Improving the sensory experiences of plant proteins

In this series of articles, NIZO Food Research Division Manager and FoodNavigator advisory panel member René Floris discusses some of the big issues in today’s food industry.

Continuing our exploration of the protein transition, this month I again spoke to Fred van de Velde, head of NIZO’s Protein Functionality Expertise Group. In a previous column, Fred explained all about how to choose the right plant protein for a specific product by balancing the competing requirements of consumer preferences, product developers’ technical specifications and nutritional needs. This time, we looked at the sensory experiences that plant-based proteins deliver and how they can be improved.

René Floris: The sensory experience is a big part of our enjoyment of food. Why is it an issue for plant-based foods?

Fred van de Velde: When we talk about plant-based foods, we typically mean plant-based alternatives to familiar, animal-based products. These product types tend to move through four levels of maturity in terms of consumer expectations (see fig. 1), from simply looking right and meeting relevant food safety regulations to offering a familiar sensory experience through to delivering the right nutritional composition and meeting sustainability criteria.

Figure 1: The four levels of customer expectation for new dairy and dairy-alternative food products

Different product types move through this pyramid at different rates and the order of the nutritional and societal levels in particular will depend on the individual consumer and brand. But in moving up the pyramid, new generations of products have to at least maintain the performance in the lower levels. In other words, delivering nutritional parity or a more sustainable product cannot come at the expense of the sensory experience. The challenge for the plant-based sector is that many plant protein options have issues when it comes to their sensory qualities.

RF: What are the sensory issues for plant proteins?

FvdV: The sensory experience of food is described in terms of the aroma / flavour and the mouthfeel of a product. I explained in our previous column how many plant proteins bring off-flavours, but these can be reduced through, for example, fermentation. However, many plant-based alternatives also struggle to recreate the mouthfeel of familiar dairy products.

Mouthfeel depends on the behaviour of fats, carbohydrates and proteins in the food. Specifically, it describes how these components interact with and move across the surfaces of the tongue and oral cavity. Fats and carbohydrates increase lubrication between the food and the tongue, creating creamy and smooth sensations. Meanwhile, proteins tend to reduce apparent lubrication.

This interaction can be objectively studied in the lab through tribology experiments – something we have done for a wide range of foods. Looking at the results for yoghurt and yoghurt-alternatives as a typical example (fig 2), we see that plant-based yoghurts, particularly soy, actually match the tribology performance of full-fat yoghurt better than skimmed-milk yoghurt does. This is because soy yoghurts have quite similar levels of fat and protein to full-fat dairy yoghurt. The almond- and oat-based yoghurts investigated actually have lower friction in the mouth than the dairy-based yoghurts due to their higher levels of (added) carbohydrate and fat, respectively.

Figure 2: Tribology results for dairy and plant-based yoghurts based on research carried out by Els de Hoog of NIZO.

RF: So these plant-based yoghurts should deliver a similar or perhaps even better mouthfeel than dairy yoghurt?

FvdV: At first glance, the tribology results seem to suggest that. But oat and almond yoghurts are much lower in protein than dairy or soy yoghurts. If you want to move up the pyramid and make your oat or almond yoghurt a better nutritional match, then you need to add more plant protein – and as I said, protein increases the friction in the mouth, producing a rougher, more astringent sensation. For plant protein ingredients, astringency – that drying or puckering feeling often associated with black tea or tannin-heavy red wines – is a particular issue. Any attempt to boost the nutritional composition of plant-based yoghurts by adding plant protein ingredients risks ruining the smooth, creamy mouthfeel.

RF: How can manufacturers then increase the nutritional composition of plant-based yoghurts and still deliver a pleasant sensory experience?

FvdV: This is still somewhat of an open question. But it is one that the industry is actively exploring. For example, we at NIZO are chairing an industry consortium to investigate the astringency of plant-based protein ingredients. And we see already from this project that astringency is much more complex than anyone first thought.

The first question is to understand how astringency arises. I said earlier that astringency is a characteristic of many plant protein ingredients, but it isn’t yet known whether that astringency is inherent to the proteins themselves or if it comes from polyphenols that are also present in the ingredient. These polyphenols certainly add astringency to tea and red wine, and are known to interact with proteins in our saliva which reduces the available lubrication. But the research hasn’t yet been done to determine which gives the dominant effect in plant protein ingredients: the proteins or the polyphenols.

RF: Will the consortium also explore solutions for reducing astringency?

FvdV: Once we understand the mechanism and source of astringency, we can start to think how to reduce it. But in doing so, we must be aware of the impact of such solutions on the society level of the consumer expectation pyramid. For example, if the astringency is largely due to the polyphenols, they could be removed by cleaning the ingredients. However, every additional cleaning step increases the consumption of resources and thus impacts the sustainability of the end product.

Selective breeding of novel plant strains could also be an option for reducing the astringency of the protein ingredients derived from them. But plants typically evolve such characteristics for a reason and selecting them out could impact the yield of the crop and have consequences for developing more natural, clean label products. Our own research already suggests that regular and organic variants of dairy alternatives showed differences in friction behaviour and perceived astringency.

But that is the next stage. Right now, the focus is on understanding the mechanism that causes the astringency and why it varies so much between different protein ingredients.