Effect of Roasting Degree on Physicochemical Indexes and Flavor Components of Cold Brew Coffee

In this study, light, medium, and dark roasted Catimor coffee beans from Yunnan, China and Sumatra Indonesia were selected to compare the differences in the extract concentration, extraction efficiency, titratable acid, total phenols, total sugar, caffeine, trigonelline, chlorogenic acid, antioxidant activity and volatile components of cold and hot brew coffee. Principal component analysis (PCA) was carried out to explore the effect of roasting degree on the physicochemical indexes and flavor components of cold brew coffee. The results showed that with the increase of roasting degree, the extract concentration and extraction efficiency of cold brew coffee increased significantly, and the levels of titratable acid, total phenols, total sugar, trigonelline, chlorogenic acid, and antioxidant activity decreased significantly (P < 0.05). Cold brew coffee had higher extract concentration, extraction efficiency and total sugar levels than hot brew coffee, while the levels of titratable acid, total phenolic content, and antioxidant activity were significantly lower than those of hot brew coffee (P < 0.05). The headspace solid phase microextraction combined with gas chromatography (HS-SPME-GC-MS) analysis showed that the content of volatile components in light roasted coffee was significantly lower than that in medium roasted coffee, and dark roasted coffee had the highest number and amount of volatile components. Furthermore, PCA could distinguish between cold and hot brew coffee, and the contribution rate of volatile components was quite different between them. 2-Butanone, 2-butenal and other substances responsible for floral aroma had a higher contribution rate to cold brew light roasted coffee, while compounds contributing to roasted nut-like aroma including 2-methylpyrazine and furfuryl alcohol had a higher contribution rate to hot brew light roasted coffee. 2,6-Diethylpyrazine, ligustrazine and other compounds contributing to roasted nut-like aroma had a higher contribution rate to both cold and hot brew middle roasted coffee. 2-Vinylfuran, methylfurfuryl mercaptan, 2,5-diethylpyrazine, and furfuryl methyl sulfide had a higher contribution rate to cold brew dark roasted coffee, and cresol and 1-methylpyrrole had a higher contribution rate to hot brew dark roasted coffee. Compared with hot brew coffee, roasting degree had a greater impact on the antioxidant capacity and volatile components of cold brew coffee.