Unraveling Protein – The Influence Of Ethanol On Flavor, Function, And Nutrition

Ethanol could have more to do with your protein intake than you may realize. Specifically, ethanol can influence the two most critical elements of protein nutrition: bioavailability and flavor. Maybe you have a mimosa with your eggs, white wine with your fish, and red wine with your steak. What if I told you ethanol can have implications for your protein consumption even if you’re vegan, and even if you never drink alcohol?

Protein is important – so important that it is the sole macronutrient that has yet to be demonized by diet culture. Fats are still rebranding themselves after a falling-out in the 90s. Carbohydrates made a brief come-back following the Atkins diet fad, but have been cancelled again thanks to the keto trend and may never fully recover. Protein is the only macronutrient that can do no wrong in the public opinion: it is touted for weight loss, weight gain, body composition changes, multiple basic bodily functions, and is often at the center of heated debates regarding plant-based diets. It is considered so desirable that it is offered as a supplement – called protein isolate – to be added to drinks or food.

Let’s talk about protein isolates, since this is where ethanol eventually comes into the picture. Protein isolates are highly concentrated protein fractions, produced through solubilizing protein (usually in water), filtering, precipitating, and drying. Protein concentrates are a less filtered version of isolates, and may still contain some proportion of fats. The most familiar example is whey protein isolate, or whey protein powder (concentrate). Whey is the watery biproduct of cheese production, which used to be considered waste until it was discovered that it can be dried down to produce concentrate. If desired, it can be further processed to reduce the fat and lactose content, leaving a higher proportion of protein called whey protein isolate. Common plant-based protein isolates include pea (which is actually split-pea), lentil, and soy. Like whey protein, plant-based protein is composed of all 20 amino acids – though in variable proportions depending on the source.

Protein isolates are not just used as supplements for gym bros and vegans. They can be effective as gelling agents, texturizers, colloid stabilizers, foaming agents, and emulsifiers, and are probably present in your food whether you realize it or not. Plant-based protein isolates or concentrates usually serve as a base for imitation meats. For example, Impossible Burger contains soy protein isolate whereas Beyond Burger contains pea and rice protein. Given their role not just as a supplement, but as a substitute, the function, bioavailability, and flavor of these amino acids is not incidental – it’s critical.

Both the functional properties (e.g. foaming and emulsifying capacities) and the bioavailability of protein isolates are a function of the conformation, and can therefore be manipulated through treatments that denature proteins. When the original, tertiary structure of the protein is disrupted and “unraveled,” there is increased exposure of hydrophobic groups that were previously “hidden” inside the protein structure. Furthermore, the denatured, secondary structure can form protein aggregates that will further influence the structure/function. The extent to which the protein unravels, as well as the types of aggregates that form, are factors that can be manipulated through various treatments to affect the functional properties. Therefore, it is in the interest of food scientists to manipulate the protein structure by intentionally denaturing the protein isolates. The best way to do this is arguably by treatment with ethanol-water mixtures. Ethanol is less polar compared to water, and is uniquely suited to disrupt “intramolecular forces” (between molecule interactions) like hydrogen bonding. Studies have found that treatment with 40-60% ethanol effectively denatures proteins to improve functional capabilities of protein isolates. Ethanol was found to be more effective at denaturing proteins compared to other methods, including heat treatment, acid treatment, or combined heat/acid treatment.

A similar mechanism comes into play to improve bioavailability of protein isolates. Certain bioactive peptides have antioxidant properties, but resist digestion by our digestive enzymes (e.g. pepsin) when the protein is consumed in its native form, since the cleavage sites are “hidden” inside the hydrophobic core of the protein. Therefore, treatment with 40% ethanol can actually increase the bioavailability of protein, by denaturing the protein and exposing those cleavage sites. Ethanol treatment affects not only functionality, but nutrient absorption, in almost exactly the same way.

There is one final improvement that ethanol can offer for protein isolates: flavor. Usually, we seek to increase flavor in our foods – but here is a case where we actually use ethanol to eliminate flavor. Specifically, plant-based proteins like lentils and split-peas often present with green or beany off-aromas, attributed to 6-carbon volatile organic compounds like hexanal, hexanol, and hexanone. These aromas have low odor activity thresholds, which means they can be detected by the human nose at trace levels – and risk the ruin of your fruit smoothie. Treatment with solvents can significantly reduce off-aromas to produce a neutral-flavor protein isolate that can be used in food applications without degrading the flavor of the final product.

The ability to manipulate protein isolates via ethanol treatment is the subject of recent publications and ongoing research. Ethanol provides a tool for food scientists to control flavor, texture and function, and bioavailability. As we recover from widespread national disordered eating, our enjoyment and love of food – and particularly of essential macronutrients – remains every bit as critical as the health and nutrition of those foods. Like the inner folds of a native protein structure, the inner workings of the food system may surprise you!

References

Changes of in vitro digestion rate and antioxidant activity of digestion products of ethanol-modified whey protein isolates: https://doi.org/10.1016/j.foodhyd.2022.107756

Effect of heat, pH, ultrasonication and ethanol on the denaturation of whey protein isolate using a newly developed approach in the analysis of difference-UV spectra: https://doi.org/10.1016/j.foodchem.2017.04.022

Reduction of off-flavours and the impact on the functionalities of lentil protein isolate by acetone, ethanol, and isopropanol treatments: https://doi.org/10.1016/j.foodchem.2018.10.022

Ethanol induced changes in structural, morphological, and functional properties of whey proteins isolates: Influence of ethanol concentration: https://doi.org/10.1016/j.foodhyd.2020.106379