E.K. Kemsley

Quantitative analysis of potential adulterants of extra virgin olive oil using infrared spectroscopy

Abstract The determination of food authenticity and the detection of adulteration are problems of increasing importance in the food industry. This is especially so for ‘value-added’ products, where the potential financial rewards for substitution with a cheaper ingredient are high. In this paper, the potential of infrared spectroscopy as a rapid analytical technique for the quantitative determination of adulterants in extra virgin olive oil is demonstrated. The method uses Fourier transform infrared spectroscopy, combined with attenuated total reflectance and partial least squares regression. Model systems comprising two types of ‘contaminant’ oil — refined olive and walnut — are investigated.

Discrimination between Coffea arabica and Coffea canephora variant robusta beans using infrared spectroscopy

The seed or ‘bean’ of the coffee plant is an important crop, grown commercially across the world. Two species are commonly cultivated: Coffea arabica and Coffea canephora variant robusta. Analytical techniques for species identification, in particular of coffee products such as ground or ‘instant’ coffees, are of great importance. In this paper, mid-infrared spectroscopy is proposed as a rapid alternative to existing authentication methods, which are often time-consuming or difficult to implement successfully. A Fourier-transform infrared spectrometer is used for this work, equipped with a diffuse reflectance accessory. Statistical procedures comprising principal components analysis and classical discriminant analysis are applied to spectra of ground roast arabica and robusta beans, and results presented which demonstrate that the species of such samples can readily be identified.

Mid-infrared spectroscopy and authenticity problems in selected meats : a feasibility study

Abstract This paper describes the results of a feasibility study into the use of mid-infrared spectroscopy for addressing certain authenticity problems with selected fresh meats. Preliminary analyses for meat speciation, the detection of ‘frozen-thawed’ meat, and semi-quantitative analysis of meat mixtures are reported. Fourier transform mid-infrared spectroscopy, attenuated total reflectance sample presentation, principal component analysis and partial least squares regression were used. It was possible to distinguish minced chicken, pork and turkey meats from their infrared spectra, and for each meat species it was possible to differentiate between fresh and frozen-thawed samples. Mid-infrared spectroscopy was also able to semi-quantitatively measure the levels of turkey and pork mixed with chicken meat. The method, which is rapid and easy to use, could with further development have the potential for authentication and quality control of meat products.

Approaches to adulteration detection in instant coffees using infrared spectroscopy and chemometrics

Fourier transform infrared (FTIR) spectroscopy is examined as a rapid alternative to wet chemistry methods for the detection of adulteration of freeze-dried instant coffees. Spectra have been collected of pure coffees, and of samples adulterated with glucose, starch or chicory in the range 20-100 g kg -1 . Two different FTIR sampling methods have been employed : diffuse reflectance, and attenuated total reflectance. Three different statistical treatments of the spectra were carried out. Firstly, the spectra were compressed by principal component analysis and a linear discriminant analysis performed. With this approach, a 98% successful classification rate was achieved. Secondly, a simultaneous partial least square regression was carried out for the content of three added carbohydrates (xylose, glucose and fructose) in order to assess the potential of FTIR spectroscopy for determining the carbohydrate profile of instant coffee. Lastly, the discrimination of pure from adulterated coffee was performed using an artificial neural network (ANN). A perfect rate of assignment was obtained. The generalization ability of the ANN was tested on an independent validation data set ; again, 100% correct classifications were achieved.

Authentication of beef versus horse meat using 60 MHz 1H NMR spectroscopy

Highlights • Demonstration of 60 MHz 1H NMR as a screening tool for distinguishing beef from horse meat.• A simple chloroform extraction combined with a 10 min spectral acquisition time.• A principal components-based authenticity model yielding a ‘beef’ or ‘not-beef’ outcome.

Spectroscopic method for the authentication of vegetable matter

Abstract Infrared spectroscopy, in combination with classical discriminant analysis, was used to investigate the composition of the cell walls extracted from a number of plant species. It was shown that apple cell walls gave rise to a characteristic spectrum that allowed the discrimination of apple from a range of other plant species. The conclusion drawn is that infrared spectroscopy is potentially of value for the identification of plant cell walls, opening up the possibility that the technique may be useful for the authentication of fruit-containing products.

Effects of sample heating in FT-Raman spectra of biological materials

Abstract The effects of laser-induced sample heating and fluorescence of biopolymers in Fourier transform-Raman spectroscopy were investigated. It was shown that these two phenomena are essentially independent of each other. Methods of quantifying the laser-induced heating were developed and it was shown that measurement of the thermal emission generated by the sample is not sufficient to determine its temperature. The use of a marker compound mixed with the test sample to estimate the sample temperature was explored. Monitoring the temperature-dependent phase transitions of NH 4 NO 3 provided a crude indication of a minimum sample temperature. However, using sulphur as a marker and exploiting the relationship between the intensities of its anti-Stokes and Stokes bands, it was possible to estimate the sample temperature with greater confidence. Using these techniques it was shown that sample temperatures could easily reach approximately 400 K under normal laser power inputs. Such temperatures are likely to be damaging to biological samples and it is concluded that great care must be exercised when using FT-Raman.

The identification of vegetable matter using Fourier Transform Infrared Spectroscopy

A comparison of Fourier transform infrared methods for identifying vegetable matter is presented. Results from diffuse reflectance (DRIFTS) and FTIR microscopy on samples of cell wall material from 10 different species of fruits and vegetables are presented and compared with results from a KBr disc method. All three methods are able to discriminate between a test sample (apple) and non-apple samples. However, there are significant spectral variations from method to method which preclude the use of spectral libraries obtained by one method being used to identify spectra obtained by another method.

Process control using fiber optics and Fourier transform infrared spectroscopy

A process control system has been constructed using optical fibers interfaced to a Fourier transform infrared (FT-IR) spectrometer, to achieve remote spectroscopic analysis of food samples during processing. The multichannel interface accommodates six fibers, allowing the sequential observation of up to six samples. Novel fiber-optic sampling cells have been constructed, including transmission and attenuated total reflectance (ATR) designs. Different fiber types have been evaluated; in particular, plastic clad silica (PCS) and zirconium fluoride fibers. Processes investigated have included the dilution of fruit juice concentrate, and the addition of alcohol to fruit syrup. Suitable algorithms have been written which use the results of spectroscopic measurements to control and monitor the course of each process, by actuating devices such as valves and switches.

Potential of infrared emission spectroscopy for on-line analysis☆

Abstract Many food production processes involve heating. When hot, the ingredients emit infrared radiation. In principle, this radiation may be steered directly into a spectrometer for analysis: this is the basis of infrared emission spectroscopy. This preliminary communication presents simulations and measurements of emission spectra, and demonstrates that for optically thin samples, good results can be obtained with comparative ease.