Snack foods, nuts, and other foods that taste bitter and rancid have likely fallen prey to lipid oxidation. Chemical reactions such as lipid oxidation cause products to degrade by affecting flavor, odor, and/or color when free radicals steal electrons from fatty acids in a chain reaction. Luckily, food formulators aren’t powerless when confronting lipid oxidation, and water activity is one of their most useful tools. Because water activity is a measure of the energy of water in a product, it affects how quickly lipid oxidation reactions proceed.
Controlling water activity slows lipid oxidation
In practice, lipid oxidation reaction rates decrease as water activity goes down. However, as water activity declines below 0.4 aw, rates begin to increase again. This makes the general region of 0.4 aw an important target for snack foods and nuts. However, this rule isn’t absolute for all products. The best way to know how water activity affects lipid oxidation in a product is to use accelerated shelf life testing.
Accelerated shelf life testing simplifies the process
Manufacturers can slow lipid oxidation and extend their product’s shelf life by controlling just two factors: water activity and temperature. These three simple steps illustrate how.
Step 1: Determine what causes a product to fail
Product developers often overlook the first step in determining shelf life: figuring out what causes a product to fail. Before collecting data, let the product fail to determine if lipid oxidation is the shelf-life-ending factor. Check for off-flavors and off-odors.
Step 2: Decide how to quantify changes
If lipid oxidation is causing a product to degrade, decide how to quantify it. Manufacturers often quantify levels of lipid oxidation through sensory testing, peroxide values, TBAR values, or oxygen consumption.
Step 3: Begin data collection and modeling
Begin collecting data at accelerated water activities and temperatures. Do not use data from any other product, even if the properties are similar. Collect data at three different water activities and temperatures to create empirical models that account for both temperature and water activity. This will pinpoint optimal conditions that minimize the chemical reaction.