Inhibition of yeast growth in grape juice through removal of iron and other metals

Growth of microbial spoilage organisms requires an adequate supply of essential trace metals. Removal of iron and other metals from grape juice with chelating resins was studied with a view to obtaining microbiological stability without the addition of chemical preservatives. Several chelating resins were examined for their iron and other metal removal efficiencies. High affinity and selective removal of essential trace microbial nutrient metals was investigated for its effects on the growth of Saccharomyces cerevisiae in grape juice. Iron removal from grape juice was studied in terms of removal kinetics and completeness. Iron removal was fast, and almost all of the iron was removed within 1 h. The chelating resins were able to easily remove the iron to a level below 5 p.p.b. in a batch process, and with a column process the iron concentration could be reduced to about 1 p.p.b. Other metals significantly removed by the resins in the treatment were Cu, Mn, Mg, Ca and Zn. Levels of Na and K were also significantly affected by the treatments. Grape juice with an iron content below 3 p.p.b. could be prepared by using the chelating resins. Preliminary evaluation indicated that the growth of S. cerevisiae, a bottom wine yeast, was substantially inhibited in the treated grape juice. The inhibitory effect could be abolished by re-addition of the removed metals.