Study On The Main Composition Variation During The Brewing Process Of Shanxi Aged Vinegar

Shanxi Aged Vinegar (SAV) is produced by the liquid-state alcoholic fermentation and solid-state acetic acid fermentation process, with sorghum, wheat bran, chaff as materials, and Daqu (made from barley and pea) as the saccharification agent and fermentation starter. SAV is special for the organoleptic attribute of" sweet, soft and acid taste, good aftertaste linger’ Currently, there are some researches about Zhenjiang aromatic vinegar (in China), traditional balsamic vinegar (in Italian), Kurosu (in Japanese), but fewer reports about SAV have been published and the formation mechanisms of main components in SAV are still unknown.In this study, SAV brewed by the traditional process was taken as research object and variation of main compositions was analyzed during alcoholic fermentation (from the 1st to the 16 day), acetic acid fermentation (from the 17th to the 25th day) and smoking process (from the 26th to the 31st day) by headspace solid-phase microextraction/gas chromatography-mass spectrometry, automatic amino acid anaylyzer, high performance liquid chromatography and other modern analytical techniques. Then variations of glucoamylase activities, amylase activities and protease activities in alcoholic fermentation and acetic acid fermentation, and variations of protein, starch, total sugar, total acid, organic acids, ferulic acid, amino acids, ligustrazin, y-aminobutyric acid and other components during brewing process were mainly examined. Phenolic compounds in SAV at different aging stage were extracted. In the extract, antioxidant activity and variety of phenolic acids were determined. All of these results were as follows.1 Analysis on the composition of materialsIn this study, starch, protein, fat, polyphenols and flavonoids, ferulic acid, AFB1 and citrinin in materials were determined. Contents of starch in sorghum and Daqu were 71.05% and 57.75%, respectively. Contents of protein in wheat bran and Daqu were 19.57% and 20.92%, respectively. And contents of fat in all the material were low. Polyphenols and flavonoids mainly existed in sorghum and their contents were 1.017g/100g and 56.0 mg/100g, respectively. Ferulic acid was mainly existed in wheat bran and chaff, and contents of free and conjugated ferulic acid in wheat bran were 0.70μg/g and 1634μg/g, respectively.Daqu contained of rich enzyme system in which glucoamylase, amylase, acidic protease and neutral protease activities were as high as 1500 U/g,736 U/g,152 U/g and 78 U/g, respectively. AFB1 and citrinin were not detected in Daqu.2 Analysis on composition variation during brewing process of SAV2.1 Variation of enzyme activitiesIn alcoholic fermentation process, activities of glucoamylase and amylase were 372.00-438.94 U/g and 203.00-257.23 U/g, respectively, and the activities of acidic and neutral protease were 46.61-64.56 U/g and 22.27-33.00 U/g. In acetic acid fermentation process, activities of glucoamylase, amylase, acidic and neutral protease reduced.2.2 Variation of starch, total sugar, total acid and other componentsIn alcoholic fermentation process, content of starch reduced from 64.05% to 32.91% and reduced to 18.88% at the end of smoking process. Contents of total sugar and reducing sugar reduced from 11.88% and 9.78% to 1.12%and 0.81% during alcoholic fermentation process, increased from 2.28% and 4.70% to 7.35% and 8.54% in acetic acid fermentation and decreased to 5.89% and 2.91% at the end of smoking process. In alcoholic fermentation process, alcoholicity increased from 1.3°to 5.7°and decreased to 0°on the 22nd day. From the 1st to the 22nd day, the content of total acid was increased from 1.17% to 10.23% and changed a little from the 23rd to the 31st day.2.3 Variation of organic acids and amino acidsIn alcoholic fermentation process, the content of lactic acid increased from 1.94mg/g (the 1st day) to 60.60 mg/g (the 16th day) and changed a little during acetic acid fermentation process. Content of acetic acid increased obviously from 1.03 mg/g (the 1st day) to 76.25 mg/g (the 31st day). Meanwhile, contents of tartaric acid, malic acid, citric acid and succinic acid were low and had no obvious change.In alcoholic fermentation process, leucine, valine, glutamic acid and alanine changed obviously, their contents were increased from 25.55,22.38,79.32 and 41.01mg/100g to 167.25,109.51,224.97 and 212.93 mg/100g, respectively; phenylalanine, methionine, serine, proline, isoleucine, glycine, aspartic acid, and cysteine increased; lysine, histidine, tyrosine and ornithine decreased; threonine and arginine changed a little. In acetic acid fermentation, contents of all the amino acids had no obvious change. In smoking process, contents of amino acids were decreased by different degrees.2.4 Variation of volatile flavor compoundsContents and varieties of esters, aldehydes, ketones, heterocyclic were mainly analyzed in Pei of acetic acid fermentation (the 25th day) and smoking process (the 28th and 31st day). According to the GC-MS results, in the Pei of acetic acid fermentation, phenylethyl acetate and isoamyl acetate were the main esters, and their contents were 1.92%and 1.88%, respectively, while contents of aldehydes, ketones and heterocycles were low.Contents and varieties of flavor compounds changed obviously during smoking process. The content of heptanoic acid increased and others decreased; content of phenylethanol increased from 0.09% to 0.83%, and others had no obvious change; content of esters decreased; content of aldehydes, ketones and heterocycles increased, especially furfural and tetramethyl pyrazine, their contents increased from 0.74%,0.68% to 23.53%,14.14%, respectively.2.5 Variation of functional componentsThe content of polyphenols and flavonoids had no obvious change during the brewing process, about 1.4 g/100g and 25.0 mg/100g in alcoholic fermentation,0.4g/100g and 2.0 mg/100g in acetic acid fermentation, and 0.7g/100g and 5.0mg/100g in smoking process.On the 1st day, content of free ferulic acid was 9.34μg/g and decresed to about 0.4μg/g on the 3rd day, almost had no change from the 3rd to the 16th day, and increased from 19.49μg/g to 66.54μg/g from the 17th to 31st day. The content of conjugated ferulic acid decreased during the brewing process.Ligustrazin was not detected during the 1st to the 21st day, its content was 0.11μg/g on the 22nd day, and increased to 0.13μg/g on the 25th day, and increased significantly in smoking process, up to 5.26μg/g on the 31st day.The content of GABA increased obviously in alcoholic fermentation, from 30.70mg/100g (the 1st day) to 119.78μg/g (the 16th day), and decreased slightly in acetic acid fermentation and smoking process.3 Analysis on phenolic acids and antioxidant activity of SAVIn this study, acetic ether was chose to extract phenolic compounds in SAV. As the aging time was longer, the content of phenolic compounds in SAV was higher. DPPH-radical scavenging activity and reducing capacity were important indexes evaluating antioxidant activity. The results revealed that the antioxidant activity of extract was stronger when the vinegar was aged for longer time.Ferulic acid, p-coumaric acid,p-hydroxybenzcic acid, protocatechuic acid, vanillic acid were detected in SAV. Their contents increased during the aging time. Contents of protocatechuic acid, vanillic acid, p-hydroxybenzcic acid, ferulic acid and p-coumaric acid were 16.18,26.68,22.18,5.58 and 18.81 μg/mL in the new vinegar, respectively, and up to 58.97,83.62,46.85,19.60 and 27.63 μg/mL in the 8-year vinegar, respectively.In DPPH·radical scavenging activity system, the order of scavenging rate from strong to weak was that protocatechuic acid> ferulic acid> vanillic acid> p-coumaric acid> p-hydroxybenzcic acid. In the reducing capacity system, protocatechuic acid> vanillic acid> ferulic acid> p-coumaric acid> p-hydroxybenzcic acid. In these two evaluation systems, there was no synergistic antioxidant effect between two phenolic acids.