This 5-minute video created by Michael Reid on March 26, 2017 introduces the DryCard™, a low-cost tool to address the postharvest problem of dried foods contaminated with fungi and fungi-produced toxins during storage.
The problem of aflatoxin contamination
Fungi may produce postharvest toxins such as Aspergillus flavus which produces Aflatoxin and is commonly found in stored maize, peanuts, and other products. Low concentrations of this toxin can prevent the uptake of nutrients and suppress the immune system. High concentrations can lead to liver cancer or death. Aflatoxin contamination can be reduced by ensuring products are dry enough before they are stored. Water activity is directly related to the equilibrium relative humidity (ERH), and is a better measure of the risk of fungal infection than moisture content.
An alternative, accessible solution to measure dryness
There are digital and other instruments that can be used to measure water activity, but these instruments are expensive and so not available to small scale farmers and traders. An alternative technology is the use of cobalt chloride paper which changes colors from blue to pink as the humidity increases. The DryCard was developed to make this cobalt chloride more practical and easily used by small scale farmers and traders. It is estimated that the DryCard can be sold for around $1 USD.
The DryCard has been translated to many languages including Swahili, Spanish, French, and is simple to use. The DryCard is placed in a sealed container with a sample of the dried product. After 30 to 60 minutes, the color of the cobalt chloride paper will determine the dryness of the product. The color can be compared to the color scale on the card. If the color is above the threshold line then the product is too wet and must be dried further. If the color is below the threshold line then the product is dry enough and safe for storage.