Intermittent Drying With Heated Air and Microwaves of Dragon Fruit Foams Formulated With Different Protein Sources

This study aimed to investigate red dragon fruit powder production by foam mat drying, combining a simplex centroid mixture design for foam formulation with intermittent convective drying and intermittent microwave drying. Albumin, pea protein, and soy protein were evaluated as alternative foaming agents to whey protein, and optimization was based on density, overrun, and porosity, while drainage stability was used as a qualitative screening parameter. The optimized pea protein foam and whey protein control were dried by both intermittent methods at 40°C and 60°C. Drying kinetics, powder properties, color, protein content, phenolics, flavonoids, betalains, antioxidant activity, and energy indicators were evaluated. Pea protein provided the best balance among foam responses, producing low-density foams (0.14 g/mL), with 470.75% overrun and 0.82 porosity. Intermittent convective drying required up to 233 min at 40°C and 127 min at 60°C, whereas intermittent microwave drying achieved maximum drying time reductions of 65.67% and 78.74%, respectively. Under laboratory conditions, intermittent microwave drying increased the specific moisture extraction rate (from 0.0286 to 0.3764 kg/kWh) and reduced the specific energy consumption (from 31.4380 to 3.5805 kWh/kg). All powders showed water activity below 0.50. Drying at 40°C favored bioactive retention, with total phenolics from 177.83 to 216.80 mg GAE/100 g, betalains from 40.609 to 61.880 mg/100 g, DPPH from 56.190% to 64.242%, and ABTS from 55.745% to 62.478%. These findings indicate that pea protein showed comparable performance to whey protein under the tested conditions, while intermittent microwave drying provides a faster and more energy-efficient route to obtain pitaya powders rich in bioactive compounds.