Elizabeth M. Calvey

Allium chemistry: identification of organosulfur compounds in ramp (Allium tricoccum) homogenates

Supercritical fluid (SF) extracts of homogenized ramp (Allium tricoccum Ait.) were separated and characterized with liquid chromatography coupled with atmospheric pressure chemical ionization mass spectrometric identification. The profiles of SF extracts of aqueous homogenates of ramp bulbs from three different seasons and growing regions revealed that the thiosulfinates were major components. In addition, some of the cepaenes (alpha-sulfinyldisulfides) found in extracts of onion juice, as well as allyl containing cepaenes (2-propenyl l-(2-propenylsulfinyl)propyl disulfide), are present in the ramp extracts. The amount of allicin in ramp bulb homogenates ranged from approximately 10% to 50% of that found in extracts of aqueous garlic homogenates. The greater amount of the methyl 1-propenyl thiosulfinates in the ramp extracts relative to that found in the garlic extracts correlates with the flavor characteristics of ramp bulbs.

Near infrared chemical imaging for high throughput screening of food bacteria

Introduction A ssuring food safety is an ongoing endeavour in the food industry and there is a need for fast, reliable tools to screen for pathogens from both naturally-occurring and intentional contamination. FT-IR, Raman and NIR spectroscopy have been successfully applied in food and clinical microbiology in the last two decades. Many reports have shown the possibility of identifi cation of bacteria and yeasts, down to the strain level in some cases (for reviews, see References 1 and 2). However, the sheer numbers of possibilities that must be considered in a general microbiological library and the biochemical similarity exhibited by all microorganisms have hindered the widespread deployment of these techniques. Unsupervised multivariate classifi cation schemes have shown good success when small data sets of bacteria were considered, but calibrated systems and neural networks have been favoured when larger numbers of organisms are involved. In the latter case, it becomes important to include a reasonable complement of organisms of interest in the calibration set, which in turn involves both a signifi cant time commitment for data acquisition as well as refi ned data processing strategies to sort through the thousands of samples of biochemically-similar organisms. Finally, careful consideration of critical instrument issues is needed to ensure calibration transfer. The size of the database imposes a smaller burden when its scope is limited to the microbial fl ora of food. Indeed, the target food product is always known at the time of sampling and most foods are only potentially contaminated by a fairly small number of pathogens. Of course, fi nding a totally unexpected organism is possible and may suggest intentional contamination and this dictates a requirement for some way to fl ag and trap these anomalies in an analytical system. In this work, we built on the original fi ndings that bacteria exhibit NIR spectra that are characteristic enough for identifi cation and developed a high throughput approach with signifi cant potential as a screening tool. The basis of this application is that NIR spectroscopy using a focal-plane array detector provides the additional and critical high throughput advantage required for a useful screening tool and food-specifi c bacterial arrays, or “ID cards”, can be created by placing references directly on the sampling device, thereby eliminating calibration transfer issues. Chemical imaging is often used to obtain spatially-resolved chemical information about inhomogeneous systems. This approach takes advantage of the spatial dimensions of chemical imaging to perform parallel spectral acquisition of about 42 different bacterial samples at once.

Supercritical Fluid Chromatography with FT-IR Detection

Both conventional HPLC and GC detectors have proven to be compatible with Supercritical Fluid Chromatography (SFC). For example, flame ionization, electron capture, flame photometric, thermionic, ultraviolet and fluorescence detection [1, 2] have all been successfully demonstrated. Various efforts have been made to couple spectrometric detectors with chromatographic systems in order to gain more specific information regarding eluting components. Fourier Transform infrared (FT-IR) [3], atomic emission, nuclear magnetic resonance and mass [4] spectrometry have been interfaced to SFC with varying degrees of success during the 1980s. The focus of this chapter is SFC/FT-IR. The FT-IR detector is constrained by two major problems: mid-IR absorption by most chromatographically compatible mobile phases and relatively low FT-IR sensitivity compared to some other more established detectors. In order to minimize these problems, various ingenious interface designs have been explored. These designs appear to vary greatly, but they can be classified into two approaches: solvent elimination coupled with transmission or reflectance IR, and flow cell coupled with transmission or attenuated total reflectance IR. Each approach has a unique set of characteristics that makes it attractive for certain applications.