Identification And Formation Mechanism Of Key Volatile Flavor Compounds In Pickled Ginger

Pickle is a traditional,fermented food product in China.Lactic acid bacteria and other microorganisms use the nutrients in the raw materials for fermentation,developing the unique color and flavor of the pickle.The correlation between the changes in the volatile flavor substances and the microorganisms during the pickle fermentation was examined while exploring the formation mechanism of the unique volatile flavor substances of pickle,providing guidance for industrial pickle production.This study identified the volatile flavor compounds in pickled ginger using headspace solid-phase microextraction combined with gas chromatography-mass spectrometry(HS-SPME-GC-MS)and electronic nose technology for analysis.Furthermore,the correlation between the microbial community and volatile flavor compounds during the fermentation process of pickled ginger was explored.The main results were as follows:(1)The sensory analysis of the pickled ginger revealed differences in the odor of different pickled ginger products.However,no significant differences were evident in the overall quality,while the electronic nose could not adequately distinguish six different pickled ginger brands.Moreover,a total of 72 volatile compounds were identified from six brands of pickled ginger using GC-MS and included 40 olefins,13 alcohols,five aldehydes,eight esters,and six ketones.Furthermore,36 substances displayed odor activity values(OAV)exceeding 1 in six pickled ginger brands,namely 15 alkenes,seven alcohols,four aldehydes,six esters,and four ketones.Myrcene,?-pinene,(+)-?-selinene,cineole,borneol,geraniol,citral,geranial,bornyl acetate,and geranyl acetate represented the common characteristic volatile compounds of these ginger products.(2)The sensory analysis of the pickled ginger during the fermentation process showed that inoculation fermentation was superior to natural fermentation in developing the pickled ginger flavor.In addition,the p H value of inoculation fermentation was significantly lower than natural fermentation,indicating that the inoculation fermentation process was faster.Moreover,a total of 55 and 51 volatile compounds were detected during natural fermentation and microbial fermentation,respectively.Although alkenes,alcohols,aldehydes,and esters denoted the main volatile compounds in the pickled ginger during natural fermentation and inoculation fermentation,differences were evident in the content levels of various substances,fluctuating in conjunction with fermentation time.The results showed that the volatile compounds during these two fermentation processes displayed uniquely individual characteristics,with distinct variations in the volatile compound type and content.(3)During the fermentation process,four phyla were identified in the bacterial community.Proteobacteria and Firmicutes were the two dominant phyla,while 15 bacterial genera,including Lactobacillus,were identified.However,only a few fungal phyla were identified and mainly included Ascomycota,while the primary fungal genus was the unclassified Dipodascaceae,indicating that the fermentation process of pickled ginger was mainly related to the bacterial genus.During natural fermentation,the relative abundance of Proteobacteria was the highest during the entire fermentation process compared with other bacterial phyla,with an abundance proportion of 94.54% at 6 d.However,during inoculation fermentation,Firmicutes exhibited a higher relative abundance,with an abundance proportion of 51.85% at6 d.Furthermore,during the stable stage of fermentation,Proteobacteria and Firmicutes showed a negative correlation.A total of 43 bacterial genera were highly correlated with 49 volatile flavor compounds(|?|> 0.6),including one aldehyde,two ketones,five esters,nine alcohols,and 32 alkenes.Furthermore,one genus was positively and negatively correlated with a variety of volatile flavor compounds,while one volatile flavor compound was also positively and negatively correlated with a variety of genera.Moreover,some low-abundance genera were positively and negatively correlated with a variety of volatile substances.Of these,Lactobacillus(G21)was positively correlated with ?-curcumene(X31)and(+)-?-selinene(X33)(|?|> 0.6),while geranial(X14)was correlated with eight bacterial genera(| ? | > 0.6).The relative abundance of Microbacterium(G26),Ochrobactrum(G28),and Sphingobacterium(G39)was comparatively low but displayed a strong positive correlation with ten volatile alkenes(|?|> 0.8).In conclusion,the type and content of the volatile flavor compounds varied in different brands of pickled ginger.The formation of volatile flavor compounds in pickled ginger may be primarily related to the growth,reproduction,and metabolic activity of various microorganisms during the fermentation process and may be affected by their collective action.