Isomaltose, also known as palagin, is an isomer of sucrose, a small amount of which is found in honey, Sugar cane juice and other substances. It can selectively promote the growth of bifidobacteria in the human intestinal tract, and has functional characteristics such as low calorie, caries prevention, and obesity suppression. The molecular formula of isomaltulose is C12H12O11 · H2O, with a molecular weight of 360.32. It is composed of glucose and fructose α- The reducing disaccharide formed by the linkage of 1,6 glycosidic bonds, as a crystalline disaccharide, contains 1moL of crystalline water and does not form crystals after losing the crystalline water. Its structural formula is shown in the following figure.
Isomaltose has a similar appearance and taste to sucrose, appearing as white crystals with a sweetness of approximately 42% of sucrose, and does not change with environmental changes. The solubility is only 50% of sucrose at room temperature. As the temperature increases, the solubility increases sharply, reaching 85% of sucrose at 80 ℃. Compared with the melting point of sucrose (160-185 ℃), isomaltulose has a lower melting point (123-124 ℃).
Isomaltose also has high stability, mainly manifested as: (1) good acid hydrolysis resistance. At pH 2.0, a 20% solution of isomaltose does not undergo hydrolysis reaction even after boiling for 1 hour. Therefore, it is more stable than sucrose in acidic foods; (2) Adding isomaltulose to isotonic or hypotonic beverages can maintain stable osmotic pressure; (3) Isomaltulose is resistant to most bacteria and yeast and is not easily utilized, so products with added isomaltulose are more likely to maintain sweetness.
Production and preparation of isomaltulose
Isomaltose has a low content in nature and is difficult to synthesize using chemical methods. Therefore, it is mainly produced through microbial transformation and enzyme isomerization of sucrose. Among them, enzyme isomerization of sucrose is a utilization of sucrose isomerase (SIase, EC5 4. 99 11) The enzymatic reaction that catalyzes the production of isomaltulose from sucrose has great commercial potential.
1. Microbial transformation method
In the early days, microbial transformation was generally used to produce isomaltulose, mainly including two methods: bacterial fermentation to convert sucrose and bacterial cell immobilization. So far, it has been found that various microorganisms can ferment sucrose to convert isomaltulose, such as Serratia polymethica ATCC15928, Erwinia rhapontici NX-5, Klebsiella sp. LX-3, etc., all have the ability to produce isomaltulose.
① Bacterial fermentation method. The method of fermenting sucrose to produce isomaltulose by bacteria essentially relies on the SIase expressed in the microbial body to catalyze the conversion of sucrose. Based on the different properties of the strains, they can be divided into original strain fermentation, mutant strain fermentation, and recombinant strain fermentation. After optimizing the cultivation conditions or mutagenesis treatment, the strain can achieve a high sucrose conversion rate. However, this method of fermenting and converting sucrose by bacterial cells generally has the disadvantages of long production cycle, complex fermentation liquid components, high cost of separating and purifying target products, and cannot achieve industrial production. Therefore, its application is limited. In actual industrial production, metabolic engineering is often used to construct SIase producing strains. This method involves introducing the gene encoding SIase from a certain isomaltulose producing strain into another microorganism, and then utilizing the engineering bacteria to continuously produce isomaltulose during the growth and metabolism process. Currently, the most commonly used vector for SIase expression is Escherichia coli.
② Immobilized cell transformation. The process of producing isomaltulose from immobilized cells has become increasingly mature. Compared with bacterial fermentation, immobilized cell technology is not only beneficial for cell recycling, enhancing cell mechanical strength, but also for improving sucrose conversion rate and reducing the cost of separating downstream products. There are many types of carriers used for immobilization, typical of which are sodium alginate, chitosan, polyvinyl alcohol, etc. The immobilized cells using sodium alginate as the embedding agent and CaCl2 as the crosslinking agent have good stability, strong operability, and low cost.
2. Enzymatic synthesis method
In microbial transformation, the concentration of sucrose substrate is limited, and sucrose is both a substrate for SIase and a carbon source required for cell growth. Even if sucrose can be converted to isomaltulose, it cannot avoid the additional consumption of sucrose by cell utilization. Moreover, the presence of cell walls further increases the resistance of cell mass transfer, leading to a significant decrease in reaction rate. In addition, these isomaltulose producing strains lack a food grade genetic background, and the presence of various uncertified extracellular products complicates the recovery process of isomaltulose. Therefore, directly using SIase for isomerization reaction is more suitable for the production process of isomaltulose with high substrate concentration and difficult separation of fermentation products.
① Immobilized enzymes produce isomaltulose. Generally speaking, the SIase activity secreted by wild strains is low and cannot meet the production of isomaltulose. Considering the good operability and storage stability of immobilized enzymes, attempts have been made to immobilize SIase for enzyme reuse. The immobilized enzyme prepared by adsorption crosslinking method using chitosan as a carrier has broad prospects, but this immobilization method is currently limited to the laboratory research stage, and industrial production applications still need to be studied.
② Cell surface display system. The cell surface display system is essentially an extension of enzyme application technology. The biggest feature of this technology is that the generation and self fixation of enzyme molecules on the surface of microbial cells can be carried out synchronously. At the same time, because live whole cell biocatalysts are easy to prepare and do not require further purification or enzyme fixation, they are of great research value. Although surface display system production technology has shown good performance and application prospects, there are still some uncertain factors that affect the popularization of this technology: due to the limitation of membrane area, the production of enzymes is limited, and the number of displayed enzymes is usually between 103 and 104. Some catalytic reactions require the participation of endogenous coenzymes to carry out enzymatic reactions, limiting the types of enzymes. Therefore, the development of industrialized display enzyme technology must consider factors such as enzyme types, structures, and applications.
The application of isomaltulose
Isomaltose has physicochemical properties similar to sucrose, and its application in products such as cream instead of sucrose has similar viscosity and fluid characteristics as sucrose. Isomaltose has a pure and sweet taste, which can mask off odors, balance taste, improve food flavor, and provide convenience for developing functional foods with good taste and taste using natural healthy ingredients. At the same time, its slow release of energy, no increase in blood sugar, prevention of dental caries, and improvement of brain function have health benefits, making it widely used in food for specific populations.
1. Application in dairy products
Isomaltose has been widely used in dairy products both domestically and internationally. Its application in dairy products can mask odors and provide certain health benefits, which provides assistance for the development of dairy products for children and middle-aged and elderly people. For example, Shulita launched active yoghurt with isomaltulose and sucralose as sweeteners, and Maeil functional black sesame soymilk in South Korea also added isomaltulose to cover up the bad flavor of soybean milk.
2. Application in baked goods
According to GB2760-2014, the limit requirement for the application of isomaltulose in baked goods such as bread, pastries, and biscuits is to add it in moderation as needed. Domestic enterprises have added isomaltulose to products such as biscuits and hand torn bread. The application of isomaltulose in baked goods can improve the taste and storage stability of the products. Since isomaltulose is almost non hygroscopic, its use in waffles can significantly improve the structure of the products.
3. Application in Candy Chocolate
The excellent properties of isomaltulose, such as stable physical and chemical properties, low moisture absorption, and easy refinement and grinding, give it great advantages in its application in candy and chocolate. Applied to hard candies, it can prevent candy from sticking together and is not easy to deform. Isomaltose hard candies have a high glass transition temperature and high temperature stability, making them ideal even in hot and humid climates; It can be used as coating material to prepare soft candy, chocolate beans, fructose and gel products. The low processing temperature of isomaltulose (45 ℃~55 ℃) can successfully coat the heat sensitive core materials; Isomaltose has a taste comparable to sucrose and is not affected by the cold effect. It is used in chocolate to make the sweetness natural and can combine with fat substitutes and fillers to give chocolate stable flow properties.
4. Food development for specific populations
The low GI value (insulin raising index) of isomaltulose provides a basis for its use in food for diabetics. The application of isomaltulose to develop sports food is also very widespread abroad. For example, Sports Yo Kan Sports Sheep Soup produced by Iwamura House, Japan, is a kind of instant energy supplement goat soup (Red bean cake), which can easily supplement energy. It contains Parragon TM (isomaltulose) and maltodextrin, and is a food that continues to provide energy. The Belgian 3 Action sports nutrition series products use isomaltulose as the main raw material, which can provide long-lasting energy and power.
By utilizing the efficacy characteristics of isomaltulose in inhibiting fat accumulation and accelerating fat oxidation, isomaltulose can be used as one of the raw materials and combined with other healthy ingredients to develop products with weight loss and slimming effects. At the same time, a low GI and low GL (blood glucose load) diet helps maintain weight after weight loss.
