Citrus to detect adulteration

Physical methods directly related to chemical composition have been used in efforts to detect adulterations of citrus products. Physical measurements include spectrophotometry (UV, fluorescence, colorimetry), gravimetric determinations (ash, specific gravity), mass spectrometry (isotope ratios), chromatography, and optical rotation. 

The development of the commercial amino acid analyzer based on the ion-exchange method led to the rapid accumulation of compositional data on the amino acids in citrus. Many investigators have published amino acid compositional data. A summary from a recent review (76) is presented in Table II. These data make it relatively easy to detect adulterations with amino acids, although the equipment and analyses are expensive for routine testing. 

Phenolics. The phenolics of citrus represent a varied and widely studied class of compounds. They range from the lipid-soluble methoxylated coumarins and psoralens to the water-soluble glycosides of the flavanones and flavones. They include the intensely bitter naringin and the highly insoluble hesperidin. Different classes within the group have characteristic UV spectra which have been used to detect adulterations in juices and oils. 

Authentication and the detection of adulteration are serious problems within the citrus juice industry. Traditional multicomponent analysis methods are limited by the time required to perform the individual analyses and to construct the database required. Py-MS rapidly provides fingerprints of the original juice, which facilitates the use of multivariate pattern recognition procedures to detect potentially adulterated samples and to confirm authentication, as weU as helping in quality control. More recently, the combination of Py-MS and ANNs has been applied to problems of adulteration within the olive oil industry, shellfish, and milk. ... 

Chapter 18 reports the investigations of Petrus and relates the room temperature fluorescence, and visible and UV spectral characteristics of citrus juices and related products to the detection of adulteration. 

Each situation may be unique and requires a careful balancing of all factors. Continued research will be necessary to more fully understand the many factors affecting the composition of citrus products. One single, simple, inexpensive adulteration test may never be available. The current technology for adulteration detection can be applied, keeping in mind the statistical limitations of the selected parameters. With the current trends towards multiconstituent analyses and an increasing awareness of statistical interpretations, detection of adulteration should become more sensitive and accurate in the future. 

Lifshitz et aK ( ) investigated the purity of Israeli citrus juice by a multivariate method. They selected 5 analytical parameters and concluded that adulteration or dilution of 15% or more was very likely to be detected at a 1% level of significance. However, adulteration with orange pulpwash was not included in their study. 

The oxygen heterocyclic compounds present in the nonvolatile residue of citrus essential oils have also been extensively investigated by means of HPLC-atmospheric pressure ionization-mass spectrometry (HPLC-API-MS) [99]. The mass spectra obtained at different voltages of the sample cone have been used to build a library. Citrus essential oils have been analyzed with this system, using an optimized NP-HPLC method, and the mass spectra were compared with those of the laboratory-constructed library. This approach allowed the rapid identi cation and characterization of oxygen heterocyclic compounds of citrus oils, the detection of some minor components for the rst time in some oils, and also the detection of authenticity and possible adulteration. 

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