Guidelines for Safer Rice Storage Conditions Aim to Improve Global Health

The Problem

Rice is crucial for worldwide nourishment, with half the global population relying on it as a staple. However, 15 percent of rice every year is lost because of contamination from harmful organisms such as fungi. When rice is exposed to high temperatures and humidity in storage, the likelihood of this contamination increases. The fungi can then produce naturally occurring toxic compounds called mycotoxins. Aflatoxins, a family of these mycotoxins, are poisonous Group 1 carcinogens, meaning there is sufficient evidence they can cause cancer in humans. They also pose a greater risk to children by threatening their immune systems and stunting their growth.

Even temperatures as high as 200 degrees Celsius, or 392 degrees Fahrenheit, won’t eliminate aflatoxins once fungi have produced them, meaning that rice becomes useless once contaminated. Therefore, the window of opportunity for removing risk is in the early stages of rice processing.

The Work

Researchers with the Arkansas Agricultural Experiment Station used rice collected from a Hazen, Arkansas, farm and divided it into rough, brown and milled sections. The rough rice was unprocessed and still had its hull, or hard protective covering, while the brown rice did not. The milled white rice had its hull and bran layers removed. Samples of each were then divided into steam-sterilized and non-steam-sterilized fractions, and all samples were then inoculated with Aspergillus flavus, which is a type of aflatoxin-producing fungus. They then measured how temperature, humidity, storage time and moisture affected aflatoxin levels.

The research team included Ph.D. student Faith Ouma and her advisor Griffiths Atungulu, an associate professor of grain processing and post-harvest system engineering for the Arkansas Agricultural Experiment Station. Atungulu is also director of the Arkansas Rice Processing Program, which undertook the research. Other co-authors included Kaushik Luthra, a food science postdoctoral fellow, and Abass Oduola, a former food science doctoral student.

The Results

Of all tested variables, temperature and humidity levels had the most significant impacts on fungal growth. Research showed that proper rice storage conditions to reduce the risk of aflatoxin contamination included a temperature below 20 degrees Celsius, or 68 degrees Fahrenheit, and relative humidity below 75 percent.

Researchers also found that brown rice had higher aflatoxin levels because of the fats in its bran that can provide carbon for fungal growth and, therefore, for aflatoxin production.

The Value

Aflatoxin contamination is more common in developing countries. In 2004, for example, the most extreme aflatoxin outbreak occurred in Kenya, with 317 cases and 125 deaths. Ouma, a native of Kenya, undertook this research with an aim to eradicate risk and prevent future outbreaks. Additionally, with ready-to-eat rice products such as rice cakes and instant rice increasing in popularity, aflatoxin contamination poses an even greater risk. The findings of this research offer insights into rice storage interventions that can minimize aflatoxin contamination and create safer rice products.

About the Researchers