Refractance window drying of dragon fruit: drying kinetics, mass transfer parameters and structural analysis

Area of Science:

• Food Science and Technology
• Agricultural Engineering
• Biomaterials Science

Background:

• Refractance Window (RW) drying is an advanced technique for processing fruits and vegetables into powders, slices, or leathers.
• Optimizing drying parameters is crucial for enhancing efficiency and preserving the quality of dried food products.

Purpose of the Study:

• To evaluate the impact of temperature and citric acid (CA) pretreatment on the drying behavior, mass transfer, and quality of RW-dried dragon fruit slices.
• To investigate the structural changes induced by RW drying and CA pretreatment using advanced analytical techniques.

Main Methods:

• Dragon fruit slices were dried using Refractance Window (RW) technology at temperatures of 60, 70, and 80 °C.
• Citric acid (CA) pretreatment was applied at concentrations of 0.5%, 1%, and 1.5%.
• Drying kinetics were modeled (Page model), and mass transfer, quality attributes (phenolics, antioxidant activity), and structural properties (FTIR, XRD, microscopy) were analyzed.

Main Results:

• CA pretreatment significantly reduced drying time by 36-63% at 80 °C.
• The Page model accurately described drying kinetics, particularly at 70 °C.
• 1.5% CA pretreatment yielded the highest total phenolics and antioxidant activity, with enhanced moisture transfer and reduced external resistance.
• Microscopic, FTIR, and XRD analyses confirmed structural modifications, including surface disruption and pore formation.

Conclusions:

• Higher temperatures and CA pretreatment effectively improve the drying efficiency and quality retention of RW-dried dragon fruit slices.
• CA pretreatment enhances moisture transfer and preserves bioactive compounds, making it a valuable technique for dragon fruit processing.