Characterisation of laminarin extracted from brown seaweed Laminaria digitata, using optimized ultrasound- and ultrafiltration-assisted extraction method

The present study reported the extraction and characterisation of laminarin from Laminaria digitata. Hydrochloric acid concentration and extraction time were investigated by central composite design for optimizing extraction conditions. Regarding purification of the supernatant after the extraction process, membrane ultrafiltration was selected over pH shifting, ethanol precipitation and freeze-drying. With the assistance of ultrasound technology in the extraction process, the highest laminarin extraction yield and purity were obtained up to 57.34 ± 1.58 % and 81.10 ± 0.37 %, respectively. The molecular weight of laminarin extracts is in the range of 5.61 to 5.95 kDa. The Fourier-transform infrared spectroscopy (FT-IR) spectral features of the averaged spectra were depicted as absorbance peaks at the wavelengths of 3340 cm−1 and 2922 cm−1, which were related to OH and CH stretching of laminarin. US probe extract showed the highest scavenging capacity of 52.96 % while the HCl conventional extract exhibited the lowest scavenging capacity of 30.82 %. All the optimized laminarin extracts showed higher cytotoxicity in A549, A431, and Caco-2 carcinomas, effectively inducing cancer cell death in a time- and dose-dependent manner, and lower cytotoxicity in BEAS-2B normal human bronchial epithelial cells when compared to commercial laminarin.