The impact of the ethylene inhibitor, 1-methylcyclopropene (1-MCP), on four apple cultivars (Braeburn, Fuji, Jazz and Golden Delicious) over 150 days of storage at 2 °C was assessed. Proton transfer reaction quadrupole mass spectrometry (PTR-QUAD-MS) was used to monitor changes in VOC composition, while texture analysis and X-ray microcomputer tomography (µ-CT) scanning were used to study microstructural changes. The application of 1-MCP on apples reduced VOC emissions, concurrently maintaining a firmer texture compared to the untreated apples at each time point. The µ-CT scanning revealed how changes in specific morphological characteristics such as anisotropy, connectivity and porosity, size and shape, as well as the interconnectivity of intracellular spaces (IS) influenced texture even when porosity was similar. Additionally, this study showed that the porosity and connectivity of IS were associated with VOC emission and increased simultaneously. This study highlights how the morphological parameters of an apple can help explain their ripening process during long-term storage and how their microstructure can influence the release of VOCs.
Terpenoids are a class of compounds found in hops that are responsible for the distinctive hop aromas in beer. Changes in terpenoid composition during fermentation as a result of yeast biotransformation influences beer aroma, but the pathways involved in these reactions are yet to be fully understood. In this study, eleven terpenoid standards (geraniol, nerol, citronellol, citral, α-terpineol, citronellyl acetate, caryophyllene, linalool, limonene, β-pinene and myrcene) were individually added to a model beer system fermented with commercially available S. cerevisiae yeast (SafAle US-05). Volatile organic compounds (VOCs) were measured before and after fermentation with headspace solid-phase microextraction gas chromatography/mass spectrometry (SPME-GC/MS). Upon adding a single terpenoid standard to the model beer system, multiple terpenoid products were detected in the resulting beer at the end of fermentation. For example, when geraniol (10 ppm) was added, geraniol, dihydrolinalool, dihydrocitronellyl acetate, citronellyl acetate and citronellol were detected at the end of fermentation. This research illustrates the importance of studying individual terpenoids as it provides valuable insights into the complex chemistry of beer. This information can aid in the optimisation of brewing to enhance the production of flavour and aroma in beer that is desired by consumers.
ABSTRACT A laboratory-scale model system was developed to investigate the transport mechanisms involved in the horizontal movement of bacteria in overland flow across saturated soils. A suspension of Escherichia coli and bromide tracer was added to the model system, and the bromide concentration and number of attached and unattached E. coli cells in the overland flow were measured over time. Analysis of the breakthrough curves indicated that the E. coli and bromide were transported together, presumably by the same mechanism. This implied that the E. coli was transported by advection with the flowing water. Overland-flow transport of E. coli could be significantly reduced if the cells were preattached to large soil particles (>45 μm). However, when unattached cells were inoculated into the system, the E. coli appeared to attach predominantly to small particles (<2 μm) and hence remained unattenuated during transport. These results imply that in runoff generated by saturation-excess conditions, bacteria are rapidly transported across the surface and have little opportunity to interact with the soil matrix.
Microbiological contamination during the manufacture of dairy products is the main quality issue facing the dairy industry. This contamination is generally caused by biofilm formation on manufacturing plant surfaces. High numbers of microorganisms are a common cause of unacceptable products that fail to meet customer specifications. Often, this contamination has no detrimental effect on the product. Sometimes, spoilage issues are attributable to high levels of microorganisms released form biofilms into the product or to the enzymes produced by biofilms at some stage during dairy product manufacture. In some cases, product safety is threatened by contamination with pathogens originating from biofilms. In extreme situations, blockages, inefficient heat transfer and even corrosion are possible in diary manufacturing plants due to biofilm growth. The manufacture of dairy products requires many different steps from milking, transportation, the manufacturing process, packaging and distribution. Throughout this process, there are many niches that favour the growth of specific groups of microorganisms. Each group represents a risk to product quality, and controlling these risks by understanding and managing the manufacturing process ensures consistent acceptable quality product.
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