Challenges and potentials of recombinant milk protein

The earliest domestication of livestock dates back to 11,000 years ago. Since then, humans have kept farming animals for food and labour. Milk and dairy product consumption has increased throughout history, and it is part of the diet of 80% of the global population. In recent decades, due to the increasing environmental concerns surrounding animal husbandry, the dairy industry has been scrutinised. The current agricultural system, particularly animal husbandry, is one of the largest contributors to environmental damage, mainly owing to its role in greenhouse gas emissions, land use, biodiversity loss and eutrophication. Therefore, more sustainable solutions, such as plant-based products, have become popular. These alternatives, however, present some limitations regarding nutritional content and flavour. In this context, biotechnology emerges as a promising solution as the technology that can replicate milk components while maintaining a low environmental footprint. Yet, this claim lacks strong support from peer-reviewed and independent research.

This thesis aims to cover that research gap by studying the precision fermentation of milk proteins as a sustainable solution to animal husbandry and evaluating the feasibility of this technology from biotechnological and environmental angles. The work performed in the characterisation of several microbial hosts as production platforms for β-casein highlights the biological challenges surrounding the biomanufacturing of this protein. We show that not all microorganisms are suitable for producing this protein due to their varied expression and chemical modification capacities. The environmental assessment of the recombinant production process offers a relative and absolute perspective of the status and potential future scenarios of the dairy system. We conclude that recombinant milk protein can only be considered a more sustainable alternative to cow milk if titres around 50 g/L protein are achieved in combination with a renewable energy grid. Moreover, we show that the current dairy system highly exceeds the safe environmental boundaries of the Earth and underscore that despite the reduction obtained from a transition to plant-based alternatives, a decrease in production must happen in order to have a sustainable dairy system. Finally, our work also describes the valorisation of two waste streams from the food industry as culturing media for fermentation processes. Altogether, this thesis shows the importance of combining several strategies to evaluate the feasibility of a more sustainable dairy system.