Optimization of high-density fermentation process for Kluyveromyces marxianus MK5 and its application in milk beer production

Milk beer originated in China and is a widely popular refreshing dairy beverage. Its distinctive flavor primarily stems from Kluyveromyces marxianus used during fermentation. However, the current high-density fermentation process for this yeast strain remains constrained by a dry weight yield of 70 g/L, coupled with relatively high production costs. These factors limit the application of yeast in the production of milk beer. This study aims to establish a high-density cultivation process and feeding regimen for Kluyveromyces marxianus to enhance its viable cell count and dry weight, thereby evaluating its applicability in milk beer production. First, the optimal cultivation conditions for the Kluyveromyces marxianus MK5 strain were determined in a 5 L fermenter, which was then used for fed-batch fermentation. Subsequently, the resulting milk beer was compared with milk beer produced using the commonly used Kluyveromyces marxianus MJ strain and a blank acidified milk solution. Results indicated that simulated exponential fed-batch fermentation at a specific growth rate of 0.05 h ⁻¹ significantly promoted MK5 growth. The maximum viable cell count reached 1.88 × 10 ¹⁰ colony-forming unit/mL during cultivation, with a dry cell weight of 113.7 g/L. Furthermore, milk beer samples fermented with strain MK5 demonstrated significant advantages in enhancing milk beer stability and improving flavor.