The metabolic modulation of major flavor precursors during coffee cherry ripening is critical for the characteristic coffee flavor formation. However, the formation mechanism of flavor precursors during coffee cherry ripening remains unknown. In the present study, a colorimeter was employed to distinguish different maturity stages of coffee cherry based on the coffee cherry skin colors, and proteomics and metabolomics profiles were integrated to comprehensively investigate the flavor precursor dynamics involved in Arabica coffee cherry ripening. The data obtained in the present study provide an integral view of the critical pathways involved in flavor precursor changes during coffee cherry ripening. Moreover, the contributions of critical events in regulating the development of flavor precursors during the four ripening stages of coffee cherries, including the biosynthesis and metabolism pathways of organic acids, amino acids, flavonoids, and sugars, are discussed. Overall, a total of 456 difference express metabolites were selected, and they were identified as being concentrated in the four maturity stages of coffee cherries; furthermore, 76 crucial enzymes from the biosynthesis and metabolism of sugars, organic acids, amino acids, and flavonoids contributed to flavor precursor formation. Among these enzymes, 45 difference express proteins that could regulate 40 primary amino acids and organic acids flavor precursors were confirmed. This confirmation indicates that the metabolic pathways of amino acids and organic acids played a significant role in the flavor formation of Arabica coffee cherries during ripening. These results provide new insights into the protease modulation of flavor precursor changes in Arabica coffee cherry ripening.

As primary coffee by-products, Arabica coffee husks are largely discarded during coffee-drying, posing a serious environmental threat. However, coffee husks could be used as potential material for extracting pectin polysaccharides, with high bioactivities and excellent processing properties. Thus, the present study aimed to extract the pectin polysaccharide from Arabica coffee husk(s) (CHP). The CHP yield was calculated after vacuum freeze-drying, and its average molecular weight (Mw) was detected by gel permeation chromatography (GPC). The structural characteristics of CHP were determined by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), proton nuclear magnetic resonance (¹H NMR), and scanning electron microscopy (SEM). Additionally, the rheological and antioxidant properties of CHP and the inhibition capacities of advanced glycation end products (AGEs) with different concentrations were evaluated. The interaction mechanisms between galacturonic acid (GalA) and the AGE receptor were analyzed using molecular docking. The results demonstrated that the CHP yield was 19.13 ± 0.85%, and its Mw was 1.04 × 10⁶ Da. The results of the structural characteristics results revealed that CHP was an amorphous and low-methoxyl pectic polysaccharide linked with an α-(1→6) glycosidic bond, and mainly composed of rhamnose (Rha, 2.55%), galacturonic acid (GalA, 45.01%), β-N-acetyl glucosamine (GlcNAc, 5.17%), glucose (Glc, 32.29%), galactose (Gal, 6.80%), xylose (Xyl, 0.76%), and arabinose (Ara, 7.42%). The surface microstructure of CHP was rough with cracks, and its aqueous belonged to non-Newtonian fluid with a higher elastic modulus (G′). Furthermore, the results of the antioxidant properties indicated that CHP possessed vigorous antioxidant activities in a dose manner, and the inhibition capacities of AGEs reached their highest of 66.0 ± 0.35% at 1.5 mg/mL of CHP. The molecular docking prediction demonstrated that GalA had a good affinity toward AGE receptors by −6.20 kcal/mol of binding energy. Overall, the study results provide a theoretical basis for broadening the application of CHP in the food industry.

The primary processing method of coffee plays a crucial role in determining its flavor profile. In this study, roasted coffee beans were subjected to three primary processing methods, i.e., natural processing (SC), washed processing (WC), and honey processing (MC), that were analyzed by LC-MS/MS and GC-MS metabolomics. Additionally, sensory evaluation was conducted by the Specialty Coffee Association of America (SCAA) to assess coffee flavor characteristics. The results showed that 2642 non-volatile compounds and 176 volatile compounds were detected across the three primary processing methods. Furthermore, significant differentially changed non-volatile compounds (DCnVCs) and volatile compounds (DCVCs) were detected among SC/WC (137 non-volatile compounds; 32 volatile compounds), MC/SC (103 non-volatile compounds; 25 volatile compounds), and MC/WC (20 non-volatile compounds; 9 volatile compounds). Notable compounds, such as lichenin, 6-gingerdiol 5-acetate, 3-fluoro-2-hydroxyquinoline, and 4-(4-butyl-2,5-dioxo-3-methyl-3-phenyl-1-pyrrolidiny)benzenesulfonamide, were identified as important DCnVCs, while ethyl alpha-D-glucopyranoside, 2,3-butanediol, maltol, and pentane-1,2,5-triol were identified as significant DCVCs in SC/WC. In MC/SC, 3-fluoro-2-hydroxyquinoline, etimicin, lichenin, and imazamox were important DCnVCs, whereas ethyl alpha-D-glucopyranoside, 2-pyrrolidinone, furfuryl alcohol, and pentane-1,2,5-triol were import DCVCs. Lastly, MC/WC samples exhibited notable DCnVCS, such as (S)-2-hydroxy-2-phenylacetonitrile O-[b-D-apiosyl-1->2]-b-D-glucoside], CMP-2-aminoethyphosphonate, talipexole, and neoconvallatoxoloside, along with DCVCS including citric acid, mannonic acid, gamma-lactone, 3-(1-hydroxy-1-methylethyl)benzonitrile, and maltol. Therefore, the primary processing method was a useful influence factor for coffee compositions.