The morphometric and polyphenolic analysis of indigenous and international grape varieties grown in the Maltese islands

Abstract

Five indigenous Maltese grape vine varieties (Abjad Tond , Beżżul Abjad , Miġnuna, Ġellewża and Girgentina) and five international grape varieties (Carignan, Tempranillo, Catarratto, Greco di Tufo and Grillo) were selected to study their morphometric and physicochemical properties. The results served to compare the native grapes with the international grapes. The ten grape varieties had %brix of 13.3 to 22.5%. Intrestingly, the Miġnuna variety had the highest brix value compared to those of the international varieties (<22.5%). pH ranged between 3.46 and 4.59, where the Girgentina variety had the lowest pH (3.78) and the Beżżul Abjad had the highest pH (4.51). Adding to that, the UV-Vis analysis revealed that Tempranillo had the highest colour intensity (7.5340), whist the lowest was for Abjad Tond (0.3772). Carignan showed the lowest tonality

(0.2217) and the Girgentina with the highest tonality ratio (2.9592). The highest anthocyanin content was in Tempranillo (124.00 mg/kg) while the lowest was in Girgentina (1.0 mg/kg). The polyphenolic content demonstrated that the international varieties exhibited greater polyphenolic concentrations than the the Maltese varieties (p<0.0001). Values ranged between 0.0085 and 0.101

% w/w. Furthermore, metal analysis showed that silver levels were significantly different between the ten varieties (p<0.0001). Chromium concentrations were observed to be 0.1096 - 0.2899 mg/kg for the ten grape types. The copper concentration varied between 0.6665 and 1.686 mg/kg. The iron concentration ranged between 0.8549 and 2.956 mg/kg. The Maltese varieties had iron content ranging between 0.8549 and 1.53 mg/kg. Potassium levels ranged between 211.8 and 749.2 mg/kg. The magnesium levels ranged between 36.92 and 202.9 mg/kg. The Maltese varieties exhibited the lowest magnesium content (36.92-49.98 mg/kg), as compared to the international varieties. Morphometric analysis revealed that grape width for the ten varieties varied between 8.662 and 19.22 mm. The five Maltese varieties exhibited the largest widths between 17.49 and 19.22 mm. Grape length for the ten varieties varied between 9.135 and 20.10 mm, where the Beżżul Abjad grape had largest length compared to the 10 varieties (23.49 mm).

In conclusion, statisical analysis illustrated that the physicochemical characteristics and mineral content differ between the red and white varieties. Adding to that morphometric characteristics observed indicate that there significant differences between the indigenous and international varieties. This was revealed by Agglomerative Hierarchical Clustering analysis for the metal parameters.