Adsorption of High Pressure Carbon Dioxide on Food Bio-materials.

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The adsorption isotherms for carbon dioxide on several proteins (casein, gelatin, gluten, obalbumin, and soy bean proteins) and polysaccharides (potato and corn starch, dextrin, and cellulose) were measured at the temperature of 313, 323 and 33 K, and at the pressure up to 29.4 MPa by two different micro-balances, quartz spring and quartz oscillator. The adsorption isotherms measured gravimetrically all exhibited the maximum peak near the critical pressure and remained constant at higher pressure, the level differing among the adsorbents. There appeared a hysteresis in case of soybean protein and dextrin. The adsorption isotherm on cellulose, which showed a high level at low pressure, can be explained by its micropore structure.The adsorption isotherms for three kinds of proteins were measured by a piezoelectric quartz crystal microbalance, and the results were compared with the gravimetric ones. The sample was coated on the surface of 9 MHz AT-cut quartz crystal and the frequency change was measured to follow the time course of the weight change caused by sorption. The piezoelectric microbalance could measure the "absolute" amount of fluid sorbed in the adsorbent which was larger especially at high pressure than the "excess" adsorption measured gravimetrically. The absolute adsorption increased sharply at the critical pressure and gradually in the region of high pressure, but there was no peak of adsorption.The density of the adsorbed layer of adsorbents were measured using the value of absolute and surface excess adsorption measured at the same condition. There appeared the peak in the density of the adsorbed layer near the critical pressure where the surface excess adsorption became maximum. And the maximum value 1.03g/cm^3 was nearly equal to that estimated by Dubinin-Nikolaev's equation. It is considered that the peak may be due to the condensation of the clustering fluid molecules.