The valorization of the local fig tree : a morphometric and physicochemical study

Abstract

The fig (Ficus carica) is one of the most important fruit species of the Mediterranean countries, and their fruits are sweet and have high quality of phytochemicals which can sustain human health. The morphological and physiochemical parameters of 21 Maltese local figs accessions and another 22 International figs accessions growing at the Gozo Experimental Farm (Xewkija) were investigated. The aim of this current research was to compare the locally-growing fig trees with those that have been already established scientifically. For the morphometric characteristics, the fruit length and weight ranges were higher in Maltese accessions, and fruit length to width ratio range was higher for the International accessions. With respect to leaf parameters, the petiole length, leaf width, leaf length, and mid-lobes of both Maltese and International accessions were similar except for sample J3 (petiole, width, and leaf lengths) which was significantly different from those of most of the other accessions (p<0.05) respectively. The proximate composition of fruits and leaves were determined by using of Near-Infrared Spectrophotometer. There was the absence of some of these parameters in particular fat and fibre in BKR, ZBG and F4 samples, and starch in the fruit of the BKR sample. In the case of the leaf proximate analysis for the Maltese accessions, ZTN showed the highest Ash and fibre contents whereas MSD exhibited the highest fat and starch contents. Dry matter and proteins were highest for GXQ. For the international accessions, H1 showed the highest values for both dry matter and proteins, whereas Q5 exhibited the lowest values except for fat and fibre. UV-Visible spectrophotometry was used for fruit and leaf samples. The fruits had a high % yellow as compared to % blue and % red, although some Maltese accessions exhibited a high degree of red colour. Additionally, the Maltese accessions showed high value ranges for colour intensity, flavonoid ratio (A520/A280), and a broader range of anthocyanin contents. The fruits of International accessions showed high value ranges for tint, lycopene, and carotenoid content. On the other hand, leaf extracts for both groups exhibited similar colour intensity, % red, % yellow, and % blue, flavonoid ratio (A520/A280), and total carotenoid content. The mean tint in leaves was higher in Maltese accessions, whereas the anthocyanin and lycopene contents were higher in International accessions. For total polyphenol content, the Folin-Ciocalteu test was used, showing similar patterns for the Maltese and International accessions. Also, between the leaf and fruit samples for each accession it was observed that there was no significant difference in the polyphenolic content. Four minerals, Ca, K, Mg, and Na were analysed using the Microwave Plasma-Atomic Emission Spectrophotometer. For all four minerals the contents of leaves were higher than those of fruits for the same accession. Brix, Titratable Acidity and pH were analysed for fruit samples. The values of these three parameters for the International accessions were higher than those of the Maltese accessions. The data was further statistically analysed using Principal Component Analysis (PCA). No discrimination between the characteristics of fig leaves provided potential varietal differences. Agglomerative Hierarchical Clustering was used on the leaf parameters at a similarity level of 0.9458. It was revealed that some of the Maltese accessions are relatively distinctive from the rest. These include the BHR, MLH, MSK, PMB, SAF and SGW-A2. A more extensive AHC analysis with catalogued accessions, it was revealed that the Maltese accessions and the International accessions at the Gozo Experimental Farm coincided within the groups which contained the highest number of accessions from the Varietà antiche italiane catalogue. Two Maltese accessions were clustered in an independent group (C19), which included the MSK and SGW-A2 accessions. PCAs were performed for fruit nutritional value, fruit physicochemical and morphometric parameters. Dry matter correlated positively with ash, fat and fibre contents (r=0.593, 0.509, 0.510 and 0.585, respectively). The fibre contents (ADF and NDF) showed a highly positive correlation (r=0.925). As for the fruit physicochemical and morphometric PCA, the positive and negative correlations showed between parameters, the tint ratio correlated positively with the % yellow (r=0.934) but negatively with colour intensity, % red and anthocyanin content (r<-0.594), and the %red correlated positively with the colour intensity and anthocyanin content (r=0.570 and 0.809). On the other hand, fruit width correlated positively with the weight of the fruit (r=0.698) but negatively with the L:W ratio (r=-0.433). It was concluded from this study that both the morphometric and physicochemical analyses contributed towards the characterisation of fig tree accessions in terms of their fruit and leaves.