Improved effect of flaxseed gum on the weakened gelling properties of myofibrillar protein induced by catechin
Introduction
Myofibrillar proteins (MP) are a major component of muscle proteins. They possess functional properties that are important for the sensory texture of meat and meat products, such as solubility, gelling and emulsified properties; however, MP are prone to be oxidized during processing, storage and transportation, resulting in the modification of protein structure and related deterioration of protein functionality (Lund, Heinonen, Baron, & Estevez, 2011). Most phenolics, such as chlorogenic acid, (-)-epigallocatechin-3-gallate (EGCG), blackcurrant extracts and clove extracts, have been reported to inhibit oxidation of meat proteins (Cao et al., 2016, Feng et al., 2017, Jia et al., 2012, Chen et al., 2016). However, phenolic antioxidants generally required larger doses to achieve the same antioxidant effect compared to synthetic antioxidants (Karre, Lopez, & Getty, 2013). Additionally, many studies have shown that, although larger doses of phenolic antioxidants could inhibit protein oxidation, they also induced aggregation, insolubility and structural modification of MP, leading to the deterioration of functional properties, especially gel properties. For example, a high dose of green tea extracts or rosmarinic acid could form “thiol-quinone” adducts with meat proteins, thus reducing the water holding capacity (WHC) and weakened gel strength of MP by blocking the formation of disulfide cross-links during heat-induced gelation (Jongberg et al.,, 2015, Tang et al., 2017). High doses of EGCG, gallic acid or chlorogenic acid reduced the protein carbonyl content but promoted the loss of thiol and amino groups and instability of the tertiary structure, which resulted in protein aggregation and poor gel properties, including decreased WHC and gel strength (Feng et al., 2017, Cao et al., 2016, Cao and Xiong, 2015). Therefore, when phenolics are used as antioxidants, it is necessary to determine how to reduce their adverse effects on the functional properties of MP. Although most studies have concerned the changes of structure and gel properties of meat protein after addition of phenolics, few studies were conducted on how to improve the deteriorated gel properties induced by higher dose of phenolics.
Flaxseed gum (FG) is an anionic heteropolysaccharide comprising xylose, rhamnose, galactose, glucose, arabinose, fucose and galacturonic acid; it contains both neutral and acidic polysaccharide fractions, and the acidic fraction consists mainly of pectic-like polysaccharides (Cui, Mazza, & Biliaderis, 1994). FG has been used in meat products owing to its thickening, WHC, swelling, weak-gel forming, rheological and emulsified properties (Hasanvand & Rafe, 2018). A study showed that the addition of FG enhanced the electrostatic effect of the FG-MP system and significantly improved the water retention performance of MP gels (Sun, Li, Xu, & Zhou, 2011). Similarly, FG was also found to increase the storage modulus and gel strength and decrease the syneresis of salt-soluble meat protein gels likely via electrostatic interactions with protein, improving the thermal stability of protein (Chen et al., 2007). Additionally, FG could enhance the WHC but decreased the gel strength of MP solutions at different NaCl concentrations (Feng, et al., 2018). FG could interact with meat protein and improve the gel properties of proteins. Therefore, in the present study, FG was expected to reduce the adverse effect of phenolics on the gel properties of MP to improve the quality of meat products.
It was reported that when different levels of catechin (0, 10, 50, 100 and 200 μmol/g protein) were added to MP, the surface hydrophobicity of MP was increased and the thiol content of MP was decreased at 50, 100 and 200 μmol/g of catechin, resulting in a severely deteriorated MP gel (Jia, Wang, Shao, Liu, & Kong, 2017). Thus, in the present study, the effects of different FG levels on the gelling properties of MP following the addition of 50 and 100 μmol/g of catechin were investigated, in order to illustrate whether the addition of FG could reduce the degradation of MP gel properties caused by catechin.
Section snippets
Materials
Longissimus muscle from pork carcasses (24 h post-mortem) was purchased from a local commercial abattoir (Jinzhou, China). Soybean oil was purchased from local supermarkets (Jinzhou, China). Catechin was purchased from Sigma-Aldrich (St. Louis, MO, USA). FG (purity 99.8%) was purchased from Xinjiang Lvqi Biotechnology Co., Ltd. (Xinjiang, China). All the other chemicals were purchased from Solarbio Co. (Beijing, China).
MP extraction
MP was isolated according to the method of Park, Xiong, and Alderton (2007).
Total thiol content and surface hydrophobicity
The thiol groups of MP in the myosin and actin molecules will be exposed when the protein structure changes. These exposed thiol groups will undergo oxidation to form inter-molecular or intra-molecular disulfide bonds, resulting in the cross-linking and polymerization of MP that play important roles in its gel properties (Li, Xiong, & Chen, 2012). As presented in Table 1, the effects of catechin level on the total thiol content were not significant (P > 0.05); while the FG level and its
Discussion
In present study, the addition of catechin and FG alone or together caused lower thiol content and higher surface hydrophobicity than those of the control MP without catechin and FG. Recently, the effects of phenolics on the thiol content of muscle protein have been studied extensively. The hydroxyl groups in the catechin are easily oxidized to form quinone, which usually forms orthoquinone. Additionally, the chemical structure of orthoquinone is unstable and exists only as an intermediate
Conclusions
Catechin reduced the thiol content and increased the surface hydrophobicity possibly via forming thiol-quinone adducts and unfolding the protein structure, respectively; the emulsions stabilized by MP-catechin exhibited increased apparent viscosity at low shear rate and the droplet size became lager at high catechin level due to the protein aggregation induced by catechin; consequently, catechin caused the deterioration of the gel properties, including decreasing the gel strength and WHC. The
CRediT authorship contribution statement
Na Jia: Conceptualization, Methodology, Formal analysis, Writing - original draft, Writing - review & editing. Shiwen Lin: Validation, Formal analysis, Investigation, Writing - original draft. Fengxue Zhang: Validation, Formal analysis, Investigation, Writing - original draft. Duoduo Zheng: Resources. Dengyong Liu: Project administration, Writing - review & editing.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgments
This study was funded by the First-class Discipline Project of Liaoning Province (LNSPXKBD2020204, LNSPXKBD2020306).
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