Screening Of Microorganisms From Traditional Starter Cultures And Their Effects On The Quality Of Mantou

Mantou fermented by traditional starter cultures is very popular by people because of having unique flavour. But their industrial production and application are facing a series of problems. So this paper will study microorganisms in traditional starter cultures of Mantou and their effects on quality of Mantou. The aim is to provide reference for industrial production of traditional starter cultures of Mantou and traditional Mantou.Firstly, it study effects of commercial starter cultures including active dry yeast and Sweet Wine Koji, which is rhizopus, on the quality of Mantou. Through comparing gas production and leavening state of dough, and sensory evaluation scores and texture parameter of Mantou, the result shows that the fermentation property of dough and quality of Mantou fermented by different yeasts were different. On the basis of Mantou dough fermented by active dry yeast, Sweet Wine Koji and/or laomiantuan, which were fermented by lactic acid bacteria(LAB), were added when mixing Mantou dough, through comparing sensory quality of samples fermented by different strains, it found that organoleptic quality of Mantou which was added Sweet Wine Koji is better than others, such as sweeter and more aromatic.Because different commercial starter cultures have different effects on quality of Mantou, the next task is to screen of microorganisms from traditional starter cultures of Mantou. Microorganisms of 15 LABs and 15 yeasts were obained through separating, screening and re-screening, then yeast Sq4-3 and 5 representative LABs were choosed to carry out experiments of mix-fermenting Mantou. The result showed that different LAB has different effect on quality of Mantou, and Mantou fermented by sourdough adding Sq2.2 have the highest sensory score which is 7.56 points. Then it is to optimize laomiantuan process of fermentation time and temperature, through single factor experiments and orthogonal experiment it found that sensory score is higher when fermentation time and temperature are 24h and 24℃respectively.Flavor is an important indicator when evaluating the quality of Mantou, so the following is to study volatiles in Mantou. Simultaneous distillation extraction (SDE) and gas chromatography mass spectrometry (GC-MS) were choosed to extract, separate and identificate volatiles of Mantou respectively, and experiment conditions were defined. Through comparing volatiles of Mantous fermented by four active dry yeasts, it found the overall flavor are about the same and exist difference among samples, because volatiles are all including alcohols, esters, aldehydes, ketones, benzenes and acyl groups, but constituents and contents of volatiles in Mantous which fermented by different yeasts were different. Then it was further studied that the effect of different strains on quality of Mantou through adding laomiantuan fermented by different strains. It found from researching of Saccharomyces cerevisiae (CGMCC 2.0562 ) and Lactobacillus plantarum (CGMCC 1.0510) that compositions and contents of volatile in laomiantuan change with fermentation time; the production of volatiles in laomiantuan and laomianMantou were different when fermented by different strains, and co-fermentation by S. cerevisiae and L. plantarum have positive effect on production of volatiles. Through studying of yeast Sq4-3, LAB Sq2.2 and Sq3.1, which were screened from traditional starter cultures of Mantou, it also found that fermentation by different strains have different effects on the production of volatiles.The production of volatiles in Mantou was affected by microorganism metabolism, and sugar metabolism is an important part of microbial metabolism. Finally taking Saccharomyces cerevisiae (CGMCC 2.0562)and Lactobacillus brevis (CGMCC 1.0579) for example, sugar metabolism of microorganisms was studied using high efficiency liquid chromatography-evaporative light scattering (HPLC-ELSD) to detect the soluble sugar during laomiantuan and Mantou fermentation. The result showed that concentrations and regulation change of soluble sugars were different when fermented by different strains. Therefore, we believe that starter culture also affect the production of volatiles in Mantou.