Ghent University, Food2Know, Faculty of Bioscience Engineering, Department of Food Safety and Food Quality, Laboratory of Food Microbiology and Food Preservation, Coupure Links 653, 9000 Ghent, Belgium.
Food Microbiol. 2011 Aug;28(5):1019-27. doi: 10.1016/j.fm.2011.02.002. Epub 2011 Feb 23.
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 (a(w)) 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 a(w) and pH the growth of the three yeasts was tested within an a(w) 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 a(w) 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 a(w) and pH on the growth behavior is essential for future development of adequate conservation strategies against chalk mould defects.
异常汉逊酵母、伯顿毕赤酵母和纤维侧耳酵母是导致充气包装半烘烤面包出现白垩模具缺陷的腐败酵母。本研究的第一个目的是通过随机扩增多态性 DNA (RAPD) 技术鉴定污染半烘烤面包的酵母，并确定鉴定出的优势腐败酵母。第二个目的是确定水分活度 (a(w)) 和 pH 值对异常汉逊酵母、伯顿毕赤酵母和纤维侧耳酵母生长速率和延迟期的影响。测试的酵母中，95%被鉴定为异常汉逊酵母，5%为纤维侧耳酵母，未检测到伯顿毕赤酵母。为了研究 a(w) 和 pH 值的影响，在 a(w) 范围为 0.88-0.98 和 pH 值范围为 2.8-8.0 的条件下测试了三种酵母的生长情况。异常汉逊酵母能够在 pH 2.8-8 的范围内生长，没有明显的最佳 pH 值。纤维侧耳酵母和伯顿毕赤酵母的生长最适 pH 值为 5。三种菌株的最佳生长水分活度不同，在 0.96 到 0.98 之间变化。这些生长数据进一步用于开发二次模型，以描述 a(w) 与径向或菌落生长速率 (g，mm/d) 或延迟期持续时间 (λ，d) 之间的关系。鉴定腐败菌并充分了解 a(w) 和 pH 值对生长行为的影响，对于未来开发针对白垩模具缺陷的适当保护策略至关重要。
