Yeast Diversity And Quality Analysis Of Pickled Wax Gourd

Pickled wax gourd with special flavor is very popular in eastern of Zhejiang province especially in Ningboand Shaoxing. Traditional curing process involves the fermentation of yeast and biochemical changes, which canform a special flavor, color and taste. Therefore an in-depth study to the yeast of the pickled wax gourd can help tounderstand the mechanism of its flavor formation and control the quality. In this study the yeast communities andits predominant species in the fermentation process of pickled wax gourd were investigated by using5.8SrDNA-ITS clone library technology combined with real-time polymerase chain reaction (RT-PCR) method.Meanwhile, volatile compounds produced by fermentation of predominant yeast in the pickled wax gourd werealso analyzed.For the pickled processing with cooked wax gourd, the results of5.8S rDNA-ITS clone library showed that,on the beginning of pickling process, the species of Aureobasidium pullulans are the dominant microorganism inthe initial stage of fermentation. In the later phase, the dominant microorganism is Candida tropicalis. For thepickled processing with raw wax gourd, the results showed that, on the beginning of pickling process, the speciesof Issatchenkia orientalis and Pichia kudriavzevii are the predominant yeast in the picking process. Aftermarinated30d, the predominant yeast have changed to be Issatchenkia orientalis, Pichia kudriavzevii andCandida xylopsoci. By Real-time PCR analysis experiments, on the beginning of pickling progress with cookedmaterials, the ribosomal copy number of Aureobasidium pullulans was3.24×107copies/mL, but it was notdetected in the following three phases. Candida tropicalis was less in the early time, then the number graduallyincreased over time, in the mature phase, the copy number reached1.3×108copies/mL. In the pickled wax gourdwith row materials, the ribosomal copy number of Pichia kudriavzevii remains unchanged in the beginning, thenthe number has fluctuated slightly. In15thday, the number reached2.90×108copies/mL, due to the strains ofCandida significant increasing, the number declined in30thday. In60thday, the number was more than the numberof30thday, at the end of the fermatation, the ribosomal copy number of Pichia kudriavzevii reached2.06×108copies/mL. Issatchenkia orientalis had the same trend with Pichia kudriavzevii, the first decline and thenrise, to the end, the number decline to reach3.26×107copies/mL. Candida was less in the early time, then thenumber gradually increased over time, in the mature phase, the copy number reached2.02×107copies/mL. Theconsequents of real-time PCR was consistent with the results of5.8S rDNA-ITS library no matter in the cookedpickled wax gourd and the uncooked pickled wax gourd.Using HS-GC-MS to analysis volatile compounds of pickled wax gourd and its predominant yeast, itshowed that the volatile compounds of Candida tropicalis and Aureobasidium pullulans in cooked wax gourd aremainly alcohols and easters, alcohols compounds were90.16%and84.36%in respectively. The volatilecompounds of cooked wax gourd are acids and alcohols compounds, accounting for44.33%and44.34%,respectively. Ethanol,2-methyl propanol,3-methyl alcohol, ethyl acetate, acetaldehyde and2-Methylbutyraldehyde are detected in the three samples. The volatile compounds of Issatchenkia orientalis,Pichia kudriavzevii and Candida xylopsoci in the raw wax gourd were mainly alcohols and esters compounds,3-methyl-butanol was the highest, followed by ethanol content, acetate content of about10%. The volatilecompounds of raw wax gourd are acids and alcohols compounds, accounting for30.96%and46.24%, respectively. Accounted for9.89%of its esters,3-butyric acid methyl,2-methyl butyrate, ethyl acetate,acetaldehyde3-methyl butanol and ethanol were detected in all of the four samples. The volatile compounds weredifferent in yeast and pickled wax gourd, mainly due to the pickled wax gourd is a complex system with yeast andbacteria. Interaction of microorganisms produce different volatile compounds which makes pickled wax gourdhaving special flavor.