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 �C) and proximity to FIR heaters (5 and 10 cm) was evaluated on falling
rate drying characteristics. The moisture (Deff) and thermal (a) 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 (R2, 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 a (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 a (15%),
and Deff (14.9%). RWF40-5cm dried biomass showed excellent retention of color
(DE¼4.64 ± 1.32), protein (93.8%), c-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.