| Antimicrobial deprived plant has received investigator’s attention as preservatives for their broadspectrum antimicrobial activity and healthy and natural advantages. Berries are in rich of phenolic compounds and organic acid. The antimicrobial properties of several kinds of berry juice including strawberry, blueberry, pomegranate, raspberry, sea-buckthorn, and haskapberry were preliminarily investigated in this paper. The antibacterial effect of cranberry juice and pomegranate juice were further studied and the impact factors were discussed. Minimum inhibitory concentration(MIC) of berry juices and methanol extracts were identified by using Bioscreen C. The application of natural extract to inhibit the growth of E. coli inoculated in blueberry juice was investigated. The fractions were isolated from blueberry and haskapberry, and their bacteriostatic properties were studied. The purpose of this study is to provide the theoretical base for development and application of small berry as natural antimicrobials.Results showed that the antimicrobial effects of cranberry or pomegranate juice were dependent upon the concentration of juice, culture conditions(temperature, matrix, and time), as well as bacterial species tested. Increased juice concentration resulted in greater antimicrobial effect. Both tested bacteria were more effectively killed in the distilled water(DW) systems than in the optimum broth, and L. innocua was more sensitive to cranberry juice compared to E. coli in DW systems. Low pH value and other phenolic compounds in cranberry juice contributed to the antimicrobial effect.By using Bioscreen C to monitor the growth curve of bacteria tested, MIC of different juices and methanol extracts were found. The results indicated that MICs of juices under 37 oC and 25 oC against L. innocua are same, the values of juices are as follows: 7.5% for haskapberry and cranberry, 20% for pomegranate and strawberry, and 30% for blueberry. The results of methanol extract are as below: 20 mg/ml for haskapberry, 30 mg/ml for sea-buckthorn and raspberry, and 60 mg/ml for blueberry and strawberry. MIC of different juices and methanol extracts against E. coli at 25 oC are the same with theirs against L. innocua. But MICs against E. coli under 37 oC is higher than theirs at 25 oC.The challenge test of natural extracts against E. coli inoculated in blueberry juice indicated that the extracts from cranberry and pomegranate can significantly decrease the survival of E. coli at 20 oC or 4 oC. Both extracts can be considered to apply in food system as multiple functional preservatives.The antimicrobial experiment of fraction from blueberry showed that extraction, total phenolics, total flavonoid, anthocyanin, heteropolymer, and proanthocyanidin possessed antibacterial properties on L. innocua and E. coli, and L. innocua is more susceptible to these fractions than E. coli, which has the lower MIC and minimum bacteriocidal concentration(MBC). The permeability of the bacteria cell membrane were increased by the treatment with fractions. The leakage of cytoplasm content results in the damage and the death of bacteria.Phenolic acids in haskapberry can significantly inhibit the growth of L. innocua and E. coli from 2.5 to 10.0 mg/ml. The fractions of extracts, total phenolics, chlorogenic acid, and total flavonoid have the MIC against L. innocua between 10 and 20 mg/ml. E. coli is more resistant to the fractions than L. innocua. Fluorescence analysis indicated that the damage of cell membrane with fraction treatment can be found and the permeability was increased. |
PDF Full Text Request