What I wish everyone knew about Isothermal Titration Calorimetry

Ah, the holidays are here! This is the time of year when we enjoy special ‘once a year’ holiday meals and treats with family and friends. There are the succulent cuts of meat, marbled with fat…..perhaps you have a holiday goose or duck. There are the vegetables and pastas coated with butter, cheese, or cream sauces. There are the rich, buttery desserts. Let’s not forget the candy, chips, eggnog, and almost every delicious, decadent item we eat or drink. We all have our favorite holiday dishes, which are likely high in fat content. We all know that eating too much fat can lead to weight gain.

A common misconception is that all fat is ‘bad’ and that a fat-free diet is ‘good’. Yes, eating some fats in excess has been linked to increased chances of high cholesterol and heart disease. However, several fats are linked to reducing cholesterol, improving heart health, and improving insulin levels and blood sugar. These include omega-3 fatty acids, monounsaturated fats in nuts and avocados, and polyunsaturated fats in some fish. Dietary fats are important for other reasons; for example, vitamins A and D and other nutrients are only soluble in fats. Finally, having some fat in your diet is more satisfying and filling, and you may be less likely to overeat. Most nutritionists advise people to choose their foods wisely, and enjoy in moderation.

Why am I discussing food and fats in a Malvern blog?

Good question! Because Isothermal Titration Calorimetry (ITC) is one of the tools scientists use to study how lipids and fats are processed by the human gastrointestinal (GI) system. Food scientists, nutritionists, and the medical community are all actively researching fats, what happens to fats when we eat them, and how these fats can affect our health and well-being.  The food industry is developing foods that are sources of ‘good’ fats (for example, eggs rich in omega-3 fatty acids). Food science is also developing lipids as a “delivery system” for fat-soluble (lipophilic) compounds such as vitamins, nutraceuticals, and nutrients, that can be used to improve our health – these are called ‘functional foods’. It is possible that in the future, our holiday foods and drinks may actually be good for our health!

A recent review article by Arroyo-Maya and McClements discusses the utility of ITC in food science research, focusing on how lipids and lipophilic compounds are processed in the GI tract. The gastrointestinal fate and bioavailability of lipids as well as lipophilic compounds in functional foods depends on their interactions with other food components, as well as with GI fluids and enzymes. ITC is a powerful tool for the understanding and characterization of interactions at a molecular level.

ITC provides fundamental parameters (such as binding affinity, number of binding sites, and free energy, enthalpy, and entropy changes) that can be used to establish the physicochemical origin of molecular interactions. These reactions can be studied by ITC at a variety of different ionic strengths, temperatures, and pHs, to mimic the actual reaction conditions in the GI tract (including the mouth, stomach, and small intestine).

This review article focuses on applications of ITC for understanding the molecular interactions which affect the bioavailability of lipids. These include the micellization of surface-active lipids (surfactants and bile salts) and the factors that impact this process, as well as the binding interactions between various types of food components, such as lipids, proteins, carbohydrates, and surfactants. ITC can be utilized to study the factors that influence enzymatic hydrolysis reactions, such as lipid, protein, or carbohydrate digestion. The results obtained from ITC experiments may facilitate the rational design and development of novel functional food products with improved bioavailability of the lipophilic compounds, which may increase human health and well-being.

And of course, we cannot forget about wine during the holidays! Wine tannins are major contributors to red wine texture, and qualities including astringency and mouth-coating characteristics. Tannin concentration is directly related to the intensity of astringency (drying or puckering sensations of wine) and is associated with the interactions between wine tannins and salivary proteins and/or oral epithelial cells in the mouth.

In a recent article by McRae et al, ITC (Micro-cal Auto ITC200) was used to measure the binding strength between the model salivary protein, poly(L-proline), PLP, and a range of wine tannins (from three- and a seven-year old Cabernet Sauvignon wines) across different ethanol concentrations. Tannin-PLP interactions were stronger at 5% ethanol than at 40% ethanol. The mechanism of interaction changed from a combination of hydrophobic and hydrogen binding at 10% ethanol to solely hydrogen binding at 15% ethanol. These results indicate that ethanol concentration can influence the mechanisms of wine tannin-protein interactions.

So, as you enjoy your holiday meals, think about all the ways in which Isothermal Titration Calorimetry is being used to improve your enjoyment of food and drink, and make them healthier for you as well!

Happy holidays from all at Malvern!

#MerryMalvern

References:

J. Arroyo-Maya, D.J. McClements. Application of ITC in foods: A powerful tool for understanding the gastrointestinal fate of lipophilic compounds. Biochim. Biophys. Acta 1860(5), 1026-1035 (2016).
DOI: 10.1016/j.bbagen.2015.10.001

J. M. McRae, Z. M. Ziora, S. Kassara, M.A. Cooper, and P. A. Smith. Ethanol concentration influences the mechanisms of wine tannin interactions with poly(L-proline) in model wine. J. Agric. Food Chem., 2015, 63 (17), 4345–4352 (2015).
DOI: 10.1021/acs.jafc.5b00758