Colorimetric Artificial Nose for Monitoring Traditional Solid State Fermentation Process of Vinegar Pei

In China and Southeast Asian countries, the solid-state fermentation (SSF) process is maintained empirically, especially when to fed-batch fermentation by layers. The SSF process of Chinese vinegar is typical fed-batch fermentation by layers. It generally lasts about 18 days and is divided into four stages according to the aroma. A new electronic nose technique was developed based on colorimetric sensor array for identifying the four stages and controlling the quality of SSF. Twelve chemically responsive dyes including nine pH indicators and three porphyrins materials were selected according to their sensitivity to volatile compounds typically occurring during SSF process of vinegar. When the sensor array was exposed to vinegar, a color change profile for each sample was obtained by differentiating the image of sensor array before and after exposure to the head-gas of the sample. The values of RGB (i.e., Red, Green, and Blue) color components were extracted from each dye in color change profiles, and they were analyzed using principal component analysis (PCA) and K-nearest neighbour analysis (KNN). In comparison to PCA, KNN obtained an optimum identification result, the discrimination rates were 91.67% and 86.11% in the calibration set and prediction set, respectively. This research shows that the colorimetric sensor array could be a simple method for online monitoring and controlling the fermentation process of SSF.