Effects of the spray-drying temperatures on the physiochemical properties of an encapsulated bitter melon aqueous extract powder

Bitter melon (Momordica charantia L.) is a medicinal fruit often used for the treatment of diabetes, due to its content of saponins, phenolics and flavonoids and its antioxidant capacity. The aims were to use response surface methodology (RSM) to optimise the inlet (125.6, 130, 140, 150, 154.1°C) and outlet (72.9, 75, 80, 85, 87.1°C) temperatures for the spray-drying encapsulation of a bitter melon aqueous extract using a combination of maltodextrin and gum Arabic as encapsulating agent and to determine the stability of the optimised encapsulated powder under various storage conditions. The RSM models were adequate to describe and predict the responses for the process yield, the retentions of saponins, phenolics, flavonoids and antioxidant activity, the moisture content and the water solubility index with an overall R²≥0.91. The optimal inlet and outlet temperatures were determined to be 140°C and 80°C, respectively. The optimised spray-dried powder had high values for process yield (71.4±1.4%), retention of bioactive compounds and antioxidant activity (≥87.9±2.6%), water solubility index (89.9±0.51%) and had a low moisture content (2.2±0.1%), which was below the M_o=5.71 predicted by the BET model. However, in terms of the morphology of the powder particles under scanning electron microscopy and loss of the bioactive compounds and antioxidant activity, the safest range for preserving the powder at 25°C was determined to range from 22.5% to 33.8%. The encapsulated powder was also slightly more stable at -20 and 10°C than at 30°C, over 150days. Therefore, it can be concluded that spray-drying with the inlet temperature at 140°C and the outlet temperature at 80°C resulted in a very stable encapsulated powder of the bitter melon aqueous extract.