Studies On Preparation Of Freeze-dired Lactic Acid Bacteria Sourdough Starters And Their Effects On Chinese Steam Bread

Freeze-dried lactic acid bacteria sourdough starter can improve the nutritional value ofproducts, flavor, texture, and slow down the aging effects. It also avoid the uncontrollablesecurity, large differences in the quality, story and transport as lacking of reference indicatorsand other issues which could occur while using the traditional sourdough in Chinese steamedbread (CSB). The preparation of freeze-dried L. plantarum sourdough starter (LPSS), L.sanfransiscensis sourdough starter (LSSS), and their effects on CSB were studied in thispaper.Firstly, the effect of lactic acid bacteria on the dough system was analyzed by means ofscanning electron microscope (SEM). Through the fermentation pH value, viable count,freeze-drying survival rate, and sds-page measurement, the influence of dough yield (DY)value and the effect of trehalose and sucrose of lactic acid bacteria (LAB) survival rate andactivity protection were studied. The results indicated that starch grain reunion phenomenoncan be observed obviously in sourdough fermented with LAB. The increase of DY valuespeeded up the acidification rate, but slightly reduced viable count of fresh sourdough, and thebest freeze-drying survival rate,48.23%for LPSS and45.33%for LSSS, were obtained at DY250. Storage stability results showed that, the survival rate was stable during90days storageunder4°C by adding trehalose and sucrose as protectants of freeze-dried sourdough starters,and the protective effect of trehalose was better than that of sucrose.Secondly, the dough dynamic rheological properties, as well as fermentation productionprocess pH, titratable acidity (TTA), gas production and holding capacity, and the rate of cellgrowth in CSB dough were studied, while LPSS and LSSS were added.With the increase ofthe amount of sourdough starters was added, the elastic modulus(G’) value decreases, whilethe viscous modulus (G’’) had no significant change in frequency change process; thegelatinization started at temperature of60°C (control group) was elevated to65°C, the peaktemperature also increased in temperature scanning process. During fermentation,the volumeof dough and gas production peak increased, the gas holding capacity of dough added LPSSwas better than LSSS, and dough with10%LPSS had a maximum gas production peak andvolume peak.Yeasts and lactic acid bacteria can grow synergistically, where in the appearanceof10%LPSS, both LP and yeast had higher growth rates.Thirdly, the quality and flavor characteristics of CSB were evaluated by using sensoryevaluation combined with GC-MS, texture instrument. CSB with10%LSSS got the highestscore (81.3), while with10%LPSS reached the lowest score (75.23). So the amount of itshould be added in moderation. The specific volume and the flavor were improved bysourdough starters, and at the same time the hardness of CSB were reduced, did not haveharmful flavor components which contained in traditional sourdough.Finally, the effects of sourdough starters on aging properties, hardness, elasticity, color,moisture, amylose and amylopectin retrogradation indicators, of CSB were measured during4days stored under4°C.The moisture content of CSB did not change significantly, as well asLPSS or LSSSwas added, during the storage period. In the case of adding sourdough starter, the increase of hardness, b*values (both in skin and crumb), amylopectin retrogradation andcrystallization of amylose in CSB were delayed. With the increase of added amount, the LSSShad better effects. Therefore, the LPSS and LSSS have good potential and application valuesin CSB.