Cellulose is a macromolecular polysaccharide composed of glucose. Insoluble in water and general organic solvents. It is the main component of plant cell wall. Cellulose is the most widely distributed and abundant polysaccharide in nature, accounting for more than 50% of the carbon content in the plant kingdom. The cellulose content of cotton is close to 100%, which is the purest natural cellulose source. In general wood, cellulose accounts for 40-50%, and there are10-30% hemicellulose and 20-30% lignin.
Hemp, wheat straw, rice straw and bagasse are all rich sources of cellulose. Cellulose is an important raw material for papermaking. In addition, products based on cellulose are also widely used in plastics, explosives, electricians and scientific research equipment. Cellulose (dietary fiber) in food also plays an important role in human health. ? The molecular formula of cellulose is (C6H 10O5)n, which is a macromolecular polysaccharide composed of D- glucose and β- 1 4 glycosidic bond. The molecular weight is 50000 ~ 2500000, which is equivalent to 300 ~ 15000 glucose groups. Insoluble in water and general organic solvents. It is the main component of plant cell wall.
Cellulose in human diet mainly exists in vegetables and miscellaneous grains. Although it can't be digested and absorbed, it can promote intestinal peristalsis and facilitate fecal excretion. Herbivores rely on microorganisms in their digestive tract to decompose cellulose so that it can be absorbed and utilized.
nature
1. solubility? At room temperature, cellulose is insoluble in neither water nor common organic solvents, such as ethanol, ether, acetone and benzene. It is also insoluble in dilute alkali solution. So it is relatively stable at room temperature, because there are hydrogen bonds between cellulose molecules.
2. Cellulose hydrolysis? Under certain conditions, cellulose will react with water. During the reaction, the oxygen bridge is broken, and water molecules are added at the same time, and cellulose changes from long-chain molecules to short-chain molecules until the oxygen bridge is completely broken and becomes glucose.
3. Cellulose oxidation? Cellulose reacts with oxidant to produce a series of substances with different structures from original cellulose. This reaction process is called cellulose oxidation. (Document protection technology quoted from Guo) The base ring of cellulose macromolecule is a macromolecular polysaccharide composed of D- glucose with β- 1 4 glycosidic bond, and its molecular weight is about 50,000 ~ 2,500,000, which is equivalent to glucose-based dehydrated glucose of 300 ~15,000. The molecular formula is: (c6h/kloc-0. Due to different sources, the number of glucose residues in cellulose molecules, that is, the degree of polymerization (DP), is in a wide range. The molecular formula can be written as (C6H 10O5) n, which is the main component of the cell wall of vascular plants, lichens and some algae. Cellulose was also found in vinegar vesicles and chordates. The purity of cotton seed cotton is high (98%). The so-called α -cellulose refers to the part that can not be extracted from the original cell wall intact cellulose standard sample with 17.5%NaOH. β -cellulose and γ -cellulose are celluloses corresponding to hemicellulose. Although α -cellulose is usually crystalline cellulose, β -cellulose and γ -cellulose contain various polysaccharides besides cellulose. Cellulose in the cell wall forms microfibers. The width is 10-30 nm and the length is several microns. By X-ray diffraction and negative staining, according to the observation of electron microscope, the crystalline parts of chain molecules arranged in parallel constitute basic microfibers with a width of 3-4 nanometers. It is speculated that these alkaline microfibers together constitute microfibers. Cellulose can be dissolved in Schwitzer reagent or concentrated sulfuric acid. Although it is not easy to hydrolyze with acid, dilute acid or cellulase can make cellulose produce D- glucose, cellobiose and oligosaccharide. Cellulose synthase (UDP forming EC 2.4.1.12) transfers glucoside from UDP glucose primer in Acetobacter to synthesize cellulose. Standard samples of granular enzymes with the same activity have been obtained in higher plants. This enzyme usually uses GDP glucose (GDP formation) EC 2.4. 1.29), and glucose is mixed with β- 1, 3 bond when it is transferred from UDP. The formation position of microfibers and the mechanism of controlling cellulose arrangement are not clear. On the other hand, as far as cellulose decomposition is concerned, it is estimated that when the primary cell wall is stretched and grown, a part of microfibers will be decomposed and become soluble due to the action of cellulase. ? Cellulose is insoluble in water and organic solvents such as ethanol and diethyl ether, but soluble in copper ammonia Cu(NH3)4(OH)2 solution and copper ethylenediamine [NH2CH2 NH2] Cu (OH) 2 solution. Water can cause limited swelling of cellulose, and some aqueous solutions of acid, alkali and salt can penetrate into the fiber crystallization area, resulting in unlimited swelling and dissolution of cellulose. When cellulose is heated to about 150℃, it will not change obviously, and it will gradually coke due to dehydration when it exceeds this temperature. Cellulose reacts with concentrated inorganic acid to produce glucose and so on. Alkaline cellulose is generated by concentrated caustic solution, and oxidized cellulose is generated by strong oxidant. ?
4. Compliance? Cellulose has poor flexibility and high rigidity, because (1) its molecules are polar and the interaction between molecular chains is strong. (2) The six-membered pyran ring structure in cellulose makes internal rotation difficult; (3) Intramolecular and intermolecular hydrogen bonds can be formed, especially intramolecular hydrogen bonds, which make the glycosidic bond unable to rotate, thus greatly increasing its rigidity.
physiological action
The main physiological function of cellulose is to absorb a lot of water, increase the amount of feces, promote intestinal peristalsis, accelerate the excretion of feces, shorten the residence time of carcinogens in the intestine, and reduce the adverse stimulation to the intestine, thus preventing the occurrence of intestinal cancer.
dietary fibre
Cellulose in human diet mainly exists in vegetables and miscellaneous grains. Although it can't be digested and absorbed, it can promote intestinal peristalsis and facilitate fecal excretion. Herbivores rely on microorganisms in their digestive tract to decompose cellulose so that it can be absorbed and utilized. Dietary fibres includes crude fiber, semi-crude fiber and lignin. Dietary fibres is an indigestible substance. In the past, it was considered as "waste", but now it is considered to play an important role in safeguarding human health and prolonging life. So it is called the seventh nutrient. ? Among dietary fibers, various high-purity dietary fibers are extracted from natural foods (konjac, oats, buckwheat, apples, cacti, carrots, etc.). ) generally used. The main functions of dietary fiber are: Molecular structure of cellulose
1, treating diabetes? Dietary fiber can improve the sensitivity of insulin receptor and improve the utilization rate of insulin; Dietary fiber can wrap the sugar in food and make it gradually absorbed, which has the function of balancing postprandial blood sugar, thus regulating the blood sugar level of diabetic patients and treating diabetes. ?
2. Prevention and treatment of coronary heart disease? The increase of serum cholesterol will lead to coronary heart disease. The excretion of cholesterol and cholic acid is closely related to dietary fiber. Dietary fiber can be combined with cholic acid, so that cholic acid can be excreted quickly. At the same time, the combination of dietary fiber and cholic acid will promote the conversion of cholesterol into cholic acid, thus reducing the cholesterol level. ?
3. What is the antihypertensive effect? Dietary fiber can adsorb ions and exchange them with sodium ions and potassium ions in the intestine, thus reducing the proportion of sodium and potassium in blood and thus lowering blood pressure. ?
4. Anti-cancer effect? Since 1970s, there have been more and more reports about dietary fiber's anti-cancer, especially the relationship between dietary fiber and digestive tract cancer. An early survey in India showed that people living in northern India consumed much more dietary fiber than southerners, and the incidence of colon cancer was much lower than that of southerners. According to this survey, scientists have done more in-depth research and found that dietary fiber can prevent and treat colon cancer for the following reasons: some saprophytic bacteria in the colon can produce carcinogens, while some beneficial microorganisms in the intestine can use dietary fiber to produce short-chain fatty acids, which can inhibit the growth of saprophytic bacteria; Cholic acid and cholic acid in bile can be metabolized by bacteria into carcinogens and mutagens of cells, and dietary fiber can be combined with cholic acid and excreted to prevent the production of these carcinogens; Dietary fiber can promote intestinal peristalsis, increase fecal volume and shorten emptying time, thus reducing the chance of carcinogens in food contacting colon; Beneficial bacteria in the intestine can use dietary fiber to produce butyric acid, which can inhibit the growth and proliferation of tumor cells, induce tumor cells to transform into normal cells, and control the expression of oncogenes. ?
5. Lose weight to treat obesity? Dietary fiber replaces some nutrients in food and reduces the total intake of food. Dietary fiber promotes the secretion of saliva and digestive juice, fills the stomach, absorbs water and swells, which can produce satiety and inhibit the desire to eat. Dietary fiber is combined with some fatty acids, so that fatty acids cannot be absorbed when passing through the digestive tract, thus reducing the absorption rate of fat. ?
6. Treat constipation? Dietary fiber has strong water holding capacity, and its water absorption rate is as high as 10 times. After absorbing water, the volume of intestinal contents is increased, which makes the stool loose and soft, and it will be smoother and more labor-saving when passing through the intestine. At the same time, dietary fiber, as a foreign body in the intestine, can stimulate the contraction and peristalsis of the intestine, accelerate stool excretion, and play a role in treating constipation. ?
7. Remove foreign harmful substances? Dietary fiber has a strong ability to combine and exchange cations, can adsorb and bind organic compounds, and can be used as the last barrier for some environmental pollutants to prevent them from finally invading the human body and play a role in detoxification. It has been found that dietary fiber can remove calcium, mercury, lead, high concentration of copper and zinc, especially organic cations. Their concentrations can range from toxic levels to safe levels. In addition, insoluble dietary fiber can shorten the retention time of feces in the intestine, dilute the concentration of harmful substances in the intestine, and reduce the retention time of harmful substances such as aflatoxin, nitrosamines, phenol and polycyclic aromatic hydrocarbons in the intestine, thus reducing their absorption by the human body. Water-soluble dietary fiber is digested and absorbed by the human body, enters the large intestine, and is utilized by Bifidobacterium to promote the proliferation of Bifidobacterium. Bifidobacterium can decompose carcinogenic nitrosamines, improve the phagocytosis of macrophages, and increase human immune function and resistance to tumors.
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