The Weak Organic Acid Preservative Resistance of Spoilage Yeasts (pp. 445-459)
Authors: (Peter W. Piper, University of Sheffield, Sheffield, UK)
Abstract: There are now some significant concerns over whether the large-scale usage of chemical preservatives in food and beverage preservation is completely safe. As a result, the food industry needs to consider whether its current practices might render it vulnerable to the risk of future litigation and whether it should seek to lower its reliance upon the use of these compounds. A major factor preventing the lowering of carboxylate weak acid preservative levels in many foods and beverages is the high resistance of spoilage yeasts to these preservatives. This chapter summarises some of the safety issues relating to preservative use, also the genetic studies that have unravelled stress responses whereby spoilage yeasts acquire their resistance to these compounds. Resistance to high acetic acid is partly achieved by loss of the plasma membrane aquaglyceroporin channel (Fps1p) through which this acid enters yeast cells. Other carboxylic acid preservatives (propionic, sorbic or benzoic acids) are too large to enter the cell this way but instead penetrate cells at appreciable rates by passive diffusion across the plasma membrane. In baker's yeast (Saccharomyces cerevisiae) resistance to the latter acids is acquired by inducing an activity that actively pumps the preservative from the cell, Pdr12p.