Rheological and Structural Study of Salmon Gelatin with Controlled Molecular Weight

Abstract

This study explores the molecular structuring of salmon gelatin (SG) with controlled molecular weight produced from salmon skin, and its relationship with its thermal and rheological properties. SG was produced under different pH conditions to produce samples with well-defined high (SGH), medium (SGM), and low (SGL) molecular weight. These samples were characterized in terms of their molecular weight (MW, capillary viscometry), molecular weight distribution (electrophoresis), amino acid profile, and Raman spectroscopy. These results were correlated with thermal (gelation energy) and rheological properties. SGH presented the higher MW (173 kDa) whereas SGL showed shorter gelatin polymer chains (MW < 65 kDa). Raman spectra and gelation energy suggest that amount of helical structures in gelatin is dependent on the molecular weight, which was well reflected by the higher viscosity and G′ values for SGH. Interestingly, for all the molecular weight and molecular configuration tested, SG behaved as a strong gel (tan δ < 1), despite its low viscosity and low gelation temperature (3–10 °C). Hence, the molecular structuring of SG reflected directly on the thermal and viscosity properties, but not in terms of the viscoelastic strength of gelatin produced. These results give new insights about the relationship among structural features and macromolecular properties (thermal and rheological), which is relevant to design a low viscosity biomaterial with tailored properties for specific applications.

Characterization of Gelatin and Hydrolysates from Valorization of Farmed Salmon Skin By-Products

“…The frequency sweep ( Figure 4 b) of salmon gelatin at a constant 0.1% strain shows that the elastic modulus G′ is greater than the viscous modulus G″ in the entire frequency range accessed [ 12 ] and both modules show a dependence of similar frequency [ 40 ]. A parallel storage and loss modulus profile of the frequency sweep from 0.05 rad/s to 10, flowing homogeneously confirming the gel network.…”

“…Rheological measurements of gelatin solution upon heating and cooling provide information about gelling kinetics, namely complex viscosity, storage, and loss moduli ( Figure 5 ). As can be seen in ( Figure 5 a), a transition occurs around 14 °C in the complex viscosity of P1 ( Figure 5 a,b) [ 12 ]. In the heating ramp, a rapid decrease in complex viscosity, having less pronounced cooling, is followed by linear behavior, suggesting that the network structure formed during gelatinization was disrupted upon temperature increase.…”

“…A number of previous studies have focused on the isolation of gelatin from salmon skin, looking at the effect of different pretreatments and thermal extraction conditions on yield and properties of the resulting gelatin. The treatments commonly applied involve an alkaline step followed by acid [ 8 , 9 , 10 , 11 , 12 ], although some authors have tried initial saline treatment [ 7 ], sometimes followed by alkaline medium and trypsin [ 13 , 14 ], or trypsin alone [ 14 ]. Generally, harsher treatments and high extraction temperatures increase yield but result in gelatin with weaker rheological properties, which seem to be influenced by the content of imino acids, hydrophopic amino acids, and molecular weight.…”

Modified Fish Gelatin as an Alternative to Mammalian Gelatin in Modern Food Technologies

“…The fish gelatin extracted under mild conditions (pH5) showed higher content of α-chains, lower content of low molecular components and narrower molecular weight distribution then gelatin obtained under more aggressive acidic and alkaline conditions. This was found for gelatin from the skin of cold water species: Atlantic cod [ 23 ] and Atlantic salmon [ 60 , 61 , 62 ]. At the same time, salmon gelatin showed lower molecular weight compared with bovine gelatin [ 60 ].…”

“…At the same time, salmon gelatin showed lower molecular weight compared with bovine gelatin [ 60 ]. Accordingly, fish gelatin samples extracted under pH5 with higher content of α-chains formed gels with higher values of gel strength, viscoelastic properties, gelling and melting temperatures [ 23 , 61 , 62 ].…”