Detection of plant oil addition to cheese by synch

Authors: Anna Dankowska Maria Małecka Wojciech Kowalewski

Publish Date: 2015/03/15

Volume: 95, Issue: 4, Pages: 413-424

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Abstract

The fraudulent addition of plant oils during the manufacturing of hard cheeses is a real issue for the dairy industry Considering the importance of monitoring adulterations of genuine cheeses the potential of fluorescence spectroscopy for the detection of cheese adulteration with plant oils was investigated Synchronous fluorescence spectra were collected within the range of 240 to 700 nm with different wavelength intervals The lowest detection limits of adulteration 30 and 44 respectively were observed for the application of wavelength intervals of 60 and 80 nm Multiple linear regression models were used to calculate the level of adulteration with the lowest root mean square error of prediction and root mean square error of cross validation equalling 15 and 18 respectively for the measurement acquired at the wavelength interval of 60 nm Lower classification errors were obtained for the successive projections algorithmlinear discriminant analysis SPA–LDA rather than for the principal component analysis PCA–LDA method The lowest classification error rates equalled 38 ∆λ = 10 and 30 nm and 00 ∆λ = 60 nm for the PCA–LDA and SPA–LDA classification methods respectively The applied technique is useful for detecting the addition of plant fat to hard cheeseMilk cheese and other dairy products are consumed worldwide and have great commercial importance within the food industry Cheese is made from milk therefore the only fat it contains is milk fat Cheeselike products are obtained by partial or total substitution of milk fat by significantly cheaper plant oils Milk fat is one of the most expensive commodity fats on the market therefore adulteration of cheese is practiced for economic purposes and detection of foreign fat in milk fat is a real issue The most common adulterants of cheese are palm coconut corn and cotton oils Alejewicz et al 2011Various instrumental methods have been proposed to establish the authenticity of cheese and to detect the level of its adulteration Among the methods focused on detecting foreign fat in milk products are the PCRbased techniques Plath et al 1997 capillary and gel electrophoresis Cartoni et al 1999 Veloso et al 2004 Guerreiro et al 2013 HPLC Veloso et al 2004 immunochemical methods Hurley et al 2006 Pizzano et al 2011 Rodríguez et al 2010 GC Kim et al 2014 frontface fluorescence spectroscopy Hammami et al 2013 Karoui et al 2007 and fluorescence spectroscopy Ntakatsane et al 2013Synchronous fluorescence spectroscopy is an alternative technique that is quick and avoids all sample preparation steps except for dilution and therefore is simpler less costly and quicker than other most widely used techniques In the synchronous fluorescence technique both excitation and emission monochromators are scanned simultaneously with a constant wavelength interval maintained between excitation and emission wavelengths As opposed to other conventional fluorescence techniques synchronous fluorescence spectroscopy makes it possible to simplify spectra to reduce spectral overlaps and to achieve greater selectivity Patra and Mishra 2002The application of chemometric methods eg multiple linear regression MLR or linear discriminant analysis LDA to spectrophotometric data requires selecting spectral variables for building wellfitted models It is a challenge to select the proper analytical wavelengths from a spectrum The successive projections algorithm SPA is an approach suitable for selecting effective wavelength variables from the spectra SPA performs simple operations in a vector space to determine a subset of variables with minimal collinearity SPA is described in detail by Araújo et al 2001 and Soares et al 2013 First in an orthogonal subspace the vector of higher projection is selected and becomes the new starting vector The choice of the orthogonal subspace at each iteration is made in order to minimise the collinearity of variables SPA has been compared to the genetic algorithm which is a popular method for variable selection in multivariate calibration and the results proved to be in favour of SPA Araújo et al 2011 It was found to be less sensitive to instrumental noise than the genetic algorithm Moreover the SPAMLR models proved to be comparable to or even better than the fullspectrum partial last squares PLS or principal component regression PCR models for UV–Vis Araújo et al 2011 as well as the lowresolution plasma spectra analysis Galvão et al 2001 SPA has been used for variable selection in studies aimed at the classification of coffees UV–Vis Polari Souto et al 2010 and edible seed oils UV–Vis and synchronous fluorescence spectroscopy Dankowska et al 2013a as well as olive oil synchronous fluorescence spectroscopy Dankowska et al 2013bThe aim of the study is to evaluate the potential of synchronous fluorescence spectroscopy followed by chemometric analysis successive projection algorithm SPA combined with multiple linear regression MLR and linear discriminant analysis LDA for the detection of cheese adulteration with plant oils This evaluation was performed on the basis of established errors of prediction of adulteration percentage of misclassified samples and calculation of limits of detection of plant oil addition into cheese fat To the best of the author’s knowledge it was the first attempt at using synchronous fluorescence for the detection of cheese adulteration and at choosing wavelengths from the synchronous fluorescence spectra of cheese fats using the successive projections algorithm SPAFat extraction from cheese and cheeselike samples was performed according to the Folch et al 1957 method using a mix of chloroform and methanol 21 v/v Then 50 g of cheese samples was mixed with 200 mL of the chloroform–methanol mixture and homogenised for 10 min The homogenised mixture was then filtered through filter paper and the first 150 mL of filtered extraction mixture was collected in the cylinder Next 30 mL of 074 KCl aqueous solution was added The alcohol–water phase was removed and the chloroform phase containing lipids was evaporated under a vacuum in a rotary evaporator

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