Comprehensive chlorophyll composition in the main edible seaweeds

Highlights

• It has been performed a complete description of the chlorophyll profile in the main seaweeds.

• It has been identified by first time new chlorophyll compounds in edible seaweeds.

• Five chlorophyll derivatives have been completely characterized (MS²) by first time.

• Series d chlorophyll derivatives seem to be common in seaweeds.

• New fragmentation patterns have been proposed for several chlorophyll derivatives.

Abstract

Natural chlorophylls present in seaweeds have been studied regarding their biological activities and health benefit effects. However, detailed studies regarding characterization of the complete chlorophyll profile either qualitatively and quantitatively are scarce. This work deals with the comprehensive spectrometric study of the chlorophyll derivatives present in the five main coloured edible seaweeds. The novel complete MS² characterization of five chlorophyll derivatives: chlorophyll c₂, chlorophyll c₁, purpurin-18 a, pheophytin d and phytyl-purpurin-18 a has allowed to obtain fragmentation patterns associated with their different structural features. New chlorophyll derivatives have been identified and quantified by first time in red, green and brown seaweeds, including some oxidative structures. Quantitative data of the chlorophyll content comes to achieve significant information for food composition databases in bioactive compounds.

Introduction

The seaweed industry provides a wide variety of products that have an estimated total annual value of US$ 5.5–6 billion, and ca. 90% of the production comprises food products for human consumption. They form part of the traditional dietary habits in Asian countries, mainly Japan, China and Korea but recently, seaweeds have drawn the interest of food industry in Western countries because of their nutritional value and as raw materials for supply of components in functional foods (Shahidi, 2009). They are excellent sources of polysaccharides, with relatively high protein content, including all of the essential amino acids, a remarkable presence of essential fatty acids with a nutritionally ideal n-6/n-3 fatty acid ratio, minerals, vitamins and trace elements. Edible seaweeds are taxonomically grouped into three different groups depending on their thallus colour, brown (Ochrophyta), red (Rhodophyta) and green (Chlorophyta). The three most important seaweeds used for human consumption (FAO, 2003) are species from Porphyra (common Japanese name, Nori), Laminaria (Kombu) and Undaria (Wakame). Among the green seaweeds, it is highly appreciated Enteromorpha (Aonori) and Ulva (Sea Lettuce).

Several kinds of secondary metabolites with potential benefits to human health have been described in seaweeds (Pangestuti & Kim, 2011). For example, it has been shown that the administration of several green seaweeds increased the fecal excretion of dioxins due to its chlorophyllic composition, and consequently the ingestion of green seaweeds can be consider as a new approach in the treatments of patients exposed to lipophilic xenobiotics. Specifically, the pheophytin a from Porphyra and Enteromorpha species has been identified as a potent suppressor against genotoxin-induced umu C gene expression in S. typhimurium (TA 1535/pSK 1002) probably associated with carcinogenesis (Okai, Okai, Yano, & Otani, 1996). According to this, pheophytin a derivatives have been proposed to display a potent suppressive activity against chemically induced mouse skin tumorigenesis. Pheophorbide a from brown seaweeds has been also proposed as a candidate for treating neurodegenerative diseases such as Alzheimer’s disease (Ina, Hayashi, Nozaki, & Kamei, 2007) due to its capacity to promote the differentiation of PC12 cells. Occasionally, consumers have shown allergic reactions after ingestion (Hwang et al., 2005), and pheophorbide a has been pointed as the hypothetic responsible compound. Consequently, different chlorophyll derivatives isolated from seaweeds have attracted considerable attention in the fields of food, cosmetic and pharmacology (Pangestuti & Kim, 2011).

A difference with microalgae, whose detailed chlorophyll composition is known (Garrido et al., 2011, Garrido and Zapata, 1996), the “recalcitrant” extracellular material of seaweeds (macroalgae) has made difficult its complete characterization. Analysis of chlorophyll compounds in seaweeds has been restricted mainly to presence of chlorophyll a, chlorophyll b (Lin et al., 2011), chlorophyll c (Fujii et al., 2012) and pheophorbide a (Amorim et al., 2012, Ferraces-Casais et al., 2012, Hwang et al., 2005).

The present work deals with the detailed and complete analysis of the chlorophyll fraction of the five seaweeds more consumed in the world. The identification is made by HPLC-hrTOF-MS, using different sources, ESI or APCI, in function of the polarity of compounds. Considering the biological activities and health benefit effects of the different chlorophyll catabolites and the high intake levels of seaweeds, it is essential to know exactly the composition of these sea foods.