Comparative Study On The Key Aroma Compounds Basis Of Traditional Fermented Yongchuan Douchi And The Fast-fermentated Yongchuan Douchi After Aroma Enhancement Fermentation

Yongchuan douchi is a seasoning food made from soybeans or black beans by microbial fermentation.Traditional Yongchuan Douchi is a typical representative of Mucor-type douchi.It is rich in protein and essential amino acids,with stong aroma and delicious taste.So,it is widely loved by the people in Sichuan and Chongqing.However,traditional Yongchuan douchi has a long fermentation cycle and is limited by seasons,which seriously hinders its industrialization and scale production.In this case,low salt quick completion douchi came into being.It uses pure Aspergillus oryzae to make koji,and the post fermentation time is only 30 days,which greatly improves the production efficiency.But because of less microorganism and single enzyme,the flavor of the Aspergillus-type douchi is not as good as that of the Mucor-type douchi.Our previous research found that adding halophilic aromatic yeasts into the Aspergillus-type douche for a secondary fermentation could improve the flavor quality,but the mechanism of flavor enhancement has not been clear.Therefore,this paper reveals the flavoring mechanism by exploring the differences among the key aroma active compounds of the traditional fermented Yongchuan douche,the Aspergillus-type douchi and the flavored douchi.The main results of this study are as follows:(1)The differences among the traditional fermented Yongchuan douchi,the Aspergillus-type douchi and the flavored douchi were clarified from the aspects of sensory evaluation and volatile composition.The results of quantitative description analysis showed that the Mucor-type douchi had the highest douchi aroma intensity,with special wine aroma and musty aroma,and the Aspergillus-type douchi aroma profile presented a single,specific soy sauce and bean flavor,and had the lowest douchi aroma intensity.In contrast,the flavored douchi improved the flavor intensity of the original Aspergillus-type douchi,with more coordinated flavor,and the aroma-increasing effect was remarkable.The volatile components of the 3 kinds of douchi were analyzed by SPME-GC × GC-MS.A total of 143 volatile compounds were detected,13 of which were first identified in douchi.Aldehydes(27%),esters(21%)and alcohols(12%)were the main chromatographic peaks of the three kinds of douchi.The total volatile compounds in the Mucor-type douchi > the flavored douchi > the Aspergillus-type douchi.The Mucor-type douchi was mainly composed of esters,aldehydes and alcohols.The Aspergillus-type douchi had the highest proportion of aldehydes,heterocyclization and acids,while flavored Douchi was mainly composed of aldehydes,phenols and alcohols.(2)The key aroma active volatiles in the traditional fermented Yongchuan douchi were studied.A total of 64 aroma regions were detected and 63 compounds were identified.Combined with aroma extraction dilution analysis(AEDA)and odor active values(OAV)calculation,32 potential key flavor substances were selected.After accurate quantification,the aroma characteristics of the traditional fermented Yongchuan douchi were restored through aroma recombination experiment.Finally,the contribution of single aroma substance to the overall aroma was determined through the aroma elimination experiment,and the key aroma active substances of the traditional fermented Yongchuan douchi were determined: ethyl 2-methylbutanoate,oct-1-en-3-ol,3-methylbutanoic acid,dimethyl trisulfide,ethyl isobutyrate,ethyl isovalerate,methional,5-methyl-2-phenylhex-2-enal,2-phenyl-2-butenal,ethyl hexanoate,ethyl acetate,ethyl benzoate,isovaleraldehyde,4-methyl-2-phenyl-2-pentenal,guaiacol,acetic acid,ethanol and acetophenone.(3)By analyzing and comparing the key aroma active substances of the flavored douchi and the Aspergillus-type douchi,the flavoring mechanism was revealed.The results showed that ethyl 2-methylbutanoate,ethyl hexanoate and(2E)-2-Isopropyl-5-methyl-2-hexenal were the new aroma compounds after aroma enhancement fermentation,while the concentrations of methional,guaiacol,5-methyl-2-phenylhex-2-enal,2-phenyl-2-butenal,ethanol,3-methylbutanoic acid and acetic acid increased after the flavoring fermentation.When these aroma components were directly added to the Aspergillus-type douchi,the flavor intensity was significantly improved(α < 0.05),which was consistent with that of the original douchi(α > 0.05),indicating that these aroma compounds are the material basis for the aroma enhancement of douchi.