## 1 Introduction  
_Spirulina_, commonly called'space food', which has been used for astronauts in National Aeronautics and Space Administration (NASA) projects [1], is considered a high-quality food and/or dietary supplement for humans because it contains large amounts of high-quality protein and many lipids and bioactive substances [2; 3]. Therefore, _Spirulina_ has been studied mostly to investigate its biological activity and to develop processing technologies to upgrade its quality. However, to date, most _Spirulina_ consumed worldwide has been in the form of simple dried powders in spite of their unpalatable flavors, as most bioactive components of _Spirulina_, such as C-phycocyanin (C-PC), xanthophylls, and chlorophylls, are extremely unstable and especially susceptible to heat [4; 5]. That is why, in processing _Spirulina_, minimal heat should be applied; however, the use of less heat to process natural resources that contain _Spirulina_ inevitably reduces the production yield as well as the biological activity of the products. Therefore, several low-heat extraction processes have been introduced for _Spirulina_, such as processes with simple and/or combined ultrasonic extraction, enzymatic hydrolysis, and various extraction solvents, which are carried out strictly at low temperatures [6; 7]. In extracting various bioactive components of _Spirulina_ by employing the above technologies, C-PC and chlorophyllsare most often the focus, since _Spirulina_ sp. is known to contain fairly high amounts of C-PC compared to many other microalgae. Chlorophyll and C-PC have many biological effects, such as anti-cancer, anti-aging, anti-inflammatory and antioxidant activity effects [8; 9]. Additionally, _Spirulina_ provides the pure intact form of chlorophyll \(a\) at the lowest production costs, since most of the chlorophyll (approximately 90%) that exists in _Spirulina_ is in the form of chlorophyll _a_[10; 11]. In particular, the demand for chlorophyll \(a\) has recently increased because its biological activity, such as antioxidant activity, is considered to be higher than that of other chlorophylls, such as chlorophyll \(b\) or _c_[12]. However, the abundant chlorophyll in plants is a mixture of chlorophyll \(a\), \(b\), and \(c\), which would increase the cost of extracting and purifying chlorophyll \(a\) from plant sources. Therefore, in this work, to obtain high amounts of heat-labile chlorophyll \(a\) from _Spirulina_, we developed a unique low-temperature extraction process employing high-pressure homogenization (HP). The ultrasonic extraction process has several disadvantages when scaled up, and in general, it requires the installation of more equipment than is required for conventional solvent extraction processes with water, ethanol, or other substances. Ultrasonic extraction also needs to be combined with other processes, although it has been shown to be effective in processing natural products at a low temperature [13; 14]. In general, HP has been used mostly for mixing hydrophobic and hydrophilic components in solution for the cosmetic and food industries by applying a high input pressure of 10,000-30,000 psi, and this process was shown to be more effective than a simple mixing process [15]. In addition to the original application of HP, in this work, the HP process was applied to extract chlorophyll \(a\) from _Spirulina_ at room temperature in a very short period of time, i.e., 5-10 min, since the process can easily break down the hard cell walls by applying a high shear stress only to the cells that pass through a very small orifice, approximately 70 \(\upmu\)m in diameter, with a high pressure of 10,000-30,000 psi [16; 17]. Very high shear forces can easily destroy the cell membranes of _Spirulina_ and consequently release chlorophyll \(a\) into the extraction solution without any additional effort. Thus, the extracts from this process contain large amounts of intact chlorophyll \(a\).