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Abstract
This study aims to investigate the influence of the mixture (CGO/EWP) of carrageenan oligosaccharide (CGO) and egg white protein (EWP) (CGO/EWP, CGO: EWP = 1:1, m/m) on the functional, structural, and gelling properties of Culter alburnus myofibrillar protein (MP) during repeated freezing–thawing cycles by treating MP samples separately with EWP, CGO, or CGO/EWP based on the wet weight (1%, m/m), using samples without any cryoprotectant as the blank group. After the second repeated freezing–thawing cycle, the sulfhydryl group content was found to be significantly (p < 0.05) higher in the CGO/EWP (30.57 nmol/mg) and CGO (36.14 nmol/mg) groups than in the EWP group (23.80 nmol/mg), indicating that CGO/EWP and CGO can more effectively delay the oxidative deterioration of functional groups. Additionally, the surface hydrophobicity was shown to be significantly lower in the CGO (25.74) and CGO/EWP (27.46) groups than in the EWP (34.66) and blank (39.32) groups. Moreover, the α-helix content was higher in the CGO (35.2%) and CGO/EWP (32.3%) groups than in the EWP (29.2%) and blank (25.0%) groups. These data indicated that CGO and CGO/EWP could more effectively increase the structural stability, thereby inhibiting the exposure of hydrophobic groups and curbing the decline of α-helix content. During the heat-induced gel-forming process, EWP and CGO/EWP could enhance the gel viscoelasticity and strength. After the second freezing–thawing cycle, when compared with the blank group, the CGO/EWP group showed significantly (p < 0.05) higher water-holding capacity (66.30% versus 53.93%) and shorter T22 relaxation time (413.56 versus 474.99 ms). The integrated results indicated that CGO/EWP could more effectively delay the decrease of protein–water molecular interaction forces in the MP gel. This study shed light on the mechanism of CGO/EWP as a cryoprotective mixture in improving the deterioration of MP gelation properties during repeated freezing–thawing cycles.
Highlights
As a popular freshwater fish species in China, Culter alburnus exhibits remarkable nutritional value for commercial processing
The blank group was not added with egg white protein (EWP), carrageenan oligosaccharide (CGO), or CGO/EWP
This study revealed that repeated F-T-Cs can cause the oxidation of sulfhydryl groups, the generation of carbonyl groups, and the exposure of hydrophobic groups inside the protein core, resulting in the deterioration of myofibrillar protein (MP) gelation properties, which can be reflected explicitly by the weakening of gel network, viscoelasticity, strength, and water-holding capacity (WHC) properties
Summary
As a popular freshwater fish species in China, Culter alburnus exhibits remarkable nutritional value for commercial processing. Antioxidants 2022, 11, 32 commercial transportation, accelerating the oxidation of proteins, increasing the volume of ice crystals, and deteriorating the quality of fish muscle products, such as reduced texture and juiciness [1]. Long-term freezing or repeated freezing–thawing cycles (F-T-Cs) cause the oxidation deterioration of MP functional groups and structural changes, such as the oxidation of sulfhydryl groups and the increased hydrophobicity of protein molecules, disrupting the ideal protein–protein and protein–water intermolecular interactions in heat-induced MP gels, loosening the three-dimensional gel network, reducing the gel viscoelasticity and strength, and negatively affecting gel properties [6]. In the food industries, cryoprotectants (such as sucrose and sorbitol) are usually added in the fish muscle protein products (such as surimi, meat balls, etc.) to reduce the oxidation degradation of functional groups and enhance the MP structural stability during long-term freezing or repeated F-T-Cs [2,7]. Most studies focus on the potential of a new single substance as a cryoprotectant and ignore the possibility of combining the mechanism of two different substances as a cryoprotectant
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