Lipids: fats and oils in foods

As food components, they are very important because they provide a concentrated level of energy (9.1 kcal/g), twice as much as proteins and carbohydrates.

Lipids: fats and oils in foods
In common terms, we refer to lipids as "fats" or "oils. Photo by Jessica Lewis / Unsplash

Lipids, together with proteins, carbohydrates, and water, are the four food macro components. Unlike proteins and carbohydrates, they do not have any distinctive structural compositional or chemical bonding characteristics that identify them.

Lipids are a group of organic compounds with a very varied structure based not on chemical characteristics, but the physical property of their solubility. They are not soluble in water but in organic solvents such as toluene, benzene, and ethanol, so they are completely hydrophobic (water repellent).

Thus, lipids include triglycerides, free fatty acids (triglyceride components), waxes, phospholipids, and sterols such as cholesterol and sphingosines, among others, whose chemical structures are very different from each other.

As food components, they are very important because they provide a concentrated level of energy (9.1 kcal/g), twice as much as proteins and carbohydrates. They are carriers of fat-soluble vitamins (A, D, E, K), contain essential fatty acids called omega-3 and omega-6, precursors of compounds of great physiological importance such as thromboxanes, leukotrienes, and prostaglandins, our first response as living organisms to environmental stimuli (light, heat, cold, etc.).

When we talk about food technology (production, handling, storage, preservation, and consumption), we refer to triglycerides as the only food ingredient, leaving only a small space for phospholipids, and excellent emulsifiers. So, when we deal with lipids in these terms, we are specifically dealing with this lipid component.

In common terms, we refer to lipids as "fats" or "oils," depending on their physical state; if they are liquids, they will be oils; fats, if they are solids or semisolids. However, while being liquid or solid depends on the temperature of the environment, it is much more dependent on the fatty acids that are part of the triglycerides.

The composition of a liter of oil, regardless of brand or origin, whether cottonseed, soybean, sesame, or sunflower, should be one hundred percent triglycerides. All the other lipid components mentioned above are eliminated during the purification process; otherwise, they would be "contaminants", technologically speaking.

In this sense, the main contaminant of fats and oils used in the manufacture of food or during their preparation is water, an element that promotes one of the lipid-deteriorating processes known as "hydrolytic rancidity" or simply "rancidity". This process involves the release of fatty acids from the triglyceride molecule, which can generate soapy flavors in the food, a very common problem a few decades ago, mainly in fried foods and snacks.

The other lipid deterioration process, promoted by hydrolytic rancidity, but not dependent on it, is "autooxidative rancidity" or simply "autooxidation". Here the responsible is the oxygen in the environment or occluded in the food, which interacts with the fatty acids that are part of the intact triglycerides or that were released by rancidity.

Rancidity has immediate effects that are sensory. Auto-oxidation is a slow and very complicated process that generates as one of its final products free radicals, very reactive chemical species with serious implications on our health by interacting with enzymes, vitamins, and genetic material, and are therefore potential inducers of cancer.

Much remains to be said, especially about fats and oils and their role in food technology. I only hope that this brief article is a small introduction to the importance of lipids and that when you hear the term "lipids" you will now know a little more about what it is.

By Ramón Pacheco Aguilar, researcher of the Coordination of Food Technology of Animal Origin of CIAD.