Abstract
Increasing competition in global market leads more countries to participate the “World Trade Organization” (WTO) program. This has serious impact on the economy of nations, of which the production cost of food and consumer product is increasing with higher labor cost. In an attempt to make dishonest profits, adulteration of diary products has been adopted by some manufacturers. Milk is one of the widely consumed dairy products. Its cost of production in Taiwan is estimated to be 2-3 times higher than that in major dairy products exporting countries like New Zealand, Australia, and Europe. Therefore, adulteration of milk and milk products has been suspected in Taiwan for the past two decades. Adulteration of fresh cow milk by inexpensive cow milk powder and goat milk by cow milk was noticed. Additionally, some fish oil products have been reported to be adulterated or vegetable oil products. It is difficult to characterize the quality of milk or oil by visualization or using simple portable instruments. Therefore, it is necessary to develop standard and reliable methods for the characterization of milk, oil and the detection of adulteration. In response to this demand, a variety of analytical methods were employed and integrated for reliable characterization and adulteration detection of milk and oil products. Electronic nose (EN) and electrospray ionization mass spectrometer (ESI-MS) has been exploited for food characterization and adulteration detection of aforementioned food products. The results were processed using statistical tools like hierarchical cluster analysis (HCA), principal components analysis (PCA), and factor analysis (FA), to simplify their presentation. The EN demonstrates capability of rapid screening of fresh milk from reconstituted milk. Furthermore, direct infusion electrospray ionization mass spectrometer (DI-ESI-MS) is also employed for rapid classification of cow milk adulteration in goat milk. The smell-print and triglyceride (TG) profile thus obtained show the potential to replace traditional sensory panels. To further support the developed method and confirm the adulteration, RP-HPLC/ESI-MS has been employed to detect lactoglobulins, the biomarkers. The results showed that mass spectrometry is superior to current urea sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) method in terms of accuracy and precision, enabling molecular mass identification of proteins. The analysis of whey protein by RP-HPLC/ESI-MS is complementary to currently used Chinese National Standard method (CNS 14117). It is capable of quantitatively determining the adulteration after internal normalization strategy. The method has been applied to differentiate authentic fresh milk and reconstituted milk by inspecting chromatograms and mass spectra. Additionally, calculation of thermally-induced glycation index (TGI) enables numerical representation and differentiation of milk sample quality. The TGI value is characteristic of milk quality, where lower TGI value represents better milk quality denoted as fresh milk. The results reveal that the reconstituted milk samples have median value of TGI (TGI-LGA=2.58) and possess five lactosylation sites on lactoglobulin. Moreover, RP-HPLC/ESI-MS/MS was used to probe the thermally-induced glycation sites on lactoglobulin of cow milk. The applicability of ESI-MS is further extended for characterization and adulteration detection of edible oil and fat products. Different oil and fat samples have different triglyceride composition and mass spectral patterns. Taking this as an advantage and noting that triglycerides are major components of edible oil, the triglycerides are considered as marker molecules in classifying oil samples. The edible oil and fat can be rapidly characterized via combined use of TG profiles, HCA, PCA, and FA. Further, ESI-MS/MS has been used to investigate the fatty acid constituents and detailed structure of TGs. This strategy has been successfully used to distinguish adulterated fish oil which contained vegetable oil.