| dc.description.abstract | Gelidium sesquipedale solid residue after industrial agar extraction contains high amounts
of proteins with all essential amino acids and carbohydrates such as glucans, galactans or
arabinans [1]. Therefore, although it is generally discarded, its reincorporation in the
industry as a value-added product brings an interesting solution. Traditional methods used
for bioactive compounds extraction from different raw materials present numerous
drawbacks, namely, time-consuming, costly to dispose of used products and harmful to
environment and human health [2]. Among green technologies, subcritical water
extraction (SWE) stands out as a great alternative to traditional extraction processes. SWE
consists of using hot pressurized water above its boiling point, 100 °C, and below its
critical point, 374 °C, which causes many of the properties of water to change, such as
density or dielectric constant [3,4]. Water dielectric constant, which is related to its
polarity, decreases with increasing temperature, similar to organic solvents, at 200 °C. As
a result, through the dielectric constant modulation with temperature, SWE is able to
selectively extract polar or non-polar compounds [5].
In order to assess the feasibility of industrial-scale subcritical solvent extraction, a pilot-
scale process must first be tested. Generally, the design of the industrial SWE equipment
is preceded by the study of laboratory- and pilot-scale systems. Hence, although in many
cases the pilot-scale study stage is eliminated, the scaling-up process would be much more
efficient by incorporating the pilot-scale study to obtain quality data and determination
of scale-up factor [6]. Therefore, the main goal of this research was to prove the feasibility
of industrial-scale subcritical water system through scaling-up from lab to pilot system.,
by the comparison of lab- and pilot-scale subcritical water performance. For this, many
analytical methods were applied for the comparison of the extraction yield of the two
systems; such as, polysaccharide fraction identification and quantification, total protein
content and free amino acids determination, and total polyphenol content (TPC) and
antioxidant activity.
Galactose was mainly recovered as oligomer fraction with maximum yields of 71.4 (36
minutes) and 74.5 % (45 minutes) for pilot and lab-scale, respectively (Figure 1a). Lower
yields were determined for glucans, with maximum yields of 9.5 % for both systems, in
which more than 6 % was extracted in the first minutes. Similar extraction curves and
yields were determined for protein fraction with final extraction yields close to 40 %
(Figure 1b), while free amino acids content was higher in laboratory scale. The greatest
extraction yield was accounted for the smallest amino acids, such as glycine, alanine and
aspartic acid, whereas polar amino acids such as glutamic acid and lysine were reduced,
although lysine was not detected in pilot system. Differences in total polyphenolic compounds (TPC) extraction were observed for both
systems. Increasing TPC content with time was determined for lab-scale system, while in
pilot system a plateau phase was observed after 36 minutes of extraction.
SWE has been proven to be an efficient technology for bioactive compounds recovery
such as carbohydrates, protein and amino acids from algae residue. Scaling up of
subcritical water system from laboratory to pilot scale resulted in good and reproducible
results. Therefore, feasibility of industrial-scale subcritical water system through scaling-
up from lab to pilot system has been showed. | en |
