## 1 Introduction  
Quinoa (_Chenopodium quinoa [PERSON]_) is a pseudocrereal with large applications in the food industry and represent a current trend in the human diet because it has excellent nutritional and nutraceutical value and is a gluten-free grain [1; 2]. It can be used for functional food development due to its functional and rheological properties, sensory characteristics, nutrient profile and stability [3]. This crop is considered a whole vegetable protein and whole grain carbohydrate [4] and contains high quality oil and high amounts of vitamins, minerals and a large diversity of bioactive compounds [5]. With respect to the distribution of nutritive compounds within quinoa seed tissues, carbohydrates can be found mostly in the persiperm, while proteins, fat and minerals are concentrated in the endosperm and germ or embryo, which represent approximately 30% of the whole seed [4; 6]. The most important carbohydrate from quinoa seed is starch, which varies between 52.2-69.2% of the dry matter [4; 7; 8], and having as low as 11% amylose content [9]. Total fiber content in quinoa seeds varies from 7.0 to 26.5%, being mostly comprised of insoluble polysaccharides (78 of the total dietary fiber content) [10]. The protein content of quinoa varies from 8 to 22% depending on the varieties [11; 12] and it is of very high quality compared to wheat. Proteins from quinoa seeds are rich in amino acids such as lysine, threonine and methionine, which are deficient in cereals [13], making them complete proteins [14]. Lipid levels from quinoa (4.0-7.6%) are much higher than those from wheat [15; 16], unsaturated fatty acids being the predominant fatty acids (71-84.5% of total lipids) [16; 17]. From the nutritional quality of the lipid fraction, quinoa oil presents a \(\omega\)-6/\(\omega\)-3 ratio of 4.7-19.6, with high quality and nutritious character [16; 18]. Vitamins and minerals of quinoa seeds are among the features that make quinoa such an excellent nutrient source [19; 20]. [PERSON] et al. (2010) [20] found that the total mineral content in quinoa seeds is about twice that of cereals, being particularly rich in calcium, magnesium, iron and zinc. Regarding bioactive compounds, the main phenolic compounds presented in quinoa seeds are gallic acid (167.2-308.3 mg/100 g dw) and flavonoids (rutin, quercetin and kaempfer) [21; 22], and variation in levels exists between species, and depending on the growing conditions. Nutritionally, quinoa is recognized as a super grain and can be used in the bakery industry to improve final product quality or to develop new products, and the properties of starch present in seeds is similar to those found in wheat [23]. Investigations on the substitution of wheat flour with quinoa flour at various levels has been made in many investigations [24; 25; 26], but no previous studies concerning how the variation in particle size can influence the composition, physical and rheological properties have been done. Milling of quinoa seeds, a grinding process performed to produce flour or different flour fractions, is an important step that influences the product's quality. Significant differences in the nutritional composition, especially ash, protein and starch levels were reported for different particle sizes of milled grains, which may be related to cell-wall materials [27]. Therefore, the processing techniques and final product quality is greatly dependent on the particle size of the flour used and its constituents. Particle fractions can improve water or oil-holding capacity, the release of enzymes and physical properties by exposing their surface area during processing stages such as mixing, fermenting or baking. Nutritionally, particle size has a significant impact on food digestibility in the gastrointestinal system [28], digestibility lowering with increased particle size [29]. Size reduction is also applied extensively in the grain milling industry to separate the endosperm from the undesirable components of the whole grain, such as saponins in quinoa hull.