Mechanisms of fructose-to-mannitol conversion in citrus juice fermented by fructophilic Leuconostoc mesenteroides.

Citrus juice is globally popular, yet its high sugar levels raise health concerns. Fructophilic lactic acid bacteria (FLAB) can lower sugar content by producing mannitol, thereby preserving sweetness during in situ fermentation. This study identified a Leuconostoc mesenteroides strain that converts fructose to mannitol with a yield of 0.56 ± 0.02 g/g. During citrus juice fermentation, sugar content was reduced by 51.45%, and 45.75 ± 1.39 g/L of mannitol was produced, with acidity effectively controlled. Other sugar alcohols, including sorbitol, galactitol, and allitol, were accumulated, simultaneously depleting D-arabinose, L-xylose, and solatriose. Furthermore, it enhanced α-glucosidase inhibitory activity and promoted the synthesis of bioactive compounds, including hydroxytyrosol, epigoitrin, and nicotinamide. Mannitol biosynthesis during orange juice fermentation is regulated by the phosphotransferase system (PTS), with the upregulation of a repressor open reading frame sugar kinase (ROK) family protein serving as a critical auxiliary mechanism. This study provides a viable strategy for developing low-sugar and functional citrus juice beverages.