Abstract/Summary

Acrylamide is a Group 2B carcinogen compound formed in certain foods when they are heated above 100C. The use of the enzyme asparaginase is becoming increasingly popular as a means of reducing acrylamide formation in cooked foods. Asparaginase converts the acrylamide precursor asparagine to aspartic acid. Roast coffee is one of the major sources of acrylamide in the human diet. In this thesis, asparaginase solution was initially delivered into green coffee beans by a steam & soak method. Hence, acrylamide in the roasted coffee was significantly reduced (40-91%). However, the steam & soak method showed adverse effects, including precursor loss (amino acids 20–30%, sucrose 38%, glucose 47%) and silver skin loss. To examine the impact of enzyme treatment on the aroma of roasted coffee, volatile determination was carried out. Significant differences were found (10% of identified compounds) in a broad variety of chemical families (aldehydes, ketones, furans, phenols and pyrazines). A series of sensory analyses was carried out to identify the impact of enzyme treatment on coffee organoleptic properties. Sensory analysis using descriptive and discrimination tests found significant differences (12 and 17 out of 39 attributes in light roast and medium roast groups, respectively) between enzyme-treated beans and untreated beans. Preference tests, however, showed that control and treated samples were of similar acceptability, with no unpleasant flavours or aromas associated with the enzyme treated group. Finally, a novel vacuum infusion method was used to reduce the adverse effect of the steam & soak method. The results indicated the vacuum infusion method (21–56% acrylamide reduction) was not as effective as the steam & soak method (40–91%). In conclusion, our research confirmed that the enzymatic approach could successfully reduce acrylamide in coffee. However, as the coffee had tight internal structure, the enzyme treatment process would cause the loss of silver skin on coffee beans. The consequence of this loss was a darker roast in the enzyme treated samples. The shift of roast extent leads to significant differences in volatile compounds profile and organoleptic properties of the coffee beans. The vacuum infusion experiment was carried out to reduce the loss of silver skin issue while maintaining the high acrylamide reduction rate. However, the results indicate that the vacuum failed to allow asparaginase to penetrate the coffee and still resulted in great silver skin loss. Future research should focus on minimising the adverse effect of enzyme treatment while maintaining sufficient contact of enzyme and substrate.