| The antimicrobial activity of the cashew apple extracts were tested with Streptococcus mutans CICC10387, Streptococcus salivarius CGMCC 1.2498, Staphylococcus aureus CGMCC1.72, Staphylococcus epidermidis CBL-R, Staphylococcus epidermidis TS5, Candida albicans, Bacillus proteus, Escherichia coli. The best extraction method of antimicrobial substance, raw material drying methods on inhibitory effect, and antimicrobial components of the extracts were studied. The results were as follows:The antimicrobial active ingredients of cashew apples were extracted with the method of water bath and reflux. Selecting the inhibition zone diameter as the index, the best extracting agent was chosen from solvents of different polarity (ethyl acetate, 70% acetone, 70% methanol,70% ethanol, n-butanol and water). The result showed that:70% ethanol extract of cashew apples had the best inhibitory effect; the Staphylococcus aureus was inhibited strongest, and followed by Candida albicans.In order to explore extracted optimal parameters of antimicrobial active substances in different varieties of cashew apples (yellow, red), Staphylococcus aureus, Candida albicans were selected as indicator bacteria and the sum of inhibition zone diameters was selected as response value. Base on the single-factor test, the solvent concentration (volume fraction), extraction temperature, solid to liquid ratio, extraction time were used for the trial factors, and the extracting conditions were optimized with central composite design. The optimal parameters of extracting antimicrobial active ingredient:①Yellow cashew apples:ethanol concentration 70%, extraction temperature 85℃, solid to liquid ratio 1:13.9, extraction time 2.65h.②Red cashew apples:ethanol concentration 70%, extraction temperature 85℃, solid to liquid ratio 1:14.5, extraction time 2.44h. The values of validation were 25.2mm and 26.2mm, having little difference with the values of prediction (24.82mm and 25.21mm,8< 5%). Therefore, this method of optimization was feasible and practical.In order to study the influence of material drying methods, hot air drying at 60℃and vacuum freeze-drying (cold trap-60℃, air pressure 0.42mbar) were selected. According to different varieties and processing methods, the cashew apples were respectively extracted and concentrated. Then, the 8 strains of microorganisms were tested for antimicrobial activity. The result showed:For the antimicrobial activity of Staphylococcus epidermidis CBL-R, there was not significant difference between different varieties and different drying methods (a＝0.05). For Streptococcus salivarius, Staphylococcus epidermidis TS5, Staphylococcus aureus, Bacillus proteus, Streptococcus mutans, hot air drying was better than vacuum freeze-drying, and there was significant difference between the different drying methods (a=0.05). For the inhibitions of Candida albicans and Escherichia coli, vacuum freeze-drying was better than hot air drying obviously, having significant difference also (a=0.05). From the consideration of economic costs, the method of hot air drying with 60℃was chosen.The extracts of cashew apples were separated by extraction and silica gel column chromatography. The result showed that only the ethyl acetate extract (50mg/mL) had antimicrobial activity. The phenomenon indicated that antimicrobial components were concentrated in the extract of ethyl acetate. After the separation of silica gel column chromatography, the inhibition zone diameter of Staphylococcus aureus was 8.6±0.2mm, and increased 7.5%.According to the characteristic responses, the result of qualitative analysis was as follow: The extracts of cashew apples contained flavonoids, phenols, anthraquinones and glycosides. The GC-MS analysis showed that: Among all the detected compounds, the content of furfural derivative (5-hydroxymethyl-2-furfural) was the most; and the relative peak area was 60.88%. On the basis of relevant information, the conclusion that the 5-hydroxymethyl-2-furfural was the functional component of bacteriostasis was extrapolated. |
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