Use of Refractance Window Drying as an Alternative Method for Processing the Microalga Spirulina platensis

Abstract

Microalgae such as Spirulina platensis have recently attracted the interest of the pharmaceutical, nutritional and food industries due to their high levels of proteins and bioactive compounds. In this study, we investigated the use of refractance window (RW) drying as an alternative technology for processing the microalga Spirulina biomass aiming at its dehydration. In addition, we also analyzed the effects of operating variables (i.e., time and temperature) on the quality of the final product, expressed by the content of bioactive compounds (i.e., total phenolics, total flavonoids, and phycocyanin). The results showed that RW drying can generate a dehydrated product with a moisture content lower than 10.0%, minimal visual changes, and reduced process time. The content of bioactive compounds after RW drying was found to be satisfactory, with some of them close to those observed in the fresh microalga. The best results for total phenolic (TPC) and total flavonoids (TFC) content were obtained at temperatures of around 70 °C and processing times around 4.5 h. The phycocyanin content was negatively influenced by higher temperatures (higher than 80 °C) and high exposing drying times (higher than 4.5 h) due to its thermosensibility properties. The use of refractance window drying proved to be an interesting methodology for the processing and conservation of Spirulina platensis, as well as an important alternative to the industrial processing of this biomass.

Effects of Infrared and Microwave Radiation on the Bioactive Compounds of Microalga Spirulina platensis after Continuous and Intermittent Drying

“…In continuous drying at 65 °C, for example, the PC of the dried product was 5.81 g phycocyanin/100 g in dry matter, about 40% of the value found in the fresh microalga. Phycocyanin thermosensitivity was also observed in the literature using other drying methods, such as convective, heat pump, refractance window and rotary drum drying [ 9 , 12 , 15 , 42 ]. However, similar to what was observed for the phenolic and mainly flavonoid compounds, the use of intermittence proved to be positive, since in most temperature combinations the PC was higher than the value obtained during continuous drying.…”

“…Flavonoid compounds have important biological properties, such as antioxidant, anti-inflammatory, estrogenic and antimicrobial activities [ 1 , 36 ]. Nevertheless, their presence in microalgae has been poorly explored in the literature [ 15 ]. The total flavonoid content (TFC) observed in the infrared-dried spirulina can be seen in Figure 4 b.…”

“…The fresh and dried spirulina biomasses were examined with the scanning electron microscopy (SEM) technique, using a Carl Zeiss microscope, EVO MA 10, to evaluate the microstructural characteristics of the material and the possible physical changes that may occur during dehydration [ 15 , 31 ]. The samples were attached to the microscope supports using a conductive carbon tape and then metallized with gold (Leica, SCD 050).…”

“…Some studies have shown that conventional drying systems may be ineffective in preserving the nutritional quality of microalgae during the moisture removal process, in addition to adding high costs to the process if not performed under adequate conditions. Therefore, alternative methods that better preserve its functional and nutritional properties, especially the content of bioactive compounds, should be considered and evaluated [ 13 , 14 , 15 ].…”

Effect of Refractance Window™ and oven drying on physicochemical and sensory properties of peach (Prunus persica L.) surplus

“…Water is usually recirculated to improve the thermal efficiency of the process. The thermal energy of the water passes through a plastic film by conduction and radiation, the moisture in the product is removed by the air flowing over the food layer, and the product reaches temperatures below 70°C (23)(24)(25).…”