A rheological approach to the quantitative assessment of traditional balsamic vinegar quality

This work aimed at evaluating the ability of rheological measurements to describe the quality of Traditional Balsamic Vinegars (TBV) with respect to their composition and sugar crystallization. With this aim, shearing experiments were conducted on 100 samples of TBV using a controlled-strain rotational rheometer, whereas the concentration of glucose, fructose, acetic acid, gluconic acid, malic acid as well as refractive index and titrable acidity were determined according to the normal procedure for quality assessment of TBV. A broadrange for the rheological response was observed including Newtonian and shear-thinning behavior. A Joining Tree Cluster Analysis (JTCA) was able to classify the investigated vinegars into meaningful classes based on the stress data alone. Moreover, Principal Component Analysis (PCA) was performed to link composition data to rheological properties, and finally, Multivariate Regression Analysis (MRA) evaluated the contribution of the main constituents to vinegar viscosity. The results suggested that rheological analysis must be carried out in order to spot some fundamental aspects of the vinegar texture, which cannot be detected otherwise. In particular, two rheological parameters were proposed as objective and quantitative descriptors of TBV quality: the shear viscosity measured at500 s-1 accounting for the vinegar composition, and the flow behavior index accounting for sugar crystallization.