Effect of extraction conditions on the yield and purity of ulvan extracted from Ulva lactuca
Graphical abstract
Highlights
► Influence of extraction conditions in the physicochemical characteristics of ulvan. ► Degradation of ulvan under drastic extraction conditions. ► High sugar content of extracts under drastic extraction conditions. ► The presence of proteins and high ash content in all extracts. ► The no selectivity of ethanol in the recuperation of ulvan.
Introduction
Green seaweed Ulva lactuca represents an important biomass available from proliferating algae in eutrophicated coastal water between the littoral of Taboulba and Sayada in Tunisia. It is characterized by a very interesting chemical composition and especially by its high content of cell wall polysaccharides (54% on the dry weight basis). However, the bioaccumulation of minerals and more especially the heavy metals (manganese, lead, copper and cadmium) in this algae, don't allow this seaweed to be used for human consumption or as an ingredient in some food preparations (Yaich et al., 2011). For this reason, the valorisation of this alga can be made only by the extraction of its different components such as the water soluble Ulvan. This polysaccharide displays physico-chemical and biological features of potential interest for diverse applications (Lahaye & Robic, 2007). Notably it forms unusual soft gels in the presence of divalent cations and borate (Lahaye & Axelos, 1993). Ulvan is mainly built on disaccharides repeating sequences composed of sulphated rhamnose and glucuronic acid, iduronic acid or xylose. The two major repeating disaccharides are aldobiuronic acids designated as type A: ulvanobiuronic acid 3-sulphate (A3S) and type B: ulvanobiuronic acid 3-sulphate (B3S). Partially sulphated xylose residues at O-2 can also occur in place of uronic acids. In addition, glucuronic acid can branch at O-2 of rhamnose 3-sulphate. Low proportions of galactose, glucose and protein are also generally found in ulvan (Quemener, Lahaye, & Bobin Dubigeon, 1997; Robic, Rondeau-Mouro, Sassi, Leart, & Lahaye, 2009).
Based on literature, ulvan is extracted by chemical methods using hot water often containing a calcium chelating agent such as sodium oxalate (Lahaye & Robic, 2007; Robic, Sassi, Dion, Leart, & Lahaye, 2009) or acidified ammonium oxalate (Robic, Rondeau-Mouro, et al., 2009) or alkali (Ray & Lahaye, 1995) or sodium chlorite or DMSO or phenol/acetic acid/water or acid (HCl) in very determined conditions without studying the influence of the variation of the extraction parameters such as pH, time and temperature in the same extraction conditions on the physicochemical characteristics of ulvan extracted. According to Robic, Rondeau-Mouro, et al. (2009), Robic, Sassi, et al. (2009), the sodium oxalate (50 mM, pH 6.5, 2 h, 85 °C), the acidified ammonium oxalate (20 mM, pH 4.6, 1 h, 85 °C) and acid extraction (50 mM HCl, 0.5 h or 1 h at 85 °C) are characterized by higher extraction yields and more ulvan extraction efficiency (percentage recovery of the initial rhamnose content in raw material) than other extractions using others solvents. Moreover, the uronic acid, the neutral sugars content and the molecular weight distribution of the ulvan are depends strongly on the extraction conditions.
In this context and in order to identify the conditions improving ulvan extraction without degradation, we study the influence of the acid extraction conditions by varying the pH (1.5 and 2), the temperature (80 °C and 90 °C) and the time (1 h, 2 h and 3 h) on the extraction yield and on the molecular weight distribution of ulvan extracted from U.lactuca.
Section snippets
Materials
The U.lactuca seaweed was collected from the littoral between the area of Taboulba and Sayada (Monastir – Tunisia), at a weak courantology and depth of 0.5 m, in July 2007. Fresh plants were cleaned from epiphytes, rinsed on the spot with seawater, and then placed in plastic bags. On their arrival at the laboratory, the seaweed samples were again washed with distilled water and dried in continuous air flow (35 °C, 72 h). The dried alga was then milled in a mechanical grinder for 5 min, to
Effect of extraction conditions on the alcohol precipitate yield
The dry matter content of extract juice before alcohol precipitation and the alcohol precipitate yields under different extraction conditions are reported in Table 1. According to this table, on average 3.05% and 2.85% (%dw/dw) of material was extracted respectively from the U.lactuca seaweed at pH 1.5 and pH 2. After alcohol precipitation of the acid extract juice, we recovered 65.79% and 71.22% (%dw/dw) of the material extracted at pH 1.5 and pH 2.
Depending on the extraction conditions, the
Conclusion
The effect of pH (1.5 and 2), time of extraction (1 h, 2 h and 3 h) and temperature (80 °C and 90 °C) on the chemical characteristics of acid-extracted ulvan from U.lactuca was shown. The pH was the most significant factor which affects the alcohol precipitate yield, the monosaccharide composition and the macromolecular characteristics of ulvan extracted. At pH 1.5 the alcohol precipitate yields and the recovery of uronic acids from extract juice are lower than at pH 2, whereas the ulvan
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2022, Applied Food ResearchCitation Excerpt :In fact, these molecules can account for up to 50% of the dry weight of the thallus (Catarino, Silva & Cardoso, 2018; Lahaye & Robic, 2007; Pereira, 2011). Furthermore, the methods of extraction and purification used might have a direct impact on yield and purity (Yaich et al., 2013). Due to their rheological (i.e., gelling/thickening) and increasingly broad spectrum of biological activities, such biomolecules are of considerable commercial interest in a variety of sectors, including feed, food, cosmetics, and pharmaceutical.