Detection of trace gases from fermentation processes using photoacoustic spectroscopy and proton-transfer-reaction mass spectrometry

摘要

This thesis presents novel interdisciplinary Physics - Biology research work that employed Photoacoustic Spectroscopy and Proton-Transfer-Reaction Mass Spectrometry. Both techniques were used in biological studies of trace gasses emitted by crop plants and fruit under stress situations. The findings of this research bring to light essential new features in plant physiology. A line tuneable (5 - 8 ?m) infrared CO-laser based photoacoustic detector was adapted to achieve fast, non-invasive and highly sensitive on-line monitoring of biological processes. The set-up was used to study alcoholic fermentation and concomitant processes in seedlings of various crop plants, notably of rice and wheat (Chapters 2, 3, and 4). If a large number of gases are monitored by the photoacoustic method, the time resolution of the system becomes very low. In addition, there is great interest in trace gases that cannot be monitored by photoacoustics. To overcome these drawbacks, a Proton-Transfer-Reaction Mass Spectrometer (PTR-MS) was designed, constructed and optimized. In Chapter 5 this PTR-MS is described together with its use in monitoring emission of various compounds (aldehydes, alcohols, acids, esters and C-6 compounds) related to fermentation and to fruit aroma and flavour, released by four apple cultivars under short anaerobic and post-anaerobic conditions. Detection limits similar to those reported in the literature were achieved with this system. For the first time, a comparison between PTR-MS and laser photoacoustics was made in order to ensure that fragmentation processes occurring during the PTR-MS measurements do not disturb the assignment of the ion-signals to the neutral compounds of interest. Simultaneous monitoring of alcoholic fermentation products from young rice plants by both methods gave comparable results for acetaldehyde. The preliminary results show that application of PTR-MS detectors in fruit storage opens new possibilities for revealing the kinetics of metabolic processes relevant to storage conditions, fruit quality and basic physiology