Abstract
The effect of flaxseed gum (FG) on the weakened gelling properties of myofibrillar proteins (MP) induced by catechin was investigated. Different levels of FG and catechin were incorporated into MP and the chemical changes of MP were studied; MP emulsions and gels with different levels of FG and catechin were prepared and their properties were studied. Catechin promoted the loss of thiol and the exposure of the hydrophobic groups of MP and increased the particle size and apparent viscosity of emulsions, resulting in a poor gel network. The incorporation of FG enhanced the gel strength, water holding capacity and dynamic rheological properties, which might be attributed to the formation of uniform and stabilized emulsions with high apparent viscosity and the enhanced disulfide cross-linking and hydrophobic interactions during heat-induced gelation. FG could be a potential approach in overcoming the deterioration of protein gels caused by catechin.
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Key Points
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. FG has been used in meat products owing to its thickening, WHC, swelling, weak-gel forming, rheological and emulsified properties. He addition of FG enhanced the electrostatic effect of the FG-MP system and significantly improved the water retention performance of MP gels. 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 Additionally, FG could enhance the WHC but decreased the gel strength of MP solutions at different NaCl concentrations. 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.
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 product. 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 addition of FG improved the gel strength and WHC. Regarding the emulsions, the addition of FG caused an increase in the apparent viscosity and formation of more uniform and stabilized emulsions; therefore, the gel-like structure and uniform particle size of the stabilized emulsions are favorable for the formation of a better gel network. The increased disulfide cross-linking and hydrophobic interactions during gelation may also be responsible for the improved gel properties. FG could be a potential approach in overcoming the deterioration of protein gels caused by catechin.