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"... One such substitute, allulose, is around 70% as sweet as sucrose, but contains just 10% of the calories and has even been shown to improve blood glucose levels and help in weight loss in people with type 2 diabetes. ...
Allulose – which is also known as D-psicose – is considered a rare sugar as it only exists naturally in minute amounts in a few plant foods, such as wheat, figs and raisins. When extracted, it has the texture and mouthfeel of sucrose, it has just 0.4 calories per gram, compared to four calories per gram in sucrose. And because it's a monosaccharide, or a single molecule of sugar, it undergoes a very different process in the body. Around 70% is absorbed by the small intestine and leaves the body via urine within 24 hours. The rest will exit the body ... through the large intestine, within about 48 hours. ...
The team ... edited the [E. coli] microorganism’s metabolic processes, so when the cells were fed glucose, they converted it to allulose. It immediately resulted in yields of 62% (and, importantly, a purity level in excess of 95%). ..."
From the abstract:
"Due to the rampant rise in obesity and diabetes, consumers are desperately seeking for ways to reduce their sugar intake, but to date there are no options that are both accessible and without sacrifice of palatability. One of the most promising new ingredients in the food system as a non-nutritive sugar substitute with near perfect palatability is D-psicose. D-psicose is currently produced using an in vitro enzymatic isomerization of D-fructose, resulting in low yield and purity, and therefore requiring substantial downstream processing to obtain a high purity product. This has made adoption of D-psicose into products limited and results in significantly higher per unit costs, reducing accessibility to those most in need. Here, we found that Escherichia coli natively possesses a thermodynamically favorable pathway to produce D-psicose from D-glucose through a series of phosphorylation-epimerization-dephosphorylation steps. To increase carbon flux towards D-psicose production, we introduced a series of genetic modifications to pathway enzymes, central carbon metabolism, and competing metabolic pathways. In an attempt to maximize both cellular viability and D-psicose production, we implemented methods for the dynamic regulation of key genes including clustered regularly interspaced short palindromic repeats inhibition (CRISPRi) and stationary-phase promoters. The engineered strains achieved complete consumption of D-glucose and production of D-psicose, at a titer of 15.3 g L-1, productivity of 2 g L-1 h-1, and yield of 62% under test tube conditions. These results demonstrate the viability of whole-cell catalysis as a sustainable alternative to in vitro enzymatic synthesis for the accessible production of D-psicose."
Fig. 1: Strategies for the biosynthesis of D-psicose.
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