# Insights into Native Fermentation Process of Apples (_Malus domestica_) in Low Sodium Conditions
## 1 Introduction  
Pickling is one of the oldest methods of food preservation. It could be achieved by direct acidification, introducing the material to be preserved into an acid solution, or by fermentation in brine, leading to the production of lactic acid. Even if it requires a long time, the second method is preferred by consumers due to the benefits provided by lactic bacteria and by the functional compounds developed during the fermentation process.  
Traditionally, sodium chloride (NaCl) solution is used to obtain pickles. In concentrations between 3 and 8% in brine, differing by type of the fermented vegetal material, by product or by country, NaCl has an important role in enzyme and microorganism control during fermentation, as well as in sensorial property development [1]. On the other hand, NaCl is accountable for several health issues like hypertension, cardiovascular diseases or kidney damage [2]. One of the strategies of NaCl reduction in processed foods is the use of alternative chloride salts like potassium (KCI) or magnesium (MgCl\({}_{2}\)), to mention just two of them. However, this replacement has numerous implications in the management ofsafety risks, as well as in the processing technology, solid scientific investigations being needed to validate its feasibility to be used at industrial level [3].  
Several studies regarding the influence of NaCl substitution with KCl and MgCl\({}_{2}\) on vegetal material fermentation are available in the literature. Many of them are focused on local materials like olives [4; 5; 6], cucumbers [1; 7] or sauerkraut [8; 9]. These studies are focused mainly on the microbiological issues, and their conclusions highlight the high potential of the NaCl substitution to be used in industry.  
In Romania, pickles are included in the national culinary heritage [10], the most popular vegetal materials being cucumbers, immature tomatoes or cabbage. In some regions fruits like apples, plums or grapes are added to improve the sensorial characteristics of the pickles.  
Apples are among the most produced, exported and consumed fruits in the world. They are well known as health promoters due to their high content of bioactive compounds, like phenols, which could directly influence the natural antioxidant activity [11]; flavonoids, isoflav, and phenolic acids, which could dramatically decrease the risks of obesity, chronic diseases and other types of cellular oxidation [12]. Other important compounds that induce the antioxidant activity of apples and could influence different biological and chemical processes are chlorophylls [13] and carotenoids [14]. Many phytochemicals from raw apples have been widely studied, and many potential health benefits have been attributed to these specific phytochemicals, but only a few to pickled apples.  
Considering the above-mentioned importance of the fermented plant materials, the necessity of sodium chloride reduction in food, and the health benefits of apples, the aim of this study is to investigate the apples' fermentation process in low sodium conditions achieved by totally replacing NaCl with KCl or MgCl\({}_{2}\). The main physico-chemical and phytochemical parameters were evaluated during the fermentation process and the impact of salts upon them was assessed, to the aim of proving the feasibility of obtaining low sodium fermented apples.