Temporal analysis of ampelographic and physicochemical characteristics of the Maltese grapevine variety Girgentina

Abstract

The phenological stages, morphological characteristics, physicochemical parameters and mineral content of the Girgentina grapevine were determined over a two-year time course. Phenological and morphological characteristics were determined according to standardised OIV descriptors. Titratable acidity and pH were determined using an automatic titrator and the sugar content (Brix°) was determined by a refractometer. The total content of polyphenols in grapes was determined by using the Folin-Ciocalteu assay and a UV-Visspectrophotometer was used to determine the percentage of yellow, red and blue colour contribution, colour index, tint ratio, flavonoid ratio and total anthocyanins of grape samples. The concentration of minerals was determined by Microwave-Plasma Atomic Emission Spectroscopy. The temperatures at which important phenological stages occur, i.e. bud break (14°C), full bloom (20°C), full grape maturity (27°C) and beginning of wood maturity (28°C) were determined. Mean weight of grapes and leaves at harvest was approximately 4.00g and 3.70g respectively. Internodal distance increased along time (55.08 to 77.53mm). The mean acidity at harvest was 0.12g/100g and 0.16g/100g, pH was 3.62 and 3.86 and °Brix was 16.92 and 19.64 during the first and following year respectively. Spectroscopic analysis showed a progressive increase in red, blue, flavonoid ratio, anthocyanin content and colour index but a decrease in yellow and tint. Total polyphenolic content decreased along maturity and stood at 0.076±0.016%w/w and 0.064±0.024%w/w at the first and following year respectively. The concentration of Ca, Mg and Na showed an upward trend in both grapes and leaves. K showed an upward trend along the time course in grapes but a downward trend in leaves. Cu and Fe held a consistent concentration along time. The minerals in the highest concentration in both grapes and leaves were Na, Mg and K, followed by Cu, Fe and Ca in grapes and Ca, Cu and Fe in leaves. Pearson correlation revealed a low flavonoid ratio indicating a low content of anthocyanins. Principal Component Analysis (PCA) grouped grapevines by their sun orientation and segregated samples according to harvest year.