Water Activity in Animal Feed

What is water activity and why does it matter?

Water activity is a thermodynamic property and is generally defined as the energy of water in a system or how easily water can escape into the vapor phase. This principle is vital in animal feed production because the higher the energy in the water, the more likely the water is to cause microbial growth, moisture migration, and chemical or physical reactions. 

With this in mind, it's essential to understand the distinction between water activity and moisture content and that water activity is a far more precise predictor of spoilage, degradation, and other undesirable changes.

For example, microorganisms use the water in their surrounding environment to survive. If a microbe is surrounded by a lower water activity than its interior, it will experience osmotic stress. Osmotic stress causes water from the inside to move to the outside, and it will lose trigger pressure. In this scenario, when a microorganism can't match its surrounding environment, it will go dormant, meaning it can't grow or reproduce in that environment. Each microorganism has a specific water activity level under which it can't grow, making water activity a highly effective way to control microbial growth. 

How to control water activity

Controlling water activity is incredibly important in product safety and quality. Let's examine how to do it. 

Water activity is affected by chemical and physical bonding, meaning that when water is bound, its energy decreases. Salt and sugar are each an example of additives that bind water. Total moisture content also affects water activity because less water in a product equals less water available to react. And last but certainly not least,  temperature is a critical component in water activity because as temperature increases, water activity also increases. Therefore, it is vital to understand the temperature conditions your product will encounter and how your product will react to temperature abuse. 

Here are a few effective ways to control water activity:

• Dehydration – Increasing dehydration in kibble or feed will reduce the amount of water in the product

• Edible films and coatings – Using the correct films and coatings can prevent moisture from being able to travel

• Humectants – Using additives that bind with water such as salt, sugar, amino acids, and polymers can help control water activity

When water activity is used in conjunction with another control method, such as pH levels or additives, it is known as hurdle technology. Each method serves as an additional hurdle help to keep the product safe.

Moisture sorption isotherms

The relationship between moisture content and water activity is shown through moisture sorption isotherms. Creating a moisture sorption isotherm for each ingredient and product will give you a complete moisture map of your product, allowing you to pinpoint where specific reactions to moisture—such as microbial growth or decreases in quality—will occur. This enables you to create the perfect balance between safety and quality for your product. 

Creating and using isotherms has immensely valuable application in animal feed production, especially for Research and Development teams. Here's a glance at a few of the top ways R&D teams use isotherms:

• Maximize moisture content for profit by understanding how much moisture can safely be in a product

• Avoid unwanted textural changes such as caking, clumping, and loss of flowability

• Accurately predict shelf-life more quickly than through an accelerated test

• Choose correct packaging by understanding the water vapor transmission rate needed to hit the desired shelf life

• Predict environmental effects by understanding how potential temperature abuse in transport and storage will affect each product

• Accelerating formulation processes

Big real-life impact

Our in-house examinations of animal feed confirmed that small changes in moisture content cause significant changes in water activity, making it essential to measure water activity to monitor and control moisture in animal feed. Creating isotherms allows feed processors and manufacturers to identify the ideal water activity range for their product, enabling significant optimization of production and increases in consistency, quality, and safety. 

Our analyses also showed that seemingly minor shifts in moisture could produce substantial financial impacts. For example, one company reported a moisture content target of 10% for safety. However, after creating an isotherm, we were able to show them they could safely increase the moisture content to 10.4%, which could result in huge savings on raw materials. In short, using isotherms allows you to set guardrails for your product, reduce variation in production, and maximize moisture content for profit.

Please watch the webinar for additional detailed information on the effects of water activity in animal feed.