Protein-based films

Second, sensors are often intended for a single use, or for usage over periods of one week or less, and enzymes are capable of excellent performance over these time scales, provided that they are maintained in a nfild environment at moderate temperature and with minimal physical stress. Stabilization of enzymes on conducting surfaces over longer periods of time presents a considerable challenge, since enzymes may be subject to denaturation or inactivation. In addition, the need to feed reactants to the biofuel cell means that convection and therefore viscous shear are often present in working fuel cells. Application of shear to a soft material such as a protein-based film can lead to accelerated degradation due to shear stress [Binyamin and Heller, 1999]. However, enzymes on surfaces have been demonstrated to be stable for several months (see below). 

Several studies reviewed formulations, barrier properties and possible application of edible protein-based films (Table 23.3) (Gennadios et al. 1994 Krochta and Me Hugh 1997 Torres 1994). Overall, similarly to polysaccharide films, proteins exhibit relatively low moisture barrier properties, two to four times lower than conventional polymeric packaging materials (McHugh and Krochta 1994d). The limited resistance of protein films to water vapour transmission is attributed to their substantial hydro-philicity and to the amounts of plasticizers, such as glycerol and sorbitol, incorpo-... 

Osburn, W. (2002). Collagenous casings. In "Protein Based Films and Coatings" (A. Gennadios, Ed.), pp. 253-274. CRC Press, Boca Raton. 

Han, J. 2002. Protein-based edible films and coatings carrying antimicrobial agents. In Protein-Based Films and Coatings, Gennadies, A. (ed.). CRC Press, Boca Raton, FL, pp. 485-500. 

Applications of Milk Proteins-Based Films and Composites... 

Milk proteins-based films and composites are used in different scopes of food science, some of them explained by Chen [74]. Coating of meat and fish with... 

Cutter, C. N. and Sumner, S. S. 2002. Application of edible coatings on muscle foods. In A. Gennadios (ed.), Protein-Based Films and Coatings, Boca Raton, FL CRC Press, pp. 467-484. 

Nuthong, P. Benjakul, S. Prodpran, T. Effect of phenolic compounds on the properties of porcine plasma protein-based film. Food Hydrocolloids 2009, 23, 736-741. 

Aristippos, G. 2002. Soft gelatin capsules. Protein-based films and coatings. Boca Raton CRC Press. 

Vegetable and animal proteins, which are often abundantly available as by-products of the food processing industry, are among the biopolymers being used or investigated as feedstocks for the production of films and coatings. In recent years, the scientific literature worldwide has seen an explosion of published papers, often the product of interdisciplinary research, related to protein-based films [66]. 

Two processes are currently used to prepare protein-based films the wet method ( casting ), which involves the solubilization of protein and a plasticizer in a solvent followed by the formation of a protein network on evaporation of the solvent and the dry method, which is based on thermoplastic characteristics of proteins and combines the use of pressure and heat to plasticize protein chains [25, 32]. Dehulled soybean, after solvent defatting and meal grinding, becomes a fat-free, low fibre soy flour (48.5% protein). The soy flour, after leaching out of the water/alcohol soluble sugars, is termed soy protein concentrate (above 65% protein). The soy protein concentrate, if it is further extracted by alkali and reprecipitated by acidification, becomes the purest commercially available soy protein isolate (above 90% protein). 

Two important processes are used to make protein-based films a wet process based on dispersion or solubihzation of proteins, and a dry process based on thermoplastic properties of proteins imder low water conditions [55]. 

In recent years, soy products such as soy whole flour (SF), soy protein concentrate (SPC), and soy protein isolate (SPI) have been considered as alternatives to petroleum polymers because of their abundance, low cost, perfect adhesion, and good biodegradability (Maruthi et al. 2014). SF contains about 40-60 % protein, combined with fats and carbohydrates. Soy protein concentrate contains about 60-70 % protein. SPI contains more than 90 % of protein and is the most widely used soybean product for film processing (Ciannamea et al. 2014). Moreover, SPI-based films are clearer, smoother, and more flexible compared to other plant protein-based films, and they have impressive gas barrier properties compared to those prepared from lipids and polysaccharides. When SPI films are not moist, their O2 permeability was 500, 260, 540, and 670 times lower than that of films based on low-density polyethylene, methylceUulose, starch, and pectin, respectively (Song et al. 2011). Thus, in addition to their large availability, soy protein-based materials have interesting barrier and release properties ideal for packaging applications. 

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]. 

Figure 11.8 Mechanical properties of selected protein-based films compared with some biodegradable and nonbiodegradable materials. Adapted from S. Guilbert, N. Gontard, M.H. Morel, P. Chalier, V. Micard and A. Redl in Protein-based Films and Coatings, Ed., A. Gennadios, CRG Press, Boca Raton, FL, USA, 2002 [63]. All nonreferenced data are from Saechtling [6] and from commercial data sheets.

Figure 11.9 Influence of temperature at 5 °C (A), 25 °C ( ) and 50 °C ( ), and equilibrium RH on the mechanical properties of myofibrillar protein-based films (from Cuq and co-workers [131])...

The gas barrier properties (O2, CO2 and ethylene) of protein-based materials are highly attractive since they are minimal under low RH conditions. Oxygen permeability (around 1 amol/m/s/Pa) is comparable to ethylene vinyl alcohol (EVOH) properties (0.2 amol/m/s/Pa) and much lower than the properties of LDPE (1,000 amol/m/s/Pa) [61] (Table 11.12). The O2 permeability of protein films is about 10-fold higher that EVOH-based films, mainly due to the high plasticiser content of protein-based films. 

Protein-based Films and Coatings, Ed., A. Germadios, CRC Press,... 

S. Guilbert, N. Gontard, M.H. Morel, R Chalier, V. Micard and A. Redl in Protein-based Films and Coatings, Ed., A. Gennadios, CRC Press,... 

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