| In this study,the quality variation of white radish and yellow pigment effected by curing condition was analysed.The yellow pigment formed after radish curing was extracted,isolated and purified and then its basic structure was identified.The comparison of yellow pigments from fresh radish and isothiocyanate-generated simulation was analysed.At last,the effect on yellowing with several kinds of preservatives and color fixatives were compared before curing.The main results are as follows:1.During the curing process,the contents of moisure,pH,soluble solid, polyphenol and Vitamin C in the Chinese radish varied with the curing time. When yellowing happened,pH was nearly 4.3 and moisure was about 90.5%, and the content of soluble solid was 4.5g/100g,while the content of polyphenol and Vitamin C decreased to a very low level and caused little effect on yellowing.2.Different condition in the curing process were used to study the yellowing condition.The results showed that when the condition was 8℃,shading light and pickle's pH was 7 and without salt,the yellowing speed was the fastest. Meanwhile,through the yellow△b value and△E value,temperture and salinity have comparatively great influence on yellowing speed,while other factors were pretty much the same thing,the polyphenol oxidase and peroxidase were the tiny factors.3.The yellowing pigment formed after curing was extracted by the method of water extraction which optimum was 40℃with 150min and material-liquid ratio was 1:40(w/v).Through isolation and purification,the yellow pigment was scanning in the UV-visible range(200nm-400nm) which has three characteristic peaks: 205nm,287nm,380nm.As a result,the peak of 205nm was determined to be the solvent peak of methanol;the maximum absorption wavelength at 287nm indicates the existence of carbon-oxygen double bond compounds such as carbonyl or caboxyl groups;the absorption at 380nm was in line with previous test;while,by means of infrared absorption spectroscopy,the structure of yellow pigment in the pickled radish would like contain carbonyl,a high degree of common-rail of the C=C,aromatic carboxyl,amido and other functional groups. The result of HPLC-MS showed that there were serval substances in yellow pigment,and the molecular weight of relatively high abundance of the components of them is 413.The material may be obtained by the mother ion of 2-[3-(2-thioxopyrrolidin-3-ylidene) methyl]-tryphtophan(m/z316) combining four Na~+ and 1 H~+,it can be assumed that the main component of yellow pigment contain 2-[3-(2-thioxopyrrolidin -3-ylidene)methyl]-tryphtophan. However,this information is not enough to identify the molecular structure of these several compounds,so further study should be done,on the ultimate identification of the structure of the yellow pigment.4.During curing process,the comparison of yellow pigments from fresh radish and isothiocyanate-generated simulation was analysed with liquid chromatography. Both retention time was the same 1.8min indicating that isothiocyanates have great impact on the formation of yellow pigment during curing process.5.The radish was treated with the mixture of several kinds of common preservatives and the most effective ratio of inhibitory effect was 1‰potassium sorbate and 2‰L-cysteine.The comparison of the inhibitory effect among three kinds of color fixatives showed that:Sodium＞L-cysteine＞EDTA-2Na.However, the inhibitory effect would become weak after long-time storage resulting from a lot of other unkown factors and complex mechanism of yellowing which could only slightly alleviate the inhibition but not be effectively preserved.
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