# Innovations in Wheat Bread: Using Food Industry By-Products for Better Quality and Nutrition
## 2 Chemistry of Selected By-Products  
The proper utilization of agricultural waste represents a crucial aspect in the context of sustainable development and efficient resource management. Among these raw materials, obtained as by-products of industrial food production processes, are apple, grape, olive, and flaxseed wastes. Despite their initial role as by-products, their potential as valuable resources for further utilization is increasingly being recognized. This chapter focuses on the chemical characterization of these wastes, emphasizing their value as sources of valuable nutrients and bioactive compounds. Apples (_Malus domestic_ L.) rank third among the most popular fruits worldwide, following bananas and watermelons [27]. They are extensively used for producing juices, ciders, alcoholic beverages, fruit preserves, dried products, and frozen goods. Globally, approximately 89 million tons of apples are produced annually, with 25% of them ending up as waste [11]. Apple pomace primarily consists of peels, seeds, and some pulp. After pressing, the moisture content is about 70-85%, rendering pomace highly susceptible to microbial growth. To maintain proper microbiological safety, pomace should be dried to a water content of no more than 10% [28]. The water content in dried pomace ranges from 4.4% to 10.8% according to literature data [29; 30; 31]. Apple pomace is rich in carbohydrates (45.1-84.7 g/100 g d.m. ), primarily fructose, sucrose, and glucose, and total dietary fiber (35-82 g/100 g d.m. ), with about 4.2-11.9 g being soluble fiber and 25.73-77.8 g insoluble fiber [15; 32; 33]. The main components of insoluble fiber in apple pomace are cellulose (6.7-40.4 g/100 g d.m. ), lignin (14.1-18.9 g/100 g d.m. ), and hemicelluloses (approximately 16.4 g/100 g) [32; 34]. The main soluble fiber in apple pomace is pectin, comprising up to 15% of the d.m. in pomace [34]. Studies have shown that pectins in apples can reduce the absorption of cholesterol into the blood and decrease pancreatic lipase activity by up to 94.3%, indicating anti-obesity effects [35]. Additionally, pectin consumption has been associated with lowering blood glucose levels [36]. [PERSON] et al. [37] compared the effects of apple pomace, apples, and apple juice on plasma lipid profiles in a crossover study with healthy participants. They found that pectin consumption correlated with reduced plasma cholesterol, and apple pomace intake had no effect on serum cholesterol levels. Pomace is also a source of starch, comprising 14-17%, with immature fruits containing more starch [38]. It is also rich in mineral components such as potassium, calcium, and magnesium [34], and vitamins C (22.4 mg/100 g d.m.) and E, found in the seeds (5.5 mg/100 g d.m. in pomace) [39]. The polyphenolic components in apples include five main groups: flavanols, flavonols, hydroxycinnamates, dihydrohalcones, and anthocyanins. Apples have an antioxidant activity of about 100 mmol of vitamin C equivalents per gram of fruit, ranking second after cranberries in a study of fruit consumption in the USA. Apple pomace contains polyphenols such as catechin, p-cumaric acid, caffeic acid, and ferulic acid, which exhibit stronger antioxidant activity than vitamins E and C [34; 40]. Apple pomace consumption showed a trend towards decreasing heart rate, blood pressure, and certain biomarkers associated with inflammation. Additionally, apple pomace improved gastrointestinal health, indicated by decreased lithocholic acid excretion [37]. Other studies suggest that apple pomace, rich in polyphenols, can benefit cholesterol levels, insulin sensitivity, and gut microbial functionality [40; 41; 42; 43]. However, like any by-product, apple pomace also contains substances undesirable in food. The main anti-nutritional components in apple pomace are saponins, alkaloids, and tannins [44]. Therefore, further research is needed to determine the optimal dosage and safety of apple pomace for human consumption.