Schmidt, Svenja
(2025)
Micro-flow nanoemulsions for astronaut designer beverages:
tested under simulated microgravity and conceptualised for
personal nutrition.
PhD thesis, University of Nottingham.
Abstract
In this work, a novel space beverage system is proposed, aiming to leverage food variety in space while mitigating space-related health risks. Taking inspiration from current developments in the beverage industry, strategic beverage fortification can provide astronauts with efficacious mounts of bioactive compounds to address space health hazards, while beverage personalization (flavour and nutrients) can help alleviate menu fatigue and address individual nutrient requirements.
To add hydrophobic bioactives and aroma compounds to the beverages, their formulation is based on beverage emulsions, i.e., low concentrations of stabilized oil droplets dispersed into an aqueous phase. For a resource-efficient, continuous, in-space production of beverages, a translation of a solvent-free variant of the spontaneous emulsification into microfluidics was proposed. Both a single-contact and a multi-contact microfluidic mixer could produce reliably emulsions from a 2-phase model system (medium-chain triglycerides, polysorbate 80, phosphate buffer). This variant of the spontaneous emulsification is known to require high surfactant concentrations to form nanoemulsions (diameter < 200 nm), however, surfactant use (approx. 50%) and process time (50-90%) decreased considerably using microfluidic mixers. The multi-contact microfluidic mixer outperformed the single-contact one, yet was more prone to blockage via oil phase jellification due to its complex internal geometry.
The stability of obtained (nano-)emulsions were investigated under gravity and simulated microgravity by applying both scaling law analysis and experimental studies. Modelling suggested that emulsions below an average droplet size of approx. 1.3 μm were not susceptible to gravity-induced separation mechanisms. Long-term storage of 3 years confirmed the estimation, with droplets changing in size (-60-80% or +10-50%, depending on initial size) but not setling or creaming. Estimating the limitations of simulated microgravity of a Random Positioning Machine suggested that the forced convection induced by the RPM’s rotational movements can potentially impact emulsion characteristics in certain cases, e.g., Clinostat motion modes at high frame speeds and therefore corrupt experimental studies. However, during experimentation, emulsion characteristics were generally unaffected by RPM settngs over a 2-day exposure period compared to control samples.
Addressing potential future aroma designs of the beverages, the aroma components of 4 fruit juice varieties (apple, apple-raspberry, apple-mango, grape) have been identified while testing a potential flavour diversification strategy via enzymatic (β-glucosidase) treatment. Both the recombinant β-glucosidase A expressed in Escherichia coli and the industrial product Rapidase® led to significant changes in the juice’s aroma profiles, however, only eugenol, chavicol, and 2-methyl butyric acid were consistently released in apple-based juices following enzymatic treatment, suggesting that only they were present as aroma precursors in the form of monosaccharide glucosides to react with glucosidase.
Finally, the composition of the model emulsions was expanded by the addition of typical beverage components (sweetener, acid, aroma) and a bioactive compound (omega-3 polyunsaturated faty acids). Addition of sugars generally increased droplet size (~20%), while acid had no or litle influence and hydrophobic aroma compounds and the bioactive decreased droplet size (-10-35%), suggesting that choice of ingredient influences significantly the efficiency of the emulsification. A preliminary recipe library was created and successfully translated into a continuous, single-contact microfluidic process.
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