Abstract
Ultrasound-assisted water extraction was optimized to recover gelling biopolymers and antioxidant compounds from Mastocarpus stellatus. A set of experiments following a Box–Behnken design was proposed to study the influence of extraction time, solid liquid ratio, and ultrasound amplitude on the yield, sulfate content, and thermo-rheological properties (viscoelasticity and gelling temperature) of the carrageenan fraction, as well as the composition (protein and phenolic content) and antiradical capacity of the soluble extracts. Operating at 80 °C and 80 kHz, the models predicted a compromise optimum extraction conditions at ~35 min, solid liquid ratio of ~2 g/100 g, and ultrasound amplitude of ~79%. Under these conditions, 40.3% carrageenan yield was attained and this product presented 46% sulfate and good mechanical properties, a viscoelastic modulus of 741.4 Pa, with the lowest gelling temperatures of 39.4 °C. The carrageenans also exhibited promising antiproliferative properties on selected human cancer cellular lines, A-549, A-2780, HeLa 229, and HT-29 with EC50 under 51.9 μg/mL. The dried soluble extract contained 20.4 mg protein/g, 11.3 mg gallic acid eq/g, and the antiradical potency was equivalent to 59 mg Trolox/g.
Highlights
Carrageenans are linear polysaccharides of D-galactose and 3,6-anhydro-D-galactose found in red seaweeds and commercially used as thickening, gelling, texturing, and stabilizing agents in food, cosmetics, and pharmaceuticals [1]
The extracted carrageenan fraction was precipitated with ethanol and was further characterized regarding the sulfate content and the thermo-rheological properties, whereas the remaining soluble fraction was analyzed for phenolic, protein, and antiradical properties
The carrageenan product obtained under optimal operation conditions was evaluated for the antiproliferative activity on selected humal cancer cells
Summary
Carrageenans are linear polysaccharides of D-galactose and 3,6-anhydro-D-galactose found in red seaweeds and commercially used as thickening, gelling, texturing, and stabilizing agents in food, cosmetics, and pharmaceuticals [1]. Instead of a pure compound, hybrid carrageenans are found, and κ- and ι- forms in particular are attracting interest as gelling agents [2]. These high molecular weight polymers (up to 5000 kDa, average 200–800 kDa) are approved for food applications, whereas degraded carrageenans (10–20 kDa) are not authorized [3]. Other interesting activities of these degraded polysaccharides such as antiviral, antitumoral, antibacterial, or immunostimulant have been reported [4,5,6,7,8] These properties depend on the carrageenan type and structure, sulfation degree and location, molecular weight, and processing methods [9]. Low molecular weight highly sulphated carrageenans are the most active against tumors, and oligocarrageenans induce apoptosis in cancer cells and weaken the immune suppressing effects of antitumor drugs [5,11], suggesting their coupled utilization as both adjuvant or carrier in anticancer treatments
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