Cheese analytical techniques

FIGURE 5.2 Analysis scheme for assessment of proteolysis during cheese ripening, modified from Sousa et al. (2001). Analytical techniques are highlighted in bold with shading. 

Cheese is a complex matrix of several components. Isolation of compounds of interest and the analysis of target compounds without interference from the matrix has been a challenge with analytical techniques. With the development of extraction procedures and new sampling techniques for analysis, not only has this challenge been overcome to a certain extent but also the speed, quality, accuracy, and reliability of analysis have improved tremendously. With the mechanisms behind the formation of several flavor compounds in cheese still not clearly understood, these techniques have an increasing role in the efforts to understanding cheese ripening. Often times most of the techniques provide... 

This section will deal with three aspects of cheese flavor (1) analytical techniques, (2) intervarietal comparisons, and (3) effect of composition on cheese quality. The biochemical pathways through which the principal flavor compounds are generated were described in Section VI. 

Different groups (8,11,34) have smdied the CLA composition of cheese by GC-MS, often in combination with several other complementary analytical techniques, hi one study (34), CLA fractions, isolated by RP-HPLC, were examined as the methyl esters by GC-MS on a column of medium polarity (Supelcowax 10) with the mass spectrometer in Cl mode using isobutane as reactant gas. Seven peaks comprising nine components (all possible geometrical isomers of 9,11- and 10,12-18 2 and llc,13c-18 2) were identified. The % tl 0t, 2t peak was the most abundant, but this was a result of using harsh acid conditions for methylation, which increased the levels of trans,trans isomers at the expense of the other CLA isomers. Incidentally, there have been many subsequent studies on developing the most suitable conditions for methylating CLA these have been reviewed in some detail (24,25,76,77). 

Chemical and instrumental (e.g., chromatography and mass spectrometry) methods have provided valuable information that lead to the advancement of cheese science. However, these techniques suffer from one or more of the following problems (1) the extensive use of solvents and gases that are expensive and hazardous, (2) high costs, (3) the requirement of specific accessories for different analytes, (4) the requirement of extensive sample preparation to obtain pure and clean samples, and (5) labor-intensive operation. These disadvantages have prompted for the evaluation and adoption of new, rapid, and simple methods such as Fourier-transform infrared (FTIR) spectroscopy. Many books are available on the basics of FTIR spectroscopy and its applications (Burns and Ciurczak, 2001 Sun, 2009). FTIR spectroscopy monitors the vibrations... 

Karoui De Baerdemaeker (2006) wrote a review about the analytical methods coupled with chemometric tools for the determination of the quality and identity of dairy products. Spectroscopic techniques (NIR, MIR, FFFS front face fluorescence spectroscopy, etc.), coupled with chemometric tools have many potential advantages for the evaluation of the identity dairy products (milk, ice cream, yogurt, butter, cheese, etc). 

Chronopotentiometric analytical methods have also found application in the field of food analysis. In this technique, the oxidation or reduction of species at a constant current is carried out, and the transition time is measured as the quantitative characteristic [29]. In this context, recent chronopotentiometric methods have been reported for histamine determination in foodstuffs. One of these methods was based on the oxidation of the amine at a planar gold disc electrode in the presence of electrogenerated chlorine which facilitates charge transfer between the analyte and the electrode surface. Well-defined signals were observed at +1.15 V in hydrochloric acid medium, giving rise to a linear calibration plot in the 2- 1(X) mg/1 concentration range with an LOD of 0.27 mg/1 histamine. The method was applied to the determination of histamine in fermented sausages [30]. The same authors used a mercury film electrode to develop a chronopotentiometric method for histamine in cheese [29]. 

From the results obtained in this study, it can be inferred that the use of GC-MS in combination with adequate aroma sampling techniques can solve analytical problems of aroma characterization, even in the case of very complex matrices. The combined use of the two extraction procedures proved helpful in providing a complete fingerprint of the aged Parmigiano-Reggiano cheese aroma, which can be used as a useful reference for the characterization of the product. 

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