## 1 Introduction  
Chia (_Salvia hispanica_ L.) is a one-year-old plant (_Lamiaceae_) that is a native species in Mexico and Northern Guatem, where it was bred as a cereal in pre-Columbian times. An adult plant grows up to 1 m in height and has versatile leaves that are 5 cm wide and 8 cm long, with white to purple flowers. The most important product of this plant is its seeds, which are 1-2 mm in diameter, oval, black, gray, or white, with black dots [1]. The seeds are used whole or in the form of flour or oil. Although they have a neutral taste, they are an interesting addition to diet because they form a sticky mucus in contact with water [2, 3]. Whole seeds and sprouts are added to salads and beverages to improve the density, and for the same reason, flour can be added to yogurt. The cultivation of chia sprouts is very simple, and they have also been recently used in the human diet for their nutritive and antioxidative properties [4, 5].  
Sprouts or microgreens are grown from the seeds of various kinds of grains, vegetables, nuts, and legumes. They have a high content of protein, calcium, magnesium, vitamin A, vitamin B, ascorbic acid, and vitamin E [6,7]. The use of microgreens is increasingly popular and they are considered the food of the future due to their relatively light weight, fast and easy growing, and high nutritional value [6].  
Light intensity, quality, and duration significantly influence plant growth and development through morphogenesis, the functioning of the photosynthetic apparatus, and metabolic pathways [8]. Light conditions also have the potential to evoke different actions of the antioxidant system [9] and metabolic pathways [10,11]. Light can enhance the synthesis of different antioxidants such as ascorbic acid [11,12], polyphenols, carotenoids, chlorophylls, and other enzymatic and nonenzymatic compounds that help in preventing and balancing oxidative damages in plants [13]. However, different growth conditions can have an impact on the antioxidative and nutritive properties of plant species [6].  
Sprouts used in diets are usually grown in dark conditions and consumed raw. They show a pale yellow color due to the lack of chlorophyll. After exposure to light, the expression of genes involved in chlorophyll and carotenoid biosynthesis is upregulated, leading to the change of color from pale yellow to green [14,15]. Different sprouts or microgreens are considered to be young plants of vegetables, grains, and herbs, with two fully developed cotyledons. Due to their antioxidant capacity and various bioactive compounds with antibacterial, anti-inflammatory, and other health beneficial properties, sprouts are considered \"functional food\" [16], which has recently been widely grown and used in the global food system.  
Fourier transform infrared spectroscopy (FTIR) is widely used for the identification of biomolecules, functional groups, types of bonding, and changes in molecular conformations. Due to its extensive applicability to the different kinds of tissues and a small amount of sample needed for analyses, this technique has found broad applications in the analyses of metabolic profiles of different plant species [17]. FTIR spectroscopy is used for the determination of antioxidant potential and health benefits in chia [18, 19, 20], as well as other medicinal plants [17].  
Although there have been many reports on the connection between the effect of light on nutritive properties and the antioxidant capacity of various microgreens, few studies have investigated the effect of light on nutritional properties and bioactive compounds in chia microgreens under different light regimes. Therefore, the aim of this work is to determine the effect of illumination on dark-grown chia microgreens by measuring total antioxidant capacity, the concentration of carotenoids and chlorophylls, total soluble phenolics, and ascorbic acid and cellulose content, as well changes in biochemical composition and structure of biomolecules by Fourier transform infrared spectroscopy (FTIR).