How to Fast Track Your Shelf-Life Testing

No one likes waiting. In particular, no one wants to wait any longer than absolutely necessary to launch an incredible new product—precisely when excitement is at its peak. In the competitive world of food CPGs, being first to market can become an all-important key for success. Launching first means the opportunity for market penetration before competitors enter the space, but launching too early could mean compromising quality and safety. Most companies recognize the need for shelf-life testing but remain highly motivated to speed things along, so having a way to accelerate the process is very enticing. The question is, can it really be done?

Shelf-Life Testing on the Clock

Conventional shelf-life testing involves monitoring a product over its probable lifespan with the goal of determining how long it will remain acceptable. While food safety is often an element of shelf-life testing, most best-before dates are not driven by safety—but rather, by quality. Attributes such as flavor, color, texture, and physical changes will almost certainly change over time in ways that are often difficult to reliably predict.

Conventional shelf-life testing periodically monitors the most important attributes of a product and determines acceptability over its expected life span in “real time.” For some products that might be only a couple of weeks; for others, it could be years. Real-time shelf-life testing gives a very good understanding of how a product will change over time; however, waiting for the natural degradation of foodstuffs is literally time-consuming.

Accelerated shelf-life testing (ASLT) has emerged as a technique that simulates conventional shelf-life testing in a fraction of the time. This is accomplished by storing food products under exaggerated storage conditions: warmer temperatures, higher humidity levels, intense light exposure, and other stress factors that can all be used to accelerate natural deterioration processes. This allows food scientists to obtain valuable information about product stability, quality attributes, and safety in a fraction of the time required by traditional shelf-life testing. The benefits of this are obvious. Traditional shelf-life testing often takes months or even years, but ASLT can condense this time frame to months or even weeks, enabling manufacturers to make decisions quickly about product quality, safety, and stability, ensuring that the product meets customer expectations and regulatory requirements. 

Getting Up to Speed

So, how does ASLT work? How can we seemingly speed up time? The answer is that we can’t, but we can speed up the rate at which some processes take place. The most common way to calculate this is through something called a Q₁₀ temperature value. The Q₁₀ value is a measure of the rate of change of a biological or chemical system as a consequence of increasing the temperature by 10°C. This means that if we know the Q₁₀ value of the rate of say, an enzymatic browning reaction, we can reliably increase the rate of reaction by raising the storage temperature of a product by 10°C. For example, if a process has a Q₁₀ of two (2), by storing it at 30°C instead of 20°C, we would expect that the rate of change would double.

All of this sounds fantastic, doesn’t it? Simply increase the storage temperature by 10 degrees and we can do a 12-month shelf-life study in six months! Add another 10 degrees and we can double it again, and so on. Many in the food industry have decided that this is indeed the case and rely on an over-simplified view of accelerated testing, assuming that by adding 10°C they can cut shelf-life testing time in half. Unfortunately, it is not quite that simple. Let’s recall that the Q₁₀ values are only appropriate for a single system or reaction—but, of course, most food products are complex. So, while your browning reaction may have a Q₁₀ of 2, other systems could go faster or slower, and some systems may not change at all.

While you are imagining all these different aspects of your product racing into the future at different speeds, let’s consider that some product attributes do not change when we turn up the temperature. For instance, the amount of ultraviolet light that impacts a product, consumer handling, and the effects of gravity on a product are all predominantly influenced by factors unrelated to temperature—but that doesn’t mean that they cannot be accelerated in other ways. We can mimic the type and amount of light that a product might expect to see over the course of a year. Gravity can very quickly be modeled in a centrifuge, and we can use mechanical means to shake and manipulate products to replicate logistics or consumer handling.

Considerations and Watchouts

While ASLT offers numerous advantages, there are clearly limitations that must be considered. Like all experiments, our results are only as good as the model we use. It is typically impractical to achieve full replication of real-world storage conditions simply by evaluating a product in a lab. What we can do is look at the unique combinations of packaging materials, product matrices, and environmental factors to get an early understanding of product degradation mechanisms that allow manufacturers to identify and address potential quality issues earlier in the process. We might also want to consider the importance of other factors such as consumer interaction, logistics, and extreme events, and model them if necessary. As previously discussed, products age unnaturally under accelerated conditions; for some products, this may be very close to real-time testing and in other cases, it may be very misleading.

Accelerated testing generally does a good job of modeling physical and chemical systems well, while microbiological and organoleptic changes may not track very linearly. This is especially important when we consider that most best-before dates rely on organoleptic acceptability. It can be a risky assumption to blindly follow ASLT results since we know that attributes such as taste, aroma, texture, and visual appearance often are negatively exaggerated. Similarly, product functionality such as performance under specific usage conditions and compatibility with other products may be beyond the scope of ASLT. All of this is to say that ASLT offers a greater risk of overestimating or underestimating the actual shelf life of a product because the act of acceleration introduces inherent uncertainties. The more extreme the acceleration, the less likely the results will resemble real-life outcomes.

While accelerated shelf-life testing comes with some uncertainty, for most products the risks associated are perfectly acceptable. Practical decisions can be made based on the outcomes of accelerated shelf-life tests and incredible amounts of time and money can be saved. The challenges associated with ASLT do not compromise its value as a very useful tool—unless they are ignored.

One of the best investments that can be made while planning ASLT is initiating a parallel real-time shelf-life study. By comparing the real-time results to the accelerated study, we can better understand how the accelerated model is tracking against reality. This can be invaluable for understanding what parts of the product is being over- or underestimated and by how much.

Strategic monitoring and evaluation during ASLT also are crucial for obtaining accurate results. Regular sampling and testing at predetermined time intervals enable us to track changes in sensory properties, microbial growth, chemical stability, and nutritional content. Almost any parameter can be measured, but often the question is what we should measure since cost and practicality are frequently constraints. Focusing on the product parameters that are likely to present the highest risk helps manage testing costs and allows us to focus our attention on maximizing how best to accelerate those systems. This might mean dedicating more robust testing for some parameters than others. For instance, we have many options for measuring oxidation, ranging from high-performance liquid chromatography analysis to organoleptic observations. Depending on the estimated risk of oxidation in our product, we can decide whether precise quantitative data or casual qualitative information is appropriate and allocate resources accordingly.

Finally, it may not be immediately obvious, but we need to think practically about the conditions we choose. Some products do not respond well to simple acceleration. If we increase the storage temperature of chocolate or ice cream enough, they melt. In doing so we will have initiated a cascade of physical and chemical changes that have nothing to do with the passage of time. This doesn’t mean that we can’t accelerate the shelf life of these products, it just means that we need to consider other options besides simply using elevated temperatures.

Conclusion

Accelerated shelf-life testing has revolutionized the field of product development and quality control by providing a rapid and cost-effective approach to assess product stability and safety. By simulating and accelerating the natural deterioration processes, manufacturers can obtain vital information about product shelf life in a shorter time frame, leading to improved product quality and reduced time-to-market. How-ever, careful consideration of acceleration factors, experimental design, monitoring, validation, and predictive techniques is necessary to ensure accurate and reliable results. As consumer expectations continue to rise, accelerated shelf-life testing will remain an indispensable tool for manufacturers who are prepared to invest just a little extra time in doing it right.ft