Date of Award
Master of Science
Food Science and Technology
J.R Mount, Ivon McCarty
Sodium metabisulfite (sulfite), butylated hydroxyanisole (BHA), potassium sorbate (sorbate) and tertiary butylhydroquinone (TBHQ) were evaluated for their antimicrobial effects on Saccharomyces cerevisiae and Saccharomyces cerevisiae NRRL Y567 in apple and grape juice. Combinations of sulfite with BHA, BHA with sorbate and sulfite with sorbate were tested to determine if the compounds interacted in an additive, synergistic or antagonistic manner.
A modification of the tube dilution technique outlined by Barry (1976) was used to evaluate antimicrobial efficacy. Tubes of the appropriate juice containing increasing concentrations of an antimicrobial or antimicrobial combination were inoculated with a 24 hr yeast culture grown in the juice. These tubes were then incubated 24 hr at 32°C. Tubes showing no visible growth after this time were considered to contain a concentration of antimicrobial (s) which was inhibitory to the yeast. Tubes with antimicrobial free juice were then inoculated with juice from the tubes showing no growth and incubated as before. Antimicrobial concentrations that prevented visible growth in these tubes after this additional 24 hr incubation were considered to be lethal to the yeast.
The individual antimicrobials inhibited S. cerevisiae in apple juice at the following concentrations: 80 μg/ml sulfite, 160 μg/ml BHA, 500 μg/ml sorbate and 600 μg/ml TBHQ. In grape juice against this yeast, the inhibitory concentrations were 80 μg/ml sulfite, 140 μg/ml BHA, 600 μg/ml sorbate and 900 μg/ml TBHQ. When these compounds were used against S. cerevisiae NRRL Y567 in apple juice, levels of 100 μg/ml sulfite, 120 μg/ml BHA, 400 μg/ml sorbate and 600 μg/ml TBHQ effectively inhibited growth. The corresponding values for grape juice were 100 μg/ml sulfite, 160 μg/ml BHA, 400 μg/ml sorbate and 1000 μg/ml TBHQ. The lethal concentration in apple and grape juice against S. cerevisiae for sulfite was 80 μg/ml and for BHA was 160 μg/ml. Against S. cerevisiae NRRL Y567, the lethal concentration in both juices for sulfite was 120 μg/ml and for BHA was 160 μg/ml. None of the concentrations of sorbate or TBHQ were lethal to the yeast.
In the combination testing, all combinations proved to be additive (P>0.05) in nature in both juices and with both organisms, except for the sulfite-sorbate combination in grape juice against S. cerevisiae NRRL Y567. This interaction was considered to be antagonistic in nature since higher concentrations of sulfite were needed to cause inhibition after 24 hr than in other sulfite-sorbate combinations. It was concluded, that combining the antimicrobials would allow for a reduction in sulfite concentration but no significant gain in antimicrobial activity would occur.
Knox, Tina L., "Evaluation of selected compounds in fruit juices as sodium metabisulfite replacements or adjuncts. " Master's Thesis, University of Tennessee, 1984.