Egg white protein-based delivery system for bioactive substances: a review.

Some bioactive substances in food have problems such as poor solubility, unstable chemical properties and low bioavailability, which limits their application in functional food. Recently, many egg white protein-based delivery carriers have been developed to improve the chemical stability, biological activity and bioavailability of bioactive substances. This article reviewed the structure and properties of several major egg white proteins commonly used to construct bioactive substance delivery systems. Several common carrier types based on egg white proteins, including hydrogels, emulsions, micro/nanoparticles, aerogels and electrospinning were then introduced. The biological functions of common bioactive substances, the limitations, and the role of egg white protein-based delivery systems were also discussed. At present, whole egg white protein, ovalbumin and lysozyme are most widely used in delivery systems, while ovotransferrin, ovomucoid and ovomucin are less developed and applied. Egg white protein-based nanoparticles are currently the most commonly used delivery carriers. Egg white protein-based hydrogels, emulsions, and microparticles are also widely used. Future research on the application of various egg white proteins in developed new delivery systems will provide more choices for the delivery of various bioactive substances.

Chalcone-1-Deoxynojirimycin Heterozygote Reduced the Blood Glucose Concentration and Alleviated the Adverse Symptoms and Intestinal Flora Disorder of Diabetes Mellitus Rats.

Chalcone-1-deoxynojirimycin heterozygote (DC-5), a novel compound which was designed and synthesized in our laboratory for diabetes treatment, showed an extremely strong in vitro inhibitory activity on α-glucosidase in our previous studies. In the current research, its potential in vivo anti-diabetic effects were further investigated by integration detection and the analysis of blood glucose concentration, blood biochemical parameters, tissue section and gut microbiota of the diabetic rats. The results indicated that oral administration of DC-5 significantly reduced the fasting blood glucose and postprandial blood glucose, both in diabetic and normal rats; meanwhile, it alleviated the adverse symptoms of elevated blood lipid level and lipid metabolism disorder in diabetic rats. Furthermore, DC-5 effectively decreased the organ coefficient and alleviated the pathological changes of the liver, kidney and small intestine of the diabetic rats at the same time. Moreover, the results of 16S rDNA gene sequencing analysis suggested that DC-5 significantly increased the ratio of Firmicutes to Bacteroidetes and improved the disorder of gut microbiota in diabetic rats. In conclusion, DC-5 displayed a good therapeutic effect on the diabetic rats, and therefore had a good application prospect in hypoglycemic drugs and foods.

Effects of salt and heat treatment on the physicochemical properties, microstructure, secondary structure, and simulated in vitro gastrointestinal digestion of duck egg white.

BACKGROUND: The texture and structure of the duck egg white (DEW) gel under salt and heat treatment are crucial to its digestibility. Specifically, the structural changes of food protein gels have been recognized for their potential to regulate in vitro digestion. In this study, the effects of gel characteristics and simulated in vitro gastrointestinal digestion of DEW under combined salt and heat treatment were investigated. RESULTS: With the increase in salting time and temperature, a porous opaque gel with large particles was formed, the moisture content of DEW showed a downward trend, and the same was true for hardness changes. The microstructure suggested that, with the penetration of NaCl, DEW proteins were denatured, and the protein molecules gradually unfolded and then aggregated after 7 days. The secondary structure revealed that, as the salting time and temperature increased, the proportion of intermolecular ß-sheets and α-helices decreased. In terms of in vitro digestion, the highest digestibility was obtained at 14 days of salting combined with 100 °C heat treatment, and the digestibility was the lowest when marinated for 7 days at 121 °C. Liquid chromatography and tandem mass spectrometry (LC-MS/MS) indicated that the number of different types of peptides and specific peptides was positively correlated with the salting time and temperature of the DEW at the end of gastric digestion. CONCLUSIONS: Heat treatment at 100 °C has a higher in vitro digestibility than at 121 °C. Gels with low hardness, large pores, and rough textures are easier to digest by pepsin and release more peptides. © 2021 Society of Chemical Industry.

Formation of lysinoalanine in egg white under alkali treatment.

To investigate the formation mechanism of lysinoalanine (LAL) in eggs during the alkali treatment process, NaOH was used for the direct alkali treatment of egg white, ovalbumin, and amino acids; in addition, the amount of LAL formed during the alkali treatment process was measured. The results showed that the alkali treatment resulted in the formation of LAL in the egg white. The LAL content increased with increasing pH and temperature, with the LAL content first increasing and then leveling off with increasing time. The amount of LAL formed in the ovalbumin under the alkali treatment condition accounted for approximately 50.51% to 58.68% of the amount of LAL formed in the egg white. Thus, the LAL formed in the ovalbumin was the main source for the LAL in the egg white during the alkali treatment process. Under the alkali treatment condition, free L-serine, L-cysteine, and L-cystine reacted with L-lysine to form LAL; therefore, they are the precursor amino acids of LAL formed in eggs during the alkali treatment process.

Effect of basic alkali-pickling conditions on the production of lysinoalanine in preserved eggs.

During the pickling process, strong alkali causes significant lysinoalanine (LAL) formation in preserved eggs, which may reduce the nutritional value of the proteins and result in a potential hazard to human health. In this study, the impacts of the alkali treatment conditions on the production of LAL in preserved eggs were investigated. Preserved eggs were prepared using different times and temperatures, and alkali-pickling solutions with different types and concentrations of alkali and metal salts, and the corresponding LAL contents were measured. The results showed the following: during the pickling period of the preserved egg, the content of LAL in the egg white first rapidly increased and then slowly increased; the content of LAL in the egg yolk continued to increase significantly. During the aging period, the levels of LAL in both egg white and egg yolk slowly increased. The amounts of LAL in the preserved eggs were not significantly different at temperatures between 20 and 25ºC. At higher pickling temperatures, the LAL content in the preserved eggs increased. With the increase of alkali concentration in the alkali-pickling solution, the LAL content in the egg white and egg yolk showed an overall trend of an initial increase followed by a slight decrease. The content of LAL produced in preserved eggs treated with KOH was lower than in those treated with NaOH. NaCl and KCl produced no significant effects on the production of LAL in the preserved eggs. With increasing amounts of heavy metal salts, the LAL content in the preserved eggs first decreased and then increased. The LAL content generated in the CuSO4 group was lower than that in either the ZnSO4 or PbO groups.

Physicochemical and nutritional characteristics of preserved duck egg white.

In this paper, the physicochemical and nutritional characteristics of preserved duck egg white were analyzed and compared with fresh egg and hard-cooked egg white (n = 3). The data obtained showed that the preserved egg white was rich in essential amino acids and minerals, such as Ca, Mg, Fe, Zn, Cu, K, and Na. After fresh duck eggs were processed into preserved eggs, contents of moisture, CP, amino acid, and water-soluble vitamin of egg white significantly decreased (P < 0.05); however, pH, free amino acid content, and most inorganic elemental contents of egg white significantly increased (P < 0.05). The preserved egg white had higher a* (redness/greenness) and b* values (yellowness/blueness; P < 0.05) and lower L* value (lightness; P < 0.05) than hard-cooked egg white. The gel hardness of preserved egg white was approximately 50% of hard-cooked egg white; however, its springiness and cohesiveness were approximately 1.5 times of hard-cooked egg white. The results indicated that pickling with alkaline and other additives can significantly change physical properties and chemical composition of duck egg white, which make preserved egg white with characteristics of rich elements, brown color, and high springiness, but low vitamin.

Effects of alkaline concentration, temperature, and additives on the strength of alkaline-induced egg white gel.

Egg whites can undergo gelation at extreme pH. In this paper, the effects of NaOH concentration (1.5, 2, 2.5, and 3%), temperature (10, 20, 30, and 40°C), and additives (metallic compounds, carbohydrates, stabilizers, and coagulants) on the strength of alkaline-induced egg white gel were investigated. Results showed that NaOH concentration and induced temperature significantly affected the rate of formation and peak strength of the egg white gel. Of the 6 metallic compounds used in this experiment, CuSO4exhibited the optimal effect on the strength of alkaline-induced egg white gel, followed by MgCl2, ZnSO4, PbO, and CaCl2. When CuSO4concentration was 0.2%, the gel strength increased by 31.92%. The effect of Fe2(SO4)3was negligible. Of the 5 carbohydrate additives, xanthan gum (0.2%) caused the highest increase (54.31%) in the strength of alkaline-induced egg white gel, followed by sodium alginate, glucose, starch, and sucrose. Meanwhile, propylene glycol (0.25%) caused the highest improvement (15.78%) in the strength of alkaline-induced egg white gel among the 3 stabilizing agents and coagulants used, followed by Na2HPO4and glucono-δ-lactone.

The Effect of Ionic Strength on the Formation and Stability of Ovalbumin-Xanthan Gum Complex Emulsions.

Protein-polysaccharide complexes have been widely used to stabilize emulsions, but the effect of NaCl on ovalbumin-xanthan gum (OVA-XG) complex emulsions is unclear. Therefore, OVA-XG complex emulsions with different XG concentrations at pH 5.5 were prepared, and the effects of NaCl on them were explored. The results indicated that the NaCl significantly affected the interaction force between OVA-XG complexes. The NaCl improved the adsorption of proteins at the oil-water interface and significantly enhanced emulsion stability, and the droplet size and zeta potential of the emulsion gradually decreased with increasing NaCl concentrations (0-0.08 M). In particular, 0.08 M NaCl was added to the OVA-0.2% XG emulsion, which had a minimum droplet size of 18.3 µm. Additionally, XG as a stabilizer could improve the stability of the emulsions, and the OVA-0.3% XG emulsion also exhibited good stability, even without NaCl. This study further revealed the effects of NaCl on emulsions, which has positive implications for the application of egg white proteins in food processing.

Characteristics of hen egg white lysozyme, strategies to break through antibacterial limitation, and its application in food preservation: A review.

Hen egg white lysozyme (HEWL) is used as a food additive in China due to its outstanding antibacterial properties. It is listed as GRAS grade (generally recognized as safe) by the United States Food and Drug Administration (FDA, US) and has been extensively researched and used in food preservation. And the industrial production of HEWL already been realized. Given the complex food system that can affect the antibacterial activity of HEWL, and the limitations of HEWL itself on Gram-negative bacteria. Based on the structure and main biological characteristics of HEWL, this paper focuses on reviewing methods to enhance the stability and antibacterial properties of HEWL. Immobilization tactics such as chemically driven self-assembly, embedding and adsorption address the restriction of poor HEWL antibacterial activity effected by external factors. Both intermolecular and intramolecular modification strategies break the bactericidal deficiencies of HEWL itself. It also comprehensively analyzes the current application status and future prospects of HEWL in the food preservation. There was limited research on the biological methods in modifying HEWL. If the HEWL is genetically engineered, it can broaden its antimicrobial spectrum, improve its other biological activities, so as to further expand its application in the food industry. At present, research on HEWL mainly focused on its antibacterial properties, whereas its application in anti-inflammatory and antioxidant effects also presented great potential.

Effects of different temperatures on the physicochemical characteristics, microstructure and protein structure of preserved egg yolk.

To clarify the mechanism of lower temperatures promoted the solidification of preserved egg yolk, the effects of temperature (4 °C, 10 °C and 25 °C) on the physicochemical properties, microstructure and protein structure of preserved egg yolk were studied. Results showed that the exterior egg yolk (EEY) exhibited higher pH, hardness and free sulfhydryl content at low-temperature pickling. The microstructure showed that the EEY gradually formed a denser gel network structure at lower temperatures. Electrophoresis results and Fourier transform infrared spectroscopy (FTIR) indicated that there were different degrees of protein degradation and cross-linking of proteins in the IEY (the interior egg yolk) and EEY and the decrease of ß-sheets in the secondary structure was accompanied by an increase of ß-turns during the formation of egg yolk gels. These results indicated that egg yolk solidification was faster and denser gel structure at 4 °C and 10 °C.

Recent trends in design of healthier fat replacers: Type, replacement mechanism, sensory evaluation method and consumer acceptance.

In recent years, with the increasing awareness of consumers about the relationship between excessive fat intake and chronic diseases, such as obesity, heart disease, diabetes, etc., the demand for low-fat foods has increased year by year. However, a simple reduction of fat content in food will cause changes in physical and chemical properties, physiological properties, and sensory properties of food. Therefore, developing high-quality fat replacers to replace natural fats has become an emerging trend, and it is still a technical challenge to completely simulate the special function of natural fat in low-fat foods. This review aims to provide an overview of development trends of fat replacers, and the different types of fat replacers, the potential fat replacement mechanisms, sensory evaluation methods, and their consumer acceptance are discussed and compared, which may provide a theoretical guidance to produce fat replacers and develop more healthy low-fat products favored by consumers.

Egg Yolk Lipids Alleviated Dextran Sulfate Sodium-Induced Colitis by Inhibiting NLRP3 Inflammasome and Regulating Gut Microbiota.

The increasing incidence of inflammatory bowel disease (IBD) has become a global phenomenon. Egg yolk lipids are one of the essential dietary foods, but its effects on intestinal immunity remain unclear. Here, egg yolk lipids are obtained using ethanol extraction and a total of 601 kinds of lipids are detected via lipidomics, including 251 kinds of triglycerides, 133 kinds of phosphatidylcholines, 44 kinds of phosphatidylethanolamines. Then, the study finds that egg yolk lipids significantly alleviate dextran sulfate sodium-induced colitis and reduce the production of inflammatory factors. Meanwhile, egg yolk lipids also maintain intestinal barrier integrity and decrease lipopolysaccharide translocation by alleviating intestinal structure damage and increasing the numbers of goblet cells and mucin 2. Mechanistically, egg yolk lipids attenuate colitis by inhibiting the assembly and activation of NLRP3 inflammasome. Moreover, the study also finds that egg yolk lipids reverse gut microbiota dysbiosis referring to increased relative abundance of Bacteroides acidifaciens and decrease relative abundance of Akkermansia muciniphila, as well as increased short chain fatty acids concentration in the gut. Together, the study elucidates the anti-colitis effect of egg yolk lipids and provides positive evidences for egg yolk lipids involving in dietary strategy and IBD therapy.

Mechanism of ultrasonic enhancement of the gelling properties of salted ovalbumin-cooked soybean isolate hybrid gels.

The influence of ultrasonic processing on the physicochemical characteristics, microstructure, and intermolecular forces of the hybrid gels obtained by heating the mixtures of different ratios of salted ovalbumin (SOVA)-cooked soybean protein isolate (CSPI) was investigated. With the growth of SOVA addition, ζ-potential in absolute value, cohesiveness, water-holding capacity (WHC), surface hydrophobicity, and the content of soluble protein of the hybrid gels decreased (P < 0.05), while the hardness, T2 relaxation time of the hybrid gels increased (P < 0.05). And the compactness of the network structure of the hybrid gel increased with the increase of SOVA addition. After being treated with ultrasound, significant increases (P < 0.05) of ζ-potential in absolute value, cohesiveness, WHC, and surface hydrophobicity of the hybrid gels were observed. In general, ultrasonic processing is one of the effective means to improve the gel properties of SOVA-CSPI hybrid gels.

Protective Effect of Egg Yolk Lipids against Dextran Sulfate Sodium-Induced Colitis: The Key Role of Gut Microbiota and Short-Chain Fatty Acids.

Egg yolk lipids significantly alleviate dextran sulfate sodium (DSS)-induced colitis by inhibiting NLRP3 inflammasome, reversing gut microbiota dysbiosis, and increasing short chain fatty acids (SCFAs) concentrations. However, the role of gut microbiota and the relationship between SCFAs and NLRP3 inflammasome are still unknown. Here, this study confirms that antibiotic treatment abolishes the protective effect of egg yolk lipids on DSS-induced colonic inflammation, intestinal barrier damage, and lipopolysaccharide translocation. Fecal microbiota transplantation also supports that egg yolk lipids alleviate colitis in a gut microbiota-dependent manner. Then, the study investigates the relationship between SCFAs and NLRP3 inflammasome, and finds that SCFAs significantly suppress colitis via inhibiting colonic NLRP3 inflammasome activation and proinflammatory cytokines secretions (interleukin, IL)-1ß and IL-18, and combined treatment of SCFAs and MCC950 (NLRP3 inhibitor) shows a better activity against colitis and NLRP3 inflammasome activation. Together, these findings provide positive evidence for gut microbiorta-SCFAs-NLRP3 axis as a novel target involving in the therapy of inflammatory bowel disease.

Formation mechanism of salted egg yolk mudding during storage: Protein oxidation, gel structure, and conformation.

The aim of this study was to investigate the formation mechanism of salted egg yolk (SEY) mudding during storage. Results showed that the soluble protein, hardness, and intrinsic fluorescence intensity of SEY decreased significantly during storage, while total volatile basic nitrogen, sulfhydryl group, dityrosine, adhesiveness, and surface hydrophobicity increased significantly, and the intrinsic fluorescence peak position red-shifted at first and then blue-shifted. In addition, from the results of infrared and microstructure analyses, there was an obvious oxidation reaction between protein and lipid in the late storage stage; the structure of SEY was destroyed, many random coils were formed, and the degree of protein-lipid binding and the crystallinity of SEY protein decreased during storage. Finally, the heatmap analysis revealed that the protein and lipid oxidation and conformational changes might be the main reasons for SEY mudding. This study can provide theoretical guidance for the control of SEY mudding.

Amelioration of ovalbumin gel properties by EGCG via protein aggregation, hydrogen, and van der Waals force.

The mechanism of epigallocatechin gallate (EGCG)-modified ovalbumin gel (EMOG) was investigated. Results indicated that, with the increase of EGCG concentration from 0% to 0.05%, the opacity, hardness, and cohesiveness of EMOG increased significantly from 0.058 to 0.133, 321.0 g to 377.6 g, and 0.879 to 0.951, respectively, while the soluble protein, surface hydrophobicity, and free sulfhydryl decreased significantly by 41.74%, 28.26%, and 39.36%, respectively. Moreover, EGCG promoted the formation of dense and stable microstructures of EMOG, changed the expansion rate, and improved the stability of EMOG. Moreover, the results of silico simulation showed that EGCG would insert into ovalbumin and interact with the amino acids through van der Waals force and hydrogen bonds, leading to a compact and stable protein structure. In this paper, the mechanism of modification of ovalbumin by EGCG was elucidated at the macro and micro levels, providing insights into the action of polyphenols and proteins.

Changes in physicochemical properties and lipid oxidation lead to the formation of mud on salted egg yolks during storage.

Salted egg yolk (SEY) becomes easily "muddy" during storage, leading to a decrease in the quality of salted eggs. The mechanism of SEY mudding was studied in this paper. The results showed that SEY hydrogen proton binding decreased, and SEY water and lipid fluidity increased during storage. In addition, the degree of lipid oxidation and monounsaturated fatty acids in salted egg yolk lipids (SEYL) increased, and primary oxidation products and secondary oxidation products were formed. Moreover, the structure of SEY was degraded to release lipids and proteins, and these proteins and lipids were re-emulsified to form new aggregates. Finally, by PLS-DA modeling analysis, it was found that the content of ω-3 polyunsaturated fatty acids and phospholipids changed significantly after SEY became muddy. These results suggest that the muddiness of SEY can primarily be attributed to higher fluidity and protein-lipid re-emulsification, and secondarily to the oxidation of SEYL.

Effects of ethanol treatment on the physicochemical properties, microstructure and protein structures of egg yolk gels.

The aim of this study was to investigate the effect of ethanol treatment on the properties of egg yolk gels (EYG). The hardness of EYG showed an increasing trend, and the changes in free sulfhydryl groups manifested that ethanol treatment facilitated the formation of disulfide bonds. Environment scanning electron microscopy revealed that the degree of protein aggregation increased. Low-field nuclear magnetic resonance results indicated that ethanol treatment promoted the conversion of immobile water or lipids to free water or lipids. Moreover, the increase in the absolute of zeta potential was accompanied by the decrease in surface hydrophobicity, and the secondary structure of native egg yolk (EY) proteins underwent changes with ethanol treatment. Overall, these results demonstrated that ethanol treatment induced the structural unfolding and aggregation of EY proteins, and facilitated the better stability of the gel structures. The impact of the ethanol on the EYG increased with the concentration.

Effects of citric acid crosslinking on the structure and properties of ovotransferrin and chitosan composite films.

In this study, ovotransferrin/chitosan (OVT/CS) composite films cross-linked by citric acid (CA) were prepared and the effects of CA cross-linking on the structure and physicochemical properties of the composite films were investigated. The cross-linking degree measured by 2,4,6-trinitrobenzenesulfonic acid (TNBS) method confirmed that CA was cross-linked with the matrix, and Fourier transform infrared spectroscopy confirmed that more hydrogen bonds and electrostatic interactions were formed between CA and the matrix. Differential scanning calorimetry, X-ray diffraction and Scanning electron microscope images revealed the compatibility between substances. The synergistic inhibition between the matrix results in a significantly higher antibacterial activity of the composite film than the pure film. Compared with uncross-linked films, the mechanical properties, barrier properties and water resistance of the cross-linked films were significantly improved. When the concentration of CA was 5 wt% (W/W, on a dry basis of the weight of OVT and CS), the most significant improvement in film performance was obtained. The tensile strength of the film increased from 32.05 MPa without cross-linking to 61.99 MPa and the swelling degree decreased from 51.5 % to 24.23 %. The observed phenomena suggest that cross-linking OVT and CS with CA can obtain functional edible films with improved properties.

Industrial Application of Protein Hydrolysates in Food.

Protein hydrolysates, which may be produced by the protein in the middle of the process or added as an ingredient, are part of the food formula. In food, protein hydrolysates are found in many forms, which can regulate the texture and functionality of food, including emulsifying properties, foaming properties, and gelation. Therefore, the relationship between the physicochemical and structural characteristics of protein hydrolysates and their functional characteristics is of significant importance. In recent years, researchers have conducted many studies on the role of protein hydrolysates in food processing. This Review explains the relationship between the structure and function of protein hydrolysates, and their interaction with the main ingredients of food, to provide reference for their development and further research.