Observations of Films from Previous Day (06.01.2011)
- The films cast yesterday were made with a substantial concentration of food additives: guar gum, xanthan gum, and agar. The concentrations of these substances, essentially insoluble in ethanol, was too high to make anything more than a suspension in the zein protein solution. This then resulted in films that were mottled in texture as the additives precipitated and clumped together, as depicted in the pictures at right.
The recast film that contained suspended guar gum particulate (film made on 06.01.2011)
The recast film that contained suspended agar particulate (film made on 06.01.2011)
- However, the films shown were, in a word, recast by the addition of ethanol. The alcohol solvent redissolved the zein and, once the film had reset to a solid, was notably more plastic than previously. Part of the reason for this, may be the fact that the gels had been air-dried at room temperature instead of incubated at 37°C, which meant they had been dessicated to an extreme point of dryness -- potentially an issue for maintaining the longevity of the films and preventing brittleness.
- At any rate, the films were all more plastic, though the agar film was most improved in texture. The xanthan gum film had become more sticky and gummy after recasting, though it may not have been allowed to dry completely. The guar gum film was least improved and seemed to have been rejuvenated from the brink of total desiccated brittleness but not made significantly more plastic. As an experiment, the xanthan gum was then immersed in water -- the immediate result of which had the film turn very pale and turgid. After drying, the film was thinner and more brittle than before -- disintegrating like a dried flower petal or leaf.
Testing Solubility of Additives
Since the additives are largely insoluble in ethanol they were dissolved into distilled water, though agar agar and guar gum do not dissolve quite that readily at room temperature. The agar solution (1% w/v to water) was boiled before being 'mixed' into the zein solution -- not really mixed because as soon as it was put into the solution the zein started precipitating out. The issue here of the insolubility of zein in water was much larger due to the large amount of water/agar added: 1mL. The guar gum was mixed for a long time and most of the material went into solution with a bit of particulate left in suspension. This was also mixed into the zein.
The films were left to dry overnight at room temperature.