Isolation And Separation Of Yeast During The Fermentation Of Traditional Sichuan Radish Pickle And Its Effects On The Flavor Of Pickle

In this study, the red radishes as materials by spontaneous fermentation, old brine fermentation making Sichuan pickle. The yeast were separated in pickle fermentation and its influence on pickle flavor had studied preliminary, which will provide the theoretical basis for modeling for different microorganisms specific impact on traditional Sichuan pickle flavor substances The main results were summarized as follows:1. Separated the yeast from traditional Sichuan pickles’ fermentation process by using the methods of traditional isolation and culture with pH ysiological and biochemical tests and 26S rDNA sequencing technology. There were 4 kinds of yeast which identified as Candida sake, Pichia galeiforms, Rhodotorula mucilaginosa and Kazachstania exigua from two different pickles (spontaneous fermentation, old brine fermentation). And yeast displayed four different kinds of pH enotypes on YPD1 medium.2. The dynamic changes of yeast from the fermentation process of traditional Sichuan pickle were studied. With the fermentation processing, Pichia galeiforms only detected during the spontaneous fermentation of radish pickle, while Kazachstania exigua only detected during the old brine fermentation of this showed that the yeast mainly existed in the early fermentation of radish pickle.In two different ways of fermentation process of Sichuan pickle, dynamic change trends of yeast is generally same, the species and quantity reduced gradually, finally remained steady, the quantity were about 4.5 log CFU/mL.3. The acid tolerance, salt tolerance, ability to produce acid, alcohol, film, gas of different yeast from spontaneous fermentation, old brine fermentation pickles were compared, and filtrated the excellent yeast at the same time. The results showed that Kazachstania exigua was best which produced acid, alcohol and less gas, not producing film, and it performanced best in a certain range of pH, salt concentration. So it survival ability in the pickle of low acid environment was strong. Different yeast after the test of using radish juice inoculated fermentation, Kazachstania exigua was good for the ability to use of reducing sugar, the change of amino nitrogen and the increase of total esters. Combined with the former test results, the Kazachstania exigua probably was beneficial in the fermentation process of radish pickle, and it advantaged the formation of pickles quality and flavor.4. Comparison and analysis the flavor substances in the fermentation process of lactic acid bacteria inoculated radish pickle and mixed strains inoculated radish pickle. Volatile flavor compounds of radish pickle were analyzed by headspace solid-pH ase micro-extraction (HS-SPME) and gas chromatogra pH y-mass spectrometry (GC-MS), a total of 49 kinds of volatile substances detected, of which isothiocyanate took the most abundant, accounting for 18.14% to 62.5% of the total volatile components.In the whole fermentation process, the kinds of volatile substances from mixed strains inoculated radish pickle were less than lactic acid bacteria inoculated radish pickle. The total free amino acids of radish pickle were analyzed by Auto amino acid analyzer, In the whole fermentation process, the total free amino acids of radish pickles reduced after different fermentation, and the total free amino acids of lactic acid bacteria inoculated radish pickle were higher than mixed strains inoculated radish pickle. The arrangement of flavor amino acid content in two kinds of radish pickles were sweet amino acids, bitter amino acids, umami amino acids in descending order. Total acid content in two kinds of radish pickles had no obvious difference. Sensory analysis revealed that differences between two kinds of radish pickles was no obvious, all sensory scores were the highest in middle stage of fermentation, and the radish pickles tasted best.