This study combined quantitative descriptive analysis (QDA) and liquid chromatography-triple quadrupole tandem mass spectrometry (LC-TQ-MS/MS) to elucidate the effects of initial processing methods and roast degree on the content of major phenolic acid components and astringency intensity in coffee. Based on the interaction between phenolic acids and salivary proteins (α-amylase (AMY)), it revealed the molecular mechanism by which phenolic acids induce oral astringency. Results showed that light-roasted coffee contained higher levels of phenolic acids and greater astringency. Dose-over threshold (Dot) and correlation analyses identified chlorogenic acid, cryptochlorogenic acid, neochlorogenic acid, and isochlorogenic acid B (Iso B) as the major contributors to inter-sample variations in astringency intensity. Turbidity, particle size, and zeta potential analyses demonstrated that the Iso B-AMY complex exhibited the largest particle size and the lowest stability, suggesting its susceptibility to protein aggregation and astringent perception. Isothermal titration calorimetry and molecular docking clarified that the binding of astringent phenolic acids to AMY was mainly driven by hydrophobic interactions and hydrogen bonds. Among them, Iso B had the lowest binding energy (–7.45 kcal/mol) and the lowest dissociation constant (11.80 × 10^–6 mol/L) with AMY, indicating that Iso B was the key phenolic acid. This study systematically identified the key astringent phenolic acids in coffee, and clarified the structure-activity and dose-effect relationships of coffee phenolic acids in relation to their astringency intensity, laying the foundation for understanding the relationship between the sensory characteristics and chemical components of coffee.

In this study, the physicochemical properties, fatty acid composition, volatile components and bioactive ingredients of oil from Arabica coffee beans from Yunnan roasted for different periods were systematically investigated. The results showed that as the degree of roasting increased, the color of the oil deepened, the acid value showed an increasing trend from 1.60 to 3.75 mg/g, the iodine value decreased from 142.04 to 83.12 mg/100 g, the anisidine value first increased and then decreased, ranging from 3.40 to 16.26, and the saponification value decreased slightly but not significantly. A total of 11 fatty acids were identified, the most predominant being linoleic acid, whose content ranged from 43.06% to 64.39%, followed by stearic and palmitic acids with contents ranging from 12.67% to 27.55% and oleic acid in the range of 9.03% to 17.20%. The effect of roasting degree on the type of fatty acid was not significant, but there were some differences in the content of fatty acid. A total of 25, 33, 36, 53, 54, 59, 64 and 58 volatile components were identified in oils from coffee beans roasted to eight different degrees from JQ to FZ, respectively. The major volatile components were furans, pyrazines, ketones and pyrroles, whose type and content showed a decreasing trend. The contents of bioactive ingredients including kahweol, α-tocopherol, γ-tocopherol and δ-tocopherol decreased, while the total phenolic content increased continuously from 7.75 to 15.96 mg/100 g. The results of this study provide a theoretical basis and technical support for the fine and deep processing and high-value utilization of coffee beans.

The purpose of this study was to explore the non-covalent interactions between three major polyphenols (chlorogenic acid, caffeic acid and ferulic acid) in coffee and β-lactoglobulin (β-LG) at different pH values and their effects on protein structure by multispectroscopic techniques and molecular docking. The results showed that all three coffee polyphenols statically quenched the fluorescence of β-lactoglobulin under two pH conditions. At pH 7.4 and 298 K, the quenching constants (K_sv) of chlorogenic acid, caffeic acid and ferulic acid for β-lactoglobulin were 6.53 × 10⁴, 3.16 × 10⁴ and 3.09 × 10⁴ L/mol with 1.20, 1.02 and 1.14 binding sites and energy transfer efficiency of 34.55%, 24.56% and 21.35%, respectively. At pH 3.0 and 298 K, the K_sv were 7.18 × 10⁴, 5.24 × 10⁴ and 7.12 × 10⁴ L/mol with 1.28, 1.18 and 1.25 binding sites and energy transfer efficiency of 34.70%, 30.42% and 29.65%, respectively. The results of circular dichroism showed that the α-helix content of β-LG decreased and the β-sheet content increased at pH 7.4, and the β-sheet content increased and the random coil content decreased at pH 3.0. The results of molecular docking showed that the three polyphenols could bind to the hydrophobic pocket of β-lactoglobulin mainly through hydrogen bonds, van der Waals force and hydrophobic interaction. This study preliminarily revealed the interaction mechanism between β-lactoglobulin and chlorogenic acid, caffeic acid and ferulic acid in coffee milk beverage under different pH conditions.