## 1 Introduction  
_Salvia hispanica_ L., popularly known as chia, is a member of the Lamiaceae family [1]. Chia is an annual plant widely cultivated because of its culinary and medicinal uses [2]. This plant can be grown in various climates, from tropical to subtropical [3]. The chia plant can reach a height of 1 m and has oppositely arranged leaves with small white or purple hermaphrodites. The oval, smooth, and shiny seeds can be gray, black, black spotted, or white, with sizes ranging from 1 to 2 mm [4]. When soaked in water, chia seeds become gelatinous and absorb much water [5].  
An early study reported the composition of chia seeds grown in several geographical locations under different climatic conditions [6]. Chia seeds have high antioxidant potential [7] and are widely recognized for their high amounts of alpha-linolenic acid (ALA), dietary fiber, minerals, omega 3 (n \(-\) 3), proteins, phytochemicals such as phenolic compounds [8] (such as caffe acid, daidzin, gallic acid, protocatechuic ethyl ester, and rosmarinic acid) [7], and vitamins [8]. Quercetin and kaempfer are the main substances in hydrolyzed and crude chia seed extracts, but caffe and chlorogenic acids are only found in trace amounts [9]. Fatty acids, including alpha-linolenic acid, linoleic acid (L), oleic acid, palmitic acid, and stearic acid, are predominantly observed in chia seed oil (CSO) [3; 6].  
CSO is extracted using various methods, resulting in varying quality of the oil in terms of fatty acid content, antioxidant activity, and functional properties. Conventional solvent extraction, the cold-pressing method, the ultrasound-assisted method, and the supercritical fluid extraction are techniques used to extract CSO [10]. The cold-press extraction method is a mechanical extraction technique using a screw press without organic treatment or heat application on the expeller. This technique is a cheap, nontoxic, environmentally friendly, and green method. Some parameters such as barrel temperature, restriction die, screw press speed, and seed moisture content can affect CSO extraction [11].  
The biochemical components of chia seeds increase the satiety index, improve serum lipid levels, prevent inflammation and cardiovascular diseases, and decrease the risk of chronic diseases due to chia's antioxidant properties [2; 12; 13]. Chia has also been studied for its cosmetic benefits. Preliminary findings indicate that chia seed exhibits biological functions in the skin, including maintenance of the stratum corneum epidermal barrier, the prevention of transepidermal water loss, and disruption of melanogenesis in epidermal melanocytes [13].  
However, many studies have also been conducted to assess the influencing factors of the quality and quantity of CSO. The results could be more consistent due to the variety of chia seeds and culture location. Currently, chia is popular in Thailand due to its health benefits, but there is no experimental design to extract the oil from local chia seeds. Thus, the purpose of this study was to extract CSO using the screw-pressing method and evaluate the quality of the oil. The response surface methodology (RSM) and central composite design (CCD) were used to optimize the conditions to achieve high-quality CSO.