Effect of roasting time and temperature of Sri Lankan coffee (Coffea arabica) beans on their functional properties and chemical composition

Abstract

Coffee is one of the most popular beverages globally, consumed for taste as well as healthpromoting attributes. The roasting time and temperature are the key factors that affect the functional properties and chemical composition, such as caffeine content, total antioxidant capacity (TAC), total phenolic content (TPC), total flavonoid content (TFC), and titratable acidity (TA). Therefore, this study aimed to investigate how roasting temperature and roasting time affect the final quality of coffee. Green coffee beans were roasted at temperatures ranging from 180 ◦C to 250 ◦C for durations between 6 and 17 minutes. The selected temperature and time range were determined using response surface methodology (RSM) to cover typical light, medium, and dark roasting profiles and to optimise the balance between flavour and functional compounds. The caffeine content was determined using a spectrophotometric method, TAC through the ferric reducing antioxidant power (FRAP) assay, TPC by the modified Folin–Ciocalteu method, TFC using the Aluminium Chloride method, and titratable acidity was assessed using standard titration procedures. The maximum content of caffeine was 418.54 mg/100 g, which was observed at 250 ◦C for 11 min (dark roasting–3). Moreover, the maximum TAC, TPC and TFC were recorded as 70.96±3.93 mg TE/100 ml at 240 ◦C for 7 min (dark roasting–1), 33.41±1.86 mg GAE/100 ml at 190 ◦C for 7 min (light roasting–2), and 91.88±4.11 mg RE/100 ml at 180 ◦C for 11 min (light roasting–1), respectively. The maximum titratable acidity value of 0.32±0.00% was recorded at 240 ◦C for 7 min. The results suggest that the optimum conditions for roasting are in the range of 190 ◦C to 240 ◦C and 7 min to 15 min in order to obtain favourable functional properties and chemical composition. The light roasting profiles retained higher phenolic and flavonoid compounds, whereas dark roasting profiles enhanced caffeine content and antioxidant activity but showed a marked reduction in phenolics and flavonoids. These findings indicate the importance of developing optimised roasting procedures that balance flavour, caffeine content, and bioactive compound retention, thereby guiding both industry practice and consumer health benefits.