Dipartimento di Scienza degli Alimenti, Universita` degli Studi di Napoli Federico II, Portici, Italy.
Appl Environ Microbiol. 2012 Apr;78(8):2737-47. doi: 10.1128/AEM.07302-11. Epub 2012 Feb 3.
After isolation from different doughs and sourdoughs, 177 strains of lactic acid bacteria were screened at the phenotypic level for exopolysaccharide production on media containing different carbohydrate sources. Two exopolysaccharide-producing lactic acid bacteria (Lactobacillus curvatus 69B2 and Leuconostoc lactis 95A) were selected through quantitative analysis on solid media containing sucrose and yeast extract. The PCR detection of homopolysaccharide (gtf and lev) and heteropolysaccharide (epsA, epsB, epsD and epsE, and epsEFG) genes showed different distributions within species and strains of the lactic acid bacteria studied. Moreover, in some strains both homopolysaccharide and heteropolysaccharide genes were detected. Proton nuclear magnetic resonance spectra suggest that Lactobacillus curvatus 69B2 and Leuconostoc lactis 95A produced the same exopolysaccharide, which was constituted by a single repeating glucopyranosyl unit linked by an α-(1→6) glycosidic bond in a dextran-type carbohydrate. Microbial growth, acidification, and viscoelastic properties of sourdoughs obtained by exopolysaccharide-producing and nonproducing lactic acid bacterial strains were evaluated. Sourdough obtained after 15 h at 30°C with exopolysaccharide-producing lactic acid bacteria reached higher total titratable acidity as well as elastic and dissipative modulus curves with respect to the starter not producing exopolysaccharide, but they showed similar levels of pH and microbial growth. On increasing the fermentation time, no difference in the viscoelastic properties of exopolysaccharide-producing and nonproducing samples was observed. This study suggests that dextran-producing Leuconostoc lactis 95A and Lactobacillus curvatus 69B2 can be employed to prepare sourdough, and this would be particularly useful to improve the quality of baked goods while avoiding the use of commercially available hydrocolloids as texturizing additives.
从不同的面团和酸面团中分离后，在含有不同碳水化合物来源的培养基上对 177 株乳酸菌进行表型筛选，以生产胞外多糖。通过在含有蔗糖和酵母提取物的固体培养基上进行定量分析，选择了 2 株产胞外多糖的乳酸菌（弯曲乳杆菌 69B2 和乳球菌 95A）。聚酶链反应检测同多糖（gtf 和 lev）和杂多糖（epsA、epsB、epsD 和 epsE 以及 epsEFG）基因在研究的乳酸菌种内和株间的分布不同。此外，在一些菌株中同时检测到同多糖和杂多糖基因。质子核磁共振谱表明，弯曲乳杆菌 69B2 和乳球菌 95A 产生的胞外多糖相同，由单个重复的吡喃葡萄糖基单元通过α-（1→6）糖苷键连接构成，属于葡聚糖型碳水化合物。评估了产胞外多糖和非产胞外多糖乳酸菌菌株制备的酸面团的微生物生长、酸化和粘弹特性。在 30°C 下发酵 15 小时后，产胞外多糖的乳酸菌制备的酸面团的总可滴定酸度以及弹性和耗散模量曲线均高于不产胞外多糖的起始菌，但它们的 pH 和微生物生长水平相似。随着发酵时间的增加，产胞外多糖和非产胞外多糖样品的粘弹特性没有差异。本研究表明，产葡聚糖的乳球菌 95A 和弯曲乳杆菌 69B2 可用于制备酸面团，这对于改善烘焙食品的质量特别有用，同时避免使用商业可得的水胶体作为质构添加剂。
