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

采用石英弹簧和石英振荡器两种不同的微量天平，在313、323和33 K的温度下，测定了CO2在几种蛋白质（酪蛋白、明胶、谷蛋白、乳清蛋白和大豆蛋白）和多糖（马铃薯和玉米淀粉、糊精和纤维素）上的吸附等温线。重量法测得的吸附等温线均在临界压力附近出现最大峰，并在较高压力下保持恒定，吸附剂之间的水平不同。大豆蛋白和糊精的滞后现象。用压电石英晶体微天平测定了3种蛋白质在纤维素上的吸附等温线，并与重量法测定的吸附等温线进行了比较。将样品涂覆在9 MHz AT切割石英晶体的表面上，并测量频率变化以跟踪由吸附引起的重量变化的时间过程。压电微量天平可以测量吸附剂中吸附的流体的“绝对”量，其尤其在高压下大于重量法测量的“过量”吸附。绝对吸附量在临界压力处急剧增加，在高压区逐渐增加，但没有吸附峰，用相同条件下测定的绝对吸附量和表面过剩吸附量值来测定吸附剂吸附层的密度。吸附层密度在临界压力附近出现峰值，此时表面过量吸附达到最大。最大值为1.03g/cm ^3，与Dubininin-Nikolaev方程估算值基本一致。认为该峰可能是由于成簇流体分子的凝聚所致。

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.