Research On The Volatile Compounds And Rheological Properties Of Shanxi Aged Vinegar

Aroma and texture are important sensory characters of Shanxi aged vinegar (SAV). Aroma is influenced by kinds and content of volatile compounds, and texture refers to rheological properties. In this research, the volatile compounds and rheological properties are analyzed by solid-phrase microextraction coupled with GC-MS (SPME-GC-MS) and rheometer, respectively. The main results were summarized as follows:(1) Volatile compounds in SAV were determined using a SPME-GC-MS method. Twenty-three volatile compounds were quantitative identified, including esters (6), heterocyclic compounds (4), alcohols (4), ketones (3), aldehydes (3) and volatile phenols (3). This analytical method showed satisfactory repeatability, reproducibility, accuracy and linearity and so was validated in the analysis of volatile compounds. Ten organic acids, six of which were volatile, were determined by ion chromatography too. According to the calculation of odor activity value,19 volatile compounds were identified as main aroma-active compounds. Among them, propanoic acid, acetic acid, trimethyl-oxazole, butanoic acid,3-hydroxybutanone,3-methylbutanoic acid and furfural were the most powerful odorants. The aroma wheel showed that the sensory descriptors of SAV are first fatty and roasty, next woody and nutty and minor fruity and floral.(2) The rheological property of SAV was determined by means of rheometer, and the consistency coefficient (K) and flow index (n) were obtained. The K value of SAV was correlated with several chemical indicators, including glucose, polyphenol, acetic acid, lactic acid and soluble solid content. According to n value, SAV could be classified into two groups preliminarily, namely shear-thickening and quasi-Newtonian fluid. The modification system of SAV indicated the change of SAV from shear-thickening to quasi-Newtonian fluid can be caused by the addition of macromolecular, such as CMC and pectin, but not by increasing sugar, NaCl and polyphenol. Furthermore, total release quantity of the eight key aroma compounds in all modified SAV decreased significantly. This result demonstrated the increasing of viscosity was the main factor which resulted in the significant decrease of aroma release.(3) The rheological properties of SAV for different ageing time were studied. Consistency coefficients of SAV increased with ageing time. According to value of n, which is considered as a quality indicator, samples of SAV with different ageing time could be classified into four groups, namely shear-thickening fluid (n>1.07), quasi-Newtonian fluid (1<n<1.07), Newtonian fluid (n=1) and shear-thinning fluid (n<1). A significant difference (p<0.05) was found for most physicochemical parameters among these four groups of SAV, including total acidity, total polyphenol, glucose, fructose, consistency coefficient, flow index and ageing time. Furthermore, the n values of SAV were also correlated with its response on gas sensors on the electronic nose. Our results demonstrated the rheological properties of SAV were a reliable and fast quality assessment parameter.(4) Volatile extracts from SAV exhibited high antioxidant activity in vitro. The volatile extracts exhibited dose-dependent antioxidant activity in both DPPH assay and the aldehyde/carboxylic acid assay. However, volatile extracts, except for extract from beginning of the thermal process, exhibited no protective effects on hydrogen peroxide-induced oxidative stress injury in HepG2 cells.