HS-SPME-GC-MS and Chemometrics for the Quality Control and Clustering of Monovarietal Extra Virgin Olive Oil: A 3-Year Study on Terpenes and Pentene Dimers of Italian Cultivars.

Terpenes and pentene dimers are less studied volatile organic compounds (VOCs) but are associated with specific features of extra virgin olive oils (EVOOs). This study aimed to analyze mono- and sesquiterpenes and pentene dimers of Italian monovarietal EVOOs over 3 years (14 cultivars, 225 samples). A head space-solid-phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC-MS) method recently validated was used for terpene and pentene dimer quantitation. The quantitative data collected were used for both the characterization and clustering of the cultivars. Sesquiterpenes were the molecules that most characterized the different cultivars, ranging from 3.908 to 38.215 mg/kg; different groups of cultivars were characterized by different groups of sesquiterpenes. Pentene dimers (1.336 and 3.860 mg/kg) and monoterpenes (0.430 and 1.794 mg/kg) showed much lower contents and variability among cultivars. The application of Kruskal-Wallis test-PCA-LDA-HCA to the experimental data allowed defining 4 clusters of cultivars and building a predictive model to classify the samples (94.3% correct classification). The model was further tested on 33 EVOOs, correctly classifying 91% of them.

Two-dimensional qNMR of anthraquinones in Frangula alnus (Rhamnus frangula) using surrogate standards and delay time adaption.

In the absence of adequate reference material, a problem often encountered in natural product chemistry, we investigated the use of surrogate standards in two-dimensional qNMR for the quantification of anthraquinones in the bark of alder buckthorn (Frangula alnus). Using the integrals of cross signals in the HSQC spectrum obtained from commercial standards rutin and duroquinone and adapting the delays for the 1JCH coupling, we quantified the total amount of anthraquinones and anthraquinone glucosides, as well as the content of the value-determining glucofrangulins and frangulins. Thereby, duroquinone was used as an external standard to establish the calibration curve for the methylated anthraquinone scaffold, whereas calibration curves for the glycosides were obtained using the anomeric proton signals of the rutinose disaccharide. The method was validated for accuracy, precision, specificity, linearity and limit of quantitation and shows clear advantages over the method of the European Pharmacopeia, especially in terms of specificity and meaningfulness of the results. Apart from being a useful alternative in the quality control of alder buckthorn, the presented approach demonstrates, moreover, the versatility of sophisticated 2D measurements in quantitative NMR.

Quality control of Aloe vera (Aloe barbadensis) and Aloe ferox using band-selective quantitative heteronuclear single quantum correlation spectroscopy (bs-qHSQC).

In the present study, band-selective quantitative heteronuclear single quantum correlation spectroscopy (bs-qHSQC) was applied for the quality control of the two Aloe species present in the European Pharmacopeia. After development and validation of a complete spectral range (csr-) qHSQC assay, a specific pulse program with selective excitation was applied and the measuring time was reduced from 135 to 32 min, while maintaining the same resolution. This bs-qHSQC method (method I) showed slightly higher RSD values compared to the csr-qHSQC method (maximum RSD of 2.80%), but better recovery rates in comparison to the assay of the Pharmacopeia (97.3% for Aloe vera and 96.6% for Aloe ferox). Apart from quantifying the total anthranoid content, the method moreover allows the quantitation of aloin among other aloin derivatives, such as 7-hydroxyaloin, as well as the differentiation of the two investigated species. Additionally, a second bs-qHSQC method (method II) for the fast (4 min) determination of the aloin A/B ratio was developed and compared to 13C qNMR measurements. Showing the same results in much less analysis time, the latter approach contributes to a general problem in natural product chemistry, the co-occurrence of structurally similar compounds and their analysis in complex matrices, e.g. plant extracts.