Dissertation
Dissertation > Industrial Technology > Light industry,handicrafts > Food Industry > Food processing industry > Cereal system of food > Flour-made products

Effects of Food Matrixes on the Dynamic Diversity of Yeasts and Lactic Acid Bacteria during Sourdough Fermentation

Author XiongShunQiang
Tutor XiongYongHua; WeiHua
School Nanchang University
Course Microbiology
Keywords Viable count Denaturing gradient gel electrophoresis Sourdough Dynamic changes Yeast Lactic acid bacteria
CLC TS213.2
Type Master's thesis
Year 2012
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Sourdough food is a kind of traditional cereal fermented food, served as partial daily food in Egypt and ancient Romans as early as1500B.C. Recently, with the improvement of living standards people pay much more attention on green and healthy food, and thus the sourdough foods are selected as the suitable candidate due to its plentiful nutrional value, unique taste, benificial physiological effects as well as functional properties.In this paper, five different matrix compositions (wheat, wheat+rice, wheat+buckwheat, wheat+sweet potato, wheat+corn) were used to investigate their impacts on the species and number of cell counts i.e. dynamic diversity of lactic acid bacteria (LAB) and yeasts by conventional cultivation method and denaturing gradient gel electrophoresis (DGGE) as well as16S rDNA sequencing. Moreover, the antioxidant and antimicrobial activity of LAB isolated from sourdoughs were also evaluated.The results showed that different matrixes had largely effect on the cell amount of yeast in the sourdough, while less on their species, which was mainly dominated by Saccharomyces cerevisiae in starter culture. Compared with that of yeast, the cell amount of lactic acid bacteria in sourdoughs was stable during the whole fermentation process, the highest biomass of LAB was1010CFU/mL, however, their species pattern was quite different among different matrixes groups, and the highest similarity of species composition was only80%, Most of the monitored LAB were mainly Lactobacillus helveticus, L. acetotolerans, L. plantarum, L. reuteri and Weissella confusa. The pH and Total Titratable Acids (TTA) of the five matrixes were also been evaluated simultaneously, showing that the pH value decreased as the fermentation last and reached stability phase on7tn day (around3.5); the TTA value was greatly affected by different fermentation matrix,27.5mL of TTA was achieved by the combination of wheat+buckwheat, while less than14mLof TTA in others.For further evaluation of the effects of LAB from sourdough on the fermentation of dough,23isolates were screened out by traditional separation method, classified as10species by sequencing. Thereof6of10was cataloged into LAB i.e. L. plantarum, L. fermentum, Enterococcus faecium, L. reuteri, Pediococcus acidilactici and W. confusa. The antioxidant and antimicrobial tests demonstrated that all6LAB isolates had prounced antioxidant and antimicrobial capability; thereof L. reuteri had the highest antioxidant activity, while P. acidilactici and E. faecium showed an excellent antimicrobial activity.This study provided initial data and foundation for further investigation of the interaction menchanisims of sourdough fermentated food.

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