Subcritical Water Treatment for Valorization of the Red Algae Residue after Agar Extraction: Scale-Up from Laboratory to Pilot Plant

Abstract

The feasibility of industrial subcritical water treatment on Gelidium sesquipedale residue through scaling up from the lab to pilot system in discontinuous mode (geometric scale-up factor = 50), at 130 and 175 °C (5% biomass), was investigated. The maximum volumes of the reactors were 500 mL at the lab-scale and 5 L at the pilot-scale system. At 175 °C, faster extraction/hydrolysis was observed for the pilot plant, but maximum yields were similar: 71.4 and 78.6% for galactans, 9.8 and 10.4% for glucans, and 92.7 and 86.1% for arabinans in pilot scale and lab scale, respectively, while the yields for proteins accounted nearly 40%. The highest yields for amino acids were observed for the smallest ones, while lower yields were determined for polar amino acids. The total phenolic content and color intensity progressively increased along time at lab scale, while a plateau was reached at the pilot level. Lower extraction yields but reproducible results were obtained at 130 °C. Finally, the pilot scale was essayed at a higher biomass loading (15%), and successful results were obtained, supporting the feasibility of the scaling-up process.

Onion (Allium cepa L.) Skin Waste Valorization: Unveiling the Phenolic Profile and Biological Potential for the Creation of Bioactive Agents through Subcritical Water Extraction

“…The system was heated using a ceramic electric band heater (2000 W) and pressurized with N 2 . The equipment, detailed in previous work [22], is shown in Figure 1. After cooling to 90 • C, the reactor was opened and the suspension was filtered.…”

Phenolic and Cellulose-Rich Fractions from Subcritical Water Treated Beer Bagasse

“…This neo-formed antioxidant compounds could be also quanti ed as phenols by the unspeci c Folin-Ciocalteu reagent. These compounds are formed through Maillard and/or caramelization reactions, producing 5-HMF and sugar condensation compounds, and exhibit different bioactivities, including antioxidant activity (Trigueros et al, 2023). On the other hand, the thermal degradation of the phenolic compounds at high temperatures could also occur.…”

“…The partition of the protein content during the SWE gave rise to greater content in the insoluble residues, thus suggesting a low solubility of the bagasse proteins under the used water subcritical conditions, especially at the lowest SWE temperatures. At 110 o C, the 95% of the total protein remained in the insoluble residue, this percentage decreasing to around 53% at 170 o C. These proteins are extracted and/or hydrolysed during the thermal treatment, leading to peptide chains of different sizes or free amino acids or even amino acid decomposition, especially at high temperatures, producing different carboxylic acids and other nitrogen containing compounds such as ethanolamine(Trigueros et al, 2023;Rogalinski et al, 2005). Therefore, SWE treatment of beer bagasse can be considered as an e cient extraction method to recover the protein fraction of the BSG generated in the beer industry, the maximum recovery of solubilised protein in the SWE extracts being of 47% at 170 o C.…”

Extraction of bioactive compounds from beach-cast brown algae: a review on accelerated solvent extraction and subcritical water extraction

“…In contrast, SCWE maintains pressure at/slightly above water's vapor pressure, ensuring water remains liquid within designated temperature ranges. The subcritical region for water is characterized by temperatures of 100-374 °C and pressures of 1-221 bar, 17,96 as depicted in Fig. 4.…”