Inulin

Inulins are a group of naturally occurring polysaccharides produced by many types of plants, industrially most often extracted from chicory. The inulins belong to a class of dietary fibers known as fructans. Inulin is used by some plants as a means of storing energy and is typically found in roots or rhizomes. Most plants that synthesize and store inulin do not store other forms of carbohydrate such as starch. In the United States in 2018, the Food and Drug Administration approved inulin as a dietary fiber ingredient used to improve the nutritional value of manufactured food products. Using inulin to measure kidney function is the 'gold standard' for comparison with other means of estimating glomerular filtration rate. Inulins are a group of naturally occurring polysaccharides produced by many types of plants, industrially most often extracted from chicory. The inulins belong to a class of dietary fibers known as fructans. Inulin is used by some plants as a means of storing energy and is typically found in roots or rhizomes. Most plants that synthesize and store inulin do not store other forms of carbohydrate such as starch. In the United States in 2018, the Food and Drug Administration approved inulin as a dietary fiber ingredient used to improve the nutritional value of manufactured food products. Using inulin to measure kidney function is the 'gold standard' for comparison with other means of estimating glomerular filtration rate. Inulin is a natural storage carbohydrate present in more than 36,000 species of plants, including wheat, onion, bananas, garlic, asparagus, Jerusalem artichoke, and chicory. For these plants, inulin is used as an energy reserve and for regulating cold resistance. Because it is soluble in water, it is osmotically active. The plants can change the osmotic potential of cells by changing the degree of polymerization of inulin molecules with hydrolysis. By changing osmotic potential without changing the total amount of carbohydrate, plants can withstand cold and drought during winter periods. Inulin was discovered in 1804 by German scientist Valentin Rose. He found “a peculiar substance” from Inula helenium roots by boiling-water extraction. The substance was named inulin because of I. helenium, but it is also called helenin, alatin, and meniantin. Indigestible polysaccharides were of great scientific concern in the beginning of the 20th century. Irvine used chemical methods like methylation to study the molecular structure of inulin, and designed the isolation method for this new anhydrofructose. During studies of renal tubules in the 1930s, researchers searched for a substance that can serve as a biomarker that is not reabsorbed or secreted after introduction into tubules. Richards introduced inulin because of its high molecular weight and its resistance to enzymes. Today, inulin is used as an active ingredient for functional foods, and it is also used to determine the glomerular filtration rate. Inulin is a heterogeneous collection of fructose polymers. It consists of chain-terminating glucosyl moieties and a repetitive fructosyl moiety, which are linked by β(2,1) bonds. The degree of polymerization (DP) of standard inulin ranges from 2 to 60. After removing the fractions with DP lower than 10 during manufacturing process, the remaining product is high-performance inulin. Some articles considered the fractions with DP lower than 10 as short-chained fructo-oligosaccharides, and only called the longer-chained molecules inulin. Because of the β(2,1) linkages, inulin is not digested by enzymes in the human alimentary system, contributing to its functional properties: reduced calorie value, dietary fiber, and prebiotic effects. Without color and odor, it has little impact on sensory characteristics of food products. Oligofructose has 35% of the sweetness of sucrose, and its sweetening profile is similar to sugar. Standard inulin is slightly sweet, while high-performance inulin is not. Its solubility is higher than the classical fibers. When thoroughly mixed with liquid, inulin forms a gel and a white creamy structure, which is similar to fat. Its three-dimensional gel network, consisting of insoluble submicron crystalline inulin particles, immobilizes large amount of water, assuring its physical stability. It can also improve the stability of foams and emulsions. Chicory root is the main source of extraction for commercial production of inulin. The extraction process for inulin is similar to obtaining sugar from sugar beets. After harvest, the chicory roots are sliced and washed, then soaked in a solvent; the inulin is then isolated, purified, and spray dried. Inulin may also be synthesized from sucrose. Inulin received no-objection status as generally recognized as safe (GRAS) from the US Food and Drug Administration (FDA), including long-chain inulin as GRAS. In the early 21st century, the use of inulin in processed foods was due in part to its adaptable characteristics for manufacturing. It is approved by the FDA as an ingredient to enhance the dietary fiber value of manufactured foods. Its flavor ranges from bland to subtly sweet (about 10% of the sweetness of sugar/sucrose). It can be used to replace sugar, fat, and flour. This is advantageous because inulin contains 25-35% of the food energy of carbohydrates (starch, sugar). In addition to being a versatile ingredient, inulin provides nutritional advantages by increasing calcium absorption and possibly magnesium absorption, while promoting the growth of intestinal bacteria. Chicory inulin is reported to increase absorption of calcium in young women with lower calcium absorption and in young men. In terms of nutrition, it is considered a form of soluble fiber and is sometimes categorized as a prebiotic. Conversely, it is also considered a FODMAP, a class of carbohydrates which are rapidly fermented in the colon producing gas and drawing water into the colon. Although FODMAPs can cause certain digestive discomfort in some people, they produce potentially favorable alterations in the intestinal flora that contribute to maintaining health of the colon. Due to the body's limited ability to process fructans, inulin has minimal increasing impact on blood sugar, and may potentially have use in managing blood sugar-related illnesses, such as metabolic syndrome. Inulin and its analog sinistrin are used to help measure kidney function by determining the glomerular filtration rate (GFR), which is the volume of fluid filtered from the renal (kidney) glomerular capillaries into the Bowman's capsule per unit time. Inulin is of particular use as it is not secreted or reabsorbed in any appreciable amount at the nephron, allowing GFR to be calculated. However, due to clinical limitations, inulin and sinistrin, although characterised by better handling features, are rarely used for this purpose and creatinine values are the standard for determining an approximate GFR.