Dynamic Cu(I)/Cu(II) Redox Shuttle for Maltose and Lactose Isomerization under Pulsed Electric Field

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Due to their prebiotic effects, lactulose and maltulose have garnered increasing interest from the food and pharmaceutical industries. Pulsed electric field (PEF) technology can enhance energy use efficiency, particularly in electroactivation, offering a potential means to convert reducing sugars. A specialized PEF-treated design has been developed to facilitate alternative catalyst-driven production of lactulose and maltulose by manipulating the morphology and oxidation states of copper catalysts. Under optimal conditions (4 kV/cm, 50 Hz, and 10 μs for 30 min), remarkable yields of lactulose (55.75%) and maltulose (43.27%) were achieved. Higher conversion rates were observed with an increased PEF treatment electric field strength and pulse width. The yields and selectivities of lactulose and maltulose were not significantly influenced by the frequency. Intriguingly, structural monosaccharides, including glucose, galactose, xylose, and arabinose, were also detected in the isomerization reaction. These findings suggest that PEF, utilizing CuO plates, induces glycoside bond hydrolysis and the conversion of aldose to pentose. Microscopic measurements (high-resolution transmission electron microscopy (HRTEM), high-energy X-ray diffraction (XRD), in situ Raman, and X-ray photoelectron spectroscopy (XPS)) revealed that transient Lewis acid–base pairs formed by the Cu+/Cu2+ shuttle could serve as active sites for reducing sugar isomerization, and DFT simulation further confirmed that the presence of active Cu species could promote the isomerization of lactose and maltose via a lower energy barrier. The PEF process proves to be an economical method for transforming low-value sugars into high-value carbon materials.