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Maintaining Product Texture: Research Validates a more Efficient Method



When the texture of a low moisture product such as a cracker is just right, it receives little notice. But if a cracker’s crispness begins to fail, consumers will reject it immediately. How do food manufacturers maintain correct product texture for the entire shelf life of their product? The most important factors are moisture and temperature.


Studies show that the boundary for desirable product crispness in low moisture products such as boxed cereal, crackers, and cookies is defined by a critical water activity. Typically, this critical water activity is found through an extensive texture study, but there is an easier way. High resolution dynamic isotherm curves (see Fig. 1) have been shown to identify critical water activity values (RHc) that pinpoint where correct texture is lost by sharp inflections in the moisture adsorption curve. 




Figure 1: Each product has its own unique isotherm curve due to different interactions (colligative, capillary, and surface effects) between the water and the solid components at different moisture contents.


A Cookie Crispness Study


One study performed by researchers at Washington State University tried to determine if the dynamic isotherm curves for low water activity snack cookies could be used to identify a critical water activity, and if this RHc could be used as a texture stability indicator.


Using a Vapor Sorption Analyzer, the researchers developed dynamic isotherms for two low moisture cookies at three different temperatures. They then used those isotherms to determine critical water activities. Cookie samples were preconditioned to various water activity values and temperatures and were analyzed for crispness. The researchers found that the effect of water activity on crispness was more important than temperature and that the critical water activity did indeed identify the point at which the correct texture was lost. Cookie samples at water activity values less than the critical water activity maintained their crispness, but samples at water activity values higher than the RHc suffered an abrupt loss in texture.



Critical Water Activity: An Efficient Alternative to Texture Studies


To compare their results, the researchers used another method for determining critical water activity: Fermi’s equation for sigmoidal response.


Using this equation, they modeled the response of crispness to water activity and estimated a critical water activity for texture loss. Both the RHc and Fermi’s critical water activity were found in the range of texture loss, but interestingly, the RHc corresponded with the initial loss in texture, while Fermi’s critical water activity was at the midpoint of the texture loss, illustrating that RHc allows for extreme accuracy in determining the exact point where texture is lost.


This was important because RHc can be obtained with much less labor and time than a texture study, and in products sold by weight, knowing the exact amount of water that influences textural stability directly impacts the bottom line.


Read study details in the online WSU Research Library