Waste robusta coffee husk pectin: ultrasound-assisted extraction and applications in roselle flower marmalade and fruit coating

Abstract

This study demonstrates the valorization of robusta coffee husk as a sustainable source of pectin via ultrasound-assisted extraction (UAE). The optimized process yielded 16.4% pectin with favorable gelling and physicochemical properties, comparable to commercial citrus pectin. In food application, incorporation of 0.5% coffee husk pectin into roselle marmalade, together with 1.0% citric acid and 50% sucrose, produced a desirable texture and sensory quality. In packaging application, the extracted pectin was blended with chitosan to form biofilms enriched with curcumin (CPC) or pomegranate peel extract (CPP). These composite films exhibited enhanced stability and antioxidant activity, with CPP showing the strongest effect. Postharvest trials confirmed that CPP coatings extended the storage of lychee and Japanese plum by reducing weight loss and preserving texture compared to CPC and uncoated controls. This work highlights the multifunctional potential of coffee husk-derived pectin as a food ingredient and active packaging material, contributing to waste upcycling and circular bioeconomy strategies.

Fig. 1. Microscopy and FE-SEM images of coffee husk and pectin under different treatments. (A1 and A2) Pre-extraction coffee husk; (A3 and A4) pre-extraction pectin. (B1–B4) Hydrothermal extraction: coffee husk (B1 and B2) and pectin (B3 and B4). (C1–C4) Ultrasonic bath extraction: coffee husk (C1 and C2) and pectin (C3 and C4). (D1–D4) Ultrasonic homogenizer extraction: coffee husk (D1 and D2) and pectin (D3 and D4).

Fig. 2. Effect of ampilitude (A), temperature (B) and time (C) on purity, degree of esterification, and extraction yield using ultrasonic homogenizer. Different letters indicate statistically significant differences between samples (P < 0.05).

Fig. 3. Effect of heating time and temperature on yield (A) and color parameters (B) of red roselle puree. Different letters indicate statistically significant differences between samples (P < 0.05).

Fig. 4. Influence of different pectin types (A) and coffee husk pectin content (B) on the textural properties of roselle flower marmalade. Distinct letters indicate statistically significant differences between samples (P < 0.05).

Fig. 5. Effect of saccharose concentration on color parameter (A) and sensory (B) obtained from 20 volunteer panelists. Distinct letters indicate statistically significant differences between samples (P < 0.05).

Fig. 6. Swelling ratio, and water solubility (A); tensile strength (TS) and elongation at break (EAB) (B); and water vapor permeability versus time (C) of the various biofilms: chitosan/pectin (CP); chitosan/pectin/curcumin (CPC); chitosan/pectin/pormergranate peel extract (CPP).

Fig. 7. (A) X-ray diffraction (XRD) patterns, (B) Fourier-transform infrared (FTIR) spectra, and (C) thermogravimetric analysis (TGA) curves of pectin, chitosan/pectin (CP), chitosan/pectin/curcumin (CPC), and chitosan/pectin/pomegranate (CPP) samples. SEM images and particle size distribution (inset) of CP (D and E), CPC (F and G) and CPP (H and I) at different magnifications (bar = 5 μm and 1 μm).

Fig. 8. The photos of lychee (Litchi chinensis) coated (A) and plots of mass loss versus storage time of litchi (B): blank, CP, CPC, and CPP biofilms.

Fig. 9. The photos of Japanese plum (Prunus salicina) coated (A) and plots of mass loss versus storage time of litchi (B): blank, CP, CPC, and CPP biofilms.