Natural decoloration, composition and increase in dietary fibre content of an edible marine algae, Ulva rigida (Chlorophyta), grown under different nitrogen conditions

Abstract

The colour, dietary fibre content and characteristics of the edible marine green algae, Uloa rigida, were investigated in relation with the nitrogen content of the algal culture medium. Colour brightness decreased and total nitrogen of the algae increased in nitrogen-enriched conditions. When nitrogenenriched seaweeds were grown again in normal seawater for 10 days, colour brightness increased and total nitrogen concentration fell. Total dietary fibre content of the wild and nitrogen enriched algae were close (-38.0% DW) but increased markedly when the nitrogen-rich plants were cultured in normal seawater (54.4% after 10 days). Soluble fibre were xylorhamnoglucuronan sulphate (ulvan) with close molar compositions for all the seaweed samples. Insoluble polysaccharides were composed of glucose, xylose, uronic acid, rhamnose and sulphate which molar proportions varied for the different algal samples. The soluble fibre intrinsic viscosity and the water holding capacity of insoluble fibre were not markedly affected by the growth conditions. This report demonstrates that edible seaweed aquaculture provides an alternative or a complement to post-harvest transformations of seaweeds to modify organoleptic and nutritional characteristics.

Chemical composition of cultivated seaweed Ulva clathrata (Roth) C. Agardh

“…This is in agreement with Lahaye et al (1995) who reported that the nitrogen content in the culture medium affects the biosynthesis of the algal cell wall polysaccharides as well as of proteins and pigments. Gómez-Pinchetti et al (1998) also reported, for U. rigida, that when nitrogen limits growth, carbohydrate synthesis predominates and in nitrogen enriched conditions, a decrease in fibre content is observed.…”

“…SDF in U. clathrata cultivated samples (16-22% dw) represented the main fraction of dietary fibre (>50% of TDF) and, although SDF% dw was higher for LSS Ulva sample, the soluble to insoluble dietary fibre ratio (S/I) was significantly lower (1.2) for LSS sample vs MSS samples (1.7avg), because the IDF increases at higher rate than the SDF in LSS. In Lahaye et al (1995) study, growing conditions also affected the S/I ratios. The higher proportion of soluble polysaccharides, in nitrogen enriched U. rigida (S/I = 1.23) than in wild algae (S/I = 0.93), was related to its high growth rate.…”

“…Nevertheless, TDF contents of the cultivated U. clathrata coincide well with those reported for wild U. lactuca and E. spp. (38.1% and 33.4% dw) by Lahaye (1991), and wild and cultivated U. rigida (36.9% to 54.4% dw) reported by Lahaye et al (1993Lahaye et al ( ), 1995 and Gómez-Pinchetti et al (1998). If the TDF contents are expressed on an ash free dry weight basis, they amount to 49.2%, 47.3%, 48.5% and 56% dw for MSS and LSS U. clathrata cultivated samples; thus, an increase in TDF content is observed for the LSS algae, regardless of the loss of salts eliminated in the postharvest washing and pressing process, it is most likely related to the loss or utilisation of molecules such as protein and reserve metabolites (starch, lipids, etc.).…”

“…and Enteromorpha sp. (Lahaye, 1991;Lahaye & Robic, 2007;Lahaye et al, 1995;Ray, 2006), and recently in U. clathrata (Hernández-Garibay, ZertucheGonzález, & Pacheco-Ruiz, 2011).…”

“…If the protein content is expressed on an ash free dry basis (assuming that the entire N measured comes from protein), it amounts to 45% and 28% of the MSS and LSS Ulva samples, respectively; thus, a relative reduction in protein content was observed for LSS cultured algae regardless of the loss of ash compounds during the washing and pressing postharvest processes applied to LSS. According to Gómez-Pinchetti, Del Campo Fernández, Moreno-Díez, and García-Reina (1998); Lahaye, Gómez-Pinchetti, Jimenez del Rio, and Garcia-Reina (1995) and Msuya and Neori (2008), the lower N fertilization in the LSS may explain these differences.…”