Kinetic study on the thermal resistance of E. Coli cultivated by soybean extract added medium

The aim of this study is to investigate the thermal stress resistance properties of Escherichia coli (E. coli) to construct the optimized sterilization method for the soybean based foods. The samples of E. coli incubated on the soybean extract added LB medium (test sample) and normal LB medium (control sample) were subjected to high temperature stress of 60°C.Soybean extract which is mainly consisted of protein, lipid and water was prepared to add the LB medium. Under high-temperature condition, the survival behaviors of E. coli inoculated by the control and test sample were indicated by the first-order kinetics. And the thermal resistance of E. coli was significantly enhanced by a soybean extract. Moreover the top, middle and bottom part of soybean extract were prepared by the additional centrifugation of soybean extract. Each part is characterized by lipid, phospholipid, and protein, respectively. The thermal resistance of middle part showed the quite similar behavior to that of whole soybean extract. However, those of top and bottom parts were obviously decreased faster than that of middle part. And a significantly increase of the weight of phospholipid in a cell incubated with the middle part was observed comparing with that of control sample. It is therefore very likely that the thermal resistance of E. coli is enhanced by the effect of phospholipid in soybean extract. Furthermore, under the high pressure stress of 150 and 200 MPa, the survival curve of middle part was obviously slower decrease than control sample. Consequently, results obtained in this paper, are successfully revealed that the addition of phospholipid in soybean extract is strengthened the cell membrane or surface structure of E.coli.