Objective To isolate, purify and characterize the lipopeptides produced by Bacillus subtilis strain SHT-15, and to investigate their effects on the storage quality of thick-skinned melons.
Methods The lipopeptide of Bacillus subtilis SHT-15 was extracted by organic solvent extraction, and separated and purified by SephadexG-25 dextran gel, and analyzed and identified by liquid chromatography-mass spectrometry (LC-MS). The activities of lipoxygenase (LOX), ethanol dehydrogenase (ADH), sugar-acid ratio and rind color were determined during storage.
Results The lipopeptide extract of strain SHT-15 had obvious inhibitory effect on the pathogenic bacteria, the inhibition circle was (20.12 ± 0.54) mm, and the inhibitory activity was 70.18%. After SephadexG-25 dextran gel chromatography, there were 7 lipopeptide peaks in the elution curve, and the main inhibitory effect was the 2nd lipopeptide peak, with a circle of inhibition of (21.44 ± 0.13) mm, and an inhibitory activity of 72.01 %. LC-MS analysis showed that, of the 31 inhibitory peptides isolated, the one with a retention time of 47.84 min corresponded to the peak with the highest total ionic strength in the ion-current diagram. The m/z value was 1046.58, and the peptide with retention time of 47.84 min belonged to the Surfactin family when the m/z value was in the range of 1032.4 to 1074.4. The bacteriostatic substances can improve the activity of LOX and ADH during the storage period of thick-skinned melons, inhibit the decline of sugar-acid ratio, and have a better effect on maintaining the color of the rind.
Conclusion The main component of bacteriostatic activity in strain SHT-15 is C12-C15 Surfactin, which can better maintain the quality of melon during storage.
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