Views: 0 Author: Site Editor Publish Time: 2022-11-09 Origin: Site
Pectin is a kind of polysaccharide, which consists of two types: homogeneous polysaccharide and heteropolysaccharide. They mostly exist in plant cell wall and inner layer, and a large number of them exist in citrus, lemon, grapefruit and other pericarp. It is white to yellow powder, with a relative molecular weight of about 20000~400000, and tasteless. It is more stable in acidic solution than in alkaline solution. Generally, it can be divided into high ester pectin and low ester pectin according to its esterification degree. The high ester pectin formed a non reversible gel in the range of soluble sugar content ≥ 60%, pH=2.6~3.4. A part of methyl ester of low ester pectin is converted into primary amide, which is not affected by sugar and acid, but needs to combine with divalent ions such as calcium and magnesium to form gel.
Pectin is found in all higher plants. In plant cell wall, pectin mainly covalently combines with cellulose, hemicellulose, lignin, etc. to form protopectin, which is a structural material of plants and plays a vital role in maintaining plant structure and hardness. In addition, pectin can regulate cell permeability and pH. Pectin content is the highest in plant cell wall. In dicotyledons, it mainly exists in the primary cell wall and intermediate lamella of plant cell wall, accounting for 30%~35%. At present, the main raw materials used to produce commercial pectin are citrus and apple peel residue. In addition, there are a lot of studies on the extraction of pectin from by-products such as dried bean curd leaves, banana peel, sunflower, sweet potato and Ficus pumila, but the research on these materials is still limited to the basic research in the laboratory. Pectin content in different raw materials varies greatly.
Pectin has always been a part of human natural diet. It is a safe and non-toxic natural food additive recommended by the Joint FAO/WHO Food Additives Committee. There is no daily limit on the amount of pectin added. Pectin has many functions. For example, as a natural plant colloid, pectin can be widely used in the food industry as a gelling agent, stabilizer, tissue forming agent, emulsifier and thickener; Pectin is also a water-soluble dietary fiber, which has the function of enhancing gastrointestinal peristalsis and promoting nutrient absorption. It has good efficacy in preventing and treating diarrhea, intestinal cancer, diabetes, obesity and other diseases, and is an excellent drug preparation matrix; At the same time, pectin is a good heavy metal adsorbent, because the molecular chains of pectin can form an "egg box" like network structure with high priced metal ions, which makes pectin have a good function of adsorbing heavy metals; In addition, pectin has the characteristics of film formation, good water retention and radiation resistance.
1. Food industry
Pectin, as a food additive or ingredient, it is used in the food industry, mainly for gelling, thickening, texture improvement, emulsification and stability.
(1) Yogurt products
In the production process of yogurt, different kinds of pectin have different functions. For example, adding high fat pectin can stabilize the structure of yogurt, while adding low methoxyl pectin can prevent whey precipitation. In the process of making yogurt, the dosage of pectin should be strictly controlled. Once sufficient additives are not added, the charge will be neutralized and the repulsion force will be dissipated. The structure of dairy products cannot be stabilized, and they can only be added continuously. Only after new repulsion force is generated, the structure of acidic dairy products can remain stable.
If the content of pectin in the raw materials is too low during the production of jam, 0.20% pectin can be used as the thickener by using the thickening effect of pectin. The amount of pectin used in low sugar jam is about 0.60%. The formula of low sugar strawberry jam is 50.00% strawberry, 36.00% sugar, 13.00% water, 0.60% amidated low methoxyl pectin and 0.40% citric acid. In the above strawberry jam preparation formula, amidated low methoxyl pectin or methoxyl pectin can be used. Because fruits and water contain a certain amount of calcium ions, no calcium salt is needed.
High methoxyl pectin has strong water absorption, which can not only increase the amount of dough, but also improve the freshness, stability and softness of dough. Because the dough added with pectin has good ductility, the baking volume of bread will increase. For example, in the production of hamburgers, if the volume of hamburgers is kept unchanged, but pectin is added, the amount of flour used to make hamburgers of the same volume will be reduced by 30%. In addition, bread made with dough added with pectin can prolong the selling time of bread.
With people's attention to diet health, low sugar drinks in the market have become more and more popular, but the taste of the drinks will also decline after the sweetness is reduced. In this regard, 0.05%~0.10% high methoxyl pectin can be added to increase the taste of the drink. High methoxyl pectin is a suspending agent. When it is added to a beverage containing pulp, it can react with calcium ions to produce a gelling reaction, thus reducing the hard substances caused by pulp precipitation, making the fruit grains evenly suspended in the beverage, and improving the taste of fruit juice. It not only overcomes the shortcomings of sodium alginate, such as poor pseudoplasticity, strong gum smell, and large turbidity, but also plays a health role in stomach building and contact with lead poisoning.
2. Health food and medicine
Pectin is a kind of polysaccharide, which helps to control blood sugar and blood lipids. At present, pectin has been used in domestic medicines and health products, but the amount of pectin is still small.
Different from other dietary fibers, pectin has good water solubility and high viscosity due to its structural characteristics. This soluble dietary fiber can remove food additives and metal residues from the human body system.
3. Other applications
In addition, pectin can also be used for fresh-keeping films, diapers, cosmetics and toothpastes because of its good water retention and radiation resistance.
As people pay attention to nutrition and health and have made some achievements in the structure activity relationship of pectin, people try to artificially modify some structures of pectin to obtain some pectin products with special functions. This kind of pectin is called modified pectin or modified pectin (MP). Pectin can be modified by chemical, physical and biological methods, including enzymatic methods. At present, some achievements have been made in the modification of pectin, and this research will also be a trend in the future.
Pectin is usually modified by pH method. PH modified pectin refers to that pectin extracted by acid method is treated with alkali (generally adjusted to pH 10) and incubated at relatively mild temperature (50~60 ℃) for a certain period of time. Most studies take 60min, and then adjusted to pH (generally adjusted to about 3). Its main principle is based on the fact that under neutral or alkaline conditions, especially when the temperature is raised, pectin solution will degrade rapidly and largely, including the breaking of the glycosidic bond of the main chain HG and RG, the deesterification of the galacturonic acid part of the main chain, and the decomposition of neutral sugars on the branch chain. The reaction mechanism is mainly that pectin molecules occur under alkaline conditions β- The elimination reaction and transesterification reaction break the main chain of HG to generate some polygalacturonic acid oligomers and RGI; Then some branched neutral sugars, especially arabinose residues, are removed under acidic conditions. The final MP will be GI rich in galactose chains and arabinogalactose chains.