The use of proteins in winemaking
About two thousand years ago, the Romans transformed wine from a drink for a select few to ‘mass nourishment and pleasure’, spreading it to every corner of the empire. The enormous increase in the volumes produced required a better production process, as the average quality of what was marketed was often questionable. To this end, in addition to blending, which was well-known and used at the time, numerous winemaking practices were developed that improved the quality of the wines. Among the many practices used was the treatment with milk, eggs or albumin and wild pea flour. These applications represent the ancestors of today’s clarification practices.
Taking a long leap forward and arriving at the last decades of winemaking history, we can see that although the goal of improving the general characteristics of wine has not changed, the objectives are now more detailed (e.g., reduction of astringency, improvement of colour hue, increase in olfactory cleanliness, etc.). The compounds used have also been purified (e.g., from milk to potassium caseinate, eggs to albumin, etc.).
The emergence of bovine spongiform encephalopathy (mad cow syndrome – UK 1986), the subsequent prohibition of blood albumin, and the rise in allergies and intolerances caused by milk and egg proteins created a pressing need for alternatives. In response to these health and safety concerns, the wine industry began to search for other options for animal-based clarifying proteins that could offer a better reputation and wholesomeness.
Over the past two decades, many studies have been carried out on the oenological application of various categories of plant-derived proteins, such as proteins from legumes (soybean, pea and lupin), cereals (wheat, corn and rice), and tuberous plants such as potato. Among these possible plant sources, given the potential allergenicity (Annex III European Directive 2007/68/EC) and the actual availability of products, only pea and potato proteins have an increasingly widespread and growing application today. The current OIV monograph on plant-based proteins (COEI-1-PROVEG 2016) considers wheat, pea and potato proteins usable. This monograph will be updated by excluding wheat (gluten) proteins from oenological use. This choice is because although the absence of post-treatment gluten residues has been proven by ELISA tests, for reasons of potential allergenicity, no producer is interested in using them. In this article, we describe the oenological performance of pea and potato proteins.
Pea proteins: chemical characteristics
Pea proteins are extracted from the yellow pea (Pisum sativum). Many existing studies to chemically characterise pea proteins indicate that these proteins are represented by globulins and albumins with the function of storage proteins used as a nitrogen source during the seed germination stage. Globulins, present in greater quantities, are represented by legumin, vicillin and convicillin. Three-dimensionally, these molecules have a compact quaternary structure consisting of hexamers and tetramers with molecular masses varying between 380 KDa (hexamer ligumina) and 150 KDa (trimester vicillin).
Potato proteins: chemical characteristics
Potato (Solanum tuberosum) proteins are produced by two industrial potato processing processes: starch production and frying potato chip production. Chemically, the proteins in potato juice from chips represent the most homogeneous group. These compounds, belonging to the glycoprotein family, have a molecular mass of about 40KDa and an isoelectric point between 4.5 and 5.2. At neutral pH and room temperature, patatin is a dimer stabilised by hydrophobic forces. Changes in pH significantly affect its three-dimensional structure, and temperature above 60°C easily causes its denaturation.
Solubility differences between plant-based proteins and animal proteins
It is important to note that plant proteins are only partially soluble, unlike animal proteins. Due to reactivity related to the surface characteristics of the particles, a high percentage of the product will carry out its effect in suspension. Figure 1 shows the suspension of the two plant-based proteins at pH 3.5.

FIGURE 1. Proteins hydrated to 5% in water at pH 3.5. A – pea protein, B – potato protein.
Figure 2 shows results from SDS-PAGE electrophoresis of potato and pea proteins. Potato protein is characterised by a predominant band corresponding to about 40 KDa (patatin), while pea protein consists of many protein fragments distributed in the 10 – 100 Kda range.

FIGURE 2. Electrophoretic profile of the soluble fraction of potato (A) and pea (B) proteins. (M) molecular weight markers.
Evaluating the oenological performance of plant proteins
The effects of pea and potato proteins on wine were evaluated by monitoring the following aspects: clarifying efficacy, oxidation management, astringency reduction, effect on colloidal instability and sensory impact. Generally, the suggested dosages of pea and potato proteins in winemaking vary between 5 and 30 g/hL depending on the time of application and the intended objective. Oenological trials were performed by standardising the dosage to 10 g/hL except flotation, where the dosage applied was 5 g/hL.
Clarifying efficacy
Figure 3 shows that the molecular mass of plant-based proteins influences their clarifying ability. Controlled hydrolysis can increase the clarifying ability of these proteins. As a comparative example, gelatine with a low degree of hydrolysis (100 Bloom degrees) clarified Trebbiano wine to 5 NTU and Sagrantino wine to 2 NTU (data not shown).

FIGURE 3. The effect of hydrolysis on pea and potato proteins.
Figure 4 shows the clarifying ability of potato proteins with different degrees of hydrolysis in two wines. The treated wine samples were purposely photographed in front of a background with horizontal black lines to make the difference in turbidity obtained more visible.

FIGURE 4. Turbidity 48 hours after the addition of products in Sauvignon blanc wine with pH 3.3 and Trebbiano wine with pH 3.2. A – Sauvignon blanc control, B – pea protein, C – pea protein moderate hydrolysis, D – Trebbiano control, E – potato protein, F – potato protein moderate hydrolysis.
Oxidation management
Pea proteins are better suited than potato proteins for reducing browning. This effect can be monitored by measuring the decrease in optical density at the wavelength of 420 nm, as shown in Figure 5. In this case, protein size does not seem to influence this property. Pea proteins are also found to be the best in reducing the concentration of iron, a metal with an oxidation catalyst effect, as shown in Figure 6.

FIGURE 5. Average optical density reading at 420 nm following clarification with pea and potato proteins.

FIGURE 6. Percentage reduction in average iron concentration obtained from clarifications performed on different types of wines with pea and potato proteins. The performance of PVI/PVP is shown in comparison.
Reduction of astringency
Potato proteins react better with astringent tannins than pea proteins. Clarification tests performed on different wines confirmed this effect, as shown in Figure 7. The performance of hydrolysed gelatine is shown for comparison.

FIGURE 7. Astringency values of wines clarified with plant-based proteins and hydrolysed gelatine.
In Figure 8, the appropriate hydrolysis level on pea proteins allows them to increase their effectiveness in reducing astringency.

FIGURE 8. Astringency values of wines clarified with pea protein at different degrees of hydrolysis.
Reduction in protein instability
Protein-unstable white wines clarified with plant-based proteins and subsequently heat-tested show less change in turbidity, as seen in Figure 9. Such behaviour would suggest a stabilising effect by plant proteins. No noteworthy differences occurred with HPLC analysis of the concentration of unstable proteins (chitinases and thaumatins). Further research is needed to investigate the reason for this phenomenon.

FIGURE 9. ΔNTU values of heat test (30 minutes at 80°C) performed on Traminer.
Sensory impact
It is well known that high dosages of plant-based proteins can impart ‘plant notes’ to the wines. Application trials of many products on the market have confirmed that the choice of product and its use at the correct dosage is important to avoid this effect.
The numerous wine samples treated with pea, potato and animal proteins during our clarification trials were subjected to GC analysis, analysing the main categories of aromatic compounds. The results indicated an average of 10% reduction in the concentrations of aromatic compounds. We believe this result represents an overestimation of what might occur in the winery due to the tests having been conducted on small volumes (laboratory scale). Sensory results did not pick up on this reduction in aromatic compounds. In contrast, the wines had a cleaner overall profile in most cases.
Conclusions
This work aimed to describe the characteristics and main oenological effects of pea and potato proteins and to evaluate their performance. The results highlighted that, in some cases, it is possible to increase their performance through processes that modify their reactivity, making them more suitable for industry needs.
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For more information, contact Lida Malandra at lida.malandra@enartis.co.za.
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