Aflatoxin determination in black tea (camellia sinensis) – status and development of a protocol

Aflatoxins, toxic mold metabolites, are naturally contaminants of food and have been reported on tea (Camellia sinensis), but there are no validated methods published for its determination. A method has been standardized incorporating Tween‐20, a nonionic surfactant in the extraction solvent, with use of an immunoaffinity column for cleanup followed by postcolumn photochemical derivatization reversed‐phase high‐performance liquid chromatography. Acceptable recoveries of 76–100% were observed when spiked with aflatoxins B1, B2, G1 and G2. Analysis of market samples of black tea showed the presence of aflatoxigenic molds in 25.9% of samples, and aflatoxin B1 was detected in one sample at a level of 19.2 µg/kg. Aflatoxin production was observed in tea samples artificially inoculated with the conidia of an aflatoxigenic strain of Aspergillus flavus. Major portion of the aflatoxins added to the tea leaves remains in the residue when boiled with water, and 30.6% gets partitioned into the filtrate, which is the component used to prepare the beverage. PRACTICAL APPLICATION: Tea (Camellia sinensis) beverage is widely consumed in the world. This manuscript discusses the prevalence and problems of aflatoxigenic molds and aflatoxins in black tea. A new protocol has been validated for determination of aflatoxins using a surfactant in the extraction solvent for better extraction, followed by column cleanup using immunoaffinity columns and quantification by postcolumn photochemical derivatization reversed‐phase high‐performance liquid chromatography. Aflatoxin production in tea artificially inoculated with the conidia of Aspergillus flavus (isolated in the laboratory) was also observed. The method of preparation of tea beverage by a large number of people in the country is by boiling the black tea leaves with water and using the filtrate to prepare the beverage with milk and sweetener. In the study on the partitioning of the aflatoxins added to black tea leaves before boiling, it was observed that about 30.6% of the added toxin is in the filtrate, a finding with relevance in risk assessment.