Effects of NaOH/NaCl pickling on heat-induced gelation behaviour of egg white

Isolation and Characterization of Protein Fractions for Valorization of Sacha Inchi Oil Press-Cake

The growing interest in plant-based food protein sources has provided opportunities for the valorization of agri-food by-products, driving the food industry towards more sustainable development. In this study, three extraction procedures (varying the pH value (7.0 and 11.0) and the addition of salt (0 and 5%)) were investigated to obtain seven different protein fractions (SIPF) from Sacha Inchi oil press-cake (SIPC), which were characterized in terms of their protein content, electrophoretic profile, secondary structure, and techno-functional properties. Extractions at pH 11.0 without salt addition produced the highest values of protein content, extraction yield, protein recovery, and protein concentration increase (84.0%, 24.7%, 36.5%, and 1.5-fold, respectively). Under these extraction conditions, the electrophoretic analysis indicated that most of the SIPC proteins were extracted. SIPF displayed an excellent oil absorption capacity (4.3-9.0 w/w), and interesting foam activity (36.4-133.3%). The solubility and emulsifying activity of the albumin fractions were significantly higher than those of the other fractions (~87 vs. <15.8%, and 280-370 vs. <140 m²/g, respectively). Correlation analysis showed that the secondary structure of the SIPF significantly influences their techno-functional properties. These results indicate that SIPC is a by-product of great potential for protein extraction processes, and as a valorization strategy for technical cycle solutions for the Sacha Inchi productive chain in the circular economy context.

Thermal gelation and digestion properties of hen egg white: Study on the effect of neutral and alkaline salts addition

In this study, the thermal gelation and digestion properties of hen egg white (hen EW) proteins with different salts were investigated. Results show that the addition of neutral salt - sodium chloride (NaCl) decreased the gel hardness/resilience, increased gel lightness, aggregated particle size and digestibility of hen EW proteins significantly. In contrast, alkaline salts - phosphate and carbonate addition increased the gel resilience and strain tolerance as well as reduced the aggregated particle size and gel lightness of hen EW proteins due to the increase of solution pH and negative charge. Correlation analysis shows that the digestibility of hen EW gels was affected by gel viscoelasticity, molecule forces and texture. In conclusion, thermal gelation properties of hen EW proteins could be modulated by salts with different pH/ionic strength, and thus affected the protein digestion and peptide released.

Optimization of Soybean Protein Extraction with Ammonium Hydroxide (NH4OH) Using Response Surface Methodology

Plants have been recognized as renewable and sustainable sources of proteins. However, plant protein extraction is challenged by the plant's recalcitrant cell wall. The conventional extraction methods make use of non-reusable strong alkali chemicals in protein-denaturing extraction conditions. In this study, soy protein was extracted using NH₄OH, a weak, recoverable, and reusable alkali. The extraction conditions were optimized using response surface methodology (RSM). A central composite design (CCD) with four independent variables: temperature (25, 40, 55, 70, and 85 °C); NH₄OH concentration (0.5, 1, and 1.5%); extraction time (6, 12, 18, and 24 h) and solvent ratio (1:5, 1:10, 1:15 and 1:20 w/v) were used to study the response variables (protein yield and amine concentration). Amine concentration indicates the extent of protein hydrolysis. The RSM model equation for the independent and response variables was computed and used to create the contour plots. A predicted yield of 64.89% protein and 0.19 mM amine revealed a multiple R-squared value of 0.83 and 0.78, respectively. The optimum conditions to obtain the maximum protein yield (65.66%) with the least amine concentration (0.14 Mm) were obtained with 0.5% NH₄OH concentration, 12 h extraction time, and a 1:10 (w/v) solvent ratio at 52.5 °C. The findings suggest that NH₄OH is suitable to extract soybean protein with little or no impact on protein denaturation.

Gel properties of okara dietary fiber-fortified soy protein isolate gel with/without NaCl

BACKGROUND

Soy protein isolate (SPI) is widely used as an alternative to animal-based protein, and its gelling property is essential for producing plant protein-based foods. Insoluble dietary fiber has been used to improve the properties of protein gels.

RESULTS

Effects of partial replacement of SPI by okara dietary fiber (ODF) on the gelling properties of ODF-fortified SPI gels with and without 0.1 m NaCl were investigated. The presence of ODF hindered the SPI self-aggregation and reduced the surface hydrophobicity of SPI. The presence of ODF reduced the hydrophobic interaction and improved the proportion of disulfide bonds in the gels. In the microstructure, the swollen ODF promoted the local aggregation of SPI at 0.1 m NaCl. Texture profile analysis showed that 5% and 10% ODF improved the SPI gel hardness in the absence of NaCl, whereas only 5% ODF improved the gel hardness at 0.1 m NaCl. The results of low-field nuclear magnetic resonance imaging revealed that ODF shortened the T₂ relaxation time of the free water in the gel. The gel of ODF-10 had the highest storage modulus.

CONCLUSION

Using an appropriate amount of ODF to replace SPI could improve the quality of SPI gel and increase the dietary fiber content in the product. In addition, the appropriate ratio of ODF/SPI varied in different solution environments. © 2022 Society of Chemical Industry.

The Conformational Structural Change of Soy Glycinin via Lactic Acid Bacteria Fermentation Reduced Immunoglobulin E Reactivity

This study investigated the fermentation of isolated soy glycinin by using the Lactiplantibacillus plantarum B1-6 strain, its reduction effect on immunoglobulin E (IgE) reactivity, the relationship with protein aggregation/gelation state and conformational changes. Fermentation was performed under different glycinin concentrations (0.1%, 0.5%, 1% and 2%, w/v) and varied fermentation terminal pH levels (FT-pH) (pH 6.0, 4.5, 4.0 and 3.5). L. plantarum B1-6 showed potency in reducing immunoreactivity to 0.10–69.85%, as determined by a sandwich enzyme-linked immunosorbent assay. At a FT-pH of 6.0 and 4.5, extremely low IgE reactivity (0.1–22.32%) was observed. Fermentation resulted in a great increase (2.31–6.8-fold) in particle size and a loss of intensity in A3 and basic subunits. The conformation of glycinin was altered, as demonstrated by improved surface hydrophobicity (1.33–7.39-fold), decreased intrinsic fluorescence intensity and the α-helix structure. Among the four selected concentrations, glycinin at 1% (w/v, G-1) evolved the greatest particles during fermentation and demonstrated the lowest immunoreactivity. Principal component analysis confirmed that particle size, intrinsic fluorescence intensity, α-helix and ionic bond were closely related to immunoreactivity reduction.

Salted duck eggs: the source for pathogens and antibiotic resistant bacteria

Salted duck eggs as a convenient food are very popular in China and Southeast Asia. Generally, they are produced by traditional curing methods. Here we used traditional methods to profile the bacterial community of salted duck eggs purchased from markets to systematically investigate their microbiological safety. 77 bacteria belonging to 14 genera were isolated. Bacillus related to flavor formation of salted duck eggs were the dominant genus. However, there existed some clinical pathogens which can cause food poisoning, such as Klebsiella pneumoniae, Staphylococcus aureus, and Aeromonas hydrophila. Moreover, PCA analysis showed that the composition of bacteria was related to the source and storage time rather than sampling sites. Besides, bacteria in the shell, intima and egg white of salted duck eggs were cross-linked. In addition, antimicrobial susceptibility testing indicated that resistant bacteria reached to 47.9%. And there was also no significant difference in bacterial resistance with sampling sites. Consequently, it's necessary to strengthen the food quality of salted duck eggs and improve personal dietary habit.

SUPPLEMENTARY INFORMATION

Supplementary information accompanies this paper at 10.1007/s13197-020-04962-w.

Development of a heatable duck egg white translucent jelly: an evaluation of its physicochemical properties and thermal stability

Though nutritional, the remaining separated duck egg white in duck egg processing plants presents challenges for its transportation and use, as it spoils easily and has a strong odor. Uses for the excess egg white are of paramount concern for agricultural resource reuse. The purpose of this study was to increase its value and use efficiency. Duck egg white was mixed with sodium hydroxide to produce translucent alkali-induced egg white jelly similar to that in preserved egg whites. To develop a heatable translucent egg white jelly, their physiochemical properties and thermal stabilities were investigated. A gel prepared with 150 mM sodium hydroxide at 25°C had optimal bloom strength and the densest microstructure. Storing the jelly at 5°C helped maintain its disulfide bonds and delayed liquefaction. Although heating decreased its bloom strength and total disulfide bond content as temperature increased (P < 0.05), scanning electron microscopy of the heated jelly revealed that the protein network structure was denser than that of unheated jelly. Heating caused parts of the structure to shrink and even dehydrate, leading to a wrinkled surface. However, no signs of liquefaction or collapse were observed, and the free alkali released during heating was lower than that from the white of existing preserved eggs. These results confirmed the thermal stability of the jelly and its potential to be served hot or used in food processing. Furthermore, in addition to disguising the odor and special flavor attributable to the alkaline treatment, adding ginger juice or turmeric to the preparation yielded higher bloom strength, resulted in lower free alkalinity, and delayed liquefaction, thus improving the jelly's thermal stability. Like preserved eggs on the market that can be served in hot congee, the proposed egg white jelly is rich in proteins and suitable for hot or instant serving. These findings may help address the problem of excessive remaining duck egg white created during food processing by diversifying duck egg processing and boosting its value.

Effect of κ-carrageenan addition on protein structure and gel properties of salted duck egg white

BACKGROUND

Salted duck egg white (SDEW) is a major by-product during salted egg yolk manufacturing. Due to the high salt concentration, SDEW has not been efficiently utilized. Moreover, functional properties of SDEW are altered by salt during pickling. To improve the functional properties, the effect of κ-carrageenan (κ-CAR) addition on the protein structure and gel properties of SDEW was investigated in this study.

RESULTS

The surface hydrophobicity and free sulfhydryl content of SDEW protein increased, while total sulfhydryl content decreased significantly with the addition of κ-CAR (0.02-0.10%). Fourier-transform infrared spectroscopy analysis revealed that the relative content of α-helix and β-turn decreased, β-sheet and random coil increased, indicating the variation tendency of protein structure from order to disorder. As κ-CAR addition increased, the texture profiles including hardness, gumminess, chewiness, springiness, cohesiveness and resilience of SDEW gel were all improved. Water holding capacity increased significantly by 32.33% in the presence of 0.10% κ-CAR addition. The scanning electron microscopy indicated that the microstructure of SDEW/κ-CAR mixed gel was more smooth and compact.

CONCLUSION

The results suggested that adding κ-CAR can be an effective method to improve gel quality of SDEW. This study is expected to provide theoretical basis for modification of SDEW protein, as well as preparation of food ingredients with better gel properties from SDEW. © 2020 Society of Chemical Industry.

Effect of pullulan concentration and pH on the interactions between whey protein concentrate and pullulan during gelation

BACKGROUND

Whey protein concentrate (WPC)/pullulan (PUL) hydrogel is applied as a microencapsulation wall material to protect probiotics. However, the interactions between WPC and PUL during gelation have not been clarified. In the present study, the effects of PUL concentration and pH on the interactions between WPC and PUL during gelation were evaluated with respect to appearance, zeta-potential, sulfhydryl group amount, surface hydrophobicity and infrared spectroscopy measurements. The rheological properties of WPC/PUL gels were also determined.

RESULTS

The results obtained showed that a proper concentration (0.40 g mL^-1 ) of PUL could improve the gel by enhancing the strength of hydrogen bonding, electrostatic interactions and exposure of hydrophobic groups, whereas too much PUL inhibited the formation of disulfide bonds. Furthermore, hydrophobic interactions, disulfide bonds and hydrogen bonds were destroyed in varying degrees under an alkaline environment. The rheological results also demonstrated a similar effect of PUL concentration and pH on the storage modulus (G') of WPC/PUL gels.

CONCLUSION

When the WPC/PUL gel was formed at PUL concentration of 0.40 g mL^-1 and pH 7.0, the interaction between WPC and PUL could be enhanced, which is beneficial for the future application of WPC/PUL gels in the food industry. © 2020 Society of Chemical Industry.

Influence of ultrasound-assisted sodium bicarbonate marination on the curing efficiency of chicken breast meat

Effects of ultrasound combined with sodium bicarbonate assisted curing (USC), sodium bicarbonate assisted curing (SC) and traditional wetting curing (WC) on curing efficiency and tenderization of the chicken breast meat were investigated. Compared with SC and WC treatments, the highest marinade uptake and chloride content were observed in USC treatment (P < 0.05). The lowest shear forces and the largest myofibril fragmentation indexes (MFI) were also obtained in USC chicken (6.99 N and 61.65) (P < 0.05), which were related to the larger gaps and cavities between the adjacent muscle bundles and the more broken muscle fibers in chicken by ultrasonic, followed by SC (8.01 N and 56.82) and WC (9.50 N and 52.23). Furthermore, the USC and SC decreased significantly the cooking loss and surface hydrophobicity of chicken (P < 0.05). Meanwhile, the USC and SC treatments gradually decreased the low-field nuclear magnetic resonance (LF-NMR) relaxation times (T₂₁ and T₂₂), which was related to the lower fluid losses in chicken. These results indicated that the USC and SC treatments had greater impact on the improvement of meat tenderization, water holding capacity and curing efficiency than WC, especially the USC was the best curing method.