Assessment of the Levels of Ochratoxin-A in Coffee Beans from the Coffee Growing Region of Kiambu County, Kenya

Abstract

Coffee is one of the major foreign exchange eaners in Kenya. The quality of the coffee beans determines the sustainability of the market for the same.  The presence of mycotoxins in the processed coffee is one of the greatest emerging threats to coffee quality. Mycotoxins are toxic, carcinogenic and mutagenic metabolites of certain moulds and are some of compounds encountered in the food and beverage industry. There are two main classes of mycotoxins found in stored crop produce, namely afflatoxins common in grains, and Ochratoxins being the most predominant, common in fruits. Of the Ochratoxins, Ochratoxin-A is most predominant and an emerging problem in coffee production over the world. In the present study, the presence of OTA in raw and processed coffee samples from Kiambu County, Kenya was investigated. The objective of this study was to assess the levels of OTA in Kenyan coffee. Sample clean-up was carried out using OTA immuno-affinity columns. Samples were collected from all the coffee growing areas of Kiambu County, a major source of Kenyan coffee and consisting of areas with varying climatic conditions using a stratified sampling design. OTA was determined using high performance liquid chromatography coupled with fluorescence detector after sample clean by use of immuno affinity columns. Analysis of Ochratoxin-A was on green and roasted beans to help in comparative studies. Whether, roasting causes significant reduction or increment of OTA was tested using t-test and Mann Whitney u-test. The result of this study provides baseline data as to the levels of OTA contamination in the Kenyan coffee industry and suggests possible control measures. HPLC analysis indicated non- appreciable levels of OTA in premium coffee types AA and AB while acceptable levels were detected in Mbuni. The calibration curve of OTA standards by HPLC-fluorescence procedure gave an LOD value of 2.05 µg/Kg and LOQ value of 2.441 µg/Kg. Test of the efficiency of method used was carried out by spiking the samples with standard solutions. Spiking of green coffee indicated a recovery level of 79.56%±1.31%, while that of roast coffee gave a recovery level of 50.62%±2.77%. The recovery studies showed that appreciable levels of OTA are lost during extraction and clean up procedures while roasting causes appreciable decline to OTA levels and so is processing of coffee. TLC analysis could detect up to a minimum of 150 µg/Kg of OTA and it is therefore unreliable in analysis of the low limits of OTA allowed in coffee.