Molds that contaminate dry foods, especially ground nuts and maize cause significant postharvest losses in the developing world. Mold contamination results in poor flavor, loss of dry matter, and most importantly, is a health hazard. Aflatoxin, produced by several fungi, contaminates up to one quarter of the world’s food crops and is a particular problem in sub-Saharan Africa and Asia. It causes acute poisoning, liver cancer and is associated with stunting and suppression of the immune system. It is estimated to cause about 100,000 cases of liver cancer per year and a world-wide loss of 1-2 million daily adjusted life years per year.
Fungal contamination can occur before harvest, but much of it occurs during drying and storage. Mold development can be stopped by ensuring that food and feed is adequately dried. Electronic moisture meters are commercially available but cost hundreds to thousands of dollars.
Jim Thompson and Michael Reid have developed a simple, low-cost method of determining whether foods are dry enough to prevent mold growth in dry foods. The device is called DryCard and is based on the concept that relative humidity of air around a product reflects the moisture content of the product. (This is called equilibrium relative humidity.) Molds will not grow if the relative humidity of the air around a product is lower than 65 percent. The convenient aspect of this concept is that it is not necessary to measure product moisture, but only the relative humidity in air around a food item.
The DryCard estimates relative humidity with a commercially available paper strip that changes color as air humidity changes. A blue or grey color indicates humidity is below the threshold that will allow mold growth. A pink color indicates that the product is not adequately dried and mold can develop. The materials used to make each DryCard cost less than 10 cents and the card can be reused many times.
Projects to introduce the DryCard are being planned in Zambia, Tanzania and Kenya. If you are interested in participating in the DryCard project, please contact Michael Reid, firstname.lastname@example.org or Jim Thompson, email@example.com.
The DryCard project was supported by the Horticulture Innovation Lab at UC Davis, which is supported by USAID.
Source: UC PostHarvest Technology Center newsletter, Feb. 2017