Review: Methods to determine offal adulteration in meat products to support enforcement and food security.

Offal tissues carry a lower market value compared to skeletal meats in some global markets. The inclusion of offal in any meat product in the EU and UK must be declared on the label. While many technologies have been applied to the challenge of determining adulteration with offal in meat products, no single method has been recognised and validated as a reliable test to support legislative requirements. This literature review investigated appropriate methods to determine the adulteration of meat with offal. The aim was to identify technologies suitable for future validation to underpin a high throughput, low-cost method suitable for application by enforcement laboratories. Considering all of the methods, technologies which determine elemental composition and peptide markers were particularly highlighted as demonstrating potential for future development to determine a wide range of offal tissues to support the safety and integrity of the food chain.

Application of cryoprobe 1H nuclear magnetic resonance spectroscopy and multivariate analysis for the verification of corsican honey.

Proton nuclear magnetic resonance spectroscopy ((1)H NMR) and multivariate analysis techniques have been used to classify honey into two groups by geographical origin. Honey from Corsica (Miel de Corse) was used as an example of a protected designation of origin product. Mathematical models were constructed to determine the feasibility of distinguishing between honey from Corsica and that from other geographical locations in Europe, using (1)H NMR spectroscopy. Honey from 10 different regions within five countries was analyzed. (1)H NMR spectra were used as input variables for projection to latent structures (PLS) followed by linear discriminant analysis (LDA) and genetic programming (GP). Models were generated using three methods, PLS-LDA, two-stage GP, and a combination of PLS and GP (PLS-GP). The PLS-GP model used variables selected by PLS for subsequent GP calculations. All models were generated using Venetian blind cross-validation. Overall classification rates for the discrimination of Corsican and non-Corsican honey of 75.8, 94.5, and 96.2% were determined using PLS-LDA, two-stage GP, and PLS-GP, respectively. The variables utilized by PLS-GP were related to their (1)H NMR chemical shifts, and this led to the identification of trigonelline in honey for the first time.

Non-targeted detection of chemical contamination in carbonated soft drinks using NMR spectroscopy, variable selection and chemometrics.

An efficient method for detecting malicious and accidental contamination of foods has been developed using a combined 1H nuclear magnetic resonance (NMR) and chemometrics approach. The method has been demonstrated using a commercially available carbonated soft drink, as being capable of identifying atypical products and to identify contaminant resonances. Soft-independent modelling of class analogy (SIMCA) was used to compare 1H NMR profiles of genuine products (obtained from the manufacturer) against retail products spiked in the laboratory with impurities. The benefits of using feature selection for extracting contaminant NMR frequencies were also assessed. Using example impurities (paraquat, p-cresol and glyphosate) NMR spectra were analysed using multivariate methods resulting in detection limits of approximately 0.075, 0.2, and 0.06 mM for p-cresol, paraquat and glyphosate, respectively. These detection limits are shown to be approximately 100-fold lower than the minimum lethal dose for paraquat. The methodology presented here is used to assess the composition of complex matrices for the presence of contaminating molecules without a priori knowledge of the nature of potential contaminants. The ability to detect if a sample does not fit into the expected profile without recourse to multiple targeted analyses is a valuable tool for incident detection and forensic applications.

NMR structure of the peptidyl transferase RNA inhibitor antibiotic amicetin.

In this communication, we report the solution state NMR structure determination of the peptidyl transferase RNA inhibitor antibiotic amicetin. We have successfully characterised the NMR spectrum of amicetin using a range of homo- and heteronuclear NMR techniques. Using experimental ROE-based distance and 1H--1H scalar coupling derived dihedral angle geometrical constraints as input into the three-dimensional structure determination protocol, we have generated an energy-minimised average structure of the antibiotic. Amicetin adopts a stable well-folded conformation in solution, mediated by a network of hydrogen bonds caused by proton donor and acceptor groups at either end of the molecule. The NMR structure of amicetin shows that the cytosine moiety occupies the critical turn position within the fold, which may be structurally significant for interaction with peptidyl transferase ribosomal RNA. The structure is distinctly different from the published X-ray crystal structure of amicetin in which it adopts a linear, extended chain-like conformation with a number of intermolecular hydrogen bonds. In addition to structure, we have probed the dynamics of amicetin in solution and have observed retarded exchange of the amide proton involved in folding. We have also characterised the ionisation properties of amicetin by carrying out NMR pH titration and measuring the pKa of the primary and tertiary amino groups, 7.27 and 7.52, respectively, which are in agreement with the reported values in literature. Solving the NMR structure of amicetin provides a valuable opportunity to determine the structure of its complex with RNA in solution state.

The development of cryoprobe nuclear magnetic resonance spectroscopy for the rapid detection of organic contaminants in potable water.

The detection of trace levels of a range of organic contaminants (including pesticides, toxins and an explosive) in potable water, using cryoprobe NMR spectroscopy with limited sample preparation and rapid acquisition times, is described. Emphasis is placed on the applicability of NMR spectroscopy for use in emergency scenarios as the unbiased nature of the technique facilitates the detection and characterization of unknown compounds at levels as low as 50 microg L(-1).

NMR structure determination and calcium binding effects of lipopeptide antibiotic daptomycin.

Daptomycin is an acidic lipopeptide antibiotic, whose three-dimensional structure and mechanism of action is currently unknown. Recently daptomycin, trade name Cubicin, was approved as a drug for the treatment of skin-related infections (M. Larkin Lancet, 2003, 3, 677) and became the first antibiotic of its class to be used in the clinic (A. Raja et al., Nature Rev. Drug Discov., 2003, 2, 943-944). We have carried out a systematic high field NMR study of daptomycin and its binding to calcium ions which is essential for antibiotic activity. In this first report, we demonstrate the sequence-specific resonance assignment of daptomycin under resolved NMR measurement conditions. In addition to this, we have determined the 3D structure of apo-daptomycin and demonstrated a 1 : 1 stoichiometry on the binding to calcium ions. We have also demonstrated that the binding of calcium ions does not result in major conformational changes, but does induce aggregation. This may be an important factor in the mode of action of daptomycin.