Citation: Oštari´ c, F.; Kalit, S.; Curik, I.; Mikulec, N. Influence of Sodium and Potassium Chloride on Rennet Coagulation and Curd Firmness in Bovine Milk. Foods 2023, 12, 2293. https://doi.org/10.3390/ foods12122293 Academic Editor: Agostino Sevi Received: 13 May 2023 Revised: 2 June 2023 Accepted: 5 June 2023 Published: 7 June 2023 Copyright: © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). foods Article Influence of Sodium and Potassium Chloride on Rennet Coagulation and Curd Firmness in Bovine Milk Fabijan Oštari´ c 1 , Samir Kalit 1 , Ino Curik 2 and Nataša Mikulec 1, * 1 Department of Dairy Science, Faculty of Agriculture, University of Zagreb, 10000 Zagreb, Croatia; fostaric@agr.hr (F.O.); skalit@agr.hr (S.K.) 2 Department of Animal Science, Faculty of Agriculture, University of Zagreb, 10000 Zagreb, Croatia; icurik@agr.hr * Correspondence: nmikulec@agr.hr Abstract: One of the salting methods in cheese production implies salting the milk before coagulation used in making Domiati-type cheeses and a variety of autochthonous “Liˇ cki Škripavac” cheese. The most used sodium replacer is potassium. This study investigated the influence of different added salt concentrations (1%, 1.5%, and 2%) and NaCl to KCl ratios (100%, 50:50%, 25:75%) on the rennet coagulation and curd firmness in bovine milk. The milk coagulation parameters were determined with a computerized renneting meter, Lactodinamograph. The results showed significant interactions between the salt concentrations and NaCl to KCl ratios (p < 0.0001, α = 0.05) by prolonging the beginning of coagulation (10–20 min) and curd firming rate (1–5 min) by an increase in salt concentration for all treatments. The 50:50 treatment values (RCT, k 20 ,a 30 ,a 60 ,a max ) were closest to the control (without salt) and had the best results among all treatments in the lower (1%) and medium (1.5%) salt concentration (p > 0.0001, α = 0.05) while in the highest salt concentration (2%) the treatment effect was nonsignificant (p > 0.05). These results should help future studies make a lower sodium product appealing to consumers without losing quality. Keywords: sodium; potassium; chloride; substitution; coagulation properties; bovine milk 1. Introduction Since ancient times, sodium chloride (NaCl) has been used for food flavoring and preservation. It has always been closely related to different aspects of human history [1]. Sodium chloride accounts for 95% of sodium intake [2], with table salt consisting of 40% sodium and 60% chloride by weight [3]. Average intake exceeds current guidelines and recommendations from WHO [4] of 2.300 mg/day and EFSA [5] of 2.000 mg/day in the EU, respectively. For this reason, new dairy products with lower sodium content are investigated. According to van Buren et al. [6], food producers need to ensure that products with lower sodium content remain appealing to consumers, so sodium reduction in food products should not lead to a loss in quality. The leading method for reducing sodium in food products is substitution with potas- sium (i.e., potassium chloride, KCl), the most used salt replacer [6]. Current EU recom- mendations for potassium intake are 3500 mg/day for adult men and women [7]. Studies explain its wide use because it gives a salty taste [3,8], improves shelf life due to its an- timicrobial property [3,9], and even lowers blood pressure in people with hypertension with a 24% lower chance of stroke [10]. Potassium chloride is widely used for sodium replacement in cheese production due to its salty taste and antimicrobial activity. Studies show sodium replacement with up to 50% potassium in cheese is possible without effect on sensory characteristics [3,11,12]. Cheese quality is affected by its chemical composition, microbiological quality, and production process [13]. According to Troch et al. [14], to optimize the transformation of milk into cheese, it is necessary to investigate and understand milk coagulation as an Foods 2023, 12, 2293. https://doi.org/10.3390/foods12122293 https://www.mdpi.com/journal/foods