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Why Test for Rancidity?

Whether you are producing pet or human foods, beauty products, or biodiesels, you need to be able to determine the freshness and shelf-life of your final product to make sure safe, effective and appealing products enter the marketplace.

Fat and oil quality and content are used as key indicators of overall quality, ensuring proper texture, odor, flavor, nutritional value, safety, stability, reliability and consistency, however, there are several tests to consider performing. Here, we provide an overview of the methods you can use to determine if your materials and products are fresh or rancid.

What Causes Rancidity?

There are two main causes of rancidity: oxidation and hydrolysis. Oxidative rancidity occurs when the sample absorbs oxygen from the environment causing lipids to break down into several other compounds. Hydrolytic rancidity (i.e., enzymatic oxidation) occurs when moisture is present in the absence of air, and is commonly caused by lipase enzymes, which hydrolyze fats into short-chain aldehydes, ketones and free fatty acids.

Whether oxidation or hydrolysis (or both) are the cause of rancidity, the end product ends up being unpalatable and unappealing to consumers, making it important to prevent and monitor.

Rancidity Test Methods

Many conventional rancidity test methods are available, however they often use a substantial amount of sample and are lengthy to perform—taking up to eight hours to get results.

MP Bio offers the SafTest system, which consists of an instrument platform, consumables, and kits for evaluating the fat quality and content of various liquid or solid samples. The platform utilizes a simple, easy-to-use photometric analyzer designed specifically for measuring analytes in complex materials and is integrated with software that provides the flexibility to perform a wide variety of assays.

There are six different SafTest kits containing the reagents and calibrators necessary for analyzing changes in product quality of selected samples.

SafTest Kit

Conventional Test (what SafTest can replace)

Peroxide Test Kit

AOCS extraction or titration testing methods

Free Fatty Acid Test Kit

Titration testing methods

Malonaldehyde Test Kit

Thiobarbituric acid rancidity assay (TBAR)

Alkenal Test Kit

P-anisidine testing method

Percent Fat Test Kit

Butt-tube, Soxhlets, Mojonnier and Babcock, Acid-hydrolysis

Total Glycerin Test Kit

ASTM method for total glycerin testing

Benefits of MP Bio’s SafTest Kits:

  • Requires only small amount of the sample (10 – 50 μL)
  • Results meet the standards set by AOCS and or ASTM
  • Generates results in 20-30 minutes
  • Designed for ease-of-use and convenience
  • Each kit contains up to 120 tests and comes pre-packaged with all the reagents, calibrators and controls
  • All reagents are non-toxic
Nuts, Nut Butter, Nut Flours, and Dairy.
When comparing MP Bio Percent Fat Test Kit to traditional AOCS test methods on 56 samples of various types of protein meals, MP Bio Percent Fat Test Kit was found to be more precise and had less variation.
Read more about Percent Fat Analysis with MP Bio in the Food Quality Brochure.
 

What Is Being Analyzed

There are numerous components that you can analyze to test your products for rancidity, and the appropriate endpoints largely depend on your sample type.

Peroxide Analysis

Lipid peroxides are the primary product of oxidized oils or fats and are an indicator of off-flavors and off-odors (rancidity). Testing determines the number of peroxides in the lipids. Peroxides are the initial indicators of lipid oxidation and will continue to react and produce secondary products such as aldehydes.

Free Fatty Acid Analysis

Free fatty acids are a key indicator of hydrolytic degradation associated with off-flavor and textural changes. The free fatty acid is quantitated as percent oleic acid using an indicator that responds to the acids in the sample matrices.

Conventional method requires large volumes of organic solvents, large sample aliquots, and involves a lengthy titration process, as well as extraction for some samples which can take up to eighteen hours.

Malonaldehyde Analysis

Malonaldehydes are an indicator of secondary oxidation associated with off-odors and off-flavors (rancidity). This analysis is primarily useful for low-fat samples, as the whole sample can be analyzed rather than just the extracted lipids.

Alkenal Analysis

Alkenals are products of secondary oxidation arising from the degradation of lipid peroxides. The presence of alkenals contributes to off-flavors and off-odors (rancidity) even at low concentrations.

Percent Fat

Depending on conditions of digestion and extraction processes employed, these methods determine triglyceride values as well as other lipid component values. Conventional methods (e.g., butt-tube, Soxhlets, Mojonnier and Babcock, and acid-hydrolysis) typically require the use of large volumes of toxic and flammable solvents, large sample aliquots, and extraction procedures taking up to 18 hours.

Total Glycerin

Biodiesel is a replacement for petroleum-based diesel fuel that can be used in most diesel engines. Biodiesel can be made from plant oils such as soybean, canola, cottonseed, and others or from animal fats such as beef, chicken tallow or pork lard. High levels of glycerin in biodiesel can result in clogged fuel filters and damaged injectors, making it an indicator of poor quality.

Test

Samples

 

Peroxide Test

  • Oils / Hydrogenated oils
  • Milk
  • Eggs
  • Nuts, grains, seeds
  • Fried foods
  • Crackers and Chips
  • Meals
  • Ground meats
  • Fish, digests
  • Organs
  • Finished products (wet/dry)
  • Tallow and greases
  • Cosmetics

Free Fatty Acid Test

  • Oils / Hydrogenated oils
  • Milk
  • Eggs
  • Nuts, grains, seeds
  • Fried foods
  • Crackers and Chips
  • Meals
  • Ground meats
  • Fish, digests
  • Organs
  • Finished products (wet/dry)
  • Tallow and greases
  • Cosmetics

Malonaldehyde Test

  • Oils / Hydrogenated oils
  • Milk
  • Eggs
  • Nuts, grains, seeds
  • Fried foods
  • Crackers and Chips
  • Meals
  • Ground meats
  • Fish, digests
  • Organs
  • Finished products (wet/dry)
  • Tallow and greases
  • Cosmetics

Alkenal Test

  • Oils / Hydrogenated oils
  • Milk
  • Eggs
  • Nuts, grains, seeds
  • Fried foods
  • Crackers and Chips
  • Meals
  • Ground meats
  • Fish, digests
  • Organs
  • Finished products (wet/dry)
  • Tallow and greases
  • Cosmetics

Percent Fat Test (Triglycerides)

  • Dairy
  • Cheese
  • Oils
  • Snacks
  • Eggs
  • Cosmetics

Total Glycerin Test
(Free and Bound)

  • Biodiesel
 

Perform Shelf-Life Testing By Testing Products Over Time

Testing finished products over time typically produces a curve like this:

By tracking which nutrients are decreasing and which degradants are increasing over time, you can estimate the time required for your sample to reach rancidity and get a more accurate picture of your product’s shelf life.

Relevant Resources: