Quality of limes juices based on the aroma and antioxidant properties
Kaffir (Citrus hystrix) and Key (Citrus aurantifolia) limes juices were investigated and compared. Two dimensional gas chromatography coupled with time-of-flight mass spectrometry (GC×GC-TOF-MS) was applied to assess the botanical origin of Kaffir and Key limes juices, based on volatile substances. The biggest differences in the contents of selected terpenes in Kaffir and Key limes occur in chemical compounds such as Limonene, Citral, Terpinen-4-ol. Limonene concentration is almost 8 times higher in the Key lime volatile fraction than in Kaffir lime. The difference in concentration of Citral in Kaffir lime is almost 20 mg/kg lower than in Key lime. Higher concentration of Terpinen-4-ol was noted in Kaffir lime samples and the content was almost 20 times higher. The concentrations of α-Pinene, Citronellal, Camphene, Nerol, trans-Geraniol and β-Pinene are at similar levels in the volatile fraction of both fruits. Bioactive substances (polyphenols, flavonoids, tannins and flavanols) and the values of antioxidant capacities by four radical scavenging assays (DPPH, CUPRAC FRAP, ABTS) were determined and compared in water and methanol extracts in Kaffir and Key limes juices. The bioactivity of Kaffir lime differ significantly in water extracts in comparison with Key lime juices. The 1H NMR shifts in methanol and chloroform extracts showed some differences in aromatic region between the two varieties of lime juices. Terpinen-4-ol for Kaffir lime and Citral for Key lime were used as potential markers. The GC×GC-TOF-MS allows better separation of substances originating from complex matrices than one-dimensional chromatography, based on improved resolution, increased peak capacity and unique selectivity. The possible falsification of mentioned juices can be detected by the use of GC×GC-TOF-MS, antioxidant assays and NMR shifts.
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