Research On The Rheological Behavior Of Fish Epidermal Mucus

The rheological behaviors of epidermal mucus from four kinds of fresh fishes (loach, longsnout catfish, perch, crucian carp) were studied systematically. The influence of time, concentration and temperature on the rheological behavior of fish epidermal mucus was considered as well as the shear history. Basing on analyzing the components of loach epidermal mucus, a supermolecule structure model on loach epidermal mucus was proposed roughly.It reveals that the steady shear curve of fish mucus can be divided into three regions:first Newtonian region, shear thinning region and the second Newtonian region, which is similar to semidilute polymer solutions. The relationship between apparent viscosity (ηa) of loach epidermal mucus and y can be well described by the Carreau model.ηsp-c2.7 is founded for loach epidermal mucus. When in the tested angle frequency (ω) region, the storage modulus (G') and the loss modulus (G") neither changes a lot withωincreasing. G'> G" suggests that the loach epidermal mucus exhibits more elasticity than viscosity, that is, gel like behavior. For loach epidermal mucus, there is a critical gel concentration cgel= 2.4g/L. In most cases, the concentration of fish epidermal mucus is higher than cgei, indicating that the mucus usually behaves as a gel.There is a critical temperature,35℃, for loach epidermal mucus. Below 35℃,ηa of loach epidermal mucus changes little with temperature. Above 35℃, the loach epidermal mucus appears heat-denature and exhibits thoroughly different rheological response.Component analysis shows loach epidermal mucus contains 99.5wt% of water, and only 0.5wt% or so of solids in the mucus, only polysaccharide (Mw=2.3x106) gets a long chain structure and its concentration is only 0.0016wt%, which is lower than its critical overlap concentration (c*) about one order of magnitude. Therefore, the high viscosity of fish epidermal mucus can only arises from the intermolecular interactions. That is, the network structure of mucus is formed by the electrostatic repulsion between protein molecules and the physical crosslinking between hydrophobic groups of polysaccharide.