Impact of extraction procedures on the chemical, rheological and textural properties of ulvan from Ulva lactuca of Tunisia coast

The impact of the extraction conditions has been studied on the yield, chemical composition, rheological and textural properties of ulvan from the green seaweed Ulva lactuca. High ulvan yield was obtained after combining enzymatic and chemical extraction but the lowest yield results at the drastic conditions (pH 1.5 and 90 degrees C). Besides, solvent acidity was an important parameter controlling the ulvan extraction efficiency. The different extraction processes affected chemical composition of ulvan extracts and in particular, sulphate, ash and sugar contents. Low proportions of galactose, glucose and protein were also found in sulphated polysaccharides. The extract, which is resulted from combined enzymatic and chemical extraction, was mainly composed of high peak molecular weight polysaccharides. Ulvan hydrocolloids demonstrated a pseudoplastic behavior. Viscoelastic behavior was carried out at a concentration of 1.6% (w/v) in the presence of 7 mM sodium tetraborate and at pH 7.5. However, polysaccharides formed a gel. It was not the case for the extract at pH 1.5 and 90 degrees C under the same conditions. The results showed that a significant effect of the conditions of extraction on the textural characteristic (firmness, springiness and adhesiveness) of ulvan gels. (C) 2014 Elsevier Ltd. All rights reserved.