## 1 Introduction  
The use of seaweed is ancient, dating back at least to the Neolithic period, over 8000 years ago [1]. Traditionally, seaweeds have been harvested by Asian populations for food and medicinal (or healing) purposes [2]. Only recently have Western European countries become widely interested in the use of seaweed, owing to advances in science and technology that allow the extraction and isolation of valuable natural compounds [3]. Most seaweeds are benthic organisms, attached to a substrate, and are exposed to a variety of abiotic and biotic factors. As a form of protection, these organisms adapt their metabolism by producing a wide range of metabolites. These include proteins, polysaccharides, fatty acids, sterols, pigments, phenolic compounds and many other secondary metabolites, in varying proportions, which can be extracted and used in food matrices, as well as in cosmetics, pharmaceuticals, and other biotechnological applications [4]. The biochemical profile of seaweed depends on many factors such as taxon, geographical location, harvesting season, environmental factors, cultivation conditions, life cycle stage and processing method [5; 6]. Among the diverse seaweed species, brown seaweeds (Phaeo-phycaeae) are particularly important for their high-value polysaccharides, such as alginic acid [7]. Alginic acid can provide rigidity and flexibility, allowing seaweed to withstand ocean currents and resist desiccation at low tide. Alginates are widely used as thickening, gelling and stabilizing agents, with applications in various industries: food (salad dressings, ice cream, beer and dairy drinks), cosmetics (shampoo, lipsticks, creams), pharmaceuticals, and even paper and paint production [8; 9]. Brown algae are also well known for their content of ticoanthin, the dominant accessory photosynthetic pigment xanthophyll responsible for their yellowish-brown colour. In addition to fucoxanthin, other carotenoids such as violaxanthin and \(\beta\)-carotene [10; 11] can also be found, along with chlorophyll \(a\) and chlorophylls \(c1\) and \(c2\). Fucoxanthin has antioxidant, anti-inflammatory, anti-obesity, neuroprotective and anti-cancer properties [9; 11], in addition to its potential to replace synthetic colourings in various industries such as food and cosme [12]. The brown seaweed _Saccorhiza polyschides_ (Figure 1A), known as furbeltous, is distinguished by a flattened stipe, with helical and wavy margins in adult individuals, growing from a large bulbous and rough attachment organ and eventually widening into several blades [13]. Unlike true kelps, _S. polyschides_ is a semi-annual species, which has earned it the common name \"false kelp\" [14]. According to [PERSON] et al. [15], the sporophyte phase can last between 12 and 18 months. It is characterized by rapid growth in spring and summer, with the cycle ending in autumn [16]. _S. polyschides_ has a wide distribution along the northeastern Atlantic coast and can be found in the shallow intertidal and subtidal zones, up to 19 m deep on rocky bottoms, from Norway to Ghana [17]. It is traditionally known to be edible, has biofertilizer potential [18] and may also have antioxidant and neuroprotective properties [19; 20; 21]. Figure 1: Samples of kelp used in this study. (**A**) _Saccorhiza polyschides_ (distinctive stipe and bulbous base); (**B**) _Laminaria chloroleuca_ (juvenile); (**C**) _Macrocystis pyrifera_ by the Kelp Forest Foundation and (**D**) _M. pyrifera_ residual pulp. Laminaria adroleuca_, known as kombu, is an edible seaweed, and related species are widely consumed in Asian countries. It grows to a length of up to 3 m and has a flat blade divided into linear segments, which emerge abruptly from a rigid, smooth, cylindrical stipe, while small rhizoids attach to the substrate (Figure 1B) [17]. A distinctive feature of the species is its yellowish colour.