Distribution of aflatoxins in shelling and milling fractions of naturally contaminated rice

Abstract

The objective of this study was to determine the distribution of an economically important class of mycotoxins, the aflatoxins, in rice milling fractions. Rice plants grown under field production conditions are frequently infected with types of pathogenic fungi that produce toxic metabolites (mycotoxins). Paddy (seeds) rice from healthy plants in the field was collected and stored on a farm under humid, poorly ventilated conditions. Samples were milled into four fractions (hulls, brown rice, bran and white rice) and analysed for aflatoxins (B₁, B₂, G₁ and G₂) using a validated method. Rice fractions from healthy plants, which contained low levels of aflatoxins (less than 1 µg kg⁻¹), were used to determine the efficiency of the extraction method. Seeds stored under poor conditions were found to be contaminated with aflatoxins B₁ and B₂ as were the fractions. The sums of AFB₁ and AFB₂ in stored paddy rice, hulls, brown rice, bran and white rice were 141, 39, 158, 367 and 56 µg kg⁻¹, respectively. The ratio of aflatoxin B₁ and B₂ was about 10 : 1. AFG₁ and AFG₂ were less than 1 µg kg⁻¹. Thus, brown rice contained 92.9% of the aflatoxins in paddy rice, whereas white rice contained only 27.9%.

Keywords:

• HPLC
• aflatoxins
• mycotoxins
• natural toxicants
• rice
• cereals

Acknowledgements

The authors acknowledge the excellent technical assistance of Ms Bobbie J. Johnson and Nick A. Phillips. They thank Dr Dwight G. Kanter, MSU, DREC, Stoneville, MS, for use of laboratory facilities to shell and mill rice samples. They thank Dr James Smith, Delta Rice Services, Inc., Cleveland, MS, for providing toxin-free rice, bran, and hull samples used in this study. They also thank Mr Kevin D. White, Food and Drug Administration, College Park, MD, for performing the LC/MS/MS analysis. The mention of trade names or commercial products is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the US Department of Agriculture.