In industrial yeast fermentation processes, single-cell yeast suspensions are usually preferable to cells in aggregates, as single cells exhibit a larger contact area with the nutrient medium, which in many cases helps optimize the process. In addition to affecting fermentation time and efficiency, cell aggregates (e.g., pseudohyphal yeast morphology) may also impair centrifugation systems, one of the most expensive and complex steps of the production process that involves the recovery of yeast cells for subsequent fermentation cycles. To date, no standard technique allows for a systematic diagnosis of yeast morphology in real time during sugarcane biofuel fermentation. Accordingly, we investigate an in situ microscope (ISM) for online monitoring of the density and morphology of an industrial Saccharomyces cerevisiae strain widely used in Brazilian distilleries (PE-2). During batch and repeated batch sugarcane molasses fermentation, the instrument revealed single cells, budding yeast cells, and pseudohyphae, all in a variety of sizes and shapes. The ISM image analysis indicated that the volume of single yeast cells increased by roughly 40% over the lag phase before budding and remained approximately constant thereafter. Pseudohyphae with three and more cells appeared mostly during the stationary phase. Cooling problems were simulated by raising the temperature from 33 to 45 °C. During this thermal stress, single cells as well as budding cells and pseudohyphae forming cells became smaller and exhibited intracellular inhomogeneities. From these results, we conclude that an ISM is a useful tool for monitoring yeast morphology during sugarcane fermentation. Atypical morphologies can be detected early and be used as an automatic warning system.

在工业酵母发酵过程中，单细胞酵母悬浮液通常比聚集细胞更优选，因为单细胞与营养培养基的接触面积更大，这在许多情况下有助于优化过程。除了影响发酵时间和效率外，细胞聚集体（例如假菌丝酵母形态）也可能损害离心系统，这是生产过程中最昂贵和最复杂的步骤之一，涉及回收酵母细胞用于随后的发酵循环。迄今为止，没有标准技术允许在甘蔗生物燃料发酵过程中实时系统地诊断酵母的形态。因此，我们在原地进行调查显微镜（ISM）在线监测工业酿酒酵母的密度和形态广泛用于巴西酿酒厂（PE-2）的菌株。在分批和重复分批进行的甘蔗糖蜜发酵过程中，该仪器显示了各种大小和形状的单细胞，出芽的酵母细胞和假菌丝。ISM图像分析表明，在出芽前的滞后阶段，单个酵母细胞的体积增加了约40％，此后保持大致恒定。具有三个及三个以上细胞的假菌丝主要出现在静止期。通过将温度从33升高到45°C来模拟冷却问题。在这种热应激期间，单细胞以及出芽细胞和假菌丝形成细胞变小并表现出细胞内不均匀性。根据这些结果，我们得出结论，ISM是监测甘蔗发酵过程中酵母形态的有用工具。