PTR-ToF-MS and food bioprocesses: potential in monitoring VOCs release by starter cultures during food fermentation

Abstract

In the modern agro-industry, food fermentations are usually achieved by the supplementing the row materials with starter cultures (SCs) (a microbial preparation of large numbers of cells of selected microorganisms). This practices ensures a number of benefits, including the possibility to enhance and standardize the sensory quality of fermented foods. In fact, microbes produce VOCs (volatile organic compounds) which contribute to, and often dominate, the perceived quality of food and drive consumer preference. Among the methods to monitor VOC release, Proton Transfer Reaction Time of Flight Mass Spectrometry (PTR-ToF-MS) is particularly interesting because of its high sensitivity and non-invasive analysis. Moreover, thanks to the high mass resolution, it provides in a split second highly informative spectra. A further development is the coupling of PTR-ToF-MS with an auto-sampler and with tailored data analysis tools. This paper describes our recently investigations on the possible application of this comprehensive methodology (automatic sampling, PTR-ToFMS analysis and tailored data handling and analysis) to the monitoring of fermentation in two foods, bread and yogurt, as models to respectively study the diversity of yeast (Saccharomyces cerevisiae) and bacterial (lactic acid bacteria) SCs. PTR-ToF-MS is proven to be a fast high-throughput tool for the study of food bioprocesses. In fact, the employment of PTR-ToF-MS, integrated with a multifunctional auto-sampler, allowed us to measure the time evolution of several mass peaks and highlighted reproducible differences among diverse commercial SCs with a minimal need for manual operation and in a short time. We selected a panel of VOCs as potential markers for the rapid screening of SCs in relation with flavor, off-flavor and technological properties which are relevant for the bakery and the yogurt industry.