# Innovations in Wheat Bread: Using Food Industry By-Products for Better Quality and Nutrition
## 2 Chemistry of Selected By-Products
Grapes (_Vitis vinifera_ L.) rank fifth in terms of fruit production volume, with approximately 74.94 million tons produced globally [27]. Of the total grape production in 2016, approximately 31.3% were table grapes, 6.3% were used for raisins, leaving around 62% to be crushed primarily for making wine, with about 30% potentially used for grape juice concentrate or distillation [22]. As reported by [PERSON] et al. [12], as much as 30% of grape mass used for wine production can become waste, posing a significant issue regarding disposal. Grape pomace, also known as wine pomace, is the leftover material after pressing and fermentation, primarily consisting of skins (up to 75%), grape seeds (up to 28%), seedless pulp, and stems [45; 46]. Wine pomace also includes yeast cells resulting from the wine fermentation process [47]. Water can constitute up to 64% of pomace depending on the processing technique [48]. Large quantities of grape pomace, often discarded in landfills after harvests, can hinder biodegradation due to low pH and antibacterial polyphenols [12]. Although grape pomace contains some protein (up to about 14% d.m. ), it is not efficiently digested by most animals for energy [12; 49]. Using grape pomace as compost is not economically viable due to nutrient deficiencies, but it contains significant amounts of health-promoting compounds [50]. Grape pomace is mainly composed of dietary fiber (up to 89 g/100 g d.m., depending on grape variety), with about 13 g being soluble fiber and up to 63 g insoluble fiber [12]. Typically, seeds exhibit a higher fiber content than skins, with red wine pomace demonstrating greater fiber richness compared to its white wine counterpart [51]. The protein content of wine pomace, ranging from 6% to 15% d.m., is influenced by grape variety and harvesting conditions, with skins showing a slight superiority over separated seeds. Amino acid composition resembling cereals, it is abundant in glutamic acid and aspartic acid but deficient in tryptophan and sulfur-containing amino acids. Notably, skin protein is rich in alanine and lysine, in contrast to seed proteins [52]. Grape seed oil, extensively utilized in cosmetics and recognized for its antioxidant properties [53], contains an oil content ranging from 8% to 15%, primarily composed of oleic and linoleic acids, alongside palmitic acid [54; 55]. It is rich in polyunsaturated and monounsaturated fatty acids, with \(\beta\)-sitosterol as the principal sterol and \(\alpha\)-tocopherol as the predominant tocopherol, comprising about 70% [56]. The mineral content of wine pomace varies widely due to factors like edaphoclimatic conditions and winemaking processes. Potassium, phosphorus, sulfur, and magnesium accumulate mainly in grape skin, resulting in higher levels compared to seeds, which serve as reservoirs for calcium. The predominant potassium salts, such as potassium bitartrate, can constitute a significant portion of wine pomace [47; 57]. The utilization of grape by-products in foods has limits due to the presence of antinutritional factors such as lectin and tannin [58]. Nevertheless, research highlights diverse phenolic compounds in wine pomace, influenced by grape properties and winemakingmethods [59]. Skins are rich in hydroxycinnamic acids, while seeds contain gallic and protocatechuric acids. Flavonoids like anthocyanins and flavanols are abundant in both red and white pomace, with seeds having most flavanols. Certain grape varieties may contain significant compounds like quercetin 3-O-glucuronide, and wine pomace holds nontextable polyphenols, including hydrolyzable polyphenols and nontextable proton-thocyanidins [60, 61, 62]. Grape seeds, as suggested by [PERSON] et al. [54], are notable for containing a substantial quantity of oligosaccharides, mirroring those found in wine, thereby establishing grape seeds as a novel and promising reservoir of these bioactive compounds. Research suggests that grape pomace phenolic compounds may alleviate metabolic syndrome [63, 64, 65].