Effect of κ-carrageenan on gelation and gel characteristics of Antarctic krill (Euphausia superba) protein isolated with isoelectric solubilization/precipitation

Gelation and microstructural properties of ternary composite gel of scallop (Patinopecten yessoensis) protein hydrolysates/κ-carrageenan/xanthan gum

The objective of this study was to investigate the properties of ternary composite gel of scallop (Patinopecten yessoensis) protein hydrolysates (SMGHs)/κ-carrageenan (KC)/xanthan gum (XG). The rheological properties, moisture-distribution, molecular structure, and microstructure of SMGNs/KC/XG gels were analyzed. The results showed that the G' value, melting temperature, and water holding capacity of SMGHs/KC/XG were higher than those of SMGHs, SMGHs/KC, and SMGHs/XG. FTIR spectrum showed the generation of hydrogen bonds between SMGHs and KC/XG, and the carboxylic acid group of XG interacts with SMGHs. Moreover, the cryo-SEM results showed that SMGHs/KC/XG exhibited a tighter, smoother, and more aggregated microstructure than those of SMGHs, SMGHs/KC, and SMGHs/XG. These results indicate that the gel and microstructural properties of SMGHs are significantly improved by addition of KC and XG, and SMGHs/KC/XG has potential to be used as functional hydrogels for food, pharmaceutical, and biomedical applications. PRACTICAL APPLICATION: Scallop (Patinopecten yessoensis) male gonads are rich in protein and usually regarded as byproducts during adductor processing. Because of its gelation properties, scallop male gonads have potential to be used as functional hydrogels for food. The SMGHs/KC/XG ternary composite gel showed excellent gel properties, which would be potentially applied in delivery system in food and biological fields. Further study is undergoing to apply SMGHs/KC/XG to embed bioactive compounds, such as curcumin and β-carotene.

Insight into the Effect of Ice Addition on the Gel Properties of Nemipterus virgatus Surimi Gel Combined with Water Migration

The effect of the amount of ice added (20–60%) on the gel properties and water migration of Nemipterus virgatus surimi gel obtained with two-stage heat treatment was studied. The gel strength and water-holding capability (WHC) of the surimi gel with 30% ice added were significantly higher than those of other treatment groups (p < 0.05). The addition of 30% ice was conducive to the increase of protein β-sheet proportion during heat treatment, exposing more reactive sulfhydryl groups. These promoted the combination of protein-protein through disulfide bonds and hydrophobic-hydrophobic interactions, forming an ordered three-dimensional gel network structure. Meanwhile, the increase in hydrogen bonds promoted the protein-water interaction. Low-field nuclear magnetic resonance analysis showed that more bound water was locked in the gel system, reducing the migration of immobile water to free water and finally showing better gel properties. When the amount of ice added was insufficient (20%), the gel structure lacked the support of immobile water, resulting in deterioration of gel strength. However, excessive addition of ice (>30%) was not conducive to the combination of protein-protein and protein-water, forming a large and rough gel structure, resulting in the migration of immobile water to free water and ultimately exhibited weak gel properties.

Structural characterization and functional properties of CNPP, a byproduct formed during CPP preparation

Casein nonphosphopeptide (CNPP), a byproduct formed during the preparation of casein phosphopeptide (CPP), is often discarded on a large scale. Although our previous studies have demonstrated the ameliorative effect of CNPP on muscle wasting disorders, its structure-function mechanism is still unclear. Therefore, considering the great influence of structural characteristics on function, this study aims to explain the potential mechanism by characterizing the physicochemical and functional properties of CNPP. The results of structural characterization indicated that CNPP was of low molecular weight and composed of the complete range of amino acids; it was particularly rich in leucine. Compared with casein, CNPP had a lower molecular size and total/free sulfhydryl content (reduced 2.44 and 2.02 µmol/g in CNPP, respectively). Additionally, Fourier transform infrared spectroscopic analysis revealed that enzymatic hydrolysis caused protein unfolding, and the content of β-turns and random coils reached 50.20% and 10.67%, respectively. Fluorescence-dependent detection of CNPP indicated a reduction of spectral intensity and the occurrence of a red shift. The changes in the structure of CNPP significantly affected its functional characteristics. CNPP has better solubility, foaming, and digestion properties than those of casein and whey protein. Specifically, the foam stability and emulsification properties decreased in the order of casein > CNPP > whey protein. The present study can provide a substantial basis for future application of CNPP as a functional ingredient against sarcopenia.

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.

Textural and gel properties of frankfurters as influenced by various κ-carrageenan incorporation methods

The influence of different addition forms of κ-carrageenan, including powder, pre-suspended in water, and pre-suspended in brine, on the textural and gel properties of frankfurters were investigated. Compared with the control group, each addition form of κ-carrageenan led to a lower cooking loss, as well as higher emulsion stability with more trapped water within frankfurters (P < 0.05). Moreover, κ-carrageenan powder or κ-carrageenan water suspension addition could render higher hardness, adhesiveness, springiness, chewiness, fracturability, and resilience of frankfurters than control group (P < 0.05), which was verified by dynamic rheology analysis. However, κ-carrageenan brine suspension addition had negative effects on the above characteristics. Microstructural images indicated that κ-carrageenan could help form finer and denser protein matrices. However, the interaction modes between the meat protein matrix and each addition form of κ-carrageenan were distinct. Additionally, the addition of κ-carrageenan water suspension had the best effect on the improvement of the textural and gel properties of frankfurters with an enhanced overall acceptability.

Effects of ultrasound-assisted basic electrolyzed water (BEW) extraction on structural and functional properties of Antarctic krill (Euphausia superba) proteins

A novel protein extraction method of ultrasound-assisted basic electrolyzed water (BEW) was proposed, and its effects on the structural and functional properties of Antarctic krill proteins were investigated. Results showed that BEW reduced 30.9% (w/w) NaOH consumption for the extraction of krill proteins, and its negative redox potential (-800 ~ -900 mV) protected the active groups (carbonyl, free sulfhydryl, etc.) of the proteins from oxidation compared to deionized water (DW). Moreover, the ultrasound-assisted BEW increased the extraction yield (9.4%), improved the solubility (8.5%), reduced the particle size (57 nm), favored the transition of α-helix and β-turn to β-sheet, promoted the surface hydrophobicity and disulfide bonds formation of krill proteins when compared to BEW without ultrasound. These changes contributed to the enhanced foam capacity, foam stability and emulsifying capacity of the krill proteins. Notably, all the physicochemical, structural and functional properties of the krill proteins were comparable to those extracted by the traditional ultrasound-assisted DW. This study suggests that the ultrasound-assisted BEW can be a potential candidate to extract proteins, especially offering an alternative way to produce marine proteins with high nutritional quality.

Development of soy protein isolate/κ-carrageenan composite hydrogels as a delivery system for hydrophilic compounds: Monascus yellow

The aim of the present study was to develop soy protein isolate (SPI) and κ-carrageenan (KC) composite hydrogels as a delivery system for hydrophilic compounds. The pigment of monascus yellow was used as a model. A systematic study was performed to characterize the rheological, textural, microstructural properties and in vitro digestion release profile of monascus yellow of the composite gels. The results of power law modeling, electrophoresis patterns and fourier transform infrared spectroscopy (FTIR) confirmed that non-covalent interactions were involved in the formation of SPI/KC composite hydrogels. Compared to pure κ-carrageenan hydrogels, the incorporation of SPI could promote the formation of tougher, more uniform and compact composite gels with sustained-release property. In addition, the release behaviors of monascus yellow entrapped in the hydrogel network can be well described by the Ritger-Peppas mathematical model. Overall, our study provided a promising strategy to enhance the sustained release performance of hydrogels in digestive conditions.

Low oil emulsion gel stabilized by defatted Antarctic krill (Euphausia superba) protein using high-intensity ultrasound

Emulsion gels with low oil contents have been continuously developed in recent decades. In this study, the use of high-intensity ultrasound for the preparation of low oil emulsion gel (oil fraction of 0.25) was investigated. Specifically, defatted Antarctic krill protein (dAKP) was used to stabilize the interface of soybean oil and water. Then, the microstructure and the stabilization mechanism of the formed emulsion gel were evaluated by cryo-SEM, CLSM, zeta potential, rheological measurements, and FTIR. Besides, the particle diameter was measured to be around 5 μm. The results of CLSM indicated that the emulsion gel was the oil-in-water type. The emulsion gel exhibited gel-like viscoelastic behavior even at a low concentration of dAKP due to the formation of a rigid particle network while the rheological behavior of the emulsion gel was significantly affected by the concentration of dAKP. The stabilization of the emulsion gel can be maintained by space steric hindrance and hydrophobic interactions between particles in the emulsion gel system.

Effect of hydrocolloids on gel properties and protein secondary structure of silver carp surimi

BACKGROUND

Hydrocolloids are the most commonly used additive in the processing of surimi products. However, the effect of hydrocolloids on surimi protein conformation has not been reported, and the level of hydrocolloids may be a key factor influencing the quality of surimi. Therefore, this study investigated the effect of curdlan, xanthan gum, κ-carrageenan, and gelatin at various levels on gel properties and protein conformation of surimi from silver carp.

RESULTS

Addition of curdlan, κ-carrageenan, or gelatin at lower level could significantly promote gel strength, textural profiles, and water holding capacity (WHC) of the surimi gels. However, gel strength and WHC gradually decreased with increasing amount of xanthan gum added. The addition of curdlan or κ-carrageenan remarkably increased the whiteness of surimi gel, but the whiteness decreased when the concentration of κ-carrageenan reached 5 g kg^-1 . Along with the increase of curdlan, κ-carrageenan, or gelatin concentration, the index of hydrophobic interaction and hydrogen bonds first increased and then decreased, whereas index of ionic bonds first decreased and then increased. According to Raman spectroscopy data, a small content of curdlan or κ-carrageenan promoted the conformational transition of surimi protein from α-helix to β-sheet, leading to the changes in gel properties of surimi gels. Scanning electron microscopy photographs showed surimi gels added with 4 g kg^-1 curdlan or 2 g kg^-1 κ-carrageenan had a finer and denser network structure.

CONCLUSION

Curdlan or κ-carrageenan at an appropriate concentration is a potential modifier to effectively improve the quality of surimi products. © 2020 Society of Chemical Industry.