SORBITOL SYNTHESIS FROM A LACTOBACILLUS CASEI FOOD-GRADE STRAIN USING METABOLIC ENGINEERING

Sorbitol is a sugar alcohol that is assumed to have important physiological properties for human health. It could replace high-calorie sugars such as glucose, lactose or sucrose in food products with equivalent sweetness and taste. The synthesis of sorbitol in situ during fermentation of dairy products may result in a good strategy to obtain fermented products with extra health-promoting value. A food-grade recombinant strain of Lactobacillus casei (BL232) was constructed by the integration of a D-Sorbitol-6-phosphate dehydrogenase-encoding gene (gutF) in the chromosomal lactose operon. gutF expression followed the same regulation as that of the lac genes, that is, repressed by glucose and induced by lactose. BL232 cells were induced with lactose, and using 13C-nuclear magnetic resonance analysis, sorbitol was detected by addition of glucose to resting cells. Inactivation of the L-lactate dehydrogenase gene in BL232 led to higher sorbitol production, suggesting that the novel route provides an alternative pathway for NAD+ regeneration. Since sorbitol is not absorbed in the small intestine, it could reach the colon and there it could selectively stimulate the multiplication or activity of beneficial bacteria. Results showing the influence of sorbitol on the intestinal microbiota of rats will be presented