Abstract
An exopolysaccharide (EPS) producing strain CC30 was isolated from raw milk and identified as Streptococcus thermophilus with morphological and 16S sequencing analysis. The strain was shown to produce 1.95 g/L of EPS when grown in skim milk lactose medium at 30°C by increasing the viscosity of the medium. The EPS was isolated and purified, and it was shown to consist of glucose and galactose in 1 : 1 ratio, with molecular weights ranging from 58 to 180 kDa. FTIR spectroscopy indicated the EPS to have amide, hydroxyl, and carboxyl groups. Under Atomic Force Microscopy, EPS showed spike-like lumps of EPS. Scanning Electron Microscopy (SEM) studies showed that it had irregular lumps with a coarse surface. The EPS displayed pseudoplastic nature. Thermogravimetric analysis (TGA) reported a degradation temperature of 110.84°C. The purified EPS exhibited reducing activity, hydrogen peroxide radical scavenging activity, and emulsification activity. The results of the present study indicated that EPS producing Streptococcus thermophilus could serve as a promising candidate for further exploitation in food industry.
Highlights
Many types of polysaccharides produced by algae, plants, and bacteria are most commonly used as texturizers, emulsifying agents, or viscosifiers in the food additives and to increase the consistency and texture of the fermented milk
The phylogenetic tree produced revealed that S. thermophilus strains could be clustered into three distinct branches, of which two branches are split into two subbranches
EPS produced by A. pullulans showed maximum stability with olive oil (56%) [39] whereas the EPS produced by Bacillus megaterium showed the highest emulsion index with coconut oil (76%) [40]
Summary
Many types of polysaccharides produced by algae, plants, and bacteria are most commonly used as texturizers, emulsifying agents, or viscosifiers in the food additives and to increase the consistency and texture of the fermented milk. During the last decade there was an increasing attention in the production of exopolysaccharide (EPS) by the lactic acid bacteria (LAB) which have been shown to play an important role in the prevention of whey separation (syneresis), during manufacturing of yoghurt. Because of their GRAS (Generally Regarded as Safe) status and rheological properties, the use in food fermentation could lead to the production of safe and natural products with improved stability. The EPS produced from a strain of S. thermophilus CC30 was characterized by Gas Chromatography-Mass Spectrometry (GC-MS), Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), Thermogravimetric Analysis (TGA), and rheology for its potential application in the food
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