# Innovations in Wheat Bread: Using Food Industry By-Products for Better Quality and Nutrition
## 2 Chemistry of Selected By-Products
When flaxseed is pressed, it yields oil and a solid residue called flaxseed cake. If not discarded, the cake is processed into meal for animal feed or fertilizer, providing energy for animals. Post-oil extraction, bioactive compounds remain in the cake, making it valuable. Thus, the cake can also be used in food product development, aligning with circular economy principles [14; 24]. Flaxseed cake is often ground into flaxseed flour, facilitating its use in food production. The amount of waste generated during the pressing of flaxseed oil ranges from 70 to even 75%, depending on the oil extraction method [90]. Similarly to most cases, the main component of flaxseed cake is dietary fiber, with content ranging from 32.78 g/100 g d.m. to 35.21 g/100 g d.m., of which 17.83-26.71 g/100 g d.m. is insoluble dietary fiber (IDF) and 8.5-14.95 g/100 g d.m. is soluble dietary fiber (SDF). The primary insoluble fiber fraction comprises cellulose and lignin, while the soluble fiber fractions include nucilage gums. Mucilages are hydrophilic compounds, and flaxseed nucilage (FM) comprises two distinct polysaccharides: a pectic-like material (acidic) and an arabinoxylan (neutral) [17; 91; 92]. The nucilage constitutes approximately 8% of the weight of flaxseed. Upon acid hydrolysis, these polysaccharides yield L-galactose, D-xylose, L-arabinose, L-rhamnose, D-galacturonic acid, and possibly traces of D-glucose. Mucilage gums become viscous when combined with water or other liquids, playing a crucial role in laxatives [93; 94]. Protein content in flaxseed cake ranges from 29.20 to 35.07 g/100 g d.m. [17; 95; 96]. It primarily comprises globulins (linin) (58-66% of the protein) and albumins (conlinin), along with hirudin and oleosin [97]. Literature data indicates that the digestibility of flaxseed protein is 85% [95]. The residual fat content in the flaxseed cake after extraction ranges from 4.41% to 15.27 d.m. [17; 92; 95] and, similar to flaxseed oil, it consists mainly of polyunsaturated fatty acids (approximately 68%), with SFA and MUFA accounting for approximately 8-9% and 5-6% of the oil, respectively [98]. The main fatty acid in flaxseed oil is \(\alpha\)-linolenic acid (C18:3), accounting for approximately 39-61% of the oil. The remaining fatty acids include linoleic acid (C18:2) 12.25-17.44%, oleic acid (C18:1) 13.44-19.39%, stearic acid (C18:0) 2.24-4.59%, and palmitic acid (C16:0) 4.9-8% [99; 100]. The mineral content in the form of ash constitutes 6.08-9.45% of the dry matter of the flaxseed cake [17; 92], primarily consisting of phosphorus, magnesium, calcium, iron, and zinc [98]. Flaxseed cake is also a rich source of phenolic compounds (7.40 mg GAE/g d.m.). The high presence of lignans (primarily seciosolariciresinol), predominantly found in the husk of flaxseed, is worth emphasizing. Lignans are non-nutrient, noncaloric, bioactive phenolic plant compounds. Lignans exhibit promising anticancer effects by modulating multiple targets of carcinogenesis. Additionally, they possess anti-inflammatory, antiviral, and antimicrobial properties, suggesting potential benefits in cancer prevention [101]. Cyanogenic glycosides, such as linustatin, neolinustatin, linamarin, lotaustralin, present in significant amounts in whole flaxseed, and phytic acid in flaxseed cake act as major antinutrients, hindering nutrient absorption. Despite the release of minimal hydrogen cyanide from flaxseed, well below toxic levels, roasting is commonly employed to mitigate cyanogenic glycosides' effects [98; 102].