Potravinarstvo Slovak Journal of Food Sciences Volume 14 202 2020 Potravinarstvo Slovak Journal of Food Sciences vol. 14, 2020, p. 202-207 https://doi.org/10.5219/1299 Received: 3 February 2020. Accepted: 2 April 2020. Available online: 28 April 2020 at www.potravinarstvo.com © 2020 Potravinarstvo Slovak Journal of Food Sciences, License: CC BY 3.0 ISSN 1337-0960 (online) EXTRACTIVE STRIPPING VOLTAMMETRY AT A GLASSY CARBON PASTE ELECTRODE FOR ANALYSIS OF COW'S MILK AND CREAM Granit Jashari, Michaela Frühbauerová, Milan Sýs, Libor Červenka ABSTRACT In this paper, a procedure based on extractive accumulation of milk fat globules (MFGs) into a pasting liquid (lipophilic binder) of glassy carbon paste electrode (GCPE) with subsequent electrochemical detection by square-wave voltammetry (SWV) in 0.1 mol L -1 Britton-Robinson buffer of pH 4.0 has been tested to find out whether it can be utilized as a simple screening analytical method for cow's milk and cream nutrition control. Since there is assumption that the necessary alkaline hydrolysis of cow's milk and subsequent extraction of lipophilic vitamins into an organic solvent could be avoided, several GCPEs differing in type (atactic polypropylene, paraffin oil, paraffin wax, silicone oil, and vaseline) and content (5, 10, 15, 20, and 25%; w/w) of pasting liquid used were tested as part of complex optimization. The obtained results show that MFGs contain predominantly vitamin A (carotenoids and retinoids), especially all-trans-retinol, which could serve as significant marker of the fat content. However, their individual forms were not possible to distinguish due to the considerable anodic peak broadening (overlapping). Keywords: carbon paste electrode; cow's milk; extraction; milk fortification; nutrition control; voltammetry INTRODUCTION In the mammary glands, milk fat globules (MFGs), ranging in size from 0.1 to 15 µm in diameter (Logan et al., 2014), originate as fat droplets composed largely (>98%) of triacylglycerols (TCGs). These fat droplets are evenly emulsified throughout the volume and contain lipophilic (fat-soluble) vitamins dissolved in them (Heid and Keenan, 2005). Losses of naturally occurring lipophilic vitamins are significant after mechanical separating the milk fat (cream) from the raw milk. Obtained skimmed milk is then homogenized that is a process of breaking down the large fat droplets under high pressure so that they stay together and do not separate as cream. To improve the nutritional values, the homogenized milk is usually fortified by extra vitamins (retinyl palmitate and cholecalciferol) and minerals that are not naturally found in milk in significant amounts (Trinidad et al., 2015). The cow's milk and products made from it are considered as very complex sample matrixes and their analysis is often complicated and time-consuming (Trenerry et al., 2011). Valid reference analytical methods used for lipophilic vitamins determination in foodstuffs in laboratories of the Czech Agriculture and Food Inspection Authority 211/2004 Coll4. utilize a HPLC with UV detection, known as standard: ČSN EN 12823 (vitamin A), ČSN EN 12821 (vitamin D), ČSN EN 12822 (vitamin E) and ČSN EN 14148 (vitamin K). In addition, a gravimetric method (EN 1211) is used to determine milk fat content. Evaluation of the lipophilic vitamins content in milk (also dairy produce) has its substantiation, especially in case of human nutrition which deals on provision of essential nutrients in food necessary to support human life and health (Haug et al., 2007). Moreover, analytical methods for simultaneous determination of lipophilic vitamins and their provitamins in milk using microcolumn (Gomis et al., 2000), narrow-bore column (Blanco et al., 2000) and two-dimensional liquid chromatography (Zhang et al., 2015) have been developed. Time-consuming sample preparation is the most challenging step in the analysis as it involves several steps (alkaline hydrolysis, liquid-liquid extraction, filtration and evaporation of organic solvent) in which the analytes may be lost (Trenerry et al., 2011). To avoid degradation of analytes, the alkaline hydrolysis shoud be carried out in presence of an antioxidant, under an inert atmosphere, and in absence of light. A simple semiquantitative method for the determination of vitamin D in skim milk is worth mentioning (Michlová et al., 2012) when a sample is diluted with water, ethanol, and an aqueous ammonia solution. Vitamin D is subsequently extracted with a mixture of ether and hexane