Analysis of volatile organic compounds from Chinese vinegar substrate during solid-state fermentation using a colorimetric sensor array

Abstract

Aroma is a significant index to reflect the quality of vinegar. This paper intends to investigate the volatile organic compounds (VOCs) of vinegar's substrate during solid-state fermentation. Gas chromatography and mass spectrometry (GC-MS), as well as a colorimetric sensor array, was used comparatively to characterize the VOCs in the different stages of the acetic acid fermentation. It was found from GC-MS that the chemical components of ethanol, 3-methyl-1-butanol, acetic acid, and ethyl acetate were remarkably changed during the solid-state fermentation. Furthermore, the colorimetric sensor array technique was also used to characterize the VOCs of the solid-state fermentation. The color changes of the colorimetric sensor array before and after exposure to the vinegar's substrate samples were obtained by a Charge Coupled Device (CCD) camera. The digital data (i.e., RGB components of the image) representing the color change profiles for the vinegar samples were analyzed. A principle components analysis (PCA) was employed to present the trends in the fermentation process through analyzing the signals obtained from the colorimetric sensor array. A linear discriminant analysis (LDA) model based on the PCA scores was used to distinguish vinegar's substrate samples per day during the whole fermentation process. The result show that around 60 percent of samples were correctly identified corresponding to their fermenting day; and 92.3 percent of samples were correctly identified within an error range of three days. Therefore, the colorimetric sensor array technique was considered to be an excellent method for VOCs measurement, based on its advantages of accuracy, no need for a pretreatment, fast, and low cost.