Effects of Water Quality Factors on the Main Components and Flavor of Cold Brew Coffee

In this study, six types of commercially available water were selected for preparing cold brew coffee to explore the influence of water quality factors on the main components and sensory flavor of the coffee. High-performance liquid chromatography (HPLC) and headspace solid-phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC-MS) were used for analysis of the coffee. Physical and chemical indices, volatile and non-volatile components, and sensory evaluation were analyzed and compared, and correlations and principal component analysis (PCA) were performed. It was found that the different types of water had significantly different compositions of major ions. The contents of total phenol, chlorogenic acid, and caffeic acid, as well as antioxidant activity in the cold brew coffee were not significantly affected by the water ions, but they were significantly affected by the extraction concentration, extraction rate, pH, and titratable acid, caffeine, trigonelline, and furan volatile chemical components. The Ca²⁺, Mg²⁺, and HCO₃⁻ ions in the water were positively correlated with the extraction concentration, extraction rate, and caffeine and trigonelline concentrations in the cold brew coffee (P<0.05), and negatively correlated with titratable acid (P<0.05). The ions in the water had significant effects on volatile compounds such as furfuryl alcohol, 5-methylfurfural, 1-furfurylpyrrole, furfuryl methyl sulfide, 2-isobutyl-3-methoxy-pyrazine, and furfuryl acetate. PCA showed that lower ion concentrations in the water promoted fruit and flower flavors in the coffee, and higher concentrations of Ca²⁺, Mg²⁺, and HCO₃⁻ reduced the fruit and flower flavor, as well as sweet and sour taste in different degrees. Higher ion contents (especially Na⁺ and K⁺) enhanced caramel flavors and bitterness in the coffee. Na⁺ and K⁺ significantly affected the furfuryl alcohol content, while Ca²⁺, Mg²⁺, and HCO₃⁻ influenced 1-furfuryl pyrrole, 5-methylfurfural, and furfuryl methyl sulfide. Cold brew coffee brewed in water with moderate ion contents showed better nutty, roasted, and sweet flavors, as well as better overall sensory evaluation. These results could provide a theoretical basis for further understanding the effects of water quality factors on the physicochemical properties and main components of coffee.