Sequential fermentation with Kluyveromyces marxianus and yogurt starter cultures produces stirred fermented milk with reduced lactose and enhanced natural flavor

Abstract

Traditional fermented milk products relying solely on lactic acid bacteria have monotonous flavors and high residual lactose, reducing sensory complexity and adversely affecting lactose-intolerant consumers. To address these limitations, this study developed a sequential fermentation strategy combining a Kluyveromyces marxianus strain (NWAFU 91 or NWAFU 92) with a commercial yogurt starter (YO-MIX883) to produce low-lactose fermented milk with naturally enhanced flavor. The process involved: (1) inoculating sterilized milk with a K. marxianus strain, followed by a 9-h shaking incubation at 38 °C; (2) pasteurization to inactivate yeast cells; (3) subsequent static fermentation with YO-MIX883 at 42 °C for 6 h. Compared to the control (fermentation with YO-MIX883 only), the sequential fermentation with NWAFU 91 and NWAFU 92 achieved lactose reductions of 32.3 % and 37.3 %, generating only 3.0 and 4.4 g/L of ethanol, respectively. Both sequential fermentation protocols generated seven new aroma-active compounds, with NWAFU 91 showing significantly higher ester concentrations. Compared with the control (2.96 mmol/L), the sequential fermentation with NWAFU 91 and NWAFU 92 significantly increased total free amino acid levels by 20.8 % and 19.7 %, respectively. Additionally, they improved water-holding capacity (+3.5 % and + 4.5 %) and textural properties of fermented milk. Both sequential fermentation protocols yielded smaller particle sizes and higher zeta potentials compared to the control, contributing to enhanced gel network stability and water-holding capacity in the products. This study provides an innovative strategy to diversify fermented milk products by integrating yeast-mediated lactose reduction and flavor enrichment, addressing needs of lactose-intolerant populations and flavor-driven market demands.