Factors influencing autolysis of Saccharomyces cerevisiae cells induced by pulsed electric fields

The influence of temperature (7-43 °C), pH (3.5-7.0) and ethanol concentration (6-25%) on PEFinduced autolysis and the release of mannose from Saccharomyces cerevisiae was investigated. Changes in the release of intracellular compounds absorbing at 260 nm and 280 nm depended on storage conditions and differed among untreated and PEF-treated cells. For untreated cells, the increase of the Abs260 and Abs280 values during 3 weeks of storage was very low when incubated in media of different pH, different ethanol concentrations, or at 7° and 25 °C. Conversely, Abs260 and Abs280 values progressively increased for PEF-treated cells stored under the same conditions. Although the PEF treatment intensity was the same in all cases, the amount of intracellular material released depended on incubation conditions. Except for cells stored at 43 °C, for which the concentration of mannose in the media after 21 days was around 90 mg L−1, the amount of mannose released from untreated cells after 21 days of storage was lower than 60 mg L−1 under all other conditions assayed. After the same incubation time, the amount of mannose released from PEF treated cells ranged from 80 mg L−1, when they were stored in media with 25% ethanol, to 190 mg L−1 when they were stored at 43 °C. Interaction among assayed factors affecting mannose release was investigated in a medium containing 10% ethanol (v/v) and pH 3.5 for 21 days. Although the interaction of both factors delayed mannose release, the medium containing PEF-treated yeasts had approximately twice the amount of mannoproteins as those containing untreated yeasts.