Lactic acid bacteria (LAB) have been extensively used for centuries as starter cultures to carry out food fermentations and are looked upon as burgeoning "cell factories" for production of host of functional biomolecules and food ingredients. Low-calorie sugars have been a recent addition and have attracted a great deal of interest of researchers, manufacturers, and consumers for varied reasons. These sweeteners also getting popularized as low-carb sugars have been granted generally recommended as safe (GRAS) status by the U.S. Federal Drug Administration (USFDA) and include both sugars and sugar alcohols (polyols) which in addition to their technological attributes (sugar replacer, bulking agent, texturiser, humectant, cryoprotectant) have been observed to exert a number of health benefits (low calories, low glycemic index, anticariogenic, osmotic diuretics, obesity control, prebiotic). Some of these sweeteners successfully produced by lactic acid bacteria include mannitol, sorbitol, tagatose, and trehalose and there is a potential to further enhance their production with the help of metabolic engineering. These safe sweeteners can be exploited as vital food ingredients for development of low-calorie foods with added functional values especially for children, diabetic patients, and weight watchers.

Mannitol is a naturally occurring low calorie sweetener, widely used in the food, pharmaceutical, medicine and chemical industries. In this study mannitol producing strains of Leuconostoc spp. (210) were isolated from a wide array of sources such as raw milk, fermented milks, fermented cereal foods, fruits, vegetables and sugar factory syrup. During initial screening, half of the population of these isolates (105) exhibited ability to produce mannitol to a variable extent. Only 11.4% isolate produced mannitol yield of above 80% (when fructose used @ 50 g/ l). Cultural and environmental factors affecting growth and mannitol production were studied for four high mannitol producing isolates. High mannitol production was favored by high temperature and high pH. Isolates had high osmotic tolerance as these could use fructose concentration as high as 100 g/l in batch culture. Sequencing of 16S rRNA genes of the strains revealed that Ln27, Ln104 and Ln206 were Leuconostoc mesenteroides and Ln92 was Leuconostoc fallax.

Forty standard Lactobacillus cultures were checked for their antifungal properties against nine standard fungi. Yeasts were found to be more resistant than moulds. Lactobacillus brevis NCDC 02 was selected for further studies due to the maximum antifungal activity and proteinaceous nature of antifungal substance production. The optimum production of antifungal substances was at 37°C for 48 h and at the initial pH of 6-7 of the medium. The antifungal substances were heat-and pH-stable. The antifungal substances were found to be hydrophobic and their molecular weight was found to be more than 1 kDa and less than 5 kDa.

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