The Science of Staying Fresh: Designing Long-Lasting, Delicious Natural Products
Creating shelf-stable nutritional bars and other natural food products isn’t just about mixing healthy ingredients. It’s about understanding the science behind food preservation, taste and appearance. One of the most critical factors in the formulation of long-lasting, safe and appealing products is water activity. Water activity plays a major role in maintaining texture, reducing the rate of fats oxidation preventing spoilage and ensuring safety from microbial growth.
What is water activity?
The water activity of a food (aW) is a measure of how much free water is available in a product. It is calculated by the ratio between the vapor pressure of the food itself and the vapor pressure of distilled water under identical conditions. For example, a water activity of 0.80 means the vapor pressure is 80 percent of pure water.
Low water activity foods are naturally low in moisture or have had water removed, such as dried fruits like raisins and dates. Water activity-controlled foods are those that are intentionally managed to prevent microbial growth and extend their shelf life. This is often done by adding humectant ingredients, such as sugar, to help reduce water activity. Examples of water activity-controlled food include jams, protein bars and crackers.
The Importance of Water Activity
When water activity is kept below 0.85, most harmful bacteria can’t grow, except for yeast and mold. This impacts the quality and shelf life of products. By lowering the water activity even more, to below 0.6, you can stop yeast, mold and microbial growth.
Water activity relates to other food aspects beyond microbial safety. It can also affect how a product tastes, looks and feels over time, as well as its shelf life. Ingredients with high water activity can lead to spoilage, texture changes or even unwanted browning due to reactions caused by the different product ingredients.
Case study #1: High-protein drinkable medical food
In one case studied by the Eurofins Product Development & Innovation, a high-protein drink with 17 grams of protein per serving had a high-water activity of 0.97 aW, making it susceptible to bacterial growth. Although the drink had a safe pH level, the fact that it was in a multi-use container and targeted at vulnerable consumers created a serious concern.
By adding glycerin to bind the water, researchers lowered the water activity, but that also changed the amount of protein in the drink to 12 grams and made the drink taste more bitter. By reformulating the protein with a smaller 3000 Dalton collagen fraction and adjusting the flavor systems, the team successfully developed a safe and palatable product. This new formulation effectively controlled water activity and pH, while also ensuring a pleasant taste and texture.
Tackling texture and shelf life in protein bars
Consumers today are increasingly seeking high-protein snacks, such as protein bars, and this trend is expected to grow over the next couple of years. However, incorporation more protein into the same serving size protein bar presents a challenge. he higher the protein content, the more difficult it becomes to prevent the bar from hardening over time. Additional issues like browning and changes in flavors are also common challenges that come along with higher protein content.
Protein bars are composed of two main ingredients: powdered protein from dairy or plant sources, and sweetener. The ingredient distribution varies depending on the type of bar. For example, sports nutrition bars have higher protein, while keto bars are high in fat. Breakfast bars typically have more carbohydrates because they’re meant to provide energy in the morning, and snack bars are higher in sugar. The type and proportion of the bar ingredients have a direct impact on stability.
Some strategies to use for stability in protein bars include:
- Choose the right proteins: Blends of whey proteins tend to stay softer longer.
- Watch your sugars: Ingredients like fructose can cause hardening, but reducing sugar will result in unwanted browning.
- Balance moisture: All parts of the bar — from nuts to crisps to fruit pieces — should have similar water activity levels to prevent moisture migration.
- Set shelf life and packaging: Using isotherms can help predict how the product will behave over time.
- Accelerated shelf life: Evaluate the response to high temperatures and humidity.
Case study #2
One bar manufacturer came to our team with reports of mold growth on its products distributed around the world. Testing showed that some bars had water activity levels above 0.7, high enough for yeast and mold to grow and survive, especially in warmer climates.
The culprit bars were made with brown rice syrup, which had higher-than-expected water activity than those made with raisins and dates. The fix involved switching to a lower-water-activity syrup. However, by lowering the water activity through hydrolysis, the Maltose in the product increased, which can lead to browning and possible product hardening. An alternative to brown rice syrup, like date paste or raisin paste, can be used instead, if it can be evenly distributed throughout the product.
Takeaways for food developers
As food developers are creating products, they should consider the following questions to ensure safety, quality, and consumer satisfaction:
- What methods can you use to control microbial growth (water activity, pH, or both)?
Controlling microbial growth is foundational for both food safety and shelf life. Depending on your product, you may need to reduce water activity (through drying, adding humectants, or using certain packaging techniques), lower pH (with acidulants), or combine both in a multi-hurdle approach. Consider how these interventions might impact texture, flavor, or consumer acceptance—and ensure they align with regulatory guidelines. - What impact does your food safety approach have on product performance?
Balancing food safety with product integrity is key. For example, high thermal processing might effectively reduce pathogens but compromise sensory attributes or nutrient content. A formulation that relies heavily on preservatives might spark consumer concern. Carefully evaluate how your safety interventions affect performance metrics like texture stability, shelf-life consistency, and taste experience. - Can your packaging and storage conditions protect against moisture changes over time?
Even the best-formulated products can suffer from quality loss if packaging fails to protect against moisture migration. Consider packaging with barrier properties that guard against both water vapor ingress and loss. Rethink storage recommendations—ambient vs. refrigerated—and how real-life handling might challenge the stability of your product. - What does it taste like? Can you impact flavor liking through maskers or other ingredients?
Functionality should never come at the expense of flavor. Ingredients used for preservation or fortification can introduce off-notes that diminish consumer appeal. Leverage flavor maskers, enhancers, or even innovative fermentation techniques to optimize taste. Sensory testing early and often can guide iterations that deliver a great-tasting product without compromising quality or safety.
Bringing a successful food product to market requires more than just a great idea—it demands a thoughtful balance of safety, quality, and sensory appeal while keeping an eye on the food laws and regulations By proactively addressing microbial control, evaluating the impact of safety strategies on performance, considering protective packaging, and prioritizing flavor optimization, developers can create products that are not only safe and stable but also loved by consumers. The most successful innovations are born at the intersection of science, creativity, and consumer insight.
Let our experienced team help you conquer the complexities of bar and natural product development—reach out today!
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