Transforming sustainable plant proteins into high performance lubricating microgels

Plant protein products have boomed in the supermarket aisle, however these products face numerous sensory challenges and are often inferior to animal proteins. Can we physically process plant proteins to improve their sensory properties without extra additives? Microgelation may be the answer
Published in Sustainability
Transforming sustainable plant proteins into high performance lubricating microgels
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Imagine food consumption throughout our history, let’s say 100 years ago? Compare this to the food that we eat today. The developed world currently lives in a period of vast food choices. In past centuries, sweets, meats, herbs, spices and complex food formulations were only for minority of the population in specific regions of the world. However, in modern day we do not even have to get out of our beds to order thousands of such foods, delivered straight to our door. However, In our naivety a crisis has developed. Climate change and global warming are causing havoc in modern infrastructure with our food choice playing a significant role in emission production.

Food accounts for one third of human-made greenhouse gas emissions (GHGs) with animal foods in particular contributing to 57% of those GHGs. Additionally, with an increasing population, particularly with a shift in demographics towards older adults, current protein production will strain in years to come. The consequences are being seen today and so this raises the question, what will our food look like in 10 years or let’s say 50 years from now? We must focus towards developing an environmentally responsible, sustainable and efficient consumption of food and one thing is for certain, plant proteins will play a pivotal role in developing this sustainable food system for the future. So today we are surrounded by plant protein-based foods, from meat analogues to their use as ingredients and in protein-fortified foods. The intention is not only to support the planet but to also provide protein equity and distribution across the globe whist achieving animal welfare. Despite this boom, transitioning to more plant protein-based diets are low, but why is that?

Fundamentally, plant proteins suffer with poor functionality such as limited solubility as well as poor organoleptic properties in taste (i.e. bitterness, beany) and texture, particularly astringency. These traits certainly do not help food manufacturers in successful design of plant protein-rich foods, yet alone convince the consumers to switch. In fact, our team1 did a tasting trial of plant protein commercial products available in the UK supermarket and we found them to be rather undesirable and not comparable to meat or dairy by any means.

So what is missing? In taste, much focus has been undertaken to mask off flavours, often ultra-formulation approaches have been used with addition of higher fat, sugar, salt and other additives that reduces their healthiness potential. What has been overshadowed however is the undesirable texture, such as astringency that is often termed as “dry”, “non-juicy”, “gritty” in various plant protein-based formulated foods. These perceptions are mechanosensations that are hypothetically linked to raising oral friction or lubrication failure. In this paper, we have converted these poorly lubricating plant proteins into ultralubricating, hydrated structures called “microgels” to relieve poor textural performance.

Figure 1. Microgelation process

The most exciting element is that we do add any harsh processing to create these microgels and utilise  unit operations that are fairly common in any food manufacturing premise.

So, what are these microgels? Microgels are like sponges of water that are connected via a web-like network of proteins, a water-hydrated blob. How do we make them? Firstly, plant proteins are hydrated and then gelled under heat – thanks to the hydrophobic and thiol groups present inherently in the protein allowing natural crosslinking. Finally, we shear these gels to form these microscopic sponge-like hydrated plant protein particles containing > 85% water – a microgel (Figure 1). What is remarkable is the unprecedented functionality and lubrication performance of these new particles that we show in this paper by combining theoretical and experimental studies. Firstly we characterised these particles measuring size and shape using atomic force microscopy (AFM) (Figure 2a) where we found that these microgels were spherical and sub-micron-sized. These microgels displayed excellent dispersibility and stability especially compared to native proteins (Figure 2b) with no size change upon heating or storage.

Figure 2. Overview of microgel performance. Atomic force microscopy (AFM) on plant protein microgels (a). Dispersibility and stability of native vs microgel protein (b). The excellent lubrication properties of microgels vs native protein vs O/W emulsion (c). Lubrication measured using new biomimetic tongue surfaces (d).

Next, what was remarkable was that these microgels provided orders of magnitude reduction in friction compared to native proteins of same protein concentration. This was shown both in low concentrations as well as high concentrations of the microgels no matter the protein type. Now, we further compared the lubrication against a well-known lubricating food, a 20% oil in water (O/W) emulsion, resembling single cream as a challenge. To our surprise, the plant microgels which contained no lipidic additives mimicked the lubrication performance of these O/W emulsions (Figure 2c). To further confirm such findings we also compared lubrication utilising a new biomimetic tongue-like surface, latter is a more representable surface (topography, elasticity and wettability) to our own tongue, and the outstanding lubrication results of plant protein microgels persisted (Figure 2d). Therefore, these microgels serves dual roles by making plant proteins more palatable in tactile context and reduces formulation additives.

Finally, considering that we do not add anything except structuring the plant proteins with water, why do microgels behave so brilliantly? Combining theoretical models and indentation theory, we were able to demonstrate that these microgels are able to support high loads due to their viscosity – acting as mini reservoirs of water. When squeezed under load, let’s say sheared between tongue and palate in the mouth, this encapsulated water weeps increasing localised viscosity enhancing hydration lubrication between surfaces.

In summary, using well-established physical processing techniques, we are able to create highly stable, dispersible and heat resistant plant protein microgels that reduce friction by orders of magnitude in comparison to the original native protein with comparable lubrication performance to those of creams. Next, the question is can these microgels behave like fat droplets in mouth sensorially? How do they perform in food product matrices? – this still needs to be answered. Once we answer these, microgels can be a game-changing ingredient technology in sustainable food design.

1 Team | Sarkar Lab (leeds.ac.uk)

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