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Investigation of the aroma differences among different kinds of soy sauces is beneficial for controlling their flavor quality and processing improvement from the perspectives of raw materials and brewing techniques. The aroma compounds in ten premium soy sauces (CB, HT1, HT2, LH, LJJ1, LJJ2, QH, XH1, XH2, WZ) were qualitative and quantitative analyzed by solid phase extraction and solid-phase microextraction combined with gas chromatography-mass spectrometry (GC-MS). The contributions of aroma compounds to the aroma characteristics of premium soy sauce was determined by sensory evaluation, calculation of aroma activity value (OAV) and partial least squares regression analysis (PLSR). A total of 86 volatile compounds were identified in 10 premium soy sauces, 44 of them were both detected in 10 soy sauce. The 30 aroma compounds with OAV≥1 were detected, the 5-ethyl-4-hydroxy-2-methyl-3(2H)-furanone showed the highest OAV (373~4698), followed by 4-methoxy-2,5-dimethyl-3(2H)-furanone (0~1473). WZ soy sauce had a strong smoky aroma due to the highest variety of phenolic and ketone compounds. The overall aroma profile of CB soy sauce was the weakest with the lowest concentration of ethanol (25.775 μg/L), but the highest content of pyrazine compounds (182.796 μg/L), of which 2,6-dimethylpyrazine was 66.256 μg/L. XH1 soy sauce had a strong sauce aroma and alcoholic notes, due to the highest ethanol content (147.257 μg/L) and higher phenolic content, for example the concentration of 4-ethyl-2-methoxyphenol (18240.479 μg/L) was the highest. XH2 soy sauce had a strong malty aroma. The content of 2-methyl-1-propanol (51.223 μg/L) and 2,3-butanediol (57921.798 μg/L) in LH soy sauce was the highest among others. The content of 1-octen-3-ol (61.219 μg/L) in HT1 soy sauce was the highest. Combination of OAV and PLSR analysis confirmed the ethyl acetate, 3-hydroxy-2-butanone, 2,3-butanediol, 3-ethyl-2,5-dimethylpyrazine, 4-methoxy-2,5-dimethyl-3(2H)-furanone, 4-ethylguaiacol and 4-ethylphenol were the key aroma-active components that contribute to the aroma differences among 10 kinds of premium soy sauce.

In order to reveal the protective mechanism of hydrocolloid on wheat dough gluten during freezing, Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM) were used to investigate the secondary structure, microstructure, disulfide bond content and water-binding capacity of gluten obtained from frozen-thawed wheat dough added with different amounts of flaxseed gum (FG) or Artemisia sphaerocephala Krasch. gum (ASKG). Results showed that freezing-thawing treatment destroyed the ordered network structure of gluten, while FG and ASKG could cross-link with the gluten protein network structure to form a stable cross-linked structure. Upon the addition of FG or ASKG at 0.4%, the gluten network structure was most uniform and dense. The addition of FG and ASKG increased the content of disulfide bond and the relative content of α-helix in gluten, making the gluten structure more stable under repeated freeze-thaw cycles. In addition, the addition of FG and ASKG reduced the surface hydrophobicity and consequently led to an increase in the water-binding capacity of wheat gluten. The highest water-binding capacity was obtained at an addition level of 0.4% for both FG and ASKG, 1.46 and 1.43 times higher than that of the control group without added hydrocolloid undergoing repeated freeze-thaw cycles, respectively. All these results showed that FG and ASKG could interact with gluten to form a stable cross-linked structure, thereby enhancing the water binding capacity of gluten protein and exerting a cryoprotective effect on it.