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

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 degrees C) and proximity to FIR heaters (5 and 10 cm) was evaluated on falling rate drying characteristics. The moisture (D-eff) and thermal (alpha) diffusivity coefficients were obtained in the range 1.728 x 10(-8) to 5.289 x 10(-9) and 1.322 x 10(-8) to 4.169 x 10(-9) m(2) s(-1), respectively (R-2, 0.921-0.984). RW drying at >= 50 degrees C caused loss of color, phytopigments, and lipid peroxidation. At 40 degrees 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 D-eff and alpha (5.289 x 10(-9) and 4.169 x 10(-9) m(2) s(-1)), and chlorophyll loss (32.2%). Combined RW and FIR drying at 40 degrees C and 5 cm proximity (RWF40-5cm) reduced drying time (15.1%), increased drying rate (27.8%), improved alpha (15%), and D-eff (14.9%). RWF40-5cm dried biomass showed excellent retention of color (Delta E = 4.64 +/- 1.32), protein (93.8%), gamma-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.