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Due to their richness in starch and proteins, as well as in fibres and micronutrients, cereal grains are considered as an interesting nutritional source to promote better health (Poutanen 2012). Grains are made of numerous tissues with distinct composition, structure and physiological role for the future plant. The major part of the grain (60–85% of the dry grain mass) corresponds to the starchy endosperm (Evers and Millar 2002) and contains the storage compounds, as starch and proteins, for the plant growth. Depending on the cereal, it is covered with one or several aleurone layers (2–10% of the grain mass) containing the major part of the grain vitamins, minerals and molecules with antioxidant activities. Aleurone also plays a critical role in germination with the production of hydrolytic enzymes for the degradation of the storage compounds. It is surrounded by several tissues, called envelopes, with the nucellus, testa and pericarp acting as barriers to water and pathogens for the grain protection as well as being rich in insoluble fibres and phenolic compounds. The last part of the grain (3–7% depending on the cereal) corresponds to the germ and includes the scutellum, the plumule, the radicle and the embryonic axis that leads to the new plant.

Cereal grains are rarely consumed without prior transformation. Envelopes, especially the more external ones, and the germ have to be removed from the endosperm to maintain safety, high shelf‐life and good technological and taste properties of the cereal products. The most external grain tissues may indeed be contaminated by microorganisms (Laca et al. 2006) and undesirable compounds, such as pesticides, heavy metals and mycotoxins (Balinova et al. 2006; Rios et al. 2009; Cheli et al. 2010). Moreover, the germ, which is rich in lipids, can suffer from oxidation.

Grain processing methods are mainly focused on the isolation of the starchy endosperm to produce flour or semolina, the remaining products being recovered in the technological bran and short fractions. Technologies can differ depending on the country, cereal type, food product and industry considered. They range from small batch milling units to continuous milling of large amount of grains. They also differ according to the grain anatomy (presence or absence of a crease) and are dependent on differences between tissue mechanical properties. Semolina and flour fractions therefore mainly derive from the endosperm, whereas bran and shorts mainly come from the envelopes, aleurone layer and germ. However, each fraction also respectively contains part of the other grain tissues in proportions depending on the processing methodology and steps as well as on the sample variability inherent to genetic background and environmental conditions. This means that a comparison between fractions with the same denomination remains difficult without proper characterization of the tissue composition. Traditional methods monitoring ash content or color properties of semolina or flour are found to be limited to monitor the presence of the outer layers (Greffeuille et al. 2005). Moreover, new analytical methods have shown that bran obtained from grain debranning or milling displays a distinct proportion of grain tissues (Hemery et al. 2009).

Recently, efforts have been made to increase our understanding of the grain tissue behavior throughout the fractionation process and to answer the consumer and social demands with the aim to produce cereal fractions with desired properties but without losses of nutritionally interesting compounds. These efforts have led to the development of new tools and strategies to isolate tissues or molecules in order to better exploit the grain resource and increase the nutritional value of corresponding food products. This chapter points out and summarizes this progress, mainly focusing on dry fractionation.