The effect of substrate on the radiation resistance of yeasts isolated from sausage meat.

Abstract

The radiation resistance of a selection of yeasts isolated from sausages was assessed in phosphate-buffered saline and in sausage meat. The yeasts Candida zeylanoides, Debaryomyces hansenii and Trichosporon cutaneum exhibited sigmoidal survival curves in both substrates whilst the more sensitive Sporobolomyces roseus exhibited an exponential survival curve in buffer but a sigmoidal curve in meat. Irradiating C. zeylanoides, D. hansenii and T. cutaneum in sausage meat changed the shape of their survival curves to significantly alter the calculated parameters Ds (the dose in kGy that must be achieved before reduction in numbers occurs) and D10sig (the dose in kGy required after the shoulder to achieve a 1 log cycle reduction in numbers). The Ds values were reduced while higher D10sig values were obtained demonstrating that the sausage meat contributed a protective effect to these yeasts at higher irradiation doses. For the yeast S. roseus, similar numbers of survivors were recovered from both substrates at initial low irradiation doses (0-0.5 kGy) with the protective effect being demonstrated again at higher doses (> 2 kGy). These findings should be considered when defining a commercial process to reduce the numbers of yeasts in these products.