Polysaccharides of red alga <i>Gracilaria intermedia</i>: structure, antioxidant activity and rheological behavior

Castro, Joana Paula Lima de; Costa, Luís Eduardo Castanheira; Pinheiro, Maísa Pessoa; Francisco, Thiago dos Santos; Vasconcelos, Pedro Hermano Menezes de; Funari, Lizandra Mistrello; Daudt, Renata Moschini; Santos, Gustavo Ramalho Cardoso dos; Cardozo, Nilo Sérgio Medeiros; Freitas, Ana Lúcia Ponte

doi:10.1590/0104-1428.013116

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Original Article • Polímeros 28 (2) • Apr-Jun 2018 • https://doi.org/10.1590/0104-1428.013116 copy

Polysaccharides of red alga Gracilaria intermedia: structure, antioxidant activity and rheological behavior

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Abstract

A sulfated polysaccharide fraction from the red alga Gracilaria intermedia (PLS) was obtained by papain digestion (60 °C, 30 min). The extract was subjected to colorimetry and turbidimetry analysis, Fourier transform infrared (FTIR) spectroscopy, ¹H, ¹³ C and ²D ¹H COSY nuclear magnetic resonance (NMR) and gas chromatography/mass spectrometry analysis. Antioxidant activity tests were performed (chelation of ferrous ion, total antioxidant capacity, and scavenging of DPPH radicals); significant activity of the extract indicated that these polysaccharides may be used as non-synthetic antioxidants. The rheological behavior of aqueous polysaccharide solutions was studied at 25 ± 1 °C using steady-shear and dynamic oscillatory measurements. All the solutions analyzed showed pseudoplastic behavior and potential to act as a thickening agent, as proved through a preliminary comparison with a commercial product used for this application.

Keywords:
antioxidant activities; Gracilaria intermedia; polysaccharides; rheological behavior; structure

Residue	¹H chemical shift (ppm)
Residue	H-1	H-2	H-3	H-4	H-5	H-6
3,6-α-L-anhydrogalactose linked to β-D-galactose	5.62	4.60	5.04	4.11	4.26	nd*
β-D-galactose linked to 3,6-α-L-anydrogalactose	4.69	4.44	3.91	nd*	nd*	nd*
α-L-galactose-6-sulfato linked to β-D-galactose	5.14	5.05	nd*	nd*	nd*	nd*
	¹³C chemical shift (ppm)
	C-1	C-2	C-3	C-4	C-5	C-6
3,6-α-L-anhydrogalactose linked to β-D-galactose	98.4	nd*	81.2	77.5	nd*	69.5
β-D-galactose linked to 3,6-α-L-anhydrogalactose	102.5	nd*	82.1	68.7	73.8	61.5
α-L-galactose linked to β-D-galactose	101.25	nd*	nd*	78.75	71.9	67.5
β-D-galactose linked to α-L-galactose-6-sulfato	103.7	70.5	80.2	69.3	75.6	61.8

Sample	Concentration (%)	n	K (Pa.s)
PLS G. intermedia	1.0	0.67	2.31
	1.25	0.62	5.76
	1.5	0.47	11.64
CMC	0.75	0.60	1.44
CMC	1.5	0.29	47.23
PLS + CMC	1.0 PLS + 0.5 CMC	0.43	15.83
PLS + CMC	0.75 PLS + 0.75 CMC	0.39	10.11

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