Invited review: Turning dairy food waste into valuable products via yeast bioproduction.

Dairy food waste (DFW) is a major global issue, with estimates indicating that almost 20% of production is wasted in some regions. Such losses result in economic and environmental challenges but also create opportunities to recover valuable nutrients, reduce costs, and support a more circular dairy industry. This review explores the sources and composition of DFW and highlights strategies to transform it into valuable bioproducts through yeast fermentation, focusing on lactose-fermenting species as near-term platforms and Saccharomyces cerevisiae as the longer-term alternative. Key DFW streams, particularly cheese whey and its derivatives, offer nutrient-rich substrates for bioproduction. Yeast fermentation can convert these into value-added products, such as microbial biomass, AA, vitamins, minerals, fatty acids, and enzymes with direct applications in dairy cattle nutrition. Despite this potential, challenges persist, including the inability of industrially preferred yeasts to natively metabolize lactose, the variability in DFW composition, microbial contamination, and economic, logistical, and regulatory barriers. Emerging approaches such as strain engineering, adaptive evolution, and biofoundry-based synthetic biology offer promising solutions. By integrating bioproduction into the dairy cycle, the industry has the potential to reduce DFW, lower greenhouse gas emissions, and create new revenue streams.