Abstract:

Sodium metabisulfite is commonly used as a food preservative and antioxidant for dried foods, fruit concentrate
juices and fresh fruits. It is the most efficiently preservative for table grape since table grapes are subject to serious water loss
and decay while making the long trip from the vine to tables around the world. Herein, the effects of sodium metabisulfite on
cell viability were explored in the model eukaryote Saccharomyces cerevisiae. The growth curve of yeast cells was measured
by optical density, and cell viability was examined based on methylene blue staining method. Randomly selected views
on the tested yeast cells were monitored under a microscope to determine the number of dead cells and the total number of
scored cells. The results indicated that sodium metabisulfite could inhibit yeast cell growth and division, and even cause
cell death. The toxicity of sodium metabisulfite was increased with increasing concentration and prolonged duration. Either
high concentration for a shorter-term exposure or low concentration for a long-term exposure showed significant toxic
effects on yeast cells. Exposure to 100 to 1 000 μmol/L sodium metabisulfite for 6 h could cause significant cell death, and
both antioxidant ascorbic acid and plasma membrane Ca2+ channel inhibitor LaCl3 blocked sodium metabisulfite-induced
cell death. These results indicated that sodium metabisulfite could cause yeast cell death via reactive oxygen species (ROS)
production and Ca2+ influx. However, the death rate increased in acidic environment. The cell death rate in pH 4.0 treatment
group was higher than that in pH 7.0 treatment group, demonstrating the enhanced sulfur dioxide (SO2) toxicity in acidic
medium. It was found that the pH of waterdrop on the surface of SO2-fumigated table grapes was around 3.5 to 4.0, which
was lower than the control without SO2 fumigation, suggesting that acid environment caused by SO2 fumigation is a way to
prevent infection and prolong the shelf life of table grapes.

Key words: sodium metabisulfite, preservative, yeast cell, growth inhibition, cell death