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 (D_eff) 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 (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 D_eff 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 D_eff (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.

Keywords:

• Far infrared radiation
• moisture diffusivity
• phycocyanin retention
• refractance window drying
• Spirulina platensis biomass
• thermal diffusivity

Acknowledgements

The authors thank the Director, CSIR-CFTRI, for providing the support and the necessary infrastructure for carrying out this work. The first author thanks the University Grants Commission (UGC), India, for the doctoral research fellowship (1587/NET-JAN, 2017). This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Author contribution

Hitesh Jethani: design of the study, methodology, data acquisition, data analysis and interpretation, and writing the original draft, Deependra Rajoriya: data curation, data analysis, and writing, Vikas Singh Chauhan: reviewing and editing, Umesh H. Hebbar: conceptualization, supervision, writing, reviewing, and editing.

Disclosure statement

The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.

Data availability statement

The datasets pertaining to the current study will be made available from the corresponding author on request.