Study On Antimicrobial Activity Of Old Preserved Radish In Sothern Fujian

Old preserved radish also known as Laocaipu or old dried radish is a traditional preserved food in Southern Fujian which made by processing radish with crude salt.Laocaipu was deeply favoured by people because of its unique flavour,attractive black color,Long storage time and features that are good for human health and play an important role in daily life of the locals.The aim of this research was to try to find some new antimicrobial substances in Laocaipu and explore scientific evidence of biological activities of Laocaipu through studies on antimicrobial activities of old preserved radish with different storage time.Firstly,color values of white radish and preserved radish with different preserved time were measured.The results showed that the color value of preserved radish varied with preserved time and the△E~*between white radish and different preserved radish increased with extension of storage time.And this indicated that the color of preserved radish gradually changed from dark yellow to black as the storage time increased.Secondly,Antimicrobial activities of water,methanol,ethanol,acetone,ethyl acetate and petroleum ether extracts of 5-year preserved radish and white radish against Bacillus subtilis,Escherichia coli and Saccharomyces cerevisiae were tested.Results showed that water extract of white radish exhibited good antmicrobial activity against both bacteria,and methanol and ethanol extracts showed limited activity against both bacteria,ethyl acetate and acetone extracts exhibited weak activity against Saccharomyces cerevisiae.Methanol and ethanol extracts of preserved radish showed moderate antimicrobial activity to both bacteria,and ethyl acetate and acetone extracts exhibited significant antimicrobial activity against three indicated microorganisms.Athyl acetate and acetone were chosen as extraction solvents of antimicrobial substances in preserved radish based on results above.Ethyl acetate and acetone extracts of preserved radish with different storage time were studied for their antimicrobial activities against Bacillus subtilis,Escherichia coli and Saccharomyces cerevisiae.The results showed that two solvent extracts of most preserved radish exhabited a moderate to strong antimicrobial activity against three indicated microorganisms,and antimicrobial ability of preserved radish varied depending on storage time,extraction solvent and indicated microorganism.Compared with ethyl acetate extracts,acetone extracts showed stronger antimicrobial activity and most of the extracts had higher antimicrobial effect against Saccharomyces cerevisiae than positive control of 0.5mg/m L amphotericin.Three indicated microorgnisms was more sensitive to extracts of 3-year,5-year and 10-year preserved radish.Antibacterial effects of ethyl acetate extracts of preserved radish whose storage time were within10 years was better than those whose storage time were more than 10 years.Two solvent extracts of 15-year and 20-year preserved radish showed no antimicrobial activity against Saccharomyces cerevisiae but inhibitory zone diameter of actone extract of 20-year preserved radish against two bacteria were 18.40 mm and 18.10 mm and close to positive control of 1 mg/mL Streptomycin Sulfate.The obtained results suggested that ethyl acetate and acetone extracts of preserved radish have good antimicrobial potential.Finally,antimicrobial substances of ethyl acetate and acetone extracts of 5-year preserved radish were separated,purified and identified by combined use of gel(Sephadex LH-20)column chromatography,silica gel column chromatography,NMR and ESI-MS.Results showed that antimicrobial constituents of preserved radish include p-hydroxy benzaldehyde,p-Hydroxy phenylethanol and pinoresinol.