Recent Advances Regarding the Physiological Functions and Biosynthesis of D-Allulose

Comprehensive Analysis of Allulose Production: A Review and Update

Advancements in D-allulose production have seen significant strides in recent years, focusing on enzymatic conversion methods. Key developments include traditional immobilization techniques, the discovery of novel enzymes, directed evolution studies, and biosynthesis through metabolic pathway modification. Enzymatic conversion, particularly utilizing D-allulose 3-epimerase, remains fundamental for industrial-scale production. Innovative immobilization strategies, such as functionalized nano-beads and magnetic MOF nanoparticles, have significantly enhanced enzyme stability and reusability. Directed evolution has led to improved enzyme thermostability and catalytic efficiency, while synthetic biology methods, including phosphorylation-driven and thermodynamics-driven pathways, have optimized production processes. High-throughput screening methods have been crucial in identifying and refining enzyme variants for industrial applications. Collectively, these advancements not only enhance production efficiency and cost-effectiveness but also adhere to sustainable and economically viable manufacturing practices. The past five years have witnessed critical developments with significant potential impact on the commercial viability and global demand for allulose.

D-allulose 3-epimerase for low-calorie D-allulose synthesis: microbial production, characterization, and applications

D-allulose, an epimer of D-fructose at C-3 position, is a low-calorie rare sugar with favorable physiochemical properties and special physiological functions, which displays promising perspectives in the food and pharmaceutical industries. Currently, D-allulose is extremely sparse in nature and is predominantly biosynthesized through the isomerization of D-fructose by D-allulose 3-epimerase (DAEase). In recent years, D-allulose 3-epimerase as the key biocatalyst for D-allulose production has received increasing interest. The current review begins by providing a summary of D-allulose regarding its characteristics and applications, as well as different synthesis pathways dominated by biotransformation. Then, the research advances of D-allulose 3-epimerase are systematically reviewed, focusing on heterologous expression and biochemical characterization, crystal structure and molecular modification, and application in D-allulose production. Concerning the constraint of low yield of DAEase for industrial application, this review addresses the various attempts made to promote the production of DAEase in different expression systems. Also, various strategies have been adopted to improve its thermotolerance and catalytic activity, which is mainly based on the structure-function relationship of DAEase. The application of DAEase in D-allulose biosynthesis from D-fructose or low-cost feedstocks through single- or multi-enzymatic cascade reaction has been discussed. Finally, the prospects for related research of D-allulose 3-epimerase are also proposed, facilitating the industrialization of DAEase and more efficient and economical bioproduction of D-allulose.

D-Allulose Reduces Hypertrophy and Endoplasmic Reticulum Stress Induced by Palmitic Acid in Murine 3T3-L1 Adipocytes

Natural rare sugars are an alternative category of sweeteners with positive physiologic and metabolic effects both in in vitro and animal models. D-allulose is a D-fructose epimer that combines 70% sucrose sweetness with the advantage of an extremely low energy content. However, there are no data about the effect of D-allulose against adipose dysfunction; thus, it remains to be confirmed whether D-allulose is useful in the prevention and in treatment of adipose tissue alterations. With this aim, we evaluated D-allulose's preventive effects on lipid accumulation in 3T3-L1 murine adipocytes exposed to palmitic acid (PA), a trigger for hypertrophic adipocytes. D-allulose in place of glucose prevented adipocyte hypertrophy and the activation of adipogenic markers C/EBP-β and PPARγ induced by high PA concentrations. Additionally, D-allulose pretreatment inhibited the NF-κB pathway and endoplasmic reticulum stress caused by PA, through activation of the Nrf2 pathway. Interestingly, these effects were also observed as D-allulose post PA treatment. Although our data need to be confirmed through in vivo models, our findings suggest that incorporating D-allulose as a glucose substitute in the diet might have a protective role in adipocyte function and support a unique mechanism of action in this sugar as a preventive or therapeutic compound against PA lipotoxicity through the modulation of pathways connected to lipid transport and metabolism.

D-Allulose Ameliorates Dysregulated Macrophage Function and Mitochondrial NADH Homeostasis, Mitigating Obesity-Induced Insulin Resistance

D-allulose, a rare sugar, has been proposed to have potential benefits in addressing metabolic disorders such as obesity and type 2 diabetes (T2D). However, the precise mechanisms underlying these effects remain poorly understood. We aimed to elucidate the mechanisms by which D-allulose influences obesity-induced insulin resistance. We conducted gene set enrichment analysis on the liver and white adipose tissue of mice exposed to a high-fat diet (HFD) along with the white adipose tissue of individuals with obesity. Our study revealed that D-allulose effectively suppressed IFN-γ, restored chemokine signaling, and enhanced macrophage function in the livers of HFD-fed mice. This implies that D-allulose curtails liver inflammation, alleviating insulin resistance and subsequently impacting adipose tissue. Furthermore, D-allulose supplementation improved mitochondrial NADH homeostasis and translation in both the liver and white adipose tissue of HFD-fed mice. Notably, we observed decreased NADH homeostasis and mitochondrial translation in the omental tissue of insulin-resistant obese subjects compared to their insulin-sensitive counterparts. Taken together, these results suggest that supplementation with allulose improves obesity-induced insulin resistance by mitigating the disruptions in macrophage and mitochondrial function. Furthermore, our data reinforce the crucial role that mitochondrial energy expenditure plays in the development of insulin resistance triggered by obesity.

Safety evaluation and maximum use level for transient ingestion in humans of allitol

Allitol is a hexitol produced by reducing the rare sugar D-allulose with a metal catalyst under hydrogen gas. To confirm the safe level of allitol, we conducted a series of safety assessments. From the results of Ames mutagenicity assay using Salmonella typhimurium strains TA98, TA100, TA1535, and TA1537, Escherichia coli strain WP2uvrA, and an in vitro chromosomal aberration test on cultured Chinese hamster cells, allitol did not show any significant genotoxic effect. No significant effects on general condition, urinalysis, hematology, physiology, histopathology, or at necropsy were observed at a dose of 1500 mg/kg body weight of allitol in the acute and 90-day subchronic oral-toxicity assessments for rats. A further study performed on healthy adult humans showed that the acute use level of allitol for diarrhea was 0.2 g/kg body weight for both men and women. The results of current safety assessment studies suggest that allitol is safe for human consumption.

The Engineering, Expression, and Immobilization of Epimerases for D-allulose Production

The rare sugar D-allulose is a potential replacement for sucrose with a wide range of health benefits. Conventional production involves the employment of the Izumoring strategy, which utilises D-allulose 3-epimerase (DAEase) or D-psicose 3-epimerase (DPEase) to convert D-fructose into D-allulose. Additionally, the process can also utilise D-tagatose 3-epimerase (DTEase). However, the process is not efficient due to the poor thermotolerance of the enzymes and low conversion rates between the sugars. This review describes three newly identified DAEases that possess desirable properties for the industrial-scale manufacturing of D-allulose. Other methods used to enhance process efficiency include the engineering of DAEases for improved thermotolerance or acid resistance, the utilization of Bacillus subtilis for the biosynthesis of D-allulose, and the immobilization of DAEases to enhance its activity, half-life, and stability. All these research advancements improve the yield of D-allulose, hence closing the gap between the small-scale production and industrial-scale manufacturing of D-allulose.

d-Allulose Supplementation Prevents Diet-Induced Hepatic Lipid Accumulation via miR-130-Mediated Regulation in C57BL/6 Mice

SCOPE

d-allulose is a low-calorie rare sugar. It has been reported that d-allulose supplementation significantly inhibits diet-induced hepatic fat accumulation. However, the underlying molecular mechanisms remain unclear. This study elucidates the mechanism underlying the suppressive effect of d-allulose on hepatic fat accumulation in terms of miRNA regulation.

METHODS AND RESULTS

Male C57BL/6 mice are divided into three experimental groups-normal diet and distilled water (CC group), high-fat diet (HFD) and distilled water (HC group), and HFD and 5% d-allulose solution (HA group)-and fed the respective diets for 8 weeks. Weight gain is significantly lower in the HA group than that in the HC group, although the caloric intake is the same in both. Histological analysis of liver tissues reveals excessive lipid accumulation in the HC group; this is greatly attenuated in the HA group. Real-time PCR and western blot analyses demonstrate that, compared to the HC group, the HA group exhibits decreased hepatic PPARγ and CD36 expression. Hepatic miR-130 expression levels are higher in the HA group than those in the CC and HC groups.

CONCLUSIONS

These results indicate that miRNA changes associated with PPARγ may underlie the suppression of hepatic lipid accumulation induced by d-allulose intake.

Produce D-allulose from non-food biomass by integrating corn stalk hydrolysis with whole-cell catalysis

D-allulose is a high-value rare sugar with many health benefits. D-allulose market demand increased dramatically after approved as generally recognized as safe (GRAS). The current studies are predominantly focusing on producing D-allulose from either D-glucose or D-fructose, which may compete foods against human. The corn stalk (CS) is one of the main agricultural waste biomass in the worldwide. Bioconversion is one of the promising approach to CS valorization, which is of significance for both food safety and reducing carbon emission. In this study, we tried to explore a non-food based route by integrating CS hydrolysis with D-allulose production. Firstly we developed an efficient Escherichia coli whole-cell catalyst to produce D-allulose from D-glucose. Next we hydrolyzed CS and achieved D-allulose production from the CS hydrolysate. Finally we immobilized the whole-cell catalyst by designing a microfluidic device. Process optimization improved D-allulose titer by 8.61 times, reaching 8.78 g/L from CS hydrolysate. With this method, 1 kg CS was finally converted to 48.87 g D-allulose. This study validated the feasibility of valorizing corn stalk by converting it to D-allulose.

The Characterization of a Novel D-allulose 3-Epimerase from Blautia produca and Its Application in D-allulose Production

D-allulose is a natural rare sugar with important physiological properties that is used in food, health care items, and even the pharmaceutical industry. In the current study, a novel D-allulose 3-epimerase gene (Bp-DAE) from the probiotic strain Blautia produca was discovered for the production and characterization of an enzyme known as Bp-DAE that can epimerize D-fructose into D-allulose. Bp-DAE was strictly dependent on metals (Mn²⁺ and Co²⁺), and the addition of 1 mM of Mn²⁺ could enhance the half-life of Bp-DAE at 55 °C from 60 to 180 min. It exhibited optimal activity in a pH of 8 and 55 °C, and the K_m values of Bp-DAE for the different substrates D-fructose and D-allulose were 235.7 and 150.7 mM, respectively. Bp-DAE was used for the transformation from 500 g/L D-fructose to 150 g/L D-allulose and exhibited a 30% of conversion yield during biotransformation. Furthermore, it was possible to employ the food-grade microbial species Bacillus subtilis for the production of D-allulose using a technique of whole-cell catalysis to circumvent the laborious process of enzyme purification and to obtain a more stable biocatalyst. This method also yields a 30% conversion yield.