Monitoring the Yogurt Fermentation Process and Analysis of Flavor Compounds using a Novel Ion Mobility Spectrometer

Fermentation control is very important in yogurt production as it affects product quality. Generally, the lactic acid concentration in the yogurt is measured by pH, and acidity titration has been used to monitor yogurt fermentation. However, these measurements require expertise and time, and the use of contact sampling means that there is a risk of contamination. Numerous volatile or semi-volatile organic compounds are metabolized in the yogurt headspace during yogurt fermentation, but they are not used effectively for fermentation control. The purpose of this study was to assess whether ion mobility spectrometry (IMS) could be used to monitor fermentation by measuring the headspace gas of yogurt in real time without contact. Analysis by IMS is based on the principle of ionizing gas in the atmosphere and then measuring ion mobility; a component analysis is also possible from the output spectrum. Analysis of the volatile components of the headspace by IMS showed that the peak intensity of the output spectrum increased with fermentation of yogurt and was strongly correlated with acid concentration and pH. Furthermore, a comparison of IMS and gas chromatography-mass spectrometry (GC/MS) analysis results revealed that the compounds in yogurt that confer flavor, such as formic acid, acetic acid, lactic acid, butanoic acid, hexanoic acid, octanoic acid and decanoic acid, can be identified by IMS.