Effect of fermentation modes on nutritional and volatile compounds of Huyou vinegar

Semi-solid static mode was applied to brew Huyou (Citrus changshanensis) vinegar, called HV-SS, and changes of main nutrients, volatile compounds and antioxidant capacity at different brewing stages, i.e. Huyou puree (HP), Huyou wine (HW) and HV-SS, were investigated. Meanwhile, all these parameters of HV-SS and Huyou vinegar brewed by liquid static mode (HV-LS) were compared. The contents of the main nutrients except for vitamin C (Vc) and reducing sugar increased significantly after fermentation from HP to HV-SS. DPPH radical-scavenging capacity and reducing power of HW was the highest and ABTS⁺ scavenging capacity of HV-SS was the highest. Acids, flavonoids, phenolics and Vc jointly played important roles in the antioxidant capacity of HV-SS. Forty-six aroma compounds were detected in HP and alcohols were the principal components (15 alcohols accounted for 46.2%). During HW fermentation, most of the compounds in HP (d-limonene, hexanal, hexanol and 3-hexen-1-ol) were nearly disappeared, and some new alcohols, esters and alkanes were formed, being the abundant compounds in HW and accounting for 62.99%, 18.44% and 10.52% respectively. There were 51 aroma compounds detected in HV-SS and 10 more than those in HV-LS. The types or contents of esters (22.13%), acids (50.49%) and aldehydes (7.33%) in HV-SS were markedly different from those in HP, HW and HV-LS, giving the unique aroma and good flavor to HV-SS. Therefore, semi-solid static fermentation mode was more suitable for brewing Huyou vinegar on the aspect of balancing the nutrients characteristics and flavor compounds formation.