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Most monosaccharides in nature are hexoses, which have six carbon atoms; the most well-known hexose is D-glucose. Various hexoses with distinct characteristics can be produced from inexpensive polysaccharides for applications in the food industry. Therefore, identification of the health-related functions of hexose will facilitate the consumption of hexoses in food products to improve quality of life. The hexoses available in foods include N-acetyl glucosamine, D-glucosamine, D-fructose, D-mannose, D-galactose, other D-hexoses, and l-hexoses. Here, an updated overview of food industrial production methods for natural hexoses by microbial, enzymatic, and chemical methods is provided. [ABSTRACT FROM AUTHOR]

The use of ketohexose isomerases is a powerful tool in lactose whey processing, but these enzymes can be very sensitive and expensive. Development of immobilized/stabilized biocatalysts could be a further option to improve the process. In this work, β-galactosidase from Bacillus circulans, L-arabinose (D-galactose) isomerase from Enterococcus faecium, and D-xylose (D-glucose) isomerase from Streptomyces rubiginosus were immobilized individually onto Eupergit C and Eupergit C 250 L. Immobilized activity yields were over 90% in all cases. With the purpose of increasing thermostability of derivatives, two post-immobilization treatments were performed: alkaline incubation to favor the formation of additional covalent linkages, and blocking of excess oxirane groups by reacting with glycine. The greatest thermostability was achieved when alkaline incubation was carried out for 24 h, producing L-arabinose isomerase-Eupergit C derivatives with a half-life of 379 h and D-xylose isomerase-Eupergit C derivatives with a half-life of 554 h at 50 °C. Preliminary assays using immobilized and stabilized biocatalysts sequentially to biotransform lactose at pH 7.0 and 50 °C demonstrated improved performances as compared with soluble enzymes. Further improvements in ketohexose productivities were achieved when the three single-immobilizates were incubated simultaneously with lactose in a mono-reactor system. [ABSTRACT FROM AUTHOR]

5-Hydroxymethyl-2-furfurylamine (5-HMFA) as an important 5-HMF derivative has been widely utilized in the manufacture of diuretics, antihypertensive drugs, preservatives and curing agents. In this work, an efficient chemoenzymatic route was constructed for producing 5-(hydroxymethyl)furfurylamine (5-HMFA) from biobased D -fructose in deep eutectic solvent Betaine:Glycerol-water. The introduction of Betaine:Glycerol could greatly promote the dehydration of D -fructose to 5-HMF and inhibit the secondary decomposition reactions of 5-HMF, compared with a single aqueous phase. D -Fructose (200 mM) could be catalyzed to 5-HMF (183.4 mM) at 91.7% yield by SG(SiO 2 ) (3 wt%) after 90 min in Betaine:Glycerol (20 wt%), and at 150 °C. E. coli AT exhibited excellent bio-transamination activity to aminate 5-HMF into 5-HMFA at 35 °C and pH 7.5. After 24 h, D -fructose-derived 5-HMF (165.4 mM) was converted to 5-HMFA (155.7 mM) in 94.1% yield with D -Ala ( D -Ala-to-5-HMF molar ratio 15:1) in Betaine:Glycerol (20 wt%) without removal of SG(SiO 2 ), achieving a productivity of 0.61 g 5-HMFA/(g substrate D -fructose). Chemoenzymatic valorization of D -fructose with SG(SiO 2 ) and E. coli AT was established for sustainable production of 5-HMFA, which has potential application.

Homogenous bis-sulfonic acid ionic liquids (1 mol equiv.) in DMSO (10 mol equiv.) at 100 °C efficiently mediated the conversion of D-fructose into 5-hydroxymethyl-2-furfural in 75% isolated yield, which was roughly a 10% increment compared to the case of the mono-sulfonic acid ionic liquids. [ABSTRACT FROM AUTHOR]

5-Acetoxymethyl-2-furfural (AMF) was prepared from D-fructose via 1,6-diacetylfructose (DAF) through a simple two-step reaction pathway. Immobilized enzyme (Novozym 435) was found to be the best enzymatic catalyst for the trans-esterification step (yielding 94.6% DAF). In the dehydration step, while soluble H2SO4 was found to be the best acidic catalyst (yielding 86.6% AMF), we opted to utilize heterogeneous cation exchange resin (Amberlyst 15) together with recyclable industrial solvents (1,4-dioxane) for a more sustainable AMF synthesis procedure. Although the total yield of AMF was a little lower, both the enzyme and the solid acid catalyst could be recycled for five cycles without a significant loss of activity, which has a major contribution to the cost-efficient aspect of the entire process. [ABSTRACT FROM AUTHOR]

D-allulose, a C-3 epimer of D-fructose, is a rare monosaccharide used as a food ingredient or a sweetener. In the present study, the in vitro metabolic stability of D-allulose was examined in biorelevant media, that is, simulated gastric fluid (SGF) and fasted state simulated intestinal fluid (FaSSIF) containing digestive enzymes, and in cryopreserved human and rat hepatocytes. The hepatocyte metabolic stabilities of D-allulose were also investigated and compared with those of fructose and erythritol (a sugar-alcohol with no calorific value). D-allulose was highly stable in SGF (97.8% remained after 60 min) and in FaSSIF (101.3% remained after 240 min), indicating it is neither pH-labile nor degraded in the gastrointestinal tract. D-allulose also exhibited high levels of stability in human and rat hepatocytes (94.5–96.8% remained after 240 min), whereas fructose was rapidly metabolized (43.1–52.6% remained), which suggested these two epimers are metabolized in completely different ways in the liver. The effects of D-allulose on glucose and fructose levels were negligible in hepatocytes. Erythritol was stable in human and rat hepatocytes (102.1–102.9% remained after 240 min). Intravenous pharmacokinetic studies in rats showed D-allulose was eliminated with a mean half-life of 72.2 min and a systemic clearance of 15.8 mL/min/kg. Taken together, our results indicate that D-allulose is not metabolized in the liver, and thus, unlikely to contribute to hepatic energy production. [ABSTRACT FROM AUTHOR]

Gustatory receptors (GRs) are crucial in the peripheral coding of the non-volatile compounds in insects, and thus play important roles in multiple behaviors including feeding, mating, and oviposition. However, little research has been done on GRs in lepidopteran pests. In the current work with Spodoptera litura, an important worldwide crop's pest, a candidate fructose GR gene (SlitGR8) was cloned in full length, and its spatial and temporal expression profiles were determined by quantitative real-time PCR (qPCR). It revealed that SlitGR8 was highly expressed in antennae of both male and female adults, as well as in larva of first, fifth and sixth instar. Functional analyses were further conducted using the Xenopus oocyte system. SlitGR8 responded specifically to D-fructose among 12 tested sugar compounds. In addition, the behavioral assay demonstrated that both female and male moths could respond with proboscis extension behavior to D-fructose applied onto the antenna, but females showed higher sensitivity than males. The results provide an important base for further elucidation of molecular mechanisms of gustation, and a potential target for development of feeding interfering technique in S. litura. [ABSTRACT FROM AUTHOR]

Recent literature suggests that catalytic doses (≤10 g/meal or 36 g/day) of D-fructose and D-allulose may reduce postprandial blood glucose responses to carbohydrate loads in people with and without type 2 diabetes by inducing glycogen synthesis. To assess the effect of small single doses of fructose and allulose on postprandial blood glucose regulation in response to a 75 g-oral glucose tolerance test (75 g-OGTT) in healthy individuals, we conducted an acute randomized, crossover, equivalence trial in healthy adults. Each participant randomly received six treatments, separated by a minimum one-week washout. Treatments consisted of a 75 g-OGTT with the addition of fructose or allulose at 0 g (control), 5 g or 10 g. A standard 75 g-OGTT protocol was followed with blood samples at −30, 0, 30, 60, 90, 120 min. The primary outcome was the difference in plasma glucose incremental area under the curve (iAUC). A total of 27 participants underwent randomization with data available from 25 participants. Small doses of fructose or allulose did not show a significant effect on plasma glucose iAUC or other secondary markers of postprandial blood glucose regulation in response to a 75 g-OGTT in healthy individuals. These results were limited by the low power to detect a significant difference, owing to greater than expected intra-individual coefficient of variation (CV) in plasma glucose iAUC. Overall, we failed to confirm the catalytic effects of small doses of fructose and allulose in healthy individuals. Future trials may consider recruiting larger sample sizes of healthy individuals. Trial registration: clinicaltrials.gov identifier, NCT02459834. [ABSTRACT FROM AUTHOR]