# Extraction of Pigments from Microalgae and Cyanobacteria--A Review on Current Methodologies
## 1 Introduction  
Microalgae and cyanobacteria are photosynthetic organisms that produce distinct kinds of pigments in order to harvest light. Such pigments are usually grouped in three major classes--chlorophylls, carotenoids, and phycobiliproteins [1]. The presence of different kinds of pigments in microalgae and cyanobacteria varies according to the phylum to which the organism belongs. Chlorophyll is the most fundamental one; it is responsible for oxygenic photosynthetic activity and it is present in all photosynthetic microalgae and cyanobacteria [2]. Carotenoids can be both primary and secondary pigments and the profile changes within the species and growth conditions; the most well known and commercialized ones being sataxanthin, lutein, and \(\beta\)-carotene [3]. Moreover, phycobiliproteins are a special class of pigments present only in cyanobacteria and red algae and can represent the major light absorber in these organisms, where the most well-known phycobiliproteins are phycocyanin and phycoerythrin [4]. Together, the three classes of pigments maximize light harvesting in microalgae and cyanobacteria through the whole visible light range. Pigments from microalgae and cyanobacteria are known for their highly attractive properties for industrial use in food, feed, pharmaceuticals, nutraceuticalals, and cosmetics, mainly due to their color and bioactive properties, but also for being natural and ecofriendly components [3, 4]. The demand for natural colors (instead of synthetic ones) is increasing the need for a more sustainable source, however, the use of microalgae and cyanobacteria in the market is still related to high added-value products, in part due to the scale of biomass production being small when compared to synthetic alternatives [5]. Microalgae and cyanobacteria can be sold both as raw biomass (dried) or processed for the obtention of specific compounds. When only a specific compound is the final product, it requires downstream processing of extraction and possibly purification. The cost for the production of purified pigments is still high and it restricts the application to high-value markets, for example as cosmetics [6]. Three cases of successful production of pigments from microalgae and cyanobacteria are known: phycocyanin from _Arthrospira platensis_[4]; \(\beta\)-carotene from _Dunaliella salina_[7]; and astaxanthin from _Haematococcus pluvialis_[8]. Other compounds and sources appear as potential products, such as lutein from _Scenedensmus almeriensis_[9] and phycerythrin from _Porphyridium_ spp. [10]. The market for these pigments represents about $1.5 billion (USD), including all sources (natural and synthetic). The phycocyanin market alone has a size of about $100 million (USD), \(\beta\)-carotene ca. $270 million (USD), lutein ca. $350 million (USD), and astaxanthin ca. $800 million (USD) [4]. Pigments are usually found as a part of extracts obtained from the mentioned organisms, because as already mentioned, the purification process leads to unjustifiable costs [8]. Several factors can affect the extraction of pigments, including the target pigment, organism, market trends, available technology, and costs. Extraction usually requires a cell disruption method and a compatible solvent; however, it is also possible to extract some of these compounds without a cell disruption process, using the so-called \"cell milking\", where the product is extracted while the culture grows [11]. When it comes to the available technology, many extraction methodologies were developed and optimized in recent years. In general, extraction can be performed using two distinct kinds of methodologies: (i) non-mechanical, such as chemical, thermal, and enzymatic; and (ii) mechanical, such as pressurized systems, ultrasonication, microwave, electric fields, and supercritical extraction. Some systems are based on a synergy between non-mechanical and mechanical characteristics, considering the effects of solvents, temperature and the technology mechanism (e.g., microwave-assisted extraction and ohmic heating).