Extraction of mannooligosaccharides from spent coffee grounds and its application for functional jelly with improved physical properties and immunomodulatory effect

Abstract

Mannooligosaccharides (MO) were extracted from spent coffee grounds (SCG) via combinational enzyme treatment with pectinase and mannanase from Aspergillus niger. Among 18 commercial enzymes to improve the accessibility of galactomannan, pectinase XL exhibited the highest yield, producing 235 mg hemicellulose/g of SCG. Pectinase treatment before mannanase resulted in coffee mannooligosaccharides (CMO) production 6.8 times higher than mannanase alone. This approach facilitated a 70% CMO extraction efficiency compared to the hemicellulose content present in the SCG. Additionally, HPLC analysis validated the composition of CMO, revealing 28.2% mannobiose (M2), 32.4% mannotriose (M3), 5.9% mannotetraose (M4), and 3.9% mannopentaose (M5). The CMO at different concentrations, along with fructose syrup, gelling agent, coffee extract, and coconut milk, was used to prepare jelly. CMO20 (20% CMO, w/w) jelly outperformed in both product stability and functional properties. The antioxidant activity of CMO20, measured by DPPH and FRAP assay, was 4.57 mM, with a Vit C equivalent and 15 mM FeSO₄ equivalent, respectively. Furthermore, CMO20 showed 48% greater α-glucosidase inhibition than acarbose (5 mg/mL). CMO20 showed improved immunomodulatory effects with 4.7 and 16-fold higher nitric oxide and cyclooxygenase-2 content than methotrexate-suppressed RAW264.7 cells.