Identification and characterization of yeasts causing chalk mould defects on par-baked bread

Pichia anomala, Hyphopichia burtonii and Saccharomycopsis fibuligera are spoilage yeasts causing chalk mould defects on par-baked breads packaged under modified atmosphere. The first objective of this study was to identify yeasts isolated from spoiled par-baked breads by means of a RAPD protocol and to determine the dominant spoilers amongst identified strains. The second objective was to determine the effects of water activity (aw) and pH value on the growth rates and lag phase durations of P. anomala, H. burtonii and S. fibuligera. 95% of the yeasts tested were identified as P. anomala and 5% as S. fibuligera, H. burtonii was not detected. In order to investigate the effect of aw and pH the growth of the three yeasts was tested within an aw range of 0.88–0.98 and a pH range of 2.8–8.0. P. anomala was able to grow from pH 2.8 to 8 without a clear optimum. S. fibuligera and H. burtonii showed a pH optimum for growth of 5. The optimum water activity for growth was different for the three strains and varied between 0.96 and 0.98. These growth data were further used to develop secondary models that describe the relationship between aw and the radial or colony growth rate (g, mm/d) or the lag phase duration (λ, d). The identification of the spoilage organisms and a good understanding of the effects of aw and pH on the growth behavior is essential for future development of adequate conservation strategies against chalk mould defects.

► This study identified spoilage yeasts isolated from par-baked breads with RAPD.
► 95% were identified as P. anomala and 5% as S. fibuligera.
► Influence of aw and pH on the growth rate and lag phase were modeled.
► P. anomala grew from pH 2.8–8 without optimum, S. fibuligera had an optimum of 5.
► The optimum aw for growth varied between 0.96 and 0.98.