Protein relative humidity effects

Cuq, B., Gontard, N., Cuq, J.L., and Guilbert, S. Functional properties of myfibrilar protein based biopackaging as affect by film thickness, /. Food Sci., 61,580,1996. Donhowe, l.G. and Fennema, O. The effect of relative humidity on water vapor permeance of lipid-hydrocolloid bilayer films, JOACS, 69, 1081, 1992. 

Gennadios, A., Park, H.J., and Weller, C.L. Relative humidity and temperature effects on tensile strength of edible protein and cellulose ether films, Trans. ASE, 36, 1867, 1993. 

The physical effect, which is measured quantitatively, is a marked increase in fiber saturation point, or moisture content of the substance at 100% relative humidity. With hardwoods treated with 1% NaOH, followed by washing, the swelling capacity of the cell walls is doubled. This increase in FSP not only provides for improved diffusion conditions of water-soluble materials, it also provides for improved enzyme-substrate interactions. In addition, there is an indication of a small increase in the maximum molecular weight of globular proteins capable of diffusing into the substance. 

Zhou, Q. K.R. Cadwallader. Effect of flavor compound chemical structure and environmental relative humidity on the binding of volatile flavor compounds to dehydrated soy protein isolates. J. Agric. Food Chem. 2006, 54, 1838-1843. 

The Tg of proteins is highly affected by moisture content (around 10 C decrease per 1% added water) because of their hydrophilic nature, which varies between proteins. In practice, once proteins contain more than 15% water, (i.e., which generally occurs when they are in equilibrium with 85% relative humidity (RH) at ambient temperature), the Tg of the protein material is close to ambient temperature (Figure 11.5). This effect is even more obvious in the presence of plasticisers. 

Partanen, R., Raula, J., Seppanen, R., Buchert J., Kauppinene, E., Forssell, P., 2008. Effect of relative humidity on oxidation of flaxseed oil in spray dried whey protein emulsions. J. Agric. Food Chem. 56 5717—5722. 

Physical or chemical modifications of protein-based materials (films, materials, resins, adhesives, etc.) have also been proposed to enhance their water resistance and limit the impact of relative humidity on their properties or to modify their functionality (e.g. strengthen the surfactant effect) (6,11-13). 

Chemical modifications are often aimed at enhancing water resistance and reducing the effects of relative humidity on protein material properties. However, no significant Tg modifications and especially no improvement in barrier and water resistance properties have been noted for materials formed with chemically lipophilised glutens, at different lipophilisation levels [151]. 

The data in the literature highlight that proteins are relatively stable to oxidation and that most of the alterations are ascribable to the action of humidity and to the effect of aggressive restoration practice. 

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