Production and Applications of D-Psicose, a Low Calorie Sweetener

D-Psicose (D-allulose) is a rare sugar that naturally occurs in wheat, some fruits, molasses, and maple syrup. It is low calorie sugar with 0.2 - 0.4 calories per gram compared to 4.0 calories per gram for table sugar sucrose. In addition, D-psicose is not metabolized in the body, it is just absorbed by the small intestine, and excreted in the urine. In addition, it does not elevate blood sugar or insulin level. These properties make D-Psicose a good substitute to common sugars such as sucrose, D-glucose, or D-fructose, specially to regulate daily calories intake for people with health conditions such as overweight, obese, and diabetes.

Production

D-Psicose can be produced via chemical or biological methods. One of these chemicals methods is the synthesis from D-glucose or from 1,2:4,5-di-O-isopropylidene-β-d-fructo-pyranose under high temperature in the presence of molybdate as a catalyst. The second chemical method is the synthesis from D-fructose by heating in a mixed system of alcohol and triethylamine in a multi-step reaction. In the other hand biological methods are the best approach for D-Psicose production with advantages includes the simplicity in production, friendly to environment, and in lower energy production cost. In addition, D-allulose produced by biological methods are recognized as safe for foods, pharmaceuticals and for other applications. 

There are two biological methods for the production of D-Psicose. These biological methods are enzymatic (D-Ketose 3-epimerase enzymes) method and by microbial (bacteria or yeast) fermentation method.

Mechanism of these D-keto 3-epimerase (DKEase) enzymes is transforming D-fructose as a substrate into D-allulose without phosphorylation in the presence of Adenine Tri-Phosphate (ATP), epimerization, and dephosphorylation mechanism. D-ketose 3-epimerase (DKEase) enzymatic mechanism is based on D-fructose C3 epimerization in reversable equilibrium reaction. D-Ketose 3-epimerase enzymes family have been isolated and identified from different microorganisms.

Various microorganisms' genus, and species are naturally identified or genetically manipulated to produce D-ketose 3-epemirase (DKEase) enzymes as intracellular enzymes. Some of these microorganisms includes Pseudomonas cichorii, Rhodobacter sphaeroides, Caballeronia fortuita, Sinorhizobium sp. producing D-tagatose 3-epimerase (DTEase) enzyme.

Free enzyme method for the epimerization of D-fructose into D-Psicose is not economical strategy for large scale production due to enzymes high cost and poor D-allulose recovery efficiency. This free enzyme method is currently replaced by immobilized enzyme method or by microbial whole cells immobilization method. These two methods of immobilization, extend the enzyme half-life and reduce production cost. In addition, the presence of Co2+ and Mn2+ in the enzymatic reaction.as co-factors improved the enzyme catalytic activity toward the maximum epimerization of D-fructose into D-Psicose. Also, the selection of optimum immobilized enzyme reaction conditions of PH, temperature, and metallic ions concentration are important factors to improve D-fructose epimerization rate toward higher yield of D-Psicose. The optimum enzymatic reaction condition for these D-ketos 3-epimerase (DKEase) enzymes demonstrated to be in the range of 7.5 to 9.0 for PH, and 40˚C to 70˚C for temperature at the selected optimum concentrations of co-factors (metallic ions) of Co2+ and Mn2+.

Application

D-Psicose is low calorie keto-sugar, has mild sweetness, with good solubility. It is rare natural sugar with low glycemic index, and does not raise blood sugar or insulin levels. It has Millard reaction property that give browning characteristic to foods making it a suitable sweetener in baked goods. Maillard reaction is non enzymatic chemical reaction in which reducing aldehyde or keto group in sugar reacts with amino acids in foods to form amid chemical compounds responsible for browned foods with desirable flavor and aroma characteristics.

In addition to, D-Psicose is a natural sweetness with browning property for baked goods it is also, suitable for the applications in beverages, confectionery, nutritional bars, energy bars, ketchup, low calorie sweeteners desserts, functional foods, milk beverages and other food products. D-Psicose has stronger water holding capacity in food making it a good replacement to high calorie sweeteners such as sucrose, D-glucose, and D-fructose. For health benefits D-Psicose has potential applications in anti-obesity, dental caries, pharmaceuticals formulations and in cosmetics industries.

Reference

[1] Ibrahim, O. O. (2024). A review: Manufacturing, and properties of the D-Fructose epimer D-Allulose (D-Psicose). Advances in Bioscience and Biotechnology, 15(09), 522–542. https://doi.org/10.4236/abb.2024.159033