Predict Packaging Performance

Webinar Summary and Key Points

Packaging is one of the weakest links in a product’s shelf life. An effective package can maintain a product’s water activity regardless of storage humidity. And it can do this without being too expensive—if you know what to look for. In this webinar, Dr. Brady Carter, Director of Food Science at METER Group, discusses how anyone can use a straightforward computer model with critical water activity and package permeability data to pick the right package.

Utilizing the Critical Water Activity and Food Packaging Permeability to Predict Shelf Life

This webinar explores water activity and how it can impact the packaging and shelf life of a product. The speaker assumes that participants already have a working knowledge of water activity and provides resources to learn more about water activity fundamentals. The concept of critical water activity is introduced, or the idea that a certain value of water activity could lead to microbial growth or other chemical reactions, impacting the shelf life of a product. The webinar content will explore product packaging as a means of moisture transfer or barrier and will include demonstrations.

Functions and Food Packaging Permeability 

The webinar assumes knowledge of packaging fundamentals and will examine food packaging permeability. Packaging has four essential functions: containment, convenience, communication, and protection. Containment covers transportation and storage of a product without damage. Protection includes preventing gas transfer, moisture transfer, microbial activity, humidity effects, and UV contamination. Packaging involves not only maintaining water activity, but also controlling the rate of moving water across packaging to prolong shelf life.

To understand food packaging permeability and evaporation, we need to understand the characteristics of the product and the packaging material. Food packaging permeability is the difference in water activity inside the packaging (i.e., the product) and the water activity (or relative humidity) outside the packaging. The goal is to control how much water is allowed in or out of the packaging.

Water Vapor Transmission Rate

Moisture transmission rate (MTR) is also known as water vapor transmission rate (VTR). This is a key value in determining permeability of different packaging materials. VTR directly impacts the cost level of the product. A higher VTR means that a product will need a more permeable packaging, and a low VTR requires less permeable packaging. The ideal VTR value is also influenced by how much money the manufacturer wants to allocate to the product.

When making food packaging permeability decisions, we have to convert the VTR value into perms, a unit that’s more adapted to modeling values. Glass is a packaging option that provides complete protection, though it’s also very costly. To use glass packaging, the value and cost of the products need to warrant a more expensive packaging material. Foil also has a very low VTR and is much less costly than glass. When communicating with suppliers, manufacturers need to be mindful of units used when communicating with suppliers so that they receive the appropriate packaging materials. The webinar includes a model of how a manufacturer would use these values.

The Role of Equations

By collecting a basic set of information, we can predict a number of outcomes when it comes to food packaging permeability: water activity in a stored bag in a variety of storage conditions, water vapor transmission rates, and shelf life with a given critical water activity. Values we should consider when gathering data include saturated water pressure, surface area, mass of the sample, and changes in water activity. All of these values can be combined into one equation that boils down to change in moisture / change in time. 

To work these calculations, we need to have the isotherm slope, which translates water activity into mass values. Once you have these values, you can solve for any number of factors: moisture, water activity, and VTR, to name a few. The webinar walks through an example of how to work and apply these equations and calculations.

Why Water Activity

Of all the values to consider, water activity is the most versatile in allowing us to model different outcomes. Water activity can help in determining and understanding shelf life. Water activity can contribute to the end of shelf life by increasing the rate of reactions, acting as a plasticizer, and enabling microbial growth, and water activity is also impacted by the mobility of the product. 

Water activity allows us to monitor moisture in a product in a more meaningful way than simply checking the moisture content. Identifying water activity values also allows us to set other specifications in modeling. (An example is given in the webinar.)

The webinar presents another in-depth example using spray dried milk powder and potential package requirements. Modeling work can be performed once we have the initial water activity of the product in the package, the critical water activity, how much sample is present, the storage temperature, the atmospheric pressure, and the slope. All these values can be manipulated to predict shelf life and other attributes of packaging materials. The webinar gives multiple examples of how to use these values to understand how to decide on appropriate packaging for a product.