# Valorization of Date Fruit (_Phoenix dactylifera_ L.) Processing Waste and By-Products: A Review
## 3 Nutritional and Biochemical Composition of Date Fruit and Date By-Products
### Dietary Fibers  
The date palm is a valuable source of dietary fiber, and a significant portion of that fiber can be found in the flesh of the fruit [37]. Date palm dietary fiber contains soluble and insoluble fibers, whereas both have different physiological effects on the body. Soluble fibers such as pectin and hemicellulose can be dissolved in water and form a gel-like substance in the digestive tract [50]. Besides that, soluble fibers can regulate blood sugar levels by inhibiting the rapid digestion and absorption of carbohydrates and lipids, lowering cholesterol levels, and promoting the growth of healthy gut bacteria [51]. Insoluble fibers such as cellulose and lignin can add bulk to fecal matter and maintain and promote bowel movement, which can help prevent constipation and other digestive disorders [51].  
The main dietary fiber compounds in date palms include cellulose, hemicellulose, pectin, and lignin. Cellulose is a linear polymer of glucose units that forms the structural component of plant cell walls, and its content in date palm can be over 30 g/100 g [52]. Hemicellulose is a branched polymer composed of several sugars, including xylose, arabinose, and galactose. Dates contain a significant amount of hemicellulose, ranging from approximately 24.0% to 45.1% of their overall composition [52]. The date also has a high value of pectin, which is a non-cellulosic fiber. However, the pectin amount varies widely with ripening stages of the date fruit because the process involves increased activity of fiber-hydrolyzing enzymes (pectinase). High-quality dates generally have elevated pectin and low lignin, whereas the opposite pattern results in less palatable to inedible fruit [24]. The pectin content in date palm can range from 0.78 to 1.12% [53]. Lignin is a complex phenolic polymer that gives plant cell walls rigidity and resistance to degradation, ranging from 22 to 23% in dates [54].  
Recent studies indicate that fibers from date palms have prebiotic properties, which can aid in the growth of beneficial gut bacteria. [PERSON] et al. [55] reported that date palm fibers increased the abundance of beneficial bacteria, such as _Bifidobacterium_ and _Lactobacillus_. Another study showed that date palm fibers can reduce inflammation in the human body, which may benefit those with inflammatory bowel diseases [26]. The considerable amount of dietary fiber in dates may be beneficial for individuals with diabetes by the regulation of blood sugar levels. [PERSON] et al. [56] studied the impact of date consumption on blood sugar levels in healthy individuals and those with type 2 diabetes mellitus. The findings indicated that the five types of dates examined in the study have a low glycemic index and did not cause significant increases in postprandial glucose levels when consumed by diabetic individuals. Therefore, including dates in a balanced and healthy diet may offer benefits for individuals with diabetes. This explanation was also supported by [PERSON] et al. [57], who suggested that a diet rich in dietary fiber may aid in balancing blood sugar levels, likely owing to the presence of fiber and bioactive compounds in dates, which can slow down the absorption of glucose from a meal.