Research Progress on the Biosynthesis of D-Allulose

Introduction and Overview

D-allulose, as a rare monosaccharide, has attracted widespread attention in recent years due to its unique physicochemical properties and physiological functions. Chemically, it is a C-3 epimer of D-fructose; this slight structural difference endows it with many excellent characteristics. Firstly, in terms of sensory properties, D-allulose has a high sweetness level—about 70% that of sucrose—which satisfies people's demand for sweetness. Secondly, regarding metabolic characteristics, its caloric content is extremely low at only 0.3% that of sucrose, making it an ideal low-calorie sweetener. Additionally, it exhibits excellent solubility in water with a solubility rate reaching up to 291g/100g water at 25°C; this property facilitates its application in the food industry.

Beyond these basic physicochemical properties, D-allulose also possesses various physiological functions that present broad application prospects in functional foods and pharmaceuticals. Studies have shown that D-allulose can effectively lower blood sugar levels which is significant for dietary management among diabetic patients; it also helps prevent obesity by inhibiting fat accumulation; furthermore, it demonstrates neuroprotective effects within the nervous system; additionally, it has the ability to scavenge reactive oxygen species (ROS), showcasing certain antioxidant capabilities. These diverse physiological functions make D-allulose not just a sweetener but also a health-functional food additive.

Currently, there are two main methods for producing D-allulose: chemical synthesis and biosynthesis. Although chemical synthesis has been around for quite some time, it presents clear limitations including strict reaction conditions required during production processes leading to unwanted by-products and significant environmental pollution issues. In contrast, biosynthetic methods are increasingly favored due to their environmentally friendly nature along with high efficiency and ease of product purification advantages over traditional approaches—biosynthesis primarily relies on enzyme-catalyzed reactions utilizing microbial fermentation or enzyme engineering techniques which offer milder reaction conditions while ensuring high specificity towards products generated alongside minimal side-product formation aligning well with green chemistry development principles.

Research on Biosynthetic Pathways

Pathway One: Enzyme-Catalyzed Pathway Using Starch/Glucose as Substrates The bioconversion pathway using starch or glucose as starting substrates represents one widely studied method for producing d-allulose today involving multiple key enzymes through cascading reactions forming an integrated metabolic network framework established therein begins when isoamylase (IA) catalyzes starch into dextrin marking initial degradation phase thereafter amylolytic glucosidase (AMG) further hydrolyzes dextrin into maltose completing thorough breakdown process next glucose isomerase (GI) or xylose isomerase(XI) catalyze conversion from d-glucose yielding d-fructose constituting first critical node throughout entire route finally tagatose-3-epimerase(DTE) or d-allulokinase(DPE) convert resultant fructose ultimately generating target compound d-allulose concluding whole biotransformation sequence. However notable bottlenecks exist within this pathway particularly concerning GI/XI mediated interconversion between d-glucose/d-fructose wherein reversibility significantly hampers overall transformation rates observed data indicates typical yields rarely exceed twenty percent—for instance Itoh et al., achieved merely ten percent yield employing immobilized forms both XI/DTE upon converting source material derived solely from bacterial strains under fixed experimental setups while Li et al., reported twelve percent success translating substrate sourced via yeast spores combined methodologies based off thermophilic bacillus-derived XI/DPE complex expressions likewise yielded sixteen percentage outputs indicating pressing need improve efficiencies associated herein considerably evident across numerous studies undertaken thus far... [Content continues]...