The Influence Of Antibiotics On Yogurt During The Fermentation

The objective of this thesis is what is the impact of antibiotics to yogurt compnents in yogurt fermentation and the relationship of yogurt compnents and antibiotics. Three kinds of yogurt compnents will be determined,for example the acidity of yogurt, extracellular polysaccharides and free amino acids.It was observed to the impact of four kinds of antibiotics to yogurt compnents at different time,for example Ceftiofur sodium, potassium penicillin G, streptomycin sulfate and gentamicin sulfate at different concentrations. The thesis was separated to six chapers:In chapter one, the mechanism of yogurt fermention,current yogurt research and the situation of current antibiotics'detection in milk were introduced. The relationship between antibiotics and the yogurt fermentation process was also introduced.In chapter two,the relationship between antibiotics and acidity changes was studied in the yogurt fermentation process. The effects of different antibiotic concentrations and fermentation time on the acidity changes was found. The results show:there is a certain relationship between antibiotic concentration and acidity of yogurt, generally the acidity of milk will become lower as the antibiotic concentration is higher. There is also a relationship between acidity changes and time, generally the acidity of milk will increase as the time of fermention become long.The third part,The relationship between antibiotics and extracellular polysaccharide was studied during yogurt fermentation. The effects of different antibiotic concentrations and fermentation time on the polysaccharide changes was found. The results show:the production of extracellular polysaccharides is inhibited by the antibiotic, the lower the antibiotics'concentration, the higher the content of extracellular polysaccharides. Without antibiotics in samples, there is the reguarity about cell metabolic activity throughout the fermentation process, the content of extracellular polysaccharides is also at a high level consistently. The content is higher than the content of extracellular polysaccharides in sample there is antibiotics.The fourth part, The relationship between antibiotics and the content of free amino acid was studied during the fermentation. The effects of different antibiotic concentrations and fermentation time on the free amino acid changes was found. The results show:the concentration of antibiotics is low in samples, during yogurt fermentation process, the margin of the changing of amino acids'content is not big,the active cycle of the cell is more frequent than the active cycle of the cell in sample there is higher concentration of antibiotics, the time of highest level of amino acids is also earlier than the time in sample there is higher concentration of antibiotics. In samples with high concentration antibiotics, in the early bacteria will use quickly free amino acids,but the time is short. the cell is in metabolic stagnation in the next time,the time is long.The fifth part,The apparent difference between normal yogurt and yogurt with antibiotics was studied. In the fermentation process, there is a big difference in terms of color, smell,taste and the aggregation of macromolecules under the microscope.At last chapter, there are conclusion and discussion.