## 1 Introduction  
C-phycocyan (C-PC) is a well-known bioactive substance existing in _Spirulina_ sp. and other cyanobacteria and red algae [1, 2]. Some of these, especially _Spirulina_ sp., contain fairly high amounts of C-PC in the ranges of 10-20% [1, 3] in nature; C-PC has been used as a functional blue dye since it has been known to have many biological activities such as antioxidant activities, immune-modulatory activities and anticancer activities, etc. [4, 5]. One of the main light harvesting pigments in _Spirulina_ sp. is known as phycobiliproteins that is structured by phycobilisomes, and phycobilisomes are composed of three types of biliproteins such as C-phycocyanin (C-PC), phycoerythrin (PE), and allophycocyanin (APC) [1, 6]. However, C-PC is also known to be extremely sensitive to heat and pH [7, 8], and its extraction yields were seriously affected by temperature as well as purity [9]. This sensitivity increases its production cost and also decreases its biological functions during production and storage. Therefore, many processes have been studied to obtain high amounts of intact forms of phycocyanins from _Spirulina_ by employing various extraction processes such as freezing and thawing, enzyme digestion, and extraction with various solvents at relatively low temperatures [9, 10]. However, in general, low temperature extraction process did not have high enough extraction yields from many biomaterials [11, 12]. Among them, the ultrasonic process has been proved to be very effective in extracting heat labile substances from many bioresources, because in a short time, high speed ultrasonic vibration generates many captivation bubbles that can effectively break the cell walls due to shock wave and liquid jets by collapsing the bubbles near the cell walls [13; 14; 15; 16]. Therefore, the ultrasonic process has been considered a non-thermal green extraction process that can obtain heat sensitive bioactive substances such as C-PC at low temperatures with relatively high efficiency; however, this process also has the disadvantage of scaling-up the processes up to 5-10 tons so far [17; 18; 19]. Besides effective extraction of intact C-PC, many works on the stability of C-PC have also been carried out to mainly find the effects of temperature and pH in processing _Spirulina_ sp. or for a week of short term storage [20]. Moreover, reports of the effect of the light are few, even though the importance of the exposure to the light should also be considered. Therefore, temperature and light must be accounted for as the most important variables in maintaining C-PC extracted from _Spirulina_, especially in terms of storage in many food industries. However, there have not been studies on the changes of the concentrations and purity of C-PC for long-term storage experiments, since most results have been from studies carried out for less than a week [20; 21]. Moreover, there is no report of considering the combined effects of both temperature and light on the stability of C-PC for a short-term storage condition, even though the effects associated with both major factors could represent the actual storage conditions in the fields. Therefore, in this work, comprehensive kinetic studies on degrading the C-PC in the extract will be investigated by considering simultaneous changes of temperature and light for long-term periods of storage.