Harnessing infrared and thermal storage for enhanced bioactive retention in solar-assisted drying of spirulina

This study explored how drying temperature, infrared (IR) radiation, and phase change materials (PCM) affect the drying behavior and quality of Spirulina when using a solar-assisted hybrid drying system. Experiments were carried out at three temperatures (40°C, 50°C, and 60°C), both with and without the use of IR (250 W) and PCM, to assess their influence on drying time, radical scavenging activity, phycocyanin content, phenol levels, and color retention. The fastest drying time (124 minutes) was achieved at 60°C with both IR and PCM, while the slowest (455 minutes) occurred at 40°C without either. On average, IR application shortened drying time by up to 46%. Radical scavenging activity ranged from 10.20% to 46.26%, with the highest value recorded at 50°C when both IR and PCM were used. Similarly, phycocyanin content peaked at 11.80% under the same conditions. Phenol content increased from 23.53% to 28.53% as the temperature rose from 40°C to 50°C, but declined slightly to 27.71% at 60°C, likely due to heat-induced degradation and oxidation. The least color change (∆E = 2.72) also occurred at 50°C, indicating better preservation of visual quality. Using the TOPSIS multi-criteria decision-making method, the combination of 50°C with IR and PCM was identified as the most favorable condition for preserving bioactive compounds and improving drying performance. These findings highlight the potential of integrating solar energy, IR, and PCM to develop efficient and sustainable drying systems for heat-sensitive, nutrient-rich materials such as Spirulina.