EXOPOLYSACCHARIDE PRODUCTION BY DAIRY LACTIC ACID BACTERIA: I. ISOLATION, CHARACTERIZATION OF EPS-PRODUCING CULTURES AND EFFECT OF MEDIUM SUPPLEMENTATION AND-CULTURE CONDITIONS | ||||
| Journal of Agricultural Chemistry and Biotechnology | ||||
| Article 2, Volume 31, Issue 9, September 2006, Page 5965-5998 | ||||
| Document Type: Original Article | ||||
| DOI: 10.21608/jacb.2006.222540 | ||||
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| Authors | ||||
| RJ. Refae1; G. Amln1; H. A. Murad2; Sahar H. Mohamed2 | ||||
| 1Agric. Microbiology Dept, Fac. of Agriculture, Cairo University, Giza. | ||||
| 2Food Tech and Dairy Sci. Dept. National Res. Center. Dokkl, Giza | ||||
| Abstract | ||||
| Two hundred and ten lactic acid bacterial cultures were isolated from 120 samples of different types of raw milk, traditional Egyptian fermented milk, cheese and butter. isolates were screened visually on the basis of colony ropiness for exopoiysaccharides (BPS) production on modified MRS agar medium containing glucose. sucrose, fructose, maltose or lactose. Among the 210 isolates tested. 16 (7.6%) exhibited potential activity for EPS production. Fifteen isolates metabolized only two carbohydrates; glucose and sucrose. Sucrose was an excellent substrate for abundant EPS synthesis. Compared with other carbohydrate sources, growth on lactose. maltose or fructose did not synthesis any EPS. One isolate was able to metabolize four sugars: lactose. maltose, glucose and sucrose. Based on their phenotypic features, the 16 BPS-producing isolates were identified as Leuconostoc mesenteroides (15 strains) and Lactobaciilus fermentum (one strain). The quantification of EPS was determined on different complex solid media. The amount of EPS produced was affected by the carbohydrate source. The EPS production increased with increasing sucrose concentration. Whey permeate agar medium containing 4 % sucrose supported the highest production of 6.9-16 g l‘ , depending upon Leuconostoc strain examined. suggesting that whey permeate can be used as cheap medium ingredients for EPS production. Addition of 0.5 or 1 % yeast extract as nitrogen source to whey permeate agar resulted in promising yields of 390 mg l" and 610 mg l“ by Laciobecillus strains, indicating that yeast extract can provide the nitrogen requirements. Supplementation of whey permeate medium with 5 % lactose had significant effect on EPS production by Leuc. mesenteroides strains only in rare occasions. suggesting that the natural lactose present in whey permeate might not be the limiting factor stimulating E'PS production and emphasizes the importance of other permeate components for inducing EPS formation. While the optimum pH (6.5) for EPS production coincided with those for optimal growth, the greatest EPS production was obtained at incubation temperature (25 “0) lower than those (30 ‘0) for optimal growth. 0f the all nitrogen sources tested, casein hydrolysate (0.4 %) had the highest significant influence on both bacterial biomass yield and EPS production. The addition of salts largely increased the EPS production and a strong positive interaction was observed between amino acids and salts. The extraordinary EPS production of 11000 - 25730 mg l" was obtained using Leuc. mesenteroides in the culture medium containing vitamins, amino acids and salts. Analysis of monosaccharide composition of EPS produced by Leuc. mesenteroides strains 10. 12 and 16 revealed that the polymers produced were neutral homopolysacchan'des containing only glucose and had high molecular weights of 289.1 x 10°, 263 x 10° and 221.3 x 106 De. respectively. The concentration of glucose in the isolated dried EPS was estimated to 50, 58 and 32%. respectively. A positive relationship between EPS concentration and viscosity was observed. | ||||
| Keywords | ||||
| Lactic acid bacteria; isolation; identification. exopolysaccharides; whey " permeate; Leuconostoc; Lectobaciilus. ct‘ilture conditions; medium supplementation | ||||
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