Characterisation of antibacterial peptide fractions extracted from pomelo nucleus co-incubated with Lactobacillus

Pomelo have been widely reported for its unique flavour and high nutritive value, whereas the antibacterial activity of pomelo nucleus peptides was still poorly understood. We characterised a co-incubation system of pomelo nucleus and Lactobacillus amylolyticus L6 to identify peptides of high application value. We first analysed the structure of pomelo nucleus peptides (GP) and co-incubated peptides (C-GP) by scanning electron microscopy, high-performance gel permeation chromatography, liquid chromatography–tandem mass spectrometry and amino acid analysis. The results showed that the molecular weights, 89% of peptide sequences, and amino acid composition were different in the C-GP compared with the GP fraction, and the spatial structures were quite diverse; the C-GP peptide fraction presented irregular, amorphous and interwoven flocs. Notably, only C-GP had antimicrobial activity against Escherichia coli (minimum inhibitory concentration of 12.50 μg/mL). Further assessment of the mechanism suggested that the hydrophobic groups in the C-GP peptide fraction were inserted into the hydrophilic sites on the surface of the E. coli cell membrane, leading to the formation of holes and bending. These findings suggest the potential value of pomelo nucleus as a nutrient source.