# Extraction of Bioactive Compounds from _Ulva lactuca_
## 1 Introduction  
Macroalgae (seaweeds), are macroscopic algae with high growth rate that can be cultivated with minimal use of freshwater at infrastructures installed on non-arable land. However, their cultivation cost is considerably lower compared to microalgae [1]. Macroalgae have great potential for several industrial applications [2] and therefore the interest in algal biotechnology has been increasing in the past few decades, particularly, on the exploitation of various macroalgae species for the production of a vast variety of products in the food, cosmetic and pharmaceutical industry. Consequently, during the last few decades, world macroalgae production increased at a rate of 8.7% per year [2]. _Ulva lactuca_ is a widespread macroalgae growing along the Mediterranean coast which belongs to the phylum _Chlorophyta_, commonly known as \"Sea lettuce\" [3]. _U. lactuca_, contains commercially valuable chemical compounds that can be exploited in cosmetic, pharmaceutical, chemical, food, and energy applications. It has been reported that up to 60% carbohydrates, 10-47% proteins, 1-3% lipids, and 7-38% mineral ash are contained in _U. lactuca_[4]. Bioactive compounds of major industrial importance found in _U. lactuca_ are phenolics, pigments (chlorophylls and carotenoids), and polysaccharides [5]. Phenolic compounds of macroalgae origin have been proven to confer antiallergic, skin antiaging, and whitening properties to cosmetic products [6]. Moreover, the consumption of an adequate level of polyphenols, such as myricetin, morin, and quercetin found inU. lactuca_[5], could result in the prevention of diseases such as obesity, metabolic syndrome, Alzheimer's, or cancer [7]. Carotenoids present in _U. lactuca_, such as astaxanthin, \(\beta\)-carotene, fucoxanthin, and lutein, have been proven to have anti-inflammatory, antiaging, antioxidant, and other activities. They are frequently added in vitamin supplements and cosmetics, while they are used as natural food dyes and fish and poultry feed additives [6; 8]. Carotenoids possess anti-inflammatory properties due to their ability to neutralize free radicals, creating a chemical protection against the proliferation of cancer cells [7]. _Ulva_ spp. contain a significant amount of polysaccharides, varying from 15 to 65% of the total dry mass. These polysaccharides include ulvans, sulphated polysaccharides with rhamnose, uronic acids, and xylose as major components, as well as glucans including starch [4]. Ulvan polysaccharide and its oligosaccharides have anti-viral, antioxidant, anti-tumour, anti-coagulant, antihyperlipidemic, hepato protective, immuno-stimulating, anti-depressant, and anti-anxiolytic activities [4]. Consequently, Ulvan has industrial applications in the chemical, biomedical, and agricultural sectors [4]. Regarding the outcome of the bioactive compounds' extraction process, different variables are important, such as solvent type, solvent to solid ratio, temperature, and extraction time. These operational conditions require individual or combined study in order to maximize yields, the extraction rate, and the bioactive potency of the extracts [9; 10]. The extraction yield of the targeted bioactive compounds is solvent dependent and different solvents can be used according to the polarity and location of those compounds. An aqueous solvent is suitable for the separation of polysaccharides, while phenolics and carotenoids are usually extracted with organic solvents [10; 11]. In most cases, the extracts obtained with organic solvents appear more bioactive, while it has been confirmed that extracts derived from polar solvents have higher antibacterial activity [11]. When the bioactive extracts are targeted for cosmetics, pharmaceutical, and food industries, the range of the most convenient solvents is limited. The employed solvents, apart from being efficient in separating different compounds from their natural sources, must also be non-toxic [12].