Optimization of Headspace Solid-phase Microextraction for GC-MS Analysis of Volatile Compounds Produced by Biocontrol Strain Bacillus subtilis CF-3 Using Response Surface Methodology

The volatiles of Bacillus subtilis CF-3 showed a significant (p < 0.05) suppression of the mycelial growth of Monilinia fracticola and Colletotrichum gloeosporioides which caused postharvest decay of Peach and Litchi. An 85-mu m polyacrylate (PA) extraction fiber was initially selected used for the optimized experiments. For an optimal CF-3 volatile collection, HS-SPME was suggested to be performed with extraction time of 40.8 min and extraction temperature of 38.5 degrees C and with 41.5 mL LB broth medium and 4.15 mL CF-3 fermentation liquor (1x10(8) CFU/mL) based on the response surface methodology (RSM). 61 volatile compounds, including fourteen alcohols, fifteen ketones, two aldehydes, eight acids, five phenols, three pyrazines, four esters, three olefins, two amines, two ethers, etc., were extracted using three types of fibers by the optimum method with similarity index (SI)>850 from the database search. Good predictability of the model, satisfactory repeatability for all volatile compounds according to the optimized HS-SPME conditions indicated that the HS-SPME procedure was applicable for the analysis of volatile release, six compounds were selected and assayed for antifungal activity in divided Petri plates, 1-Octanol and 2,4-Di-tert-butylthiophenol can inhibit the mycelial growth of M. fracticola and C. gloeosporioides, which will aid in further research on bio-bacterium volatile metabolites as biocontrol agents against postharvest diseases in fruits and vegetables.