NMR fingerprinting of depolymerised durian rind pectin and its antibacterial activity

This study investigated the effect of commercial sterilisation treatment (121 °C for 15 min) on durian rind pectin. The change of structure was observed by NMR (nuclear magnetic resonance) and the antibacterial activity was assessed by microdilution method to obtain the minimum inhibitory concentration (MIC) value. NMR spectra revealed the rhamnogalacturonan-I and homogalacturonan structure, with lower methyl-ester in sterilised pectin. Native pectin was unable to inhibit Escherichia coli and Staphylococcus aureus at the highest tested concentration (MIC > 25 mg/mL), but sterilised pectin showed inhibitory effect against E.coli (MIC 12.5 mg/mL) and S. aureus (MIC 6.25 mg/mL). Membrane filtration to obtain fraction < 20 kDa enhanced the inhibition against S. aureus further, but not for E.coli. The antibacterial effect was possibly correlated to the decrease of molecular weight (MW) and degree of esterification (DE) of durian rind pectin. E. coli was more resistant to pectin than S. aureus.