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The functional characteristics and development and application of inulin
Inulin is a natural fructose polymer composed of fructose formed by linking D- fructose molecule with a beta (2, 1) glycosidic bond. Each inulin molecule ends with an alpha (1, 2) glucoside bond connecting with a glucose residue. The degree of polymerization is usually 2 - 60 and the average degree of polymerization is 10. At the lower polymerization degree (DP=2 - 9), it is called oligofructose. As a kind of natural soluble dietary fiber, inulin is hardly hydrolyzed and digested by gastric acid, but it is fermented by a large number of beneficial microorganisms in the colon, therefore, it has many health functions, such as controlling blood lipids, reducing blood sugar, improving intestinal function and promoting mineral absorption, etc. Inulin can not only be used as a fat substitute for low energy food production, but also has the physiological function of dietary fiber and probiotics. It is an excellent functional food material. At present, inulin is widely used in the fields of medicine and health care,food industry and so on.
1.Sources of inulin
Inulin is widely distributed in nature. Some fungi and bacteria also contain inulin, but its main source is plants. Inulin is found in plants people eat daily such as Onions, garlic, bananas and wheat. However, inulin is mainly found in the Compositae plants in nature. The content of Jerusalem artichoke (commonly known as the main raw material of Chinese inulin) is 14%-19%, and the content of chicory (the main raw material of European inulin) is 15%-20%. The content of inulin in several common edible plants is shown in Table 1:
Table 1: The content of inulin in several common edible plants(%)
2.Raw material and process of inulin
In the world, two kinds of raw materials, Jerusalem artichoke and chicory, are used to produce inulin. In western countries such as Belgium and Holland, chicory is the main raw material, while Jerusalem artichoke is used as raw material in China.
Helianthus tuberosus, commonly known as Jerusalem artichoke, is a perennial herbaceous plant of the compositae family .It is tolerant to barren and arid. It has low demand for climate and soil conditions and strong adaptability. Many areas in China have planting, generally 2000-4000kg Jerusalem artichokes can be produced per mu,which are good raw material for processing inulin and its products.
Chicory is a biennial plant suitable for growing in marine climates. It is a widely planted vegetable species in Western European countries such as Holland. In 1993, the EU had enrolled Jerusalem and chicory into the European new crop development plan. At present, 8 European Union countries are popularizing new varieties of good Jerusalem artichoke and chicory.
The domestic processing technology of inulin mainly includes hydro-thermal method and microwave method. The process flow of hydro-thermal method is as follows: the pretreated Jerusalem artichoke, hot water extraction, concentration, activated carbon decolorization, centrifuge and supernatant by sevag method to remove protein, repeat 4 to 5 times, 95% ethanol precipitation, centrifugal, over cation and anion exchange resin removing impurities, vacuum drying and crushing products. The microwave process is as follows: shredding, weighing, Microwave leaching with water, residue filtration, impurity removal, decolorization and concentration .
3.1 Control blood lipid
Ingestion of inulin can effectively reduce serum total cholesterol (TC) and low density lipoprotein cholesterol (LDL-C), increase the ratio of HDL / LDL, and improve the status of blood lipid. Hidaka and others reported that old patients at the age of 50 to 90 years fed on 8g short chain dietary fiber daily, and levels of triglyceride and total cholesterol in the blood decreased after two weeks. Yamashita and other persons gave 8g inulin to 18 diabetic patients for two weeks, while total cholesterol decreased by 7.9%, but HDL - cholesterol did not change. In the control group, the above parameters did not change. Brighenti and others observed that 12 healthy young men had 9g inulin in a daily cereal breakfast for 4 weeks, the total cholesterol decreased by 8.2%, and the triglyceride decreased by 26.5%.
Many dietary fibers absorb fat from the intestines and form fat - fibrous complexes excreting with feces, thereby lowering blood lipid levels. Moreover, inulin is fermented into short chain fatty acids and lactate itself before the end of the intestine. Lactate is a regulator of liver metabolism. Short chain fatty acids (acetate and propionate) can be used as fuel in the blood, and propionate inhibits cholesterol synthesis.
3.2 Decrease blood glucose
For diabetics, a reasonable diet is the main method of treatment. Inulin is slightly sweet and a fructose polymer. It is not decomposed and absorbed through the mouth, stomach and small intestine of the human body. Therefore, it will not affect blood sugar levels after oral intake of inulinand can be used as food for the diabetics. More and more scientists have paid attention to the mechanism of inulin lowering blood glucose level. Some scholars believe that the high viscosity of inulin leads to an increase in the thickness of the intestinal mucosa, which reduces the absorption of glucose, and some scholars believe that, on the one hand, the short chain fatty acids produced by inulin fermentation promote the synthesis of liver glycogen, while low fructose can promote the body's absorption of Mg2+ and reduce the risk of diabetes.
3.3 Improvement of intestinal performance
Inulin is a prebiotics. Prebiotics is a non-digested food ingredient that selectively stimulates and promotes the growth and vitality of a healthy and beneficial microorganism in one or more colons to promote the health of the host. Inulin can be fermented in the human colon, which can increase the proliferation of bifidobacteria by 5 - 10 times, and also inhibit the growth of potential harmful bacteria. It can improve the diarrhea caused by constipation and abuse of antibiotics. After the inulin was fermented in the colon, the microbial flora and gas increased, thus promoting the intestinal peristalsis, shortening the residence time of the feces in the colon, accelerating the movement, reducing the water absorption time, increasing the weight of the feces and preventing constipation effectively. At the same time, the excretion of feces is also increased, so that the carcinogens in the intestinal tract have been diluted. Therefore, the stimulation of carcinogens to the intestinal wall cells is reduced, which is beneficial to the prevention of colon cancer.
3.4 Promoting mineral absorption
Dietary fiber in daily diet can reduce intestinal absorption of certain minerals. However, inulin, as a soluble dietary fiber, does not inhibit the absorption of mineral elements, but instead promotes the absorption of mineral elements such as Ca2+, Mg2+, Zn2+, Cu2+ and Fe2+. Any inulin mineral complex is degraded in the fermentation process of intestinal flora, releasing mineral elements, making them more conducive to intestinal absorption. In addition, the acid produced by fermentation can reduce the pH value of colon 1 - 2 units, so that the solubility and bioavailability of many minerals can be improved. Moreover, short chain fatty acids, especially butyric acid, stimulate the growth of colonic mucosal cells and enhance intestinal mucosa.
4.Development and application of inulin
In recent years, the development and utilization of inulin has been highly valued by the international food industry, and has been successfully applied in the fields of dairy products, beverages, baked food, low fat and low heat food, health food and so on. Statistics show that inulin consumption per capita in the United States is 1-4g/d, and Europe is 3-10g/d. Industrialized production of inulin has been carried out abroad, and a series of functional food ingredients of inulin have been developed successfully. In addition, after the modification of inulin by enzyme or chemical method, the modified inulin can be used as the main component of drug carrier, vaccine supplement, metal chelator and descaling agent .
Dairy products are the ideal food system using inulin because it can effectively improve the rate of the body calcium absorption , and can simulate the taste of milk fat in the application of low milk products, increase the content of fiber in the products, not only improve the overall nutritional value of the product, but also do not sacrifice the quality of the product, but also have the probiotic characteristics. Therefore, in recent years, inulin has developed rapidly in dairy products. It has been widely used in low fat or skimmed milk, dairy products rich in dietary fiber, dairy products and milk tablets suitable for diabetics.
After adding inulin, such as high fiber juice drinks, functional drinks, sports drinks, solid drinks and vegetable protein beverages, besides the replacement of fat and sugar, the water binding ability and the viscosity of the products,it can also increase the function of dietary fiber and oligosaccharides, and increase the absorption of calcium, magnesium, iron and other minerals more than 20%, and can cover up bitterness, give a soft feeling, make the beverage flavour and texture better.
4.3 Foods with Low-fat, low-calorie
Inulin can replace 20% to 50% fat. It is an excellent fat substitute. When inulin is used as a sugar product in chocolate products, there is no need to make major adjustments in the processing proces,it can produce chocolate products without sugar, low sugar or suitable for diabetes. Combined with sorbitol, the effect is better. Inulin can stabilize the water into a creamy structure with the same taste as oil, so it can replace oil to produce low fat, skimmed milk or vegetable butter, and can also replace the oil in ice cream and other similar products. Inulin can stabilize the structure of water or fat, improve cheese characteristics (such as smearing) and taste, and can replace whey protein or starch derivatives.
Inulin can replace the fat of low-fat meat products, improve the structure of meat products, and maintain quality stability. Such as meat products in Frankfurt, etc. Inulin can replace the fat and sugar in the baked food and improve the crisp of the baked food; it can be used in the development of new concepts in cakes, biscuits and bread, such as probiotic bread and high fiber bread.
4.4 Health foods
At present, inulin has been approved as a nutritional supplement in food by more than 40 countries in the world. As raw materials and carriers for various health foods against the constipation, diabetes and obesity. Inulin is one of the best ingredients or functional ingredients for health foods, such as regulating intestinal flora, regulating blood lipids, promoting calcium or mineral absorption, or functional food (diet food).
5.1 The food and Drug Administration of the United States（FDA）
In 2016, FDA announced a new definition of dietary fiber, as part of the final rule to update the nutritional ingredients label, which was designated as "natural fiber found in fruits, vegetables and whole grains, and seven independent (NDCs) non - digestive carbohydrates (from plant sources) or synthetic (from plant sources) (from plant sources). Each of them has a physical health benefit. If scientific evidence proves the beneficial physiological effects of human health, FDA will solicit citizens or independent NDC citizenship applications outside the list of initial ingredients.
It is worth noting that several common non - digestive carbohydrates, such as the epidemic component inulin, are ignored in the initial definition, letting suppliers do not know whether these ingredients will be labeled as dietary fiber for nutritional components.
With the announcement of the Scott Gottlieb Committee's new ruling, eight new fibers were added to the list, including:
Mixed plant cell wall fibers (including broad categories such as sugarcane fiber and Apple Fiber);
An inulin and inulin type fructan;
High amylose (resistant starch 2);
Resistant maltose dextrin / dextrin.
So far, all kinds of dietary fiber are natural and water-soluble, and fructose (Ju Fen) is the only one that can be produced in large scale.
5.2List of new food materials
In 2009, No. 5 inulin has been included in the list of new food ingredients. See Table 2 below.
Table 2 a summary of the efficacy of new food raw materials
With the inclusion of new food ingredients, the health-care function should be able to enter the preparation system without functional measurement.
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