Rare sugar D-allulose: Potential role and therapeutic monitoring in maintaining obesity and type 2 diabetes mellitus

A study of D-allulose-associated reproductive toxicity in rats

In this study, we assessed whether D-allulose was associated with reproductive toxicity in rats, assessing reproduction and offspring growth following gavage of parents with 0, 500, 1000, and 2000 mg/kg of this compound. Specifically, female rats were continuously dose from 2 weeks prior to mating until day 21 of lactation, while males were dose for the 10 weeks before mating. We did not observe any direct toxicity or mortality upon D-allulose administration, with no changes in body weight or eating behavior between study and control groups. We also did not observe any significant alterations in precoital time, copulation index, fertility index (male), or pregnancy index (male) between groups. Relative to controls, there was also no effect of D-allulose treatment on pregnancy rates, implantation, pregnancy length, gender ratios, viability indexes, lactation indexes, prenatal death rates, or number of live young at time of birth. Organ weights and indexes were also comparable between groups at time of sacrifice, and treatment was not linked to any obvious manifestations upon necropsy or histopathological examination. In the F1 offspring, the body weights of pups born to parents administered D-allulose (2000, 1000, and 500 mg/kg) were slightly higher on days 1-9 postnatally relative to controls (p < 0.05), however after day 9 these effects were no longer evident. Together, these results indicate a no-observed-adverse-effect level (NOAEL) of D-allulose of 2000 mg/kg, the highest dose tested, in parental animals and their offspring.

Biochemical characterization and biocatalytic application of a novel d-tagatose 3-epimerase from Sinorhizobium sp

Sinorhizobium sp. d-tagatose 3-epimerase (sDTE) catalyzes the conversion of d-tagatose to d-sorbose. It also recognizes d-fructose as a substrate for d-allulose production. The optimal temperature and pH of the purified sDTE was 50 °C and 8.0, respectively. Based on the sDTE homologous model, Glu154, Asp187, Gln213, and Glu248, form a hydrogen bond network with the active-site Mn²⁺ and constitute the catalytic tetrad. The amino acid residues around O-1, -2, and -3 atoms of the substrates (d-tagatose/d-fructose) are strictly conserved and thus likely regulate the catalytic reaction. However, the residues at O-4, -5, and -6, being responsible for the substrate-binding, are different. In particular, Arg65 and Met9 were found to form a unique interaction with O-4 of d-fructose and d-tagatose. The whole cells with recombinant sDTE showed a higher bioconversion rate of 42.5% in a fed-batch bioconversion using d-fructose as a substrate, corresponding to a production of 476 g L⁻¹d-allulose. These results suggest that sDTE is a potential industrial biocatalyst for the production of d-allulose in fed-batch mode.

Sinorhizobium sp. d-tagatose 3-epimerase (sDTE) catalyzes the conversion of d-tagatose to d-sorbose.

Calorie Restriction Mimetics: Upstream-Type Compounds for Modulating Glucose Metabolism

Calorie restriction (CR) can prolong the human lifespan, but enforcing long-term CR is difficult. Therefore, a compound that reproduces the effect of CR without CR is needed. In this review, we summarize the current knowledge on compounds with CR mimetic (CRM) effects. More than 10 compounds have been listed as CRMs, some of which are conventionally categorized as upstream-type CRMs showing glycolytic inhibition, while the others are categorized as downstream-type CRMs that regulate or genetically modulate intracellular signaling proteins. Among these, we focus on upstream-type CRMs and propose their classification as compounds with energy metabolism inhibition effects, particularly glucose metabolism modulation effects. The upstream-type CRMs reviewed include chitosan, acarbose, sodium-glucose cotransporter 2 inhibitors, and hexose analogs such as 2-deoxy-d-glucose, d-glucosamine, and d-allulose, which show antiaging and longevity effects. Finally, we discuss the molecular definition of upstream-type CRMs.

Role of Synbiotics Containing d-Allulose in the Alteration of Body Fat and Hepatic Lipids in Diet-Induced Obese Mice

The effects of allulose and two probiotic species on diet-induced obese (DIO) mice were investigated. Lactobacillus sakei LS03 (10⁹ cfu/day) and Leuconostoc kimchii GJ2 (10⁹ cfu/day) were used as probiotics, and allulose (AL) as a prebiotic. The synergistic effect of prebiotics and probiotics in improving obesity was evaluated. Orally fed Lactobacillus sakei LS03 (LS) or Leuconostoc kimchii GJ2 (GJ), significantly decreased hepatic triglyceride (TG) and fatty acid (FA) compared to the high-fat diet (HFD) control. AL markedly decreased visceral adiposity and pro-inflammatory adipokines (leptin and resistin) and cytokines (IL-6 and IL-1β) as well as hepatic TG and FA. In addition, AL exerted synergic effects with probiotics (LS and/or GJ) on the reduction of visceral white adipose tissue (WAT), associated with a decreased leptin: adiponectin ratio. There was no significant differences between the AL-SL and AL group, allulose and GJ combination (AL-GJ) was more effective than allulose in improving dyslipidemia, and decreasing WAT weight and hepatic FA, suggesting allulose may act as a favorable prebiotic for GJ supplement than LS. Combination of allulose with LS and GJ supplementation (AL-LSGJ) was the most effective for improving obesity related complications among the synbiotics groups containing allulose. In conclusion, this study demonstrated that the synbiotic mixture with allulose was more effective in suppressing diet-induced obese (DIO) and its complications via the regulation of lipid metabolism, than the probiotics or allulose alone, suggesting allulose may act as a prebiotic for the two probiotics tested in the study. This new synbiotic mixture with allulose may help ameliorate the deleterious effects of diet-induced obesity and contribute to the growth of the food industry.

d-Allulose is a substrate of glucose transporter type 5 (GLUT5) in the small intestine

d-Allulose has been reported to have beneficial health effects. However, the transport system(s) mediating intestinal d-allulose transport has not yet been clearly identified. The aim of this study was to investigate whether intestinal d-allulose transport is mediated by glucose transporter type 5 (GLUT5). When d-allulose alone was gavaged, plasma d-allulose levels were dramatically higher in rats previously fed fructose. This suggests enhanced intestinal d-allulose absorption paralleled increases in GLUT5 expression observed only in fructose-fed rats. When d-allulose was gavaged with d-fructose, previously observed increases in plasma d-allulose levels were dampened and delayed, indicating d-fructose inhibited transepithelial d-allulose transport into plasma. Tracer D-[¹⁴C]-fructose uptake rate was reduced to 54.8% in 50 mM d-allulose and to 16.4% in 50 mM d-fructose, suggesting d-allulose competed with D-[¹⁴C]-fructose and the affinity of d-allulose for GLUT5 was lower than that of d-fructose. GLUT5 clearly mediates, likely at lower affinity relative to d-fructose, intestinal d-allulose transport.

The effect of small doses of fructose and allulose on postprandial glucose metabolism in type 2 diabetes: A double-blind, randomized, controlled, acute feeding, equivalence trial

AIM

To assess and compare the effect of small doses of fructose and allulose on postprandial blood glucose regulation in type 2 diabetes.

METHODS

A double-blind, multiple-crossover, randomized, controlled, acute feeding, equivalence trial in 24 participants with type 2 diabetes was conducted. Each participant was randomly assigned six treatments separated by >1-week washouts. Treatments consisted of fructose or allulose at 0 g (control), 5 g or 10 g added to a 75-g glucose solution. A standard 75-g oral glucose tolerance test protocol was followed with blood samples at -30, 0, 30, 60, 90 and 120 minutes. The primary outcome measure was plasma glucose incremental area under the curve (iAUC).

RESULTS

Allulose significantly reduced plasma glucose iAUC by 8% at 10 g compared with 0 g (717.4 ± 38.3 vs. 777.5 ± 39.9 mmol × min/L, P = 0.015) with a linear dose response gradient between the reduction in plasma glucose iAUC and dose (P = 0.016). Allulose also significantly reduced several related secondary and exploratory outcome measures at 5 g (plasma glucose absolute mean and total AUC) and 10 g (plasma glucose absolute mean, absolute and incremental maximum concentration [Cmax ], and total AUC) (P < .0125). There was no effect of fructose at any dose. Although allulose showed statistically significant reductions in plasma glucose iAUC compared with fructose at 5 g, 10 g and pooled doses, these reductions were within the pre-specified equivalence margins of ±20%.

CONCLUSION

Allulose, but not fructose, led to modest reductions in the postprandial blood glucose response to oral glucose in individuals with type 2 diabetes. There is a need for long-term randomized trials to confirm the sustainability of these improvements.

Thermostability Improvement of the d-Allulose 3-Epimerase from Dorea sp. CAG317 by Site-Directed Mutagenesis at the Interface Regions

d-Allulose is a low-calorie sweetener and has broad applications in the food, cosmetics, and pharmaceutical industries. Recently, most studies focus on d-allulose production from d-fructose by d-allulose 3-epimerase (DAEase). However, the major blocker of industrial production of d-allulose is the poor thermostability. In this study, site-directed mutagenesis at the interface regions of Dorea sp. DAEase was carried out, and the F154Y/E191D/I193F mutation was obtained. The mutant protein displayed much higher thermostability, with a t_1/2 value of 20.47 h (50 °C) and a T_m value of 74.18 °C. Compared with the wild-type DAEase, the t_1/2 value at 50 °C increased by 5.4-fold, and the T_m value increased by 17.54 °C. In the d-allulose production from 500 g/L d-fructose, 148.2 g/L d-allulose could be obtained by F154Y/E191D/I193F mutant protein. The results suggest that site-directed mutagenesis at the interface regions is an efficient approach for improving the thermostability of DAEase.

Rare sugars, d-allulose, d-tagatose and d-sorbose, differently modulate lipid metabolism in rats

BACKGROUND

Rare sugars including d-allulose, d-tagatose, and d-sorbose are present in limited quantities in nature; some of these rare sugars are now commercially produced using microbial enzymes. Apart from the anti-obesity and anti-hyperglycaemic activities of d-allulose, effects of these sugars on lipid metabolism have not been investigated. Therefore, we aimed to determine if and how d-tagatose and d-sorbose modulate lipid metabolism in rats. After feeding these rare sugars to rats, parameters on lipid metabolism were determined.

RESULTS

No diet-related effects were observed on body weight and food intake. Hepatic lipogenic enzyme activity was lowered by d-allulose and d-sorbose but increased by d-tagatose. Faecal fatty acid excretion was non-significantly decreased by d-allulose, but significantly increased by d-sorbose without affecting faecal steroid excretion. A trend toward reduced adipose tissue weight was observed in groups fed rare sugars. Serum adiponectin levels were decreased by d-sorbose relative to the control. Gene expression of cholesterol metabolism-related liver proteins tended to be down-regulated by d-allulose and d-sorbose but not by d-tagatose. In the small intestine, SR-B1 mRNA expression was suppressed by d-sorbose.

CONCLUSION

Lipid metabolism in rats varies with rare sugars. Application of rare sugars to functional foods for healthy body weight maintenance requires further studies. © 2017 Society of Chemical Industry.

GLP-1 release and vagal afferent activation mediate the beneficial metabolic and chronotherapeutic effects of D-allulose

Overeating and arrhythmic feeding promote obesity and diabetes. Glucagon-like peptide-1 receptor (GLP-1R) agonists are effective anti-obesity drugs but their use is limited by side effects. Here we show that oral administration of the non-calorie sweetener, rare sugar d-allulose (d-psicose), induces GLP-1 release, activates vagal afferent signaling, reduces food intake and promotes glucose tolerance in healthy and obese-diabetic animal models. Subchronic d-allulose administered at the light period (LP) onset ameliorates LP-specific hyperphagia, visceral obesity, and glucose intolerance. These effects are blunted by vagotomy or pharmacological GLP-1R blockade, and by genetic inactivation of GLP-1R signaling in whole body or selectively in vagal afferents. Our results identify d-allulose as prominent GLP-1 releaser that acts via vagal afferents to restrict feeding and hyperglycemia. Furthermore, when administered in a time-specific manner, chronic d-allulose corrects arrhythmic overeating, obesity and diabetes, suggesting that chronotherapeutic modulation of vagal afferent GLP-1R signaling may aid in treating metabolic disorders.

The sweetener D-allulose has beneficial metabolic effects in animal models, but its mechanism of action was unclear. Here the authors report that D-allulose triggers GLP-1 release in the gut and GLP-1R signaling on vagal afferents, counteracting arrhythmic overeating, obesity and diabetes.

The scientific basis for healthful carbohydrate profile

Dietary guidelines indicate that complex carbohydrates should provide around half of the calories in a balanced diet, while sugars (i.e., simple carbohydrates) should be limited to no more than 5-10% of total energy intake. To achieve this public health goal a collective effort from different entities including governments, food & beverage industries and consumers is required. Some food companies have committed to continually reduce sugars in their products. Different solutions can be used to replace sugars in food products but it is important to ensure that these solutions are more healthful than the sugars they replace. The objectives of this paper are, (1) to identify carbohydrates and carbohydrates sources to promote and those to limit for dietary intake and food product development, based on current knowledge about the impact of carbohydrates on the development of dental caries, obesity and cardio-metabolic disorders (2) to evaluate the impact of food processing on the quality of carbohydrates and (3) to highlight the challenges of developing healthier products due to the limitations and gaps in food regulations, science & technology and consumer education.

The long-term safety of D-allulose administration in healthy dogs

The safety and biological effects of a long-term dose of D-allulose were evaluated in healthy dogs. For 12 weeks, the dogs were administered D-allulose (0.2 g/kg) or placebo daily. Plasma total cholesterol concentrations in the D-allulose group were significantly lower than those in the control group at and after week 2 (P<0.05). D-Allulose administration did not cause clinical signs or changes in hematological and biochemical levels, except for lipids. D-Allulose administration also did not influence body weight. Plasma glucose and insulin concentrations in the glucose tolerance test, performed one day after the termination of D-allulose administration, were not different between groups, suggesting no cumulative effects of D-allulose on glucose metabolism in healthy dogs. In conclusion, long-term administration of D-allulose caused no harmful effects in dogs.

Characterization of L-rhamnose isomerase from Clostridium stercorarium and its application to the production of D-allose from D-allulose (D-psicose)

OBJECTIVE

To characterize L-rhamnose isomerase (L-RI) from the thermophilic bacterium Clostridium stercorarium and apply it to produce D-allose from D-allulose.

RESULTS

A recombinant L-RI from C. stercorarium exhibited the highest specific activity and catalytic efficiency (k _cat/K _m) for L-rhamnose among the reported L-RIs. The L-RI was applied to the high-level production of D-allose from D-allulose. The isomerization activity for D-allulose was maximal at pH 7, 75 °C, and 1 mM Mn²⁺ over 10 min reaction time. The half-lives of the L-RI at 65, 70, 75, and 80 °C were 22.8, 9.5, 1.9, and 0.2 h, respectively. To ensure full stability during 2.5 h incubation, the optimal temperature was set at 70 °C. Under the optimized conditions of pH 7, 70 °C, 1 mM Mn²⁺, 27 U L-RI l^-1, and 600 g D-allulose l^-1, L-RI from C. stercorarium produced 199 g D-allose l^-1 without by-products over 2.5 h, with a conversion yield of 33% and a productivity of 79.6 g l^-1 h^-1.

CONCLUSION

To the best of our knowledge, this is the highest concentration and productivity of D-allose reported thus far.

D‑Tagatose inhibits the growth and biofilm formation of Streptococcus mutans

Dental caries is an important global health concern and Streptococcus mutans has been established as a major cariogenic bacterial species. Reports indicate that a rare sugar, D-tagatose, is not easily catabolized by pathogenic bacteria. In the present study, the inhibitory effects of D-tagatose on the growth and biofilm formation of S. mutans GS-5 were examined. Monitoring S. mutans growth over a 24 h period revealed that D-tagatose prolonged the lag phase without interfering with the final cell yield. This growth retardation was also observed in the presence of 1% sucrose, although it was abolished by the addition of D-fructose. S. mutans biofilm formation was significantly inhibited by growth in sucrose media supplemented with 1 and 4% D-tagatose compared with that in a culture containing sucrose alone, while S. mutans formed granular biofilms in the presence of this rare sugar. The inhibitory effect of D-tagatose on S. mutans biofilm formation was significantly more evident than that of xylitol. Growth in sucrose media supplemented with D-tagatose significantly decreased the expression of glucosyltransferase, exo-β-fructosidase and D-fructose-specific phosphotransferase genes but not the expression of fructosyltransferase compared with the culture containing sucrose only. The activity of cell-associated glucosyltransferase in S. mutans was inhibited by 4% D-tagatose. These results indicate that D-tagatose reduces water-insoluble glucan production from sucrose by inhibiting glucosyltransferase activities, which limits access to the free D-fructose released during this process and retards the growth of S. mutans. Therefore, foods and oral care products containing D-tagatose are anticipated to reduce the risk of caries by inhibiting S. mutans biofilm formation.

Effects of rare sugar d-allulose on heat-induced gelation of surimi prepared from marine fish

BACKGROUND

d-Allulose (Alu), the C3-epimer of d-fructose, is a non-caloric sweetener (0.39 kcal g^-1 ) with a suppressive effect on postprandial blood glucose elevation. The aim of this study was to investigate the effects of Alu used as a sweetener and gel improver instead of sucrose on heat-induced gelation of surimi.

RESULTS

The puncture test of a heat-induced surimi gel showed that with 50 g kg^-1 Alu the gel had 15% and 6% higher gel strength than the corresponding gel with sucrose (Suc) and with sorbitol (Sor), respectively. In addition, Alu-gel had 26% and 25% higher water-holding capacity (WHC) than Suc- and Sor-gel. Heating of myofibrillar protein with Alu, unlike Suc and Sor, facilitated the formation of both disulfide and non-disulfide crosslinks that might be associated with the mechanical properties and WHC of Alu-gel.

CONCLUSION

Alu improves the mechanical properties and WHC of the heat-induced surimi gel. Furthermore, Alu is low in calories compared with Suc (4.0 kcal g^-1 ) and Sor (3.0 kcal g^-1 ). Thus Alu will be an alternative of Suc or Sor for developing surimi-based products with health benefits. © 2017 Society of Chemical Industry.

Recent advances in the synthesis of rare sugars using DHAP-dependent aldolases

The occurrence rates of non-communicable diseases like obesity, diabetes and hyperlipidemia have increased remarkably due to excessive consumption of a high-energy diet. Rare sugars therefore have become increasingly attractive owing to their unique nutritional properties. In the past two decades, various rare sugars have been successfully prepared guided by the "Izumoring strategy". As a valuable complement to the Izumoring approach, the controllable dihydroxyacetone phosphate (DHAP)-dependent aldolases have generally predictable regio- and stereoselectivity, which makes them powerful tools in C-C bond construction and rare sugar production. However, the main disadvantage for this group of aldolases is their strict substrate specificity toward the donor molecule DHAP, a very expensive and relatively unstable compound. Among the current methods involving DHAP, the one that couples DHAP production from inexpensive starting materials (for instance, glycerol, DL-glycerol 3-phosphate, dihydroxyacetone, and glucose) with aldol condensation appears to be the most promising. This review thus focuses on recent advances in the application of L-rhamnulose-1-phosphate aldolase (RhaD), L-fuculose-1-phosphate aldolase (FucA), and D-fructose-1,6-bisphosphate aldolase (FruA) for rare sugar synthesis in vitro and in vivo, while illustrating strategies for supplying DHAP in efficient and economical ways.

d-Allulose, a stereoisomer of d-fructose, extends Caenorhabditis elegans lifespan through a dietary restriction mechanism: A new candidate dietary restriction mimetic

Dietary restriction (DR) is an effective intervention known to increase lifespan in a wide variety of organisms. DR also delays the onset of aging-associated diseases. DR mimetics, compounds that can mimic the effects of DR, have been intensively explored. d-Allulose (d-Alu), the C3-epimer of d-fructose, is a rare sugar that has various health benefits, including anti-hyperglycemia and anti-obesity effects. Here, we report that d-Alu increased the lifespan of Caenorhabditis elegans both under monoxenic and axenic culture conditions. d-Alu did not further extend the lifespan of the long-lived DR model eat-2 mutant, strongly indicating that the effect is related to DR. However, d-Alu did not reduce the food intake of wild-type C. elegans. To explore the mechanisms of the d-Alu longevity effect, we examined the lifespan of d-Alu-treated mutants deficient for nutrient sensing pathway-related genes daf-16, sir-2.1, aak-2, and skn-1. As a result, d-Alu increased the lifespan of the daf-16, sir-2.1, and skn-1 mutants, but not the aak-2 mutant, indicating that the lifespan extension was dependent on the energy sensor, AMP-activated protein kinase (AMPK). d-Alu also enhanced the mRNA expression and enzyme activities of superoxide dismutase (SOD) and catalase. From these findings, we conclude that d-Alu extends lifespan by increasing oxidative stress resistance through a DR mechanism, making it a candidate DR mimetic.

Production of d-allulose from d-glucose by Escherichia coli transformant cells co-expressing d-glucose isomerase and d-psicose 3-epimerase genes

BACKGROUND

d-Allulose is a novel and low-calorie rare monosaccharide that is a C-3 epimer of d-fructose. Because of its excellent physiological properties and commercial potential, d-allulose has attracted researchers' interests. Based on the Izumoring strategy, d-allulose is converted from d-fructose by d-psicose 3-epimerase (DPEase), while d-fructose is converted from d-glucose by d-glucose isomerase (GIase). In this study, we created a cellular system capable of converting d-glucose to d-allulose in a one-step process that co-expressed the GIase from Acidothermus cellulolyticus and the DPEase from Dorea sp. CAG.

RESULTS

The co-expression plasmid pETDuet-Dosp-DPE/Acce-GI was generated and transformed into Escherichia coli BL21(DE3) cells. The recombinant co-expression cells exhibited maximum catalytic activity at pH 6.5 and 75 °C. These cells were thermostable at less than 60 °C. The addition of Co²⁺ significantly increased the catalytic activity by 10.8-fold. When the reaction equilibrium was reached, the ratio of d-glucose, d-fructose and d-allulose was approximately 6.5:7:3, respectively.

CONCLUSION

A recombinant co-expression strain that catalysed the bioconversion of d-allulose from d-glucose in a one-step process was created and characterised. When adding 500 g L^-1 d-glucose as a substrate, 204.3 g L^-1 d-fructose and 89.1 g L^-1 d-allulose were produced. © 2016 Society of Chemical Industry.

d-Allulose enhances postprandial fat oxidation in healthy humans

OBJECTIVE

d-Allulose, a C-3 epimer of d-fructose, has been reported to decrease body weight and adipose tissue weight in animal studies and is expected to be a potent antiobese sweetener. Our animal study suggested that one of the mechanisms of d-allulose's antiobesity function is an increase in energy expenditure. However, a few studies have thus far explored the underlying mechanism in humans. The aim of this study was to examine the effects of a single ingestion of d-allulose on postprandial energy metabolism in healthy participants.

METHODS

Thirteen healthy men and women (mean age of 35.7 ± 2.1 y and body mass index 20.9 ± 0.7 kg/m²) were studied. The study was a randomized, single-blind crossover design with a 1-wk washout period. At 30 min after taking 5 g of d-allulose or 10 mg of aspartame without any sugar as a control, overnight-fasted participants ingested a standardized meal, and energy metabolism was evaluated by a breath-by-breath method. During the experiment, blood was collected and biochemical parameters such as plasma glucose were analyzed.

RESULTS

In the d-allulose-treated group, the area under the curve of fat oxidation was significantly higher than in the control group (10.5 ± 0.4 versus 9.6 ± 0.3 kJ·4 h·kg^-1 body weight [BW]; P < 0.05), whereas that of carbohydrate oxidation was significantly lower (8.1 ± 0.5 versus 9.2 ± 0.5 kJ·4 h·kg^-1 BW; P < 0.05). Furthermore, plasma glucose levels were significantly lower, and free fatty acid levels were significantly higher in the d-allulose group than in the control group. No other parameters such as insulin, total cholesterol, or triacylglycerol were modified.

CONCLUSION

d-Allulose enhances postprandial fat oxidation in healthy humans, indicating that it could be a novel sweetener to control and maintain healthy body weight, probably through enhanced energy metabolism.

Rare Sugar Syrup Containing d-Allulose but Not High-Fructose Corn Syrup Maintains Glucose Tolerance and Insulin Sensitivity Partly via Hepatic Glucokinase Translocation in Wistar Rats

Ingestion of high-fructose corn syrup (HFCS) is associated with the risk of both diabetes and obesity. Rare sugar syrup (RSS) has been developed by alkaline isomerization of HFCS and has anti-obesity and anti-diabetic effects. However, the influence of RSS on glucose metabolism has not been explored. We investigated whether long-term administration of RSS maintains glucose tolerance and whether the underlying mechanism involves hepatic glucokinase translocation. Wistar rats were administered water, RSS, or HFCS in drinking water for 10 weeks and then evaluated for glucose tolerance, insulin tolerance, liver glycogen content, and subcellular distribution of liver glucokinase. RSS significantly suppressed body weight gain and abdominal fat mass (p < 0.05). The glucose tolerance test revealed significantly higher blood glucose levels in the HFCS group compared to the water group, whereas the RSS group had significantly lower blood glucose levels from 90 to 180 min (p < 0.05). At 30, 60, and 90 min, the levels of insulin in the RSS group were significantly lower than those in the water group (p < 0.05). The amount of hepatic glycogen was more than 3 times higher in the RSS group than that in the other groups. After glucose loading, the nuclear export of glucokinase was significantly increased in the RSS group compared to the water group. These results imply that RSS maintains glucose tolerance and insulin sensitivity, at least partly, by enhancing nuclear export of hepatic glucokinase.

Effect of d-allulose on rheological properties of chicken breast sausage

d-Allulose (Alu), a rare sugar, was applied to chicken breast sausage as a sucrose (Suc) substitute. The ratio (w/w) of Alu to Suc in sugar that was added to the sausage batter was 0/1 (A0S1), 3/7 (A3S7), 7/3 (A7S3), and 1/0 (A1S0). The total amount of Suc used was 2.5% of the weight of minced chicken breast meat. Substituting Suc with Alu did not affect water content, cooking loss, breaking stress, breaking strain, and modulus of elasticity of chicken breast sausage, but a 100% substitution with Alu caused a 10% decrease in viscosity and a 31% decrease in expressible water. A significant difference appeared in the rheological properties of elasticity, viscosity, and water-holding capacity of chicken breast sausage frozen-stored (-20°C) for 90 d. Particularly, the modulus of elasticity for A1S0 chicken breast sausage was 19% higher than that of the control A0S1 chicken breast sausage, suggesting that Alu appreciably reduced the deterioration in elasticity that is caused by long-term frozen storage of sausage. The quality improvement of frozen-stored chicken breast sausage demonstrates the feasibility and benefits of the application of Alu to frozen foods.

Effects of D-allulose on glucose metabolism after the administration of sugar or food in healthy dogs

D-allulose is a C-3 epimer of D-fructose and has recently been investigated for its hypoglycemic effects. In the present study, the effects of D-allulose on glucose metabolism were evaluated in healthy dogs administrated sugar or food. The oral administrations of D-allulose decreased plasma glucose concentrations after oral glucose or maltose administration, with a diminished plasma insulin rise. The glucose suppressive effect of D-allulose was also observed after intravenous glucose administrations without increase in plasma insulin concentration. In contrast, D-allulose showed no effect on plasma glucose and insulin concentrations after feeding. The present results suggest that D-allulose administration may be beneficial in dogs with impaired glucose tolerance. Further studies investigating the therapeutic efficacy of D-allulose in diabetic dogs are required.

Food-Grade Expression of d-Psicose 3-Epimerase with Tandem Repeat Genes in Bacillus subtilis

An integrative food-grade expression system with tandem repeat target genes was constructed for the expression of d-psicose 3-epimerase (DPEase; EC 5.1.3.30). The DPEase gene fused with the P43 promoter constituted an independent monomeric expression cassette. Multimers of the expression cassette were constructed in vitro using the isocaudamer strategy. The recombinant integration plasmids pDG-nDPE (n = 1, 2, 3), which contained one, two, or three consecutive P43-DPEase tandem repeats, were integrated into the genome of B. subtilis. Then, the antibiotic resistance gene was deleted by the Cre/lox system, and the food-grade recombinant B. subtilis 1A751-nDPE (n = 1, 2, 3) with integrated tandem repeats of the P43-DPEase expression cassette were generated. The specific activity of the B. subtilis 1A751-3DPE was the highest among the recombinant strains and was ∼2.2-fold that of the 1A751-1DPE strain. Under the optimal conditions, 8 g/L of freeze-dried enzyme powder could convert 20% d-fructose (300 g/L) into d-allulose after 1 h.