In situ and ex situ adsorption and recovery of betalains from hairy root cultures of Beta vulgaris

摘要

Various adsorbents were screened for in situ recovery of betalain pigments effluxed from hairy root cultures of red beet, Beta vulgaris. Alumina/silica (1:1) appeared ideal, showing in situ adsorption of 97% in a unit time of 30 min accounting for in situ recovery of 71.39% of the total betalaine effluxed. Other adsorbents such as Amberlite series (XAD-2 and -4), cyclodextrin, maltodextrin, dextrin white, and starches such as wheat starch and corn starch exhibited very poor in situ adsorption properties. Pretreatment of adsorbents with methanol significantly improved the adsorption capacities of some of the adsorbents, with a highest adsorption of 97.2% for alumina followed by alumina/silica (1:1) and higher adsorption by XAD-2 and -4. Complete in situ adsorption equilibrium was reached in 20 min for a solution containing 2.5 mg mL(-1) of betalain in adsorbents alumina, silica, and a mixture of alumina and silica. In situ betalain adsorption parameters for alumina/silica were determined using the Langmuir isotherm model where the adsorption capacity was found to be 0.174 mg g(-1) and the adsorption energy was 0.9 at pH 5.5 and 25 degreesC. Desorption of pigments from the adsorbents was invariably highest in poor adsorbents, indicating their poor adsorption energy for betalaines. Similarly, recovery by desorption was low in those adsorbents having high adsorption capacity, indicating that adsorbents such as activated ones with highest adsorption capacity with zero desorption property were unsuitable for the recovery of effluxed pigments. Ex situ recovery of betalain done using various combinations of alumina/silica and processed sand and different column geometries indicated that alumina with processed sand at a 2:1 ratio (w/w) and a minimum column material of 2 cm. height and 2 cm diameter was good enough to cause 97% pigment adsorption from a solution containing 1.6 mg mL(-1). Desorption and recovery of pigments ex situ from columns were affected by various elution mixtures, where a gradient elution with ascending levels of HCl/ethanol in water resulted in 100% recovery of adsorbed pigments in a significantly lesser volume of eluent in a short period of 1 h. Different pigment flow rates of 0.2, 0.3, and 3.1 mL s(-1) through a column of alumina/processed sand indicated that a pigment equilibrium concentration of 0.18 mg mL(-1) at flow rates of 0.02 and 0.3 mL s(-1) resulted in a breakthrough at 110 and 14 min adsorbing 16.9 and 16.91 mg g(-1) betalain, respectively. From the breakthrough curves, the column capacities for respective flow rates were calculated as 8.86 and 9.6 mg g(-1), and the higher flow rates resulted in earlier breakthrough with lower capacity. Observations made in the present study are useful to develop a process for the on-line recovery of betalains effluxed from hairy roots.