Joual of Scient fic & Industrial Research Vol. 60 June 00 I , pp 5 3-50 The Effect of pH and Air Superfcial Velocity on the Foam Fractionation of Okra (Hibiscus esculentusl Ernest E Butler Fahd Raab, Ales Prokop and Robert D Tanner ' Department of Chemical Engineering Vanderbilt University Nashvil le, N 3735, USA Received 13 February00 I accepted: 5 March 00 I Okra (Hibiscus esculentus) was chosen for foam fractionation studies due to its unique, highly viscous properties. It was 10 know if a highly viscous natural proteinaceous material could be foamed and then concentratedĪ Foam fractionation is an adsorp tive bubble separation technique that utilizes the differences in surface activities of molecules in a bulk solution. Fresh frozen cut okra a product ofEI Salvador Guatemala, or Mexico was obtained from a local grocery store. Surface tension analysis indcated that a pH value of 7 yielded the best separalion due to the increased surfaceactivity of the proteins n solution (minimization or surface tension). he optimum concentration to be used in foam fractionation for the in itial bu lk solution has also been deter mined via surface tension analysisg Laboratory experiments show that a 14-weight per cent solution (a 7-fold dilut ion has been used to pre-remove the cel lulose by vacuum filtration) maximize the separation ratio during the foam fractionation experiment. he superficial air velocity, V"' maximized the separation ratio of 1 0 cm/min in the range 70� V, ,� 50 sec/min. he effect of pH on the separation ratio has been examined for two okra samples® he resul ts show that sample hard ly foamed over the entire pH range whie sample completey foamed over the same range® t is speculated that the presence of antifoaming agents n the okra detemines the extent of foaming and their presenc could possibly be related to the location in which the sample i harvested. Actual harvest locations were not given on the okra package. he mean viscosity of the okra solution has bee determined to be about 67 greater than that of waterī he addi tion of an emuls ifying agent (carboxymethyl cel lulose CMC) t the okra solution has been found to first enhance and then suppress the total foamate volume as the concentration of the CMC is increasedg Introduction Okra (Hibiscus esculentus) is a member of the Malvaceae fami ly and is a close relative to the cotton plant. It is believed that okra was first cultivated in Af rica. Today, various species of the plant are located throughout India and the old wor ld. There is evidence to suggest that okra was taken from Africa to Spain by the invading Moors of the 81h century. Some historians sus pect that okra was introduced in the Americas shortly after the discoveries of Christopher Columbus I . There are many varieties of okra that vary in plant height and in the length. Pods vary in texture from ridged to smooth. Some popular varieties found in the United States include: Perkins Spine less, Dwarf Long Pod or Dwarf Green Long Pod, Clemson Spineless, Louisiana Author to whom all correspondence should be addreed Green or Green Velvet, White Ve lvet or Ladyfinger, Emerald, Gold Coast, and French Market 2 • The nutritional qualities of okra have been studied widely to determine a dietary profile for the okra plant, the one reported by TindalP is given in Table I. The amino acid content of okra as profiled by the Food and Agriculture Organization of the United Nat ions4 IS given in Table 2. Characteristics of the specific proteins of okra were not found in the literature �.arch performed for this in vestigation; however, it was reported that okra contains a 1 .7 mil lion-molecular-weight glycoprotein, which acts as a polyanion in solution'. Surprisingly, okra has been found to have a variety of uses other than as a direct source of food. Approximately