The potential application of vanillin in preventing yeast spoilage of soft drinks and fruit juices.

The preservative effect of vanillin, the major constituent of vanilla beans, was studied in an apple juice and peach-flavored soft drink. Vanillin activity was tested against Saccharomyces cerevisiae and Candida parapsilosis at 8 and 25 degrees C over an 8-week storage period. Initial results in laboratory media indicated minimum inhibitory concentration values of 17 and 9 mM vanillin for the two yeast strains. Concentrations of 20 and 10 mM vanillin, respectively, were required to achieve complete inhibition of both yeast strains inoculated at a level of approximately 10(4) CFU/ml in the apple juice and peach-flavored soft drink over the 8-week storage at 25 degrees C. These effective levels were reduced to 5 and 1 mM, when the storage temperature was reduced to 8 degrees C. A biocidal effect against both yeasts was observed within 96 h to 8 weeks, with vanillin concentrations of 5 to 40 mM depending on the beverage and the storage temperatures used. The increased activity of vanillin in the peach-flavored soft drink (pH 3.1) in comparison to the apple juice (pH 3.5) is probably a result of the lower intrinsic pH of the former; however, variation in vitamin and mineral levels or the presence of other phenolic compounds between the two drinks might also have contributed to the observed differences. Furthermore, the increased activity at the lower temperature could be linked to the combination of the increased membrane fluidity and the membrane-perturbing action of vanillin. We conclude that vanillin has the potential to preserve fruit juices and soft drinks that are low in both lipid and protein content against S. cerevisiae and C. parapsilosis.