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Food Science, Applications of Mass Spectrometry
592 FOOD SCIENCE, APPLICATIONS OF MASS SPECTROMETRY
Stewart K and Whitaker JR (1984) Modern Methods of Food Analysis. Westport CT: AVI Publishing Company. Taylor A, Branch S, Crews H, Halls D, Owen L and White M (1997) Atomic spectrometry update – clinical and
biological materials, food and beverages. Journal of Analytical Atomic Spectrometry 12: 119R–221R. Wolf W (1984) Biological Reference Materials, Availability, Uses and Need for Validation of Nutrient Measurement. New York: Wiley.
Food Science, Applications of Mass Spectrometry John PG Wilkins, Unilever Research, Sharnbrook, Bedfordshire, UK
MASS SPECTROMETRY Applications
Copyright © 1999 Academic Press
The exquisite analytical sensitivity and specificity of MS have found numerous and diverse applications in the field of food science. Trace analysis for undesirable chemical contaminants in foodstuffs is conducted in many laboratories around the world. This may be for quality control, regulatory or surveillance purposes. MS is frequently the analytical method of choice because of its ability to produce unequivocal data. Organic compounds sought include naturally derived materials, such as mycotoxins and offflavours (produced by rancidification or spoilage), and man-made/industrial chemicals, e.g. pesticides, veterinary drugs, environmental contaminants (such as polychlorodibenzo-p-dioxins, polychlorinated biphenyls, polynuclear aromatic hydrocarbons, etc.) and food tainting compounds (e.g. 2,4,6-trichloroanisole, the compound responsible for musty cork taint in wine, arising from the inappropriate use of wood preservatives). GC-MS and HPLC-API-MS are widely used for these types of analyses. Desirable food components present at trace levels, such as nutrients, are also determined using these techniques. Trace levels of inorganic chemical species, e.g. lead, arsenic, cadmium, are also monitored in foodstuffs, often using ICP-MS. The advantage of MS over AAS is that several elements may be measured simultaneously and the concentrations of individual isotopes may be measured, facilitating metabolism/ nutrient studies with stable isotope materials. Precise determination of isotope ratios (e.g. C, N and O) by IRMS is also important in agricultural and food authenticity studies. Accelerator mass spectrometry is used in tracer studies, for the determination of extremely low levels of carbon-14 (and other) isotopes.
The table below summarizes the ranges of analytical sensitivities required for different classes of food analysis. Much work has been done on the characterization of food flavours and aromas by GC-MS. A significant recent advance has been the use of APCI and drift tube MS techniques for sensitive, on-line (‘real time’) monitoring of trace volatiles, e.g. in human breath during flavour release studies. Characterization of unfractionated foodstuffs and related materials for screening or taxonomic purposes may be performed by pyrolysis MS and direct headspace MS. These techniques generate rather simple mass spectra that may be classified using pattern recognition/chemometric software. MS is also used for the analysis of the more abundant (non-trace) components of food, e.g. oils and fats (triglycerides), proteins and carbohydrates. Analysis of these materials is often challenging, as they may comprise complex mixtures of isomeric compounds. Modern MS techniques (MALDI TOF and electrospray ionization) have become extremely important in protein and peptide studies.
Table 1 Typical analytical sensitivities required for various classes of food contaminant/component
Class
Typical concentraion sought (by weight)
Flavours
% - ppb
Food taints
% - ppq
Pesticide residues
ppm - ppb
Trace elements
ppm - ppb
Mycotoxins
ppb
Dioxins
ppt - ppq
FOOD SCIENCE, APPLICATIONS OF NMR SPECTROSCOPY 593
See also: Biochemical Applications of Mass Spectrometry; Food and Dairy Products, Applications of Atomic Spectroscopy; Food Science, Applications of NMR Spectroscopy; Inorganic Chemistry, Applications of Mass Spectrometry; Peptides and Proteins Studied Using Mass Spectrometry; Time of Flight Mass Spectrometers.
Further reading Belton PS, Mellon FA and Wilson RH (1993) Spectroscopy in Food Science, Spectroscopy in Europe 5: 8–14.
Crews H (1993) A decade of ICP MS analysis. International Laboratory 23: 38–42. Gilbert J (ed.) (1987) Applications of Mass Spectrometry in Food Science. Amsterdam: Elsevier Applied Science. Horman I (1979) Mass spectrometry in food science. Mass Spectrometry 5: 211–233. Self R, Mellon FA, McGaw BA, Calder AG, Lobley GE and Milne E (1996) The application of mass spectrometry to food and nutrition research. NATO ASI Series, Series C 475 (Mass Spectrometry in Biomolecular Sciences) 483–515.
Food Science, Applications of NMR Spectroscopy Brian Hills, Institute of Food Research, Norwich, UK Copyright © 1999 Academic Press
The applications of NMR in food science have been the subject of several international conferences, reviews and books which are cited in the Further reading section. This intense interest in the NMR spectroscopy of food is driven not only by the commercial importance of food, but also by the intellectual challenge of unravelling the physicochemical properties of this exceedingly diverse and complex group of materials. In order to focus on food aspects, it will be assumed that the reader is familiar with the principles of NMR and magnetic resonance imaging (MRI), which are lucidly explained in other articles of this encyclopedia.
Spatially resolved NMR applications MRI is beginning to have a major impact on our understanding and control of the growth of food crops, on our assessment of fruit and vegetable quality and in developing the best methods of fruit and vegetable preservation. Moreover, by providing noninvasive, real-time images of moisture and lipid distributions, as well as spatial maps of temperature and food quality factors, MRI has the potential for making a major impact on food processing science. We therefore begin with a brief review of whole-plant functional imaging, then progress on to MRI applications in food processing and storage.
MAGNETIC RESONANCE Applications Functional imaging of whole plants
The growth of agricultural crops is affected by many factors, including drought (osmotic stress), luminescence, disease and soil pollutants, such as heavy metals. By permitting noninvasive monitoring of a whole plant under realistic environmental conditions, MRI has become a powerful tool in the plant physiologists’ armoury. The development of small seedlings can be observed directly inside adapted NMR tubes. Larger plants can be grown in controlledenvironment boxes, which bathe the root system in nutrients, and control humidity, temperature and luminescence. The root system, stem or leaf areas can then be imaged noninvasively. Root imaging is now an established technique, though it is not applicable to all soil types because paramagnetic impurities in the soil can severely shorten the water relaxation time. Nevertheless, three-dimensional (3D) T1weighted imaging has been used to distinguish roots and soil in developing pine seedlings, to follow water depletion zones around the tap root, lateral roots and fine roots, and to follow the effects of symbiotic relationships, such as infection with mycorrhizal fungus, on water uptake. The increase in root network volume and surface area can also be measured from the 3D images. A combination of flow imaging and chemical shift imaging has been used to monitor the effect of
Stewart K and Whitaker JR (1984) Modern Methods of Food Analysis. Westport CT: AVI Publishing Company. Taylor A, Branch S, Crews H, Halls D, Owen L and White M (1997) Atomic spectrometry update – clinical and
biological materials, food and beverages. Journal of Analytical Atomic Spectrometry 12: 119R–221R. Wolf W (1984) Biological Reference Materials, Availability, Uses and Need for Validation of Nutrient Measurement. New York: Wiley.
Food Science, Applications of Mass Spectrometry John PG Wilkins, Unilever Research, Sharnbrook, Bedfordshire, UK
MASS SPECTROMETRY Applications
Copyright © 1999 Academic Press
The exquisite analytical sensitivity and specificity of MS have found numerous and diverse applications in the field of food science. Trace analysis for undesirable chemical contaminants in foodstuffs is conducted in many laboratories around the world. This may be for quality control, regulatory or surveillance purposes. MS is frequently the analytical method of choice because of its ability to produce unequivocal data. Organic compounds sought include naturally derived materials, such as mycotoxins and offflavours (produced by rancidification or spoilage), and man-made/industrial chemicals, e.g. pesticides, veterinary drugs, environmental contaminants (such as polychlorodibenzo-p-dioxins, polychlorinated biphenyls, polynuclear aromatic hydrocarbons, etc.) and food tainting compounds (e.g. 2,4,6-trichloroanisole, the compound responsible for musty cork taint in wine, arising from the inappropriate use of wood preservatives). GC-MS and HPLC-API-MS are widely used for these types of analyses. Desirable food components present at trace levels, such as nutrients, are also determined using these techniques. Trace levels of inorganic chemical species, e.g. lead, arsenic, cadmium, are also monitored in foodstuffs, often using ICP-MS. The advantage of MS over AAS is that several elements may be measured simultaneously and the concentrations of individual isotopes may be measured, facilitating metabolism/ nutrient studies with stable isotope materials. Precise determination of isotope ratios (e.g. C, N and O) by IRMS is also important in agricultural and food authenticity studies. Accelerator mass spectrometry is used in tracer studies, for the determination of extremely low levels of carbon-14 (and other) isotopes.
The table below summarizes the ranges of analytical sensitivities required for different classes of food analysis. Much work has been done on the characterization of food flavours and aromas by GC-MS. A significant recent advance has been the use of APCI and drift tube MS techniques for sensitive, on-line (‘real time’) monitoring of trace volatiles, e.g. in human breath during flavour release studies. Characterization of unfractionated foodstuffs and related materials for screening or taxonomic purposes may be performed by pyrolysis MS and direct headspace MS. These techniques generate rather simple mass spectra that may be classified using pattern recognition/chemometric software. MS is also used for the analysis of the more abundant (non-trace) components of food, e.g. oils and fats (triglycerides), proteins and carbohydrates. Analysis of these materials is often challenging, as they may comprise complex mixtures of isomeric compounds. Modern MS techniques (MALDI TOF and electrospray ionization) have become extremely important in protein and peptide studies.
Table 1 Typical analytical sensitivities required for various classes of food contaminant/component
Class
Typical concentraion sought (by weight)
Flavours
% - ppb
Food taints
% - ppq
Pesticide residues
ppm - ppb
Trace elements
ppm - ppb
Mycotoxins
ppb
Dioxins
ppt - ppq
FOOD SCIENCE, APPLICATIONS OF NMR SPECTROSCOPY 593
See also: Biochemical Applications of Mass Spectrometry; Food and Dairy Products, Applications of Atomic Spectroscopy; Food Science, Applications of NMR Spectroscopy; Inorganic Chemistry, Applications of Mass Spectrometry; Peptides and Proteins Studied Using Mass Spectrometry; Time of Flight Mass Spectrometers.
Further reading Belton PS, Mellon FA and Wilson RH (1993) Spectroscopy in Food Science, Spectroscopy in Europe 5: 8–14.
Crews H (1993) A decade of ICP MS analysis. International Laboratory 23: 38–42. Gilbert J (ed.) (1987) Applications of Mass Spectrometry in Food Science. Amsterdam: Elsevier Applied Science. Horman I (1979) Mass spectrometry in food science. Mass Spectrometry 5: 211–233. Self R, Mellon FA, McGaw BA, Calder AG, Lobley GE and Milne E (1996) The application of mass spectrometry to food and nutrition research. NATO ASI Series, Series C 475 (Mass Spectrometry in Biomolecular Sciences) 483–515.
Food Science, Applications of NMR Spectroscopy Brian Hills, Institute of Food Research, Norwich, UK Copyright © 1999 Academic Press
The applications of NMR in food science have been the subject of several international conferences, reviews and books which are cited in the Further reading section. This intense interest in the NMR spectroscopy of food is driven not only by the commercial importance of food, but also by the intellectual challenge of unravelling the physicochemical properties of this exceedingly diverse and complex group of materials. In order to focus on food aspects, it will be assumed that the reader is familiar with the principles of NMR and magnetic resonance imaging (MRI), which are lucidly explained in other articles of this encyclopedia.
Spatially resolved NMR applications MRI is beginning to have a major impact on our understanding and control of the growth of food crops, on our assessment of fruit and vegetable quality and in developing the best methods of fruit and vegetable preservation. Moreover, by providing noninvasive, real-time images of moisture and lipid distributions, as well as spatial maps of temperature and food quality factors, MRI has the potential for making a major impact on food processing science. We therefore begin with a brief review of whole-plant functional imaging, then progress on to MRI applications in food processing and storage.
MAGNETIC RESONANCE Applications Functional imaging of whole plants
The growth of agricultural crops is affected by many factors, including drought (osmotic stress), luminescence, disease and soil pollutants, such as heavy metals. By permitting noninvasive monitoring of a whole plant under realistic environmental conditions, MRI has become a powerful tool in the plant physiologists’ armoury. The development of small seedlings can be observed directly inside adapted NMR tubes. Larger plants can be grown in controlledenvironment boxes, which bathe the root system in nutrients, and control humidity, temperature and luminescence. The root system, stem or leaf areas can then be imaged noninvasively. Root imaging is now an established technique, though it is not applicable to all soil types because paramagnetic impurities in the soil can severely shorten the water relaxation time. Nevertheless, three-dimensional (3D) T1weighted imaging has been used to distinguish roots and soil in developing pine seedlings, to follow water depletion zones around the tap root, lateral roots and fine roots, and to follow the effects of symbiotic relationships, such as infection with mycorrhizal fungus, on water uptake. The increase in root network volume and surface area can also be measured from the 3D images. A combination of flow imaging and chemical shift imaging has been used to monitor the effect of