The effect of preservatives on the sterility of microorganisms introduced into different fruit juices.
Basil C. Nzeako, Sheikha Al-Hashmi
Med Sci Monit 2006; 12(5): BR179-186
Available online: 2006-05-01
Background: The aim of this study was to investigate the degree of sterilityof some fruit juices post manufacture and to determine how effective the preservatives in them aid thekilling of some microorganisms introduced into them. Material/Methods: Blackcurrant/raspberry, apple,guava, orange, mango, and mixed fruits were each checked for sterility by inoculating 100 microl separatelyin tryptone soy broth, Robertson's cooked meat, and Sabouraud broth and incubating for growth for 72hours at 37 degrees C. Twenty-milliliter aliquots of each juice were subsequently kept in a 37 degreesC water bath and inoculated separately with S. aureus, P. aeruginosa, E. coli, and C. albicans. At predeterminedtime intervals, a 1:250 dilution of each juice with the individual organism was made and the dilutionswere plated on blood and Sabouraud plates for viable counts. Each 1:250 dilution was then incubated alongwith the plates. The pH of each undiluted juice was determined. Results: All the juices were found tobe sterile. The growth inhibition exhibited by each juice was bactericidal or bacteriostatic, fungicidalor fungistatic, depending on the type of juice. The pH of the juices varied from 2.53-3.75. Conclusions:We found the juices to be bacteriologically free of organisms associated with food infection. Thoughthe juices were sterile, they could allow the survival of some bacteria and yeasts if these gained accessinto 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.
Keywords: Candida albicans - growth & development, Beverages - microbiology, Antifungal Agents - pharmacology, Anti-Bacterial Agents - pharmacology, Colony Count, Microbial, Escherichia coli - growth & development, Food Microbiology, Food Preservatives - pharmacology, Fruit, Hydrogen-Ion Concentration, Oman, Pseudomonas aeruginosa - growth & development, Staphylococcus aureus - growth & development