The fat content in food has always been a widely discussed and scrutinized element of nutrition for both consumers and food industry professionals. Many shoppers are interested in the amount of fat in food for a variety of reasons—health, nutrition, weight loss, and more—and want to know the precise amount before making nutritional decisions.
Many shoppers are interested in the amount of fat in food for a variety of reasons and want to know the precise amount before making nutritional decisions.
Consumers want a product that lists accurate, verifiable fat content in food, but the process of analyzing fat content can seem convoluted—especially when there are many types of fat, as well as a variety of ways to test it. As a food industry professional, you might have a lot of questions about the best way to test, interpret, and analyze test results regarding fat content in the food you’re producing. After all, different types of foods require different types of testing.
We’re here to assist you in understanding the fundamentals of fat in food, as well as the basics of testing the fat content in your particular product. There are a variety of procedures that can help us understand the breakdown of fat in food, and we can make things clearer by answering four fundamental questions: 1) What is fat? 2) How many methods are used to test fat content? 3) What procedures are used to test and analyze fat? 4) Which foods require which procedures?
What is Fat?
Fats are primarily the triesters of fatty acids and glycerol and thus are commonly called triglycerides. Solid triglycerides are referred to as fat while liquid triglycerides are called oils. Lipids, on the other hand, include all the “fatty” materials—the substances dissolved in a fat-solubilizing solvent in a food. This includes but is not limited to the following:
|Table 1: Lipids|
|Monoglycerides, diglycerides, triglycerides||Free fatty acids|
For nutrition labeling purposes, fat is defined as the sum of the fatty acids in the food, regardless of source, and this is expressed as triglyceride equivalents. These fatty acids may be present as the following:
|Table 2: Fatty Acids|
|Free fatty acids||Glycolipids|
|Monoglycerides, diglycerides, triglycerides||Sterol lipids|
Individual fatty acids are classified according to their degree of unsaturation. Common references to fatty acids include:
|Table 3: References to Fatty Acids|
|Saturated fat||Polyunsaturated fat|
|Monounsaturated fat||Trans fatty acids|
Fat Analyzing Methods
Historically, a number of methods have been developed for the analysis of fats in various food products. These methods are based upon the ease of removing fat from a given matrix, and the selected method also depends on whether fat or total lipids are to be extracted from the sample. There are two common methods used to test and analyze fat in food:
- Gas chromatograph (GC) method
- Solvent extraction-gravimetric method
The gas chromatograph (GC) method is used for accurate nutritional labeling to include trans fats, and it’s used for research projects. The GC method also provides accurate quantitation of total fat, as well as the individual fatty acids, which include saturated fat, monounsaturated fat, polyunsaturated fat, and trans fatty acids.
The solvent extraction-gravimetric method can be used for quick fat determinations and relative comparisons between samples. However, it’s important to note that the results can be approximately 10% higher than fat revealed in results from the gas chromatograph (GC) method. These erroneously high results are due to certain nonfat components that are typically extracted with the fat. These nonfat components include:
|Table 4: Nonfat Components|
|Organic acids||Low molecular weight carbohydrates|
Fat Testing Procedures
Under the umbrella of fat-analyzing methods are the following fat testing procedures.
Gas Chromatograph Procedure
FAT by GC (FATGC)
The following steps are taken in the FATGC procedure:
- Step 1: Triglycerides and other molecules containing fatty acids are released from food matrices using an acid or base hydrolysis
- Step 2: The triglycerides and molecules are extracted into a mixture of ethyl and petroleum ether
- Step 3: Pyrogallic acid is added to minimize oxidative degradation of fatty acids
- Step 4: The fatty acids found in certain compounds are then esterified or transesterified with a solution of boron trifluoride in methanol (BF3/MeOH) to form fatty acid methyl esters (FAMEs)
- Step 5: FAMEs are quantitatively measured by capillary gas chromatography by comparing them to a known quantity of internal standard
- Step 6: Total fat is calculated as the sum of individual fatty acids expressed as their respective triglyceride equivalents
- Step 7: Saturated, monounsaturated and polyunsaturated fats are calculated as the sum of the respective component fatty acids
- Step 8: Cis and trans fatty acids and omega 3s can be totaled
The acid-hydrolysis method extracts fat from the sample by subjecting it to hydrochloric acid and mixed ethers. The following steps are taken in the acid hydrolysis procedure:
- Step 1: The hydrochloric acid breaks fatty acids from the glycerides, glycolipids, phospholipids, and sterol esters
- Step 2: Acid hydrolysis also breaks lipid-carbohydrate bonds, assists in the hydrolyzing of proteins and polysaccharides, and disrupts cell walls
- Step 3: All of this makes the lipids available for complete extraction with mixed ethers
- Step 4: The ether is evaporated, and the extracted residue is weighed
Food samples tested and analyzed using the acid-hydrolysis procedure are baked products, bread, cereal, cooked products, eggs, fish, flour, food dressings, fruit, grain, mixes, pasta, products with cocoa, seafood, and vegetables.
The base-hydrolysis method, typically used for dairy matrices (Roese-Gottlib), extracts fat from the sample by treating it with ammonium hydroxide and subjecting it to mixed ethers. The following steps are taken in the base hydrolysis procedure:
- Step 1: The ammonium hydroxide weakens lipid-protein bonds in order to disrupt the casein, breaks up fat emulsions, and neutralizes any endogenous acid prior to the extraction with mixed ethers
- Step 2: A centrifugation step also aids in the breaking of emulsions, which are common in dairy products, and it aids in separating the ether layer from the aqueous phase
- Step 3: Samples are extracted into mixed ethers
- Step 4: Total fat is calculated gravimetrically after evaporation and residue weighing
- Food samples tested and analyzed using the base hydrolysis procedure are dairy products such as cream cheese, milk, non-fat dry milk, yogurt, and whey.
Acid & Base Hydrolysis
The combined acid-and-base-hydrolysis method, sometimes necessary for matrices where the fat is difficult to remove, extracts fat from the sample by treatment with ammonium hydroxide. After that, the fat is subjected to a hydrochloric acid solution and extracted using mixed ethers. The following steps are taken in the acid and base hydrolysis procedure:
- Step 1: The ammonium hydroxide weakens the lipid-protein bonds
- Step 2: The acid breaks the lipid-carbohydrate bonds making the lipid available for complete extraction
- Step 3: Samples are extracted into mixed ethers
- Step 4: Total fat is calculated gravimetrically
Food samples tested and analyzed using the acid and base hydrolysis procedure are cheese, cheese blends, entrees with cheese, products with cheese, pizza-roll filling, and pizza.
You do food, we’ll do the science
Testing and analyzing fat in food can be a complex process, but we understand the importance of nutrition, analytic food testing, and responsible nutrition labels, and we’re here to keep you informed and help you get your product to consumers.
Understanding the amount of fat in food is important to consumers and food industry professionals, which is why we’re happy to show you how it’s done. To stay competitive, food entrepreneurs today have to make safe food products that include reliable nutritional information. We’re here to help.
If you want to learn more about the basics of nutrition labels or you’re curious about testing and analyzing other nutrients in the goods you manufacture, check out our recent blog post, Nutrition Labels 101: What’s Required? What’s Optional?