Abstract
The rising global population continues to threaten the world’s food security. The discovery of new technologies to produce food of nutritional and functional properties is urgently needed. One beneficial food to humans of known nutritional value is the prebiotic levan. To address the problem, the present work is aimed at isolating levansucrase enzyme-producing microorganisms from traditional fermented food in Thailand. Bacterial colony morphology was observed for mucoidal consistency on culture plates. Isolated colonies were characterized morphologically by gram staining methods. Dinitrosalicylic acid (DNS) and thin-layer chromatography (TLC) reported the highest microbial enzyme activity of 8.51 IU/ml at 12 hours via hydrolysis and frutotransferase activities. Structural characterization of levan via Fourier-transform infrared spectroscopy (FTIR) and 1H and 13C nuclear magnetic resonance (NMR) spectroscopy showed β-(2,6)-fructofuranose linkages. The highest enzyme activity was exhibited by bacterium B-6 identified as Bacillus siamensis NR 11274.1 based on the 16s rDNA gene sequence analyses. Thus, the isolated bacterium from the traditional food was confirmed to produce levansucrase enzyme of high industrial importance for the synthesis of levan as a functional food.
Highlights
Exopolysaccharides (EPSs) have been widely utilized in the food industries and dairy products as functional ingredients due to their multifunctional properties as viscosifying [1], stabilizing [2], emulsifying [3], gelling [4], and waterbinding agents [5]
Levansucrase enzyme biosynthesis in gram-positive bacteria includes enzyme accumulation into the periplasmic space and by the excretion of the enzymes out of the cell into the surrounding environment by the cleavage of a signal peptide, whereas in gramnegative bacteria, the signal peptide pathway initiates the secretion of levansucrase into the outer environment [49]
The results showed that the enzyme activity of the three bacterial strains, B-2, B-4, and B-6, synthesized fructans shown at a bottom spot by fructotransferase activity along with the hydrolysis activity exhibited in the spots of glucose and fructose
Summary
Exopolysaccharides (EPSs) have been widely utilized in the food industries and dairy products as functional ingredients due to their multifunctional properties as viscosifying [1], stabilizing [2], emulsifying [3], gelling [4], and waterbinding agents [5]. The consumption of prebiotics has been reported to improve health by metabolizing the products by the intestinal microbiota in the likes of Bifidobacteria and Lactobacilli species [10, 11]. These microbiota consume the EPSs to synthesize several products such as short-chain fatty acids [12], lactic acid, and peptides [13]. The metabolized products are found to possess various beneficial effects in the intestinal environment, such as in International Journal of Food Science maintaining normal luminal pH in the colon, in growth stimulation of the lactic microflora in the human gastrointestinal tract, and in the production of antimicrobials against pathogens [14, 15] [16]. The recommended intake of prebiotics to confer health benefits should be followed as in inulin (8-40 g/day, 15-64 days) or fructooligosaccharides (FOSs) (4-12.5 g/day, 8-12 days) [15, 19]; both are polysaccharides found in fruits and vegetables
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