Morphological and physicochemical analysis of local varieties of prickly pears (Opuntia ficus-indica (L.) Mill.) from Malta

Abstract

The prickly pear (Opuntia ficus-indica) is a drought resistant fruit-producing cactus that originated from Mexico but nowadays is widely found throughout the world. While locally, prickly pears have been neglected despite their huge potential in surviving ahrsh conditions, in other parts of the world, large industries were developed in manufacturing products from prickly pears. This study aimed to characterise morphologically and physiochemically local prickly pear varieties in order to safeguard these varieties and prevent the loss of more varieties. For this study, a total of eight varieties spread over fifteen accession found within the largest prickly pear collection found in Malta were studied, where each variety being represented by three/four trees. The morphological assessment investigated the fruit and its peel and one-year-old cladodes which included dimentions, weight and thickness among others. UV-Vis absorbance was determined through spectroscopy. The %yellow, %red and %blue in the fruit pulp were found between 88.4 – 96.8, 1.95 – 5.61 and 1.22 – 3.75 respectively. Colour density, tint, flavonoid and anthycyanin contents were also determined. Total polyphenol content was measured between 0.332 – 1.09 %w/w GAE DM in the pulp of fruit and 0.681 – 1.69 %w/w GAE DM in the peel of fruit using Folin-Ciocalteu assay. Total acidity of fruit pulp was determined by titration was found between 73.5 – 167 mg/100g (expressed as citric acid). Dry matter content in prickly pear fruit pulp, peel and cladode were found between 2.61 – 5.9%, 8.32 – 15.22% and 5.79 – 14.11% respectively. Nutritional composition (Ca, Cr, Cu, K, Mg, Na, Zn) of prickly pear fruit pulp, peel and one-year-old cladodes were determined through digestion followed by Microwave-Plasma Atomic Emission Spectroscopy. Proximate analysis of the one-year-old cladodes which was carried out via N-IR Spectrophotometer constituted mainly of starch (0.28 – 3.34% FW), while fat was very low (<0.01% FW). Based on quantitative parameters, three Principal Component Analysis (PCAs) were performed for morphology, physicochemical and nutritional parameters. The weight and dimentions of fruit correlated strongly the most within the variability in the morphological PCA. As for the physicochemical PCA, the three colours correlated strongly the most to describe the variability, with some of the rvalues measured at 1.000 and -1.000. As for the nutritional PCA,all the minerals described the variability especially Ca and Mg. In addition, the strongest positive correlations occured with minerals within the same plant part followed by correlations between the peel of fruit and cladodes. A dichotomous key was created successfully based on quantitative and visual parameters assessed. This key is solely based on the varieties assessed in this study. Conclusively, despite that fact that this study took a horizontal way of assessing the local prickly pears, several important factors were determined which can unlock the potential of these varieties. Such data has revealed the potential of these prickly pears for geneti breeding, conservation programs and the establishment of its cultivation for various uses as the market demands.