Combined refractance window and far infrared radiation drying of Spirulina platensis biomass: Drying behavior, moisture and thermal diffusivity, and biochemical characterization

Abstract

A 2 mm thin layer of wet Spirulina platensis biomass was dried using two methods: refractance window drying (RW) and combined RW and FIR drying (RWF). The effect of drying temperature (40–60 °C) and proximity to FIR heaters (5 and 10 cm) was evaluated on falling rate drying characteristics. The moisture (Deff) and thermal (α) diffusivity coefficients were obtained in the range 1.728 × 10−8 to 5.289 × 10−9 and 1.322 × 10−8 to 4.169 × 10−9 m2 s−1, respectively (R 2, 0.921–0.984). RW drying at ≥50 °C caused loss of color, phytopigments, and lipid peroxidation. At 40 °C, RW drying led to a long drying period (300.50 ± 3.53 min), poor drying rate (0.039 ± 0.002 g-H2O/min), lowest Deff and α (5.289 × 10−9 and 4.169 × 10−9 m2 s−1), and chlorophyll loss (32.2%). Combined RW and FIR drying at 40 °C and 5 cm proximity (RWF40-5cm) reduced drying time (15.1%), increased drying rate (27.8%), improved α (15%), and Deff (14.9%). RWF40-5cm dried biomass showed excellent retention of color (ΔE = 4.64 ± 1.32), protein (93.8%), γ-linolenic acid (90.1%), chlorophyll (87.9%), and phycocyanin (86.7%) from freeze-dried biomass (FD). Low-temperature RWF40-5cm drying could be a potential alternative to freeze-drying for effective and safe drying of heat-sensitive Spirulina platensis biomass.