Examination of exopolysaccharide produced by Lactobacillus delbrueckii subsp. bulgaricus using confocal laser scanning and scanning electron microscopy techniques

• Published in: Journal of food science Vol. 70; no. 4; pp. M224 - M229
• Main Authors: Goh, K.K.T, Haisman, R.D, Singh, H
• Format: Journal Article
• Language: English
• Published: Oxford, UK Blackwell Publishing Ltd 01.05.2005; Institute of Food Technologists; Wiley Subscription Services, Inc
• Subjects: alkali treatment; Alkalies; Bacteria; Biological and medical sciences; cell aggregates; chemical structure; confocal scanning laser microscopy; culture media; dairy protein; exopolysaccharide; Food industries; Food microbiology; Fundamental and applied biological sciences. Psychology; lactic acid bacteria; Lactobacillus delbrueckii subsp. bulgaricus; lectin; lectins; Microscopy; Milk; polysaccharides; scanning electron microscopy; Lectin; Scanning electron microscopy; Lactic acid bacteria; alkali treatment; Lactobacillus delbrueckii; Extracellular; exopolysaccharide; Alkali; Laser; Bacteria; Lactobacillaceae; microscopy; Polysaccharide
• ISSN: 0022-1147; 1750-3841
• DOI: 10.1111/j.1365-2621.2005.tb07192.x

Exopolysaccharide (EPS) produced by Lactobacillus delbrueckii subsp. bulgaricus NCFB 2483 (2483) was examined using confocal laser scanning microscopy (CLSM) and scanning electron microscopy (SEM) techniques. These microscopy techniques were used to probe the location and distribution of EPS in milk permeate-based media. In CLSM, lectin (SBA) (from Glycine max) Alexa Fluor 488 conjugate was used to stain the EPS. The EPS appeared randomly distributed as aggregates in the culture media. The CLSM technique was simple to perform with minimal sample preparation, was nonintrusive, and allowed in-situ examination of EPS. At high magnifications using SEM, the EPS aggregates appeared as web-like structures distributed through the interstices of the protein matrix. The web-like structures were apparent, especially in the sample treated with Flavourzyme, which hydrolyzed the milk proteins. The formation of the intricate web-like structures could be attributed to the dehydration of the EPS during the critical point drying process of the SEM specimens. The present investigation also found that the 2483 EPS network remained intact at neutral or low pH (approximately 3.9). However, the 2483 EPS was highly susceptible under alkaline pH conditions. Increasing the pH from 8 to 10 appeared to destroy EPS structure as indicated by a loss of its "ropy" characteristics as well as the EPS levels.