Microwave-assisted extraction of betalains from red beet (Beta vulgaris)

The use of microwave assisted extraction (MAE) was investigated in this work for the extraction of betalains from diced red beets. Several treatments with different combinations of time, power and duty cycle applied to the samples were studied. The combination of 400 W and 100% duty cycle for 90-120 s resulted in the highest amount of recovered betanines; whereas at 140-150 s the highest amount of betaxanthins was obtained. The addition of ascorbic acid (0.040 mol/L) to the extracting solvent and the development of a two-step MAE process with a cooling period in-between and after processing steps led to an enhancement in the amount of pigments obtained. The effect of extraction time at each extraction step on betalains yield was determined by applying a factorial design and surface plots were constructed. The duration of the second step significantly affected the yield of betanines and betaxanthins obtained (p < 0.05). A prediction model was proposed and validated to meet the optimal extraction times. Betalain yields obtained by MAE were twice as high as those obtained during conventional extraction and conventional extraction at 80 °C.