Mechanical properties of proteins

It has been said that the most studied component of foods using DSC is protein [97]. The following are just a few examples from the enormous range of proteins from various sources, which have been studied. In general, denaturation studies are carried out in solutions, whereas glassy behaviour is observed in lower moisture materials. 

Much work has been reported on dried and whole fish. Tg s in frozen fish such as cod, tuna, mackerel, sea bream and bonita have been determined using DSC [98 ]. This work is normally carried out with a view to determining the safe storage conditions for these products. Both dried fish muscle and extracted protein fractions showed glass transitions. The 2 s of muscle and myofibrillar proteins from red-muscle fish tended to be lower than those from white-muscle fish. There was no difference in the Tg of sarcoplasmic reticulum. The myofibrillar proteins are responsible for the contractile mechanisms in muscle. These are predominantly 

Significant thermal denaturation in cod fillets in the region of 30-80°C was found to be a function of storage conditions, with differences being found between long-term storage at —30°C and subsequent short-time storage at - -2°C [99]. 

In a separate study [100], cod and tuna were found to have transitions at —10, —15 and —21°C, with an additional low-temperature transition at —72°C for tuna. These transitions were related to glassy behaviour however, the storage stability at — 18°C was found to be poor, suggesting that these were not the transitions governing the deterioration process. 

The effect of salting herring has also been reported to increase the thermal stabihty of proteins but decrease the enthalpy of transition, possibly reflecting an increase in the proteolytic activity in the muscle [101 ]. Increased stability of proteins in this type of work is equated with an increase in transition onset temperature. 

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M. G. M. Pryor. Pro. Biophys, and Biophys. Chem. 1, 216-68 (1950). Mechanical properties of protein fibers, muscles. 

As a remarkable example to demonstrate how hydration greatly affects the mechanical properties of protein-based proteins, it is worth mentioning the case of the spider major ampullate silk, which in the dry state shows a tensile modulus of 7-10 GPa, but upon hydration it decreases by a hundredfold [86]. 

Table 3 Mechanical Properties of Protein Polymer Films (Dry)... 

Wang Z, Zhou J, Wang X, Zhang N, Sun X, Ma Z (2014) The effects of ultrasonic/microwave assisted treatment on the water vapor barrier properties of soybean protein isolate-based oleic acid/stearic acid blend edible films. Food Hydrocolloids 35 51-58 Wihodo M, Moraru Cl (2013) Physical and chemical methods used to enhance the structure and mechanical properties of protein films a review. J Food Eng 114(3) 292-302 Woehl MA, Canestraro CD, Mikowski A, Sierakowski MR (2010) Bionanocomposites of thermoplastic starch reinforced with bacterial cellulose nanofibers effect of enzymatic treatment on mechanical properties. Carbohydr Polym 80 866-873 Xu YX, Kim KM, Hanna MA, Nag D (2005) Chitosan-starch composite film preparation and characterization. Ind Crops Prod 21 185-192... 

The mechanical properties of protein-based materials are substantially lower than those of standard synthetic materials, such as polyvinylidene chloride (PVDC) or polyester (Table 11.11). The mechanical properties of protein-based materials were measured and modelled as a function of film characteristics [74, 131, 132]. For stronger materials (e.g., based on wheat gluten, corn gluten and myofibrillar proteins, critical deformation (DC) = 0.7 mm) and elastic modulus (K = 510 N/m) values are slightly lower than those of reference materials such as LDPE (DC = 2.3 mm, K = 135 N/m), cellulose (DC = 3.3 mm, K = 350 N/m) or even PVC films. The mechanical properties of corn gluten-based material are close to those of PVC. 

The mechanical properties of protein-based films can be markedly improved by adding fibres (i.e., composite materials). Mechanical properties are always highly dependent on the temperature and RH of the protein material (Figure 11.9). This modification, (i.e., sharp increase in deformation at break and decrease in mechanical strength), occurs suddenly when the material crosses the Tg range [174]. 

The mechanical properties of protein-based materials have been studied (Table II) and modeled (9,31-33). 

The mechanical properties of protein-based materials closely depend on the plasticizer content, temperature and ambient relative humidity (16,34,35). At constant temperature and composition, an increase in relative humidity leads to a major change in the material properties, with a sharp drop in mechanical strength and a concomitant sharp rise in distortion. These modifications occur when the Tg of the material is surpassed (Figure 1). These variations can be reduced by implementing crosslinking treatments (physical or chemical) or using high cellulose or mineral loads (22). 

Measurement of mechanical properties of proteins, especially those of fibrous proteins, has been an important interdisciplinary concern in the history of protein science. In fact, the very early X-ray work by Astbury and his colleagues established the force dependent conformational transition of keratin fiber between a- and /3-forms [15]. A large body of work has since been accumulated on the measurement of mechanical parameters of fibrous structures made of keratin, collagen, dentin and other structural proteins [10, 14, 16, 17]. Measurement was done at the macroscopic level on higher order assemblies of fibrous proteins, applying established methods in materials science for the determination of, for example, static and/or dynamic elastic modulus [14],... 

The mechanical properties of protein-based materials can partly be related to the distribution and intensity of inter- and intra-molecular interactions that take place in primary and spatial structures. The cohesion of protein materials mainly depends on the distribution and intensity of intra- and inter-protein interactions, as well as interactions with other components. For example, in soy-based materials, hydrophobic interactions... 

Mitropoulos, V., Miitze, A., Fischer, P. (2014). Mechanical properties of protein adsorption layers at the arr/water and oil/water interface A comparison in light of the thermodynamical stability of proteins. Advance in Colloid and Interface Science, 206, 195-206. 

The first humidity sensor was known a polymer sensor and used to detect the mechanical properties of protein of hair [26]. Sensors have been deeply... 

Microstructure and mechanical properties of protein-nanoparticle composites... 

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