The Salt Crystal Liquefaction Test - A Simple Method for Testing the Water Activity of Foods

Area of Science:

• Food Science
• Analytical Chemistry
• Physical Chemistry

Background:

• Water activity (a_w) is a critical parameter in food preservation, affecting microbial growth and chemical stability.
• Accurate and accessible methods for determining a_w are essential for quality control and regulatory compliance in the food industry.

Purpose of the Study:

• To develop a simple, reliable method for testing the water activity (a_w) of food products.
• To provide a practical tool for verifying that food products meet required a_w standards.

Main Methods:

• The method utilizes the principle of salt crystals attracting water vapor and liquefying when exposed to a product with a higher a_w than the salt's specific a_w.
• A range of salts with specific a_w values (0.68 to 0.98) are employed to assess products across various a_w levels.
• Test sensitivity is less than 0.02 a_w, with reading times varying from 3 to 24 hours based on salt, product, and temperature.

Main Results:

• The salt crystal method effectively determines food a_w, offering a practical approach for compliance testing.
• Tests using high a_w salts require temperature control, necessitating a thermostat-controlled cabinet.
• Copper(II) chloride dihydrate (CuCl₂•2H₂O) crystals (0.68 a_w) demonstrated promise for field applications under diverse environmental conditions.

Conclusions:

• A straightforward salt-based method for food water activity testing has been successfully developed.
• This method offers a viable alternative for routine a_w monitoring and quality assurance in the food sector.
• The CuCl₂•2H₂O variant shows potential for field deployment, enhancing on-site testing capabilities.