| Shanxi aged vinegar is one of the most famous traditional cereal vinegars in China,which has significant differences in the production technology from other vinegars.In particular,it has some unique processes such as fumigation(heating)of 1/3 of the vinegar mash before leaching vinegar to improve the color of Shanxi aged vinegar.After the heating process of the vinegar mash,in addition to color improvement,flavor and functional compounds,such as ethyl acetate,furaldehyde and ligustrazine,can also be produced.Currently,two heating approaches exits for the fumigation process,that is,a traditional long-term heating method that gradually warms up and cools down(at a daily heating rate of 20-30℃,from about 30℃ to the highest temperature of about 90℃,and then gradually cools down)and lasts for about 5 d(hereinafter referred to as the traditional heating method,THM),as well as a modern shortterm(only about 24 h)high-temperature(about 100℃)heating method(hereinafter referred to as the modern heating method,NHM).However,there is little research on the effects of these two heating methods on SAV.This study takes the vinegar mashes from a certain SAV production enterprise before and after THM and NHM treatment as the research object,analyzes the changes in conventional,functional and flavor components in the vinegar mashes.In addition,boiling(at about 95℃for 30 min)of the fresh vinegar(freshly leached vinegar),as an important heating process during the vinegar production,has very significant impacts on the qualities and flavors of SAV.As a result,in this study the conventional,functional and flavor components also are analyzed and compared in fresh SAV obtained from the vinegar mash,which is heated with NHM.The research results will provide reference value for the improvement of SAV production process,especially the improvement of vinegar mash heating process.1.Effects of different heating processes on conventional componentsThe vinegar mashes treated by THM and NHM and the fresh vinegars before and after frying(BFV and AFV)were determined by quality indexes including total acid contents,p H values,total sugar and reducing sugar contents,ammonia nitrogen contents,amino acid types and contents and organic acid types and coontents.In the vinegar mashes treated by THM,the total acid contents increased with the heating process,significantly increasing from 7.19 ±0.05 g/100 g before heating(P < 0.05)to 8.34 ± 0.07 g/100 g after heating,and the p H values remained basically unchanged.However,in the vinegar mashes treated by NHM,the total acid contents and p H values did not show significant changes before and after heating;Both in the vinegar mashes treated by THM and NHM,the total sugar contents significantly decreased from 7.92 ± 0.41 g/100 g and 8.61 ± 0.24 g/100 g before heating(P < 0.05)to 5.78 ± 0.55g/100 g and 6.01 ± 0.24 g/100 g,respectively.However,there was no significant difference in reducing sugar contents before and after heating;The ammonia nitrogen contents significantly decreased from 0.41 ± 0.05 g/100 g and 0.36 ± 0.08 g/100 g before heating(P < 0.05)to 0.21± 0.07 g/100 g and 0.20 ± 0.08 g/100 g,respectively;In the vinegar mashes treated with THM and NHM,15 amino acids were detected before and after heating,and the contents of most amino acids significantly decreased(P < 0.05)after heating.There was no significant change in total acid contents and p H values before and after boiling with fresh vinegar;The total sugar contents significantly decreased from 7.38 ± 0.47g/100 m L(P < 0.05)to 6.55 ± 0.24 g/100 m L,and the reducing sugar contents decreased from5.91 ± 0.11 g/100 m L to 5.25 ± 0.19 g/100 m L;The ammonia nitrogen contents decreased significantly from 1.64 ± 0.02 g/100 m L(P < 0.05)to 1.25 ± 0.02 g/100 m L;14 amino acids can be detected in new vinegar,and the amino acid contents slightly decreased after boiling;6 organic acids,acetic acid,citric acid,lactic acid,malic acid,succinic acid,and tartaric acid,were detected before and after the boiling of fresh vinegar,and the organic acid contents slightly decreased after the boiling.2.Effects of different heating processes on functional componentsThe changes of phenyllactic acid(PLA)and ligustrazine(LIG),the main functional components,in vinegar mashes before and after heating and fresh vinegars were analyzed.The PLA contents both in vinegar mashes and fresh vinegars decreased slightly after heating.In the vinegar mashes treated by THM and NHM,the LIG contents significantly increased from0.97 ± 0.41 μg/g and 0.87 ± 0.08 μg/g before heating(P < 0.05)to 1.81 ± 0.09 μg/g and 1.33± 0.02 μg/g after heating,respectively,while in the fresh vinegars,the LIG contents significantly increased from 0.33 ± 0.01 μg/m L(BFV)(P < 0.05)to 0.68 ± 0.08 μg/m L(AFV).3.Effects of different heating processes on volatile flavor componentsThe changes in volatile flavor compounds(VFCs)in vinegar mashes and fresh vinegars before and after heating were analysed using solid phase microextraction gas chromatography mass spectrometer.The VFCs in all samples mainly include esters,alcohols,aldehydes,acids,heterocycles,ketones,and phenols,totaling 7 types of compounds.A total of 55 VFCs were detected in THM treated vinegar mashes,and 44 VFCs were detected in NHM treated vinegar mashes.After heating,the contents of acids and alcohols slightly decreased,while the contents of furfural and LIG significantly(P < 0.05)increased,reaching 107.46 ± 18.23 μg/g,23.86 ±3.45 μg/g(THM)and 23.04 ± 4.30 μg/g,24.14 ± 5.47 μg/g(NHM)in the vinegar mashes heated by THM and NHM,respectively.Only 31 VFCs were detected before and after the boiling of fresh vinegar,and the furfural contents significantly increased from 8.65 ± 1.93μg/m L to 12.81 ± 3.50 μg/m L.4.Effects of the heating process on antioxidant capacities of fresh vinegarDPPH,ATBS,and FRAP methods were used to determine the antioxidant capacities of fresh vinegars before and after boiling.The results showed that although the contents of total polyphenols and flavonoids increased to a certain extent after boiling,its antioxidant activity was basically the same.The DPPH,ATBS,and FRAP antioxidant capacities of fresh vinegar are 38.92 ± 0.18%,44.05 ± 0.2% and 35.27 ± 0.32%,respectively. |
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