The Effect of pH and Air Superficial Velocity on the Foam Fractionation of Okra (<i>Hibiscus esculentus</i>)

Abstract

separation technique that utilizes the differences in surface activities of molecules in a bulk solution. Fresh frozen cut okra, a product of EI Salvador, Guatemala, or Mexico, was obtained from a local grocery store. Surface tension analysis indicated that a pH value of 7 yielded the best separation due to the increased surface-activity of the proteins in solution (minimization of surface tension). The optimum concentration to be used in foam fractionation for the initial bulk solution has also been determined via surface tension analysis. Laboratory experiments show that a 14-weight per cent solution (a 7-fold dilution has been used to pre-remove the cellulose by vacuum filtration) maximize the separation ratio during the foam fractionation experiments. The superficial air velocity, <i>V</i>_{<span style="font-size:12.0pt;font-family:" times="" new="" roman";mso-fareast-font-family:="" fd1634814-identity-h;mso-bidi-font-style:italic"="">o</span>}, maximized the separation ratio of 110 cm/min in the range 70 ≤ <i>V</i>_{<span style="font-size:12.0pt; font-family:" times="" new="" roman";mso-fareast-font-family:fd1634814-identity-h;="" mso-bidi-font-style:italic"="">o</span>} ≤ 150 sec/min. The effect of pH on the separation ratio has been examined for two okra samples. The results show that sample 1 hardly foamed over the entire pH range while sample 2 completely foamed over the same range. It is speculated that the presence of anti-foaming agents in the okra determines the extent of foaming and their presence could possibly be related to the location in which the sample is harvested. Actual harvest locations were not given on the okra package. The mean viscosity of the okra solution has been determined to be about 67% greater than that of water. The addition of an emulsifying agent (carboxymethyl cellulose, CMC) to the okra solution has been found to first enhance and then suppress the total foamate volume as the concentration of the CMC is increased.