The effect of preservatives on the sterility of microorganisms introduced into different fruit juices

The aim of this study was to investigate the degree of sterility of some fruit juices post manufacture and to determine how effective the preservatives in them aid the killing of some microorganisms introduced into them.

Blackcurrant/raspberry, apple, guava, orange, mango, and mixed fruits were each checked for sterility by inoculating 100 microl separately in tryptone soy broth, Robertson's cooked meat, and Sabouraud broth and incubating for growth for 72 hours at 37 degrees C. Twenty-milliliter aliquots of each juice were subsequently kept in a 37 degrees C water bath and inoculated separately with S. aureus, P. aeruginosa, E. coli, and C. albicans. At predetermined time intervals, a 1:250 dilution of each juice with the individual organism was made and the dilutions were plated on blood and Sabouraud plates for viable counts. Each 1:250 dilution was then incubated along with the plates. The pH of each undiluted juice was determined.

All the juices were found to be sterile. The growth inhibition exhibited by each juice was bactericidal or bacteriostatic, fungicidal or fungistatic, depending on the type of juice. The p[H of the juices varied from 2.53-3.75.

We found the juices to be bacteriologically free of organisms associated with food infection. Though the juices were sterile, they could allow the survival of some bacteria and yeasts if these gained access into them. We found the orange, blackcurrant/raspberry, and mango juices to be bactericidal and fungicidal, while pineapple, mixed fruit, and guava were fungistatic, though with varying bactericidal activities.