Recovery of heat‐stressed yeasts in media containing plant oleoresins

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Abstract
Conner, D.E. & Beuchat, L.R. 1985. Recovery of heat‐stressed yeasts in media containing plant oleoresins. Journal of Applied Bacteriology59, 49–55.Oleoresins from seven plants (allspice, cinnamon, clove, garlic, onion, oregano, and thyme) were tested for their effects on eight genera of sublethally heated food‐spoilage and industrially important yeasts (Candida lipolytica, Debaryomyces han‐senii, Hansenula anomala, Kloeckera apiculata, Lodderomyces elongisporus, Rhodotorula rubra, Saccharomyces cerevisiae, and Torulopsis glabrata). All heat‐stressed yeasts had increased sensitivity to oleoresins in recovery media. Heated cells were most sensitive to cinnamon oleoresin, a lethal effect being observed to concentrations as low as 5 μg/ml. Results indicate that all eight yeasts underwent metabolic and/or structural injury as a result of exposure to elevated temperature. Whilst changes in sensitivity to oleoresins were not the same for all yeasts, it is concluded that the oleoresins may have a pronounced synergistic or additive effect on thermal inactivation of yeasts in foods. Furthermore, carryover of oleoresins in low dilutions of food to enumeration media could adversely influence the recovery of heat‐stressed cells, thus resulting in apparent low populations.