Valorization of unsalable Amaranthus tricolour leaves by microwave-assisted extraction of betacyanin and betaxanthin

Betacyanin and betaxanthin are natural colouring compounds found in Amaranthus tricolour leaves. Microwave-assisted extraction was performed to extract betacyanin and betaxanthin from the unsalable leaves. A set of different process parameters like microwave power, temperature and time was applied in this study. The combination of 450-W microwave power, 90 °C temperature and 15 min of extraction time resulted in the highest amount of betacyanin (71.95 mg/g of dw) recovery. The highest amount of betaxanthin (42.30 mg/g of dw) was extracted at 200-W microwave power, 60 °C temperature and 15 min of extraction time. Green extraction was done by using water as the solvent based on the solubility of compounds being highest in it. The combined effect of time and temperature was also found to be significant for the extraction. The betacyanin and betaxanthin also exhibited good scavenging ability against superoxide and hydrogen peroxide. The recovery was maximum at higher temperatures with a shorter time of extraction. The SEM images showed that the plant matrix ruptured due to microwaves. The FTIR spectroscopy showed the existence of betacyanin and betaxanthin in the leaf extract. The microwave technique was also proved to be better than ultrasound extraction and Soxhlet extraction. The colour change in the powdered sample was observed after extraction which shows the efficient recovery of pigments. The A. tricolour leaves are the cheaper source of betacyanin and betaxanthin. These compounds not only possess colouring properties but also exhibit antioxidant and medicinal properties. Hence, betacyanin and betaxanthin extracted from these leaves can be used as additives and colourants in food products.