Conductimetry: a rapid alternative technique for chlorides determination in cheese

Univ. Sci. 24 (2): 307-322, 2019. doi: 10.11144/Javeriana.SC24-2.cara Bogotá original article Conductimetry: a rapid alternative technique for chlorides determination in cheese Jessica Aguirre-Londoño1; Víctor Alexander Aristizabal-Ferreira1; Sandra Patricia Castro-Narváez1, *; Juan Sebastián Ramírez-Navas1, 2, * Edited by Juan Carlos Salcedo-Reyes () 1. Universidad Santiago de Cali, Facultad de Ciencias Básicas, Programa de Química, GIEMA, Calle 5 # 62-00, Cali, Colombia, A.A. 4102. 2. Universidad del Valle, Facultad de Ingeniería, Escuela de Ingeniería de Alimentos, GIPAB, Calle 13 # 100-00, Cali, Colombia, A.A. 25360. * Received: 01-02-2018 Accepted: 13-02-2019 Published on line: 10-04-2019 Citation: Aguirre-Londoño J, Aristizabal-Ferreira VA, Castro-Narváez SP, Ramírez-Navas JS. Conductimetry: a rapid alternative technique for chlorides determination in cheese, Universitas Scientiarum, 24(2): 307-322, 2019. doi: 10.11144/Javeriana.SC24-2.cara Abstract The correlation of two instrumental techniques for chlorides determination in Colombian cheese, Queso Molido Nariñense (a type of white cheese), was analyzed. Potentiometry of chloride precipitation is the standard technique to determined salt in cheese. Conductimetry is an alternative technique. Samples of Queso Molido Nariñense were made. In the processed cheeses the salt concentration (NaCl: 0.5 %, 0.8 %, 1.0 %, 2.0 %, 3.0 % and 6.0 %) was varied. Chlorides were determined by titration with silver nitrate in the potentiometric technique. In the conductimetric technique, each sample was analyzed by direct measuring its conductivity at room temperature. It was found that there is an adequate correlation between potentiometry and conductimetry. A maximum concentration of 2 % NaCl in cheese is equivalent to 2.9 S/cm for conductivity readings. Additionally, it was verified that the conductimetry constitutes an analytically reliable technique for the determination of chlorides in cheese, it is friendlier to the environment, cheaper and faster. Keywords: Colombian cheese; potentiometry; conductimetry. white cheese; sodium chloride; Funding: N.A. Electronic supplementary material: N.A. Introduction Queso Molido Nariñense is a kind of fresh cheese, not acid, made with cow’s milk. It is one of the typical Colombian cheeses made in the southern part of the country. Ramírez-Navas (2010) described the process to make this cheese, with a high content of salt. The salting process has great influence on cheese quality due to its effects on its composition, microflora and enzymatic activity (Guinee, 2004). Salt increases the osmotic pressure in the aqueous phase of food, causing the dehydration of the bacteria, hence their death or preventing their growth and proliferation (Cruz et al., 2011). Universitas Scientiarum, Journal of the Faculty of Sciences, Pontificia Universidad Javeriana, is licensed under the Creative Commons Attribution 4.0 International Public License 308 Chlorides determination in cheese Some physicochemical studies in a large variety of cheeses show that salt has an important impact on rheological and textural aspects and shelf life. However, one of the main limitations currently in the determination of salt in cheeses is the environmental impact that the chemical tests cause due to the use of silver nitrate (AOAC-983.14, 1997; IDF-88A, 1988). Therefore, it is necessary to search for new analytical techniques. To evaluate the saltiness of cheese in the manufacturing process, the traditional way is the determination of chlorides by potentiometry (Ramírez Navas et al., 2017). In the literature, there are several methods to determine the salt content in foods; for example, Mercurimetry is a volumetric method using a standard solution of mercuric nitrate in nitric acid medium and diphenylcarbazone as an indicator, for the direct evaluation of chlorides in cheeses (Farias & Boscan, 1980). The Mohr method (Argentometry, AgNO3 as a titrant) based on the fact that soluble chlorides precipitate in acidic solutions in the presence of silver nitrate to form a pale silver chloride solid. The chromate ion is used as an indicator, and the detection of the endpoint is carried out by the formation of the second precipitate of red-orange silver chromate (Sierra Alonso, Morante Zarcero & Pérez Quintanilla, 2007). The Charpentier-Volhard method, based on determining the content of chlorides by recoil, in which a solution of nitric acid and an excess amount of silver nitrate is added to the sample. Titration determines excess silver ions with a standard solution of an alkali thiocyanate. The indicator is a ferric alum, and the equivalence point is detected by the appearance of a red color due to the formation of the thiocyanate iron complex (III) (Burgot, 2012). The selective ion electrode potentiometry (ISE) employs a solid-state electrode that develops a voltage due to an ion exchange that is generated between the sample and the inorganic membrane. An equilibrium mechanism occurs due to the limited solubility of the membrane material in the sample. Chloride precipitation potentiometry uses a silver electrode as an indicator and a reference electrode. The potential difference experienced by the indicator electrode in the presence of silver ions generates a potential difference that is easily detectable with a multimeter. The Silver ions reaction with chloride anions can estimate the concentration of this anion in the study system (AOAC-983.14, 1997; Harris, 2007; IDF-88A, 1988). Finally, the conductimetric method, where the percentage of chlorides is measured with an automatic titrator, uses an acid chloride buffer containing polyvinyl alcohol, glacial acetic acid, nitric acid and sodium chloride to calibrate and maintain an electrolytic bridge between the two indicator electrodes. A standard chloride solution, consisting of sodium chloride, antimycotic preservative and deionized water, is used to standardize the equipment (González & Medina, 2005). However, information available about new methods of salt determinations in cheese is limited in the literature. Universitas Scientiarum Vol. 24 (2): 307-322 http://ciencias.javeriana.edu.co/investigacion/universitas-scientiarum 309 Aguirre-Londoño et al. 2019 Potentiometric methods of analysis are simple and economical (Skoog, Holler & Nieman, 2001). However, the conductimetric method is characterized by being a clean technique. The aim of this study was to evaluate the correlation between two instrumental techniques for the determination of chlorides in cheese, potentiometry as standard technique and conductimetry as an alternative technique. Material and methods Manufacture of cheeses The complete random design was used in this investigation. In the Queso Molido Nariñense manufactured with salt concentration (NaCl: 0.5 %, 0.8 %, 1.0 %, 2.0 %, 3.0 % and 6.0 %) was varied. Each day three cheeses were made, each one with different concentration of NaCl. For each N (...truncated)