Acrylamide content of selected processed Ugandan Coffee varieties

Abstract

Coffee beans are roasted at high temperatures above 120 oC, which results in a Maillard reaction leading to acrylamide formation. Acrylamide is carcinogenic and causes damage to the nervous and renal systems of the body. The formation of acrylamide in coffee is dependent on factors such as roasting time, temperature, and bean variety. Much as there is a plethora of information regarding acrylamide and its presence in coffee, there still exists a dearth of literature on the effect of processing coffee on acrylamide levels, specifically for coffee varieties grown in Uganda. Therefore, this study assessed the effect of processing on acrylamide levels of selected Ugandan coffee varieties. Coffee cherries of eleven varieties were collected from Luwero district and sun-dried to a moisture content below 12%. The dried coffee cherries were hulled and analyzed for moisture content, screen retention, out-turn, defect count, glucose, fructose, and crude protein contents using standard methods. The coffee beans were then roasted and brewed under different conditions then analyzed for acrylamide using Liquid Chromatography–Mass Spectrometry. The moisture content, defect count, and out turn 2 ranged from 8.7 to 11.0 %, 3.2 to 18.5 %, 81.5 to 96.8 %, and 42.1 to 57.1%, respectively. The overall retention of beans on screen 15 for Kituza Robusta (KR) 6, Kisansa (KS) and Nganda (NG) varieties was above 60%. Glucose levels ranged from 1.7 to 2.9 g/100g, while fructose ranged from 0.9 to 6.9 g/100g, and the crude protein was 11.0 to 16.8%. The acrylamide levels varied significantly (p<0.05) across coffee varieties, with the highest occurring in the Elite D (ED) variety, with 444.8 µg/kg at dark roast. Acrylamide levels also varied significantly (p<0.05) with roasting time. Higher levels of acrylamide occurred in the dark roasted coffee and were lowest in very dark roasted coffee. Acrylamide levels for coffee brewed using the espresso method were 1.7 to 21.9 µg/L. They were highest in Kisansa coffee brewed for 60 s and lowest in the same variety brewed for 10 s. Whereas for the coffee brewed using the French press method, the acrylamide levels were 9.2 to 66.3 µg/L, with the highest (p<0.05) occurring in KR7 brewed for 10 min and the lowest in Kisansa brewed for 3 min. Therefore, the study indicated that there are varietal differences in the physicochemical properties of coffee beans, which in turn influence their acrylamide levels upon roasting and brewing.