Vol.:(0123456789) 1 3 Journal of Food Measurement and Characterization https://doi.org/10.1007/s11694-018-9892-3 ORIGINAL PAPER The potential of near and mid-infrared spectroscopy for rapid quantifcation of oleuropein, total phenolics, total favonoids and antioxidant activity in olive tree (Olea europaea) leaves Aygül Can 1  · Hüseyin Ayvaz 1  · Çiğdem Uysal Pala 1  · Nicola Condelli 2  · Fernanda Galgano 2  · Roberta Tolve 2 Received: 28 May 2018 / Accepted: 4 August 2018 © Springer Science+Business Media, LLC, part of Springer Nature 2018 Abstract Natural foods and food-related antioxidants such as phenolic phytochemicals are of great interest due to their preventive properties against oxidative damage. Olive tree leaves contain high quality and amount of phenolic compounds including oleuropein and therefore considered as nutraceutically valuable materials. The composition of olive leaves, its phenolics and antioxidant power are infuenced by numerous factors causing great variation among samples. Additionally, traditional analytical methods performed to quantify these parameters in each product entail long and complicated sample preparation procedures, the use of toxic chemicals, skilled labors, instrumentation and sophisticated laboratory conditions. One appeal- ing alternative is the use of infrared spectroscopy since it gives information about the food composition quickly and it is a multi-parametric and environmentally friendly choice. Therefore, we investigated the oleuropein, total phenolic content, total favonoid content and antioxidant activity levels of 23 common cultivars of olive leaves harvested from Turkey and Italy using traditional reference methods and also developed near and mid-infrared based partial least squares regression (PLSR) models to predict these parameters without the need of sample preparation. Internal validations of the PLSR calibration models were done using full cross-validation and yielded very high correlation coefcients (≥ 0.95) and low errors in predictions (% standard error of cross-validation for parameters were lower than 7.54%). The levels of all the parameters of interest could be successfully predicted using both NIR and MIR instrumentation within seconds. Overall, infrared spectroscopy along with chemometrics exhibited great potential for future olive leave studies. Keywords Chemometrics · Infrared spectroscopy · Oleuropein · Olive leaves · Phenolics · Antioxidant activity Introduction According to historical records, the olive tree was cultivated in Crete as early as 3500 BC [1]. The long-lived olive trees have an important role in the culture and economy of the inhabitants, gives a character to the rural cultivation and also constitutes the backbone of traditional medicine [2, 3]. Throughout the history of civilization, the olive fruit, oil and the leaves have a countless nutritional, medicinal and other uses [1] especially in some European and Mediterranean countries [4] including its use as an herbal tea in the treat- ment of diabetes in Turkey [5]. Medicinal use of olive leaves was ofcially reported as a recipe for preparing the olive leaf tea in the Pharmaceutical Journal in 1854 [6]. Turkey has a very suitable climate and soil conditions that allow growing many fruit species including pome and stone fruits, nuts, and subtropical fruits [7]. Olive products make up a considerable part of the Medi- terranean diet due to their rich phenolic content and high antioxidant activity [8]. Lately, diferent extracts made from plants have become well-liked and characterization of the bioactive compounds was on the rise for pharmaceutical and food processing applications [9]. In the pharmaceutical and food industries, studies have shown that olive leaf extract (OLE) efectively inhibits oxidative degradation due to the activity of some important antioxidants and phenolic com- pounds [10]. OLE has also recently marketed and consumed * Çiğdem Uysal Pala cupala@gmail.com 1 Food Engineering Department, Engineering Faculty, Çanakkale Onsekiz Mart University, Çanakkale, Turkey 2 School of Agricultural, Forestry, Food and Environmental Sciences, University of Basilicata, Potenza, Italy