Microwave Assisted Foam Mat Drying of Grapefruit ( <i>Citrus Paradisi</i> ): Drying Kinetics, Powder Characteristics and Bioactive Properties

ABSTRACT Grapefruit ( Citrus paradisi ) is consumed less frequently than many other fruits because of its pronounced bitterness. Therefore, processing this fruit into a stable powder using an appropriate method will contribute to the sustainability of food products by creating a value‐added product. In this study, response surface methodology combined with a desirability function approach was used to optimize the grapefruit juice foam formulation. The effects of whey protein concentrate (WPC; 2%–6%), guar gum (GG; 0.1%–0.3%), and mixing time (MT; 4–12 min) on foaming capacity and foam stability were evaluated. The optimal conditions for producing grapefruit foam were 6% WPC, 0.24% GG, and an MT of 12 min. The optimized foam was dried using microwave powers of 100, 300, 450, 600, and 800 W. The impact of microwave intensity on the drying characteristics, powder properties, and bioactive compounds was then investigated. The results revealed that, among the six thin‐layer models, the Midilli model was identified as the most suitable for predicting drying kinetics at all microwave power levels. The activation energy (E a ) was determined to be 4.69 W/g. Increasing microwave power resulted in a significant reduction in drying time and a gradual increase in the average drying rate and effective moisture diffusivity (D eff ), together with improved powder flowability and reduced moisture content. However, excessive microwave radiation adversely affected the color difference (∆E) and solubility. Moreover, the degradation of phenolics at higher microwave power was accompanied by a gradual decrease in antioxidant activity and flavonoid content, whereas vitamin C retention improved. Overall, a power setting of 600 W was found to provide the best balance of drying performance, powder quality, and preservation of bioactive compounds in grapefruit powder.