielded lowest droplet size (8.16 ± 0.10 µm), flocculation (8.18%) and Turbiscan stability index (8.78 ± 0.36) of emulsion but most improved microrheological properties. Overall, phosphorylation functioned itself in fortifying the intradroplet protein-protein interaction but restraining the interdroplet aggregation, and STPP phosphorylation endowed the protein with most enhanced interfacial stabilization and emulsifying efficiency.

Exploring the binding mechanisms of thermally and ultrasonically induced molten globule-like ß-lactoglobulin with heptanal as revealed by multi-spectroscopic techniques and molecular simulation.

This work employed the model protein ß-lactoglobulin (BLG) to investigate the contribution of microstructural changes to regulating the interaction patterns between protein and flavor compounds through employing computer simulation and multi-spectroscopic techniques. The formation of molten globule (MG) state-like protein during the conformational evolution of BLG, in response to ultrasonic (UC) and heat (HT) treatments, was revealed through multi-spectroscopic characterization. Differential MG structures were distinguished by variations in surface hydrophobicity and the microenvironment of tryptophan residues. Fluorescence quenching measurements indicated that the formation of MG enhanced the binding affinity of heptanal to protein. LC-MS/MS and NMR revealed the covalent bonding between heptanal and BLG formed by Michael addition and Schiff-base reactions, and MG-like BLG exhibited fewer chemical shift residues. Molecular docking and molecular dynamics simulation confirmed the synergistic involvement of hydrophobic interactions and hydrogen bonds in shaping BLG-heptanal complexes thus promoting the stability of BLG structures. These findings indicated that the production of BLG-heptanal complexes was driven synergistically by non-covalent and covalent bonds, and their interaction processes were influenced by processes-induced formation of MG potentially tuning the release and retention behaviors of flavor compounds.

Insights into the mechanism of extracellular proteases from Penicillium on myofibrillar protein hydrolysis and volatile compound evolutions.

To investigate the mechanism of Penicillium proteases on the hydrolysis of myofibrillar protein (MP) and volatile compound evolutions, enzymatic characteristics of Penicillium proteases, hydrolysis capacities for MP, interactions between Penicillium proteases and MP, and profile changes of volatile compounds were investigated. P. aethiopicum (PA) and P. chrysogenum (PC) proteases showed the largest hydrolysis activities at pH 9.0 and 7.0, and were identified as alkaline serine protease and serine protease by LC-MS/MS, respectively. The proteases of PA and PC significantly degraded myosin and actin, and PA protease showed higher hydrolysis capacity for myosin than that of PC protease, which was confirmed by higher proteolysis index (56.06 %) and lower roughness (3.99 nm) of MP after PA treatment. Molecular docking revealed that hydrogen bond and hydrophobic interaction were the major interaction forces of Penicillium proteases with myosin and actin, and PA protease showed more binding sites with myosin compared with PC protease. The total content of free amino acids increased to 6.02-fold for PA treatment and to 5.51-fold for PC treatment after 4 h hydrolysis of MP, respectively. GC-MS showed that aromatic aldehydes and pyrazines in PA showed the largest increase compared with the control and PC during the hydrolysis of MP. Correlation analysis demonstrated that Phe, Leu and Ile were positively related with the accumulation of benzaldehyde, benzeneacetaldehyde, 2,4-dimethyl benzaldehyde and 2,5-dimethyl pyrazine.

Investigation into the characteristic volatile flavor of old duck.

In order to explore the characteristic aroma flavor and its formation mechanism of old ducks, two ages (30 days and 60 days) of young ducks and three ages of old ducks (300 days, 900 days, and 1500 days) were selected and studied. An electronic nose was applied to evaluate the overall aroma flavor, and the result showed significant differences between the five duck samples. By gas chromatography-mass spectrometry (GC-MS), forty-eight volatile flavor compounds were detected, including seven aldehydes, six esters, five alcohols, five nitrogen compounds, twenty-one hydrocarbons, and four others. Among these compounds, twelve components, such as hexanal and dimethyl anthranilate, were considered as the characteristic flavor compounds along with duck aging. Furthermore, correlation analysis indicated that meat's unsaturated free fatty acids, especially linoleic acid (C18:2), were responsible for the duck's characteristic flavor formation. These data contribute to the flavor research and identification of old ducks.

Phenolic structure dependent interaction onto modified goose liver protein enhanced by pH shifting: Modulations on protein interfacial and emulsifying properties.

The appropriateness of animal by-product proteins as emulsifiers is barely explored compared to their meat counterparts. This paper focused on improving interfacial and emulsifying properties of modified goose liver protein using three structurally relevant polyphenols either enhanced by pH shifting (P-catechin, P-quercetin and P-rutin) or not (catechin, quercetin and rutin). Due to its high hydrophobicity and limited steric hindrance, quercetin was more sufficient to hydrophobically interact (ΔH > 0, ΔS > 0) with MGLP than catechin and rutin. Results showed that polyphenol interactive affinity was positively correlated to surface hydrophobicity but negatively to size and aggregation extent of MGLP. Interfacial pressure and dilatational elastic modulus implied that synergistic polyphenol interaction and pH shifting favored the interfacial adsorption and macromolecular association of MGLP, particularly for P-quercetin with the values reached to 19.9 ± 2.0 mN/m and 22.9 ± 1.2 mN/m, respectively. Emulsion stabilized by P-quercetin also maintained highest physical and oxidative stabilities regarding the lowest D [4,3] (3.78 ± 0.27 µm) and creaming index (8.38 ± 0.43 %), together with highest mono- (19.51 %) and polyunsaturated fatty acid content (29.39 %) during storage. Overall, chemical structure of polyphenols may be determining in fabricating MGLP-polyphenol complexes with improved emulsion stabilization efficiency.

Protection Mechanism of Metal Ion Pre-Stress on Lactobacillus acidophilus CICC 6074 under Acid Tolerance.

The prerequisite for the probiotic effect of lactic acid bacteria is that they could survive the acid stress environment of production and application. In this experiment, the mechanism for the effect of different metal ion pre-stress on the acid-tolerant survival of Lactobacillus was investigated. Scanning electron microscopy, Fourier infrared spectroscopy, and flow cytometry were used to analyze the condition of bacteria after acid treatment, which revealed that different metal ion pre-stress could improve the survival ability of Lactobacillus acidophilus CICC 6074 under low acid conditions by improving cell morphology, mitigating cell membrane damage, and regulating surface protein expression. Furthermore, Tandem Mass Tags (TMT) proteomic analysis revealed that Mn2+ pre-stress showed relatively more superior protective effects on acid tolerance in L. acidophilus CICC 6074 through activation of DNA replication, RNA synthesis, S-layer protein secretion, H+-ATPase enzyme activity, etc. This study will provide new ideas and a theoretical basis for the development and application of lactic acid bacteria.

The combination of high-throughput sequencing and LC-MS/MS reveals the mechanism of Staphylococcus inoculation on bacterial community succession and taste development during the processing of dry-cured bacon.

BACKGROUND: To understand the mechanism of co-inoculation of Staphylococcus vitulinus and Staphylococcus xylosus (SX&SV) on taste quality of dry-cured bacon, physicochemical parameters, microbial community, metabolite compositions and taste attributes were investigated during the processing of dry-cured bacon with Staphylococcus inoculation. The potential correlation between core bacteria and metabolites was evaluated, and the metabolic pathway of key metabolites was further explored. RESULTS: The values of pH, water activity and adhesiveness were significantly lower in SX&SV, and more than 2.56- and 2.15-fold higher values in richness and overall acceptance were found in SX&SV bacon than in CK bacon. The overwhelming advantage of Staphylococcus was confirmed in SX&SV by high-throughput sequencing. Sixty-six metabolites were identified by liquid chromatography-tandem mass spectrometry, and oligopeptides, amino acid derivatives and organic acids were the key components. Pearson correlation demonstrated that the accumulation of oligopeptides, amino acid derivatives and organic acids were positively correlated with high abundance of Staphylococcus. The pathways of purine metabolism, glutathione metabolism and glutamate metabolism were mainly involved in developing the taste quality of SX&SV. CONCLUSION: The co-inoculation of Staphylococcus vitulinus and Staphylococcus xylosus enhanced the taste attributes of dry-cured bacon. The present study provides the theoretical reference with respect to regulating the taste quality of fermented meat products by starter cultures of Staphylococcus during manufacture. © 2023 Society of Chemical Industry.

Ultrasound-assisted phosphorylation of goose myofibrillar proteins: improving protein structure and functional properties.

BACKGROUND: Goose meat is rough and embedded with dense connective tissue, impairing protein solubility. Therefore, to improve the functional properties of goose myofibrillar protein (GMP), ultrasound was used to assist the phosphorylation of GMP. RESULTS: The fact that GMP attached covalently with the phosphate group of sodium tripolyphosphate (GMP-STP) was disclosed directly by Fourier transform infrared spectroscopy. Furthermore, ultrasound significantly improved the hydrophobicity and solubility of GMP-STP, which could be attributed to the conversion of α-helix to ß-sheet, ß-turns, and random coils by sonication. The spatial stabilization of the protein phosphorylation process was boosted by ultrasound, making the droplets more dispersed, and thus an improvement in the functional properties of GMP-STP was observed. Water-holding capacity, oil-binding capacity, and emulsifying and foaming properties were best at an ultrasound power of 400 W. CONCLUSION: Ultrasound-assisted phosphorylation has great potential to modulate the structure-function relationship of proteins. © 2023 Society of Chemical Industry.

Effect of lentinan on gelling properties and structural changes of goose myofibrillar protein under oxidative stress.

BACKGROUND: The reduction of protein oxidation is important for maintaining the product quality of reconstituted meat. In this study, the dose-dependent effects of lentinan (LNT) on gelling properties and chemical changes in oxidatively stressed goose myofibrillar protein were investigated. RESULTS: Myofibrillar protein (MP) with 200 µmol g-1 protein LNT increased gel strength by 87.90 ± 9.26% in comparison with LNT-free myofibrillar protein after oxidation. Scanning electron microscopy analysis revealed that the gel network containing LNT was compact, with small pores and uniform distribution. The absolute value of the zeta potential reduced significantly following oxidation of LNT with 200 µmol g-1 protein at 4 °C for 12 h compared with the zeta potential without LNT, according to the laser particle size analyzer. The incorporation of LNT increased protein solubility and -SH content, inhibited carbonyl formation, enhanced α-helix content and tryptophan intrinsic fluorescence intensity, and reduced exposure of hydrophobic groups and protein aggregation. CONCLUSION: The results indicated that adding LNT to myofibrillar protein could improve gel. This is related to its protective effect on conformational changes in the oxidation system. Lentinan is therefore recommended for oxidatively stressed goose meat processing to enhance the MP gelling potential. © 2023 Society of Chemical Industry.

Colloidal Nanoparticles Isolated from Duck Soup Exhibit Antioxidant Effect on Macrophages and Enterocytes.

Food-derived colloidal nanoparticles (CNPs) have been found in many food cooking processes, and their specific effects on human health need to be further explored. Here, we report on the successful isolation of CNPs from duck soup. The hydrodynamic diameters of the obtained CNPs were 255.23 ± 12.77 nm, which comprised lipids (51.2%), protein (30.8%), and carbohydrates (7.9%). As indicated by the tests of free radical scavenging and ferric reducing capacities, the CNPs possessed remarkable antioxidant activity. Macrophages and enterocytes are essential for intestinal homeostasis. Therefore, RAW 264.7 and Caco-2 were applied to establish an oxidative stress model to investigate the antioxidant characteristics of the CNPs. The results showed that the CNPs from duck soup could be engulfed by these two cell lines, and could significantly alleviate 2,2'-Azobis(2-methylpropionamidine) dihydrochloride (AAPH)-induced oxidative damage. It indicates that the intake of duck soup is beneficial for intestinal health. These data contribute to revealing the underlying functional mechanism of Chinese traditional duck soup and the development of food-derived functional components.

Contribution of process-induced molten-globule state formation in duck liver protein to the enhanced binding ability of (E,E)-2,4-heptadienal.

BACKGROUND: Extracted proteins of alternative animal origin tend to present strong off-flavor perception due to physicochemical interactions of coextracted off-flavor compounds with proteins. To investigate the relationship between absorption behaviors of volatile aromas and the processes-induced variations in protein microstructures and molecular conformations, duck liver protein isolate (DLp) was subjected to heating (65/100 °C, 15 min) and ultra-high pressure (UHP, 100-500 MPa/10 min, 28 °C) treatments to obtain differential unfolded protein states. RESULTS: Heat and UHP treatments induced the unfolding of DLp to varied degrees, as revealed by fluorescence spectroscopy, ultraviolet-visible absorption, circular dichroism spectra and surface hydrophobicity measurements. Two types of heating-denatured states with varied unfolding degrees were obtained, while UHP at both levels of 100/500 MPa caused partial unfolding of DLp and the presence of a molten-globule state, which significantly enhanced the binding affinity between DLp and (E,E)-2,4-heptadienal. In particular, significantly modified secondary structures of DLp were observed in heating-denatured samples. Excessive denaturing and unfolding degrees resulted in no significant changes in the absorption behavior of the volatile ligand, as characterized by observations of fluorescence quenching and analysis of headspace concentrations. CONCLUSION: Defining process-induced conformational transition behavior of matrix proteins could be a promising strategy to regulate food flavor attributes and, particularly, to produce DLp coextracted with limited off-flavor components by modifying their interaction during extraction processes. © 2023 Society of Chemical Industry.

Antioxidant Activity and Cell Protection of Glycosylated Products in Different Reducing Sugar Duck Liver Protein Systems.

Duck liver is an important by-product of duck food. In this study, we investigated the effects of glucose, fructose, and xylose on the antioxidant properties of glycosylated products of duck liver protein and their protective effects on HepG2 cells. The results show that the glycosylation products of the three duck liver proteins (DLP-G, DLP-F, and DLP-X) all exhibit strong antioxidant activity; among three groups, DLP-X shows the strongest ability to scavenge DPPH, ·OH free radicals, and ABTS+ free radicals. The glycosylated products of duck liver protein are not toxic to HepG2 cells and significantly increase the activity of antioxidant enzymes such as SOD, CAT, and GSH-Px in HepG2 cells at the concentration of 2.0 g/L, reducing oxidative stress damage of cells (p < 0.05). DLP-X has a better effect in reducing oxidative damage and increasing cellular activity in HepG2 cells than DLP-G and DLP-F (p < 0.05). In this study, the duck liver protein glycosylated products by glucose, fructose, and xylose were named as DLP-G, DLP-F, and DLP-X, respectively.

Recent developments in off-odor formation mechanism and the potential regulation by starter cultures in dry-cured ham.

Foul-smelling odors are main quality defects of dry-cured ham, which are connected with the excessive degradation of the structural proteins and excessive oxidation of lipids caused by the abnormal growth of spoilage microorganisms, threatening the development of dry-cured ham industry. Characterizing the key microorganisms and metabolites resulted in the spoilage of dry-cured ham, and discussing the relationship between spoilage microorganisms and metabolites are the key aspects to deeply understand the formation mechanism of off-odor in dry-cured ham. Until now, there is no detailed discussion or critical review on the role of spoilage microorganisms in developing the off-odor of dry-cured ham, and the regulation of off-odor and spoilage microorganisms by starter cultures has been not discussed. This review shows the recent achievement in the off-odor formation mechanism of dry-cured ham, and outlines the potential regulation of off-odor defects in dry-cured ham by starter cultures. Results from current research show that the abnormal growth of Lactic acid bacteria, Micrococcaceae, Enterobacteriaceae, Yeasts and Molds plays a key role in developing the off-odor defects of dry-cured ham, while the key spoilage microorganisms of different type hams are discrepant. High profile of aldehydes, acids, sulfur compounds and biogenic amines are responsible for off-odor development in spoiled dry-cured ham. Several starter cultures derived from these species of Staphylococcus, Penicillium, Debaryomyces, Pediococcus and Lactobacillus show a great potential to prevent microbiological hazards and improve flavor quality of dry-cured ham, whereas, the ecology, function and compatibility of these starter cultures with the processing parameters of dry-cured ham need to be further evaluated in the future.

The enhancement and mechanism of the perception of saltiness by umami peptide from Ruditapes philippinarum and ham.

To explore the saltiness enhancement effect and mechanism of umami peptides, umami peptides from Ruditapes philippinarum and ham were mixed with NaCl and determined using electronic tongue, sensory evaluation, and the aroma chicken model (ACM), then transmembrane channel-like protein 4(TMC4) receptor was constructed for molecular docking. The results showed that KEMQKN, NGKET, RGEPNND, AHSVRFY, LSERYP, NRTF, TYLPVH, EV, AGAGPTP, and GPAGPAGPR had saltiness enhancement effect, which could be increased to 0.4-0.6 % NaCl salty taste in 0.3 % NaCl. Under neutral conditions (pH6.5), most umami peptides were in negative ion state which may be the main reason that umami peptides could bind to the TMC4 receptor and enhance saltiness. The lowest docking energy was -113.325 kcal/mol among 10 peptides and the active sites Lys568, Trp145, Tyr565, Arg151, and Gln155 in TMC4 may play a key role. Thus, this study provides basic theory and data for salt-reduction strategies.

Interaction between Kidney-Bean Polysaccharides and Duck Myofibrillar Protein as Affected by Ultrasonication: Effects on Gel Properties and Structure.

The interaction of polysaccharides-protein with varied origins and structures provides opportunities for tailoring the physicochemical qualities of food protein-based materials. This work examined the feasibility of ultrasound-modified interaction between kidney bean dietary fiber (KSDF) and duck myofibrillar proteins (MP) to improve the physicochemical properties of the gel matrices. Accordingly, gel strength, water holding capacity, solubility, chemical interaction, secondary structure, and network structure of MP were determined. The addition of KSDF combined with the ultrasound treatment contributed to the improved water retention capability, G' values, and the reduced particle size of protein molecules, corresponding with the formation of dense pore-like structures. The results demonstrated that 1% KSDF and ultrasonication at 400 W significantly enhanced gel strength by up to 109.58% and the solubility increased by 213.42%. The proportion of α-helices of MP gels treated with 1% KSDF and ultrasonication at 400 W was significantly increased. The sonication-mediated KSDF-MP interaction significantly improved hydrophobic interactions of the proteins, thus explaining the denser network structure of the MP gels incorporated KSDF with ultrasound treatments. These results demonstrated the role of ultrasonication treatments in modifying KSDF-protein interaction to improve the gel and structural properties of the MP gels.

Identification and Characterization of Domains Responsible for Cell Wall Binding, Self-Assembly, and Adhesion of S-layer Protein from Lactobacillus acidophilus CICC 6074.

Lactobacillus S-layer protein (SLP) is a biologically active protein on the cell surface. To further elucidate the structures and functions of SLP in Lactobacillus acidophilus CICC 6074, this study was conducted to identify the functional domains of SLP which is responsible for cell wall anchoring, self-assembly, and adhesion. The gene (slpA) of L. acidophilus CICC 6074 SLP was amplified by polymerase chain reaction and speculated functional domains. Fusion proteins of C-terminal truncations from SLP were exogenously expressed in Escherichia coli BL21 (DE3). FITC-labeling N-terminal truncations of SLP were synthesized. The C-terminal domain was more likely to be the binding region, and the cell wall-anchored receptor of SLP was teichoic acid. Furthermore, N-terminal truncations could self-assemble to milk fat globule membrane polar lipid liposomes observed using a fluorescence microscope. Notably, SAN1 (region 32-55) of N-terminal truncations was mainly responsible for the adhesion of SLP to HT-29 cells. These results showed that SLP played a crucial role in the functions of L. acidophilus CICC 6074, which might be of significant reference value for future studies.