Determination of the Variability of Bioactive Compounds and Minerals in Olive Leaf along an Agronomic Cycle

Abstract

Olive leaves are still considered waste in the oil industry; however, the leaves have a content of oleuropein and other bioactive compounds that gives them great potential to be transformed into by-products. The most appropriate moment along an agronomic cycle (November 2019 to October 2020) has been evaluated to take advantage of this potential of the olive leaves varieties of Picual, Cornicabra and Manzanilla. In addition, factors that affect the content of phenolic compounds such as absolute maximum and minimum temperatures, relative humidity, sunshine hours, rainfall, differential of temperatures and mineral nutrition have been studied. The results show that the pruning season was the best time to take advantage of the olive leaf due to its high oleuropein content, especially in Picual and Manzanilla. The variety was the factor that most affected all the phenolic compounds studied, while the absolute minimum temperature factor notably affected verbascoside. Particular mineral nutrients, such as Mg and Fe, turned out to be most useful for differentiating locations. The content of verbascoside and hydroxytyrosol was also affected by agronomic conditions (location/conventional or ecological).

Quantitative Determination of the Main Phenolic Compounds, Antioxidant Activity, and Toxicity of Aqueous Extracts of Olive Leaves of Greek and Spanish Genotypes

“…Apigenin-7-O-glucoside was only found in the 'Picual' and 'Arbequina' at concentrations of 2.21 and 2.05 mg/g, respectively. Previous studies carried out by Martínez-Navarro et al [11,16] on the same plots during the 2019/2020 season showed that, for the same month, 'Arbequina' leaves contained oleuropein values similar to those found in the present study (63.80 mg/g), while 'Picual' had a slightly lower value (103.41 mg/g). In a study carried out by Petridis et al [17], comparing the phenolic compounds of olive leaves of different genotypes, including 'Koroneiki' and 'Kalamon', they also observed that 'Kalamon' had the highest phenolic content.…”

“…As expected, oleuropein was negatively correlated with the hydroxytyrosol (p < 0.01, r = −0.851) and hydroxytyrosol hexoside contents (p < 0.01, r = −0.683) and positively correlated with verbascoside (p < 0.01, r = 0.685). All of these correlations were observed by the authors of previous works [11,16]. The hydroxytyrosol content was negatively correlated with hydroxytyrosol hexoside (p < 0.01, r = −0.605) and was positively correlated with the verbascoside content (p < 0.01, r = −0.741), with the former suggesting that the hydroxytyrosol in the plant could be derived from glucosides or vice versa.…”

“…Olive leaves (O. europaea) were collected around harvest time [11] from typical Spanish and Greek olive genotypes. In Spain, 'Picual' and 'Arbequina' genotypes were selected in the Castilla-La Mancha region (southwest Spain, 881 m altitude, 38 • 58 40 N latitude and 1 • 51 21 W longitude).…”

Updated Mineral Composition and Potential Therapeutic Properties of Different Varieties of Olive Leaves from Olea europaea

“…In general, Na, Mg, P, K, Ca, Mn, Fe, Cu, Zn, and Pb contents are possible to find and are usually measured the most in olive leaves [ 4 , 5 ]. However, several additional mineral elements, even under residual levels, can be found and constitute a particular interest for evaluating eventual specific conditions in complementary therapy, namely Li, Si, B, Al, Cr, Co, Ni, As, Se, Rb, Sr, Mo, Cd, Sn, Sb, and Ba [ 6 , 7 ]. As is naturally expected, the mineral composition of leaves varies according to the soil and climate where the tree was planted.…”

Assessment of Soil Fertility and Leaf Nutrients in Olive Orchards

“…In olive leaves cv. Picual, Cornicabra and Manzanilla sampled in harvest (November) and usual pruning (March) in the southwest region of Spain, the concentration of nutrients were P: 0.09−0.15%, K: 0.66−0.98%, Mg: 0.07−0.18%, Ca: 1.73−2.70%, Fe: 76−117 ppm, Mn: 36−64 ppm, Zn: 14−19 ppm and Cu: 24−111 ppm (Martínez-Navarro et al, 2021). The content of Mg, Zn, P and K was similar to higher, but lower for Fe, Mn and Cu in tested samples of 'Žutica' and 'Leccino' in Montenegro. In the study of 21 olive cultivars (17 Turkish), the concentration of nutrients in leaves taken at the beginning of December were N: 1.89−2.03%, P: 0.12−0.2%, K: 0.84−1.02%, Ca: 1.72−2.12%, Mg: 0.15−0.27%, Fe: 53.6−78.8 ppm, Mn: 23.1−32.92 ppm, Zn: 15.1−26.8 ppm and Cu: 11−25 ppm (Toplu et al, 2009).…”