Study On The Formation And Changes Of Volatile Compounds In Pickled Mustard Tuber During The Pickling Process

The pickled mustard tuber, which is produced by pickling the stem mustard (Brassica juncea coss var tnmida Tsen et Lee) in salt solution, is an indigenous Chinese fermented vegetable product. With its fresh, fragrant, crisp and tender quality, Fuling Pickled mustard tuber has become famous all over the world. Its unique volatile flavor is an important factor which is used to evaluate the quality of the pickled mustard tuber. However, the research on the formation and changes of volatile compounds of pickled mustard tuber during the pickling process is limited. There is also little known about the effect of desalting and dewatering process on volatile flavor of pickled mustard tuber. It's necessary to research the formation and changes in volatile compounds of pickled mustard tuber during the pickling process in order to improve the flavor quality of pickled mustard tuber.In this work, stem mustards which pickled with traditional method were used as experiment material. The changes of sinigrin content during the pickling process were studied. Myrosinase was isolated and purified from the extraction by DEAE-52 and Sephadex G-100 chromatography, and the changes of myrosinase activity in pickled mustard tuber during the pickling process were detected in this paper. The formation and changes in volatile compounds of pickled mustard tuber during the pickling process were investigated, and the effect of desalting and dewatering process on volatile flavor was also studied in this paper. The results were as follows:①The content of sinigrin gradually decreased during the pickling process, as tested by improved palladium chloride method.②The activity of myrosinase in pickled mustard tuber was tested by hexokinase (HK) method, the results showed that the activity of myrosinase gradually decreased during the pickling process, and the activity of myrosinase was significantly influenced by temperature, pH and salt content.③The volatile oil was obtained from the pickled mustard tuber by simultaneous distillation extraction method (SDE), and the volatile compositions were analyzed by gas chromatography-mass spectrometry (GC-MS). A total of 45 volatile compounds were isolated and identified from fresh stem mustard and the pickles. They were grouped into 9 major chemical classes. The relative abundance of acids, sulfides, aldehydes, alcohols, phenols, esters, nitriles and heterocyclic compounds showed gradually increased during the pickling process, especially for sulfides, sulfides, aldehydes and esters. The relative abundance of isothiocyanate compounds increased at the first and second pickling stages, then started to decrease in the last pickling stage.④The hydrolysis of myrosinase and fermentation of lactic acid bacteria were the main formation ways of volatile flavor in pickled mustard tuber during the pickling process, and the anabolic and catabolic metabolism in the cell of pickled mustard tuber and the reaction of the degradation products were also important ways to form the volatile flavor in pickled mustard tuber during the pickling process.⑤After desalting and dewatering process, there were 22 volatile components lost in pickled mustard tuber. Acids, sulfides, aldehydes, alcohols, phenols, esters, nitriles, isothiocyanates and heterocyclic compounds all decreased in the process, especially for alcohols, aldehydes, phenols and acids.