Edible fat refers to foodstuffs primarily composed of triglycerides, which are esters of fatty acids and glycerol. These fats can originate from vegetables, animals, or marine life. Edible fats function as a concentrated energy source, providing more than twice the calories per gram compared to proteins or carbohydrates. They are fundamental macronutrients, playing a significant role in cell structure and function.
Types and Sources of Edible Fats
Edible fats are broadly categorized by their chemical structure, specifically the double bonds in their fatty acid chains. Saturated fats contain no double bonds. These fats are solid at room temperature and are commonly found in animal products like butter, lard, cheese, and fatty meats, as well as some plant-based sources such as coconut and palm oils.
Unsaturated fats contain one or more double bonds, which generally keeps them liquid at room temperature. Monounsaturated fats (MUFAs) have one double bond and are abundant in olive oil, canola oil, peanut oil, avocados, and most nuts. Polyunsaturated fats (PUFAs) have multiple double bonds and are found in corn, safflower, sunflower, and soybean oils, as well as in flaxseed, walnuts, and fatty fish like salmon.
A third category, trans fats, can occur naturally in small amounts in meat and dairy products from ruminant animals or be formed industrially through partial hydrogenation. Industrially produced trans fats are found in some processed foods, snack foods, baked goods, and fried foods that use “partially hydrogenated vegetable oil”. Structurally, trans fats have hydrogen atoms on opposite sides of a double bond, which gives them a more linear shape, similar to saturated fats.
Functional Roles in Food
Fats provide numerous functional benefits in cooking, baking, and food manufacturing. They influence food appearance, creating a glossy or moist texture and contributing to golden-brown color during cooking. Fats also play a role in milk opacity and aid browning reactions.
Fats are important for developing desired texture and mouthfeel. In baked goods, fats “shorten” gluten strands, resulting in a tender, softer crumb in items like cakes, pastries, and biscuits. Solid fats like butter or shortening also help trap air bubbles during creaming, contributing to a lighter, airier texture and volume. Fats contribute to the creamy texture of foods like ice cream and mayonnaise, and they can create a crispy exterior in fried items.
Fats absorb and preserve flavors, allowing herbs and spices to be infused into oils for longer shelf life. They contain their own flavor compounds and can enhance the taste of other ingredients, like chocolate or nuts, by carrying and intensifying their flavors. Fats are efficient for heat transfer during cooking processes such as deep-fat frying and sautéing. They also help food retain moisture and can prolong the freshness of baked goods by slowing moisture evaporation.
Nutritional Impact and Health Considerations
Beyond energy, fats facilitate the absorption of fat-soluble vitamins A, D, E, and K. Certain polyunsaturated fats, known as essential fatty acids, cannot be produced by the human body and must be obtained through diet. These include omega-3 fatty acids, such as alpha-linolenic acid (ALA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA), found in flaxseed, walnuts, canola oil, soybeans, and oily fish like salmon and mackerel. Omega-6 fatty acids are found in oils like corn, cottonseed, soybean, and sunflower oil.
The type of fat consumed impacts cholesterol levels and cardiovascular health. Saturated fats, found in animal meats, butter, and some tropical oils like palm and coconut oil, tend to increase low-density lipoprotein (LDL) cholesterol. High levels of LDL cholesterol are associated with an increased risk of heart disease. Monounsaturated and polyunsaturated fats can help lower LDL cholesterol levels, supporting heart health.
Trans fats, particularly those industrially produced through partial hydrogenation, are particularly harmful for cardiovascular health. They raise LDL cholesterol, decrease high-density lipoprotein (HDL) cholesterol, and can increase blood triglyceride levels, further elevating heart disease risk. Current dietary guidelines recommend limiting saturated fat intake to less than 10% of total calories and prioritizing monounsaturated and polyunsaturated fats from sources like nuts, seeds, avocados, olives, and oily fish to promote better heart health.
Processing and Manufacturing
Raw fats and oils undergo various industrial processes to become edible products. Rendering is a method for animal fats, involving heating fatty tissues to melt and separate the fat from other components. This process involves heating fatty tissues to melt and separate the fat, which floats to the surface for collection.
For plant-derived oils, pressing is a common extraction method where seeds or fruits are mechanically pressed. Cold-pressed or virgin oils, obtained without heating, contain fewer impurities and require minimal further processing. To maximize oil yield, seeds are often heat-treated before pressing, resulting in oils with stronger flavors that need additional refining.
Refining processes improve the taste, appearance, and shelf life of extracted fats. Alkali refining treats vegetable oil with caustic lye to remove free fatty acids. Bleaching removes undesirable colors, and deodorization eliminates unpleasant odors and flavors.
Hydrogenation is a modification process that adds hydrogen to unsaturated fatty acids, converting liquid oils into solid or semi-solid fats. This “hardening” process increases the melting point and oxidative stability, making them suitable for products like shortenings and margarines. Full hydrogenation, which aims to eliminate trans fats, is often complemented by interesterification and fractionation to achieve desired textures for various food applications.