(96h) Saponin Removal from Bitter Quinoa Ecotypes in Spouted BEDS (SB)

The removal of saponin from bitter quinoa grains (Chenopodian quinoa Willd) by means of a Spouted Bed (SB) was experimentally studied. Basic SB performance characteristics and operation conditions were optimized on grains of various ecotypes of Royal Quinoa, grown in the Bolivian southern Altiplano.

Experimental runs were carried out using different laboratory-scale cylindrical-conical SBs of 7.5, 15 and 20 cm in diameter, nozzles of 1.4 – 5 mm outlet diameter at static bed heights within 7.5 and 29 cm. Air was supplied by a 400 Lmin^-1 piston compressor, which included a 10 – 300 Lmin^-1rotameters and digital air flow controller.

A two level factorial design was applied, including bed diameter, air linear inlet velocity (measured at the nozzle outlet diameter), bed height and ecotype as independent variables. Processing time was established at 30 min. Dependent variables were: residual saponin content and mass loss percentage of processed grains. The effect of process conditions on the primary nutrient content of the processed grains were evaluated and the morphology of both unprocessed and processed grains were also compared at micrograph scale.

Factors with larger effect on residual saponin content were air inlet linear velocity, reactor diameter followed by ecotype and bed height. The SB process achieved a saponin concentration of 0.00 - 0.02% in processed grains and a mass loss percentage < 7% using the following combination: air inlet velocity, 1200 ms^-1 (1.4 mm nozzle diameter); 7.5 cm reactor diameter and 12.5 cm bed height. Primary nutrient contents (protein and lipids) in the treated grains increased with the outer layer removal, indicating that the optimum operation conditions do not damage the embryo as observed at micrograph scale. Moreover, the process allowed total recovery of the removed saponin powder.

The kinetic studies as tested on different ecotypes showed that both, saponin removal and mass loss percentages, occur at higher rates during the first period of 5 min and that both removal rates decrease afterwards. This behavior can be explained because of the fragility of the episperm’s outer layer where the saponins are concentrated. The same kinetic studies showed a strong linear correlation between air inlet linear velocity and powder removal rates (measured at 5 min operation). There is also a strong linear correlation between air inlet linear velocity and saponin removal efficiencies as tested in different laboratory scale spouted beds.

These experiments show that the spouted bed dry process is an excellent technological alternative when applied to saponin removal from bitter quinoa grains.