# Insights into Native Fermentation Process of Apples (_Malus domestica_) in Low Sodium Conditions
## 3 Results
### Physical and Chemical Analysis
#### 3.1.5 Reducing Sugar  
The success of pickling vegetable products in brine solutions depends largely on the initial content of fermentable sugars, the main source of carbon and energy for their native microbiota [29]. Apples contain appreciable amounts of monosaccharides such as glucose, fructose, galactose and uronic acids (mainly galacturonic and glucuronic acids), but also non-reducing sugars (primarily sucrose) and oligomers of pectin substances that can be used in the early stages of fermentation [30]. The total content of reducing carbohydrates and uronic acid, as well as the level of sugars and also di- and trimers of uronic acids, was measured in order to follow the dynamics of spontaneous fermentation of apples in magnesium, calcium and sodium chloride brine. Figure 4 shows that at the end of the fermentation period, the apples fermented in MgCl\({}_{2}\) brine solution exhibit the highest decrease in the level of reducing carbohydrates (45.35%), as compared to the samples  
Figure 3: Changes in salinity in apple pickle fermentation with different brine solutions. The values on the same line marked with different letters are different in a statistically significant manner (\(p<0.05\)).  
fermented with NaCl (39.08%) and KCl (39.6%), respectively. The evolution of the level of reducing carbohydrates and that of fermentable sugars is similar.  
During the first 7 days of fermentation, the variation in simple and fermentable carbohydrates, as well as uronic acids, is different between samples. However, at the end of the second week, regardless of the type of brine used, the sugar concentration decreased by 21%, while the uronic acids decreased by 16%. This aspect can be explained by the different adaptation capacity of the microorganisms involved in the fermentation process. The results show that after 3 weeks of fermentation, the level of reducing sugars and uronic acids in the pulp of pickled apples is approximately 35% lower than in unfermented apples, for all brine variants.  
The aspect of the relative variation curves of the carbohydrates analyzed throughout the fermentation period differs depending on the type of salt used. Differences are also noted regarding the classes of carbohydrates (reducing carbohydrates and uronic acids, fermentable sugars and uronic acids); present in the samples. These variations, observed weekly, result from microbial interactions (competition, cooperation, inhibition) and the enzymatic reactions of the microbiota. Carbohydrate levels change due to their consumption in metabolic processes, reactions that occur simultaneously with the hydrolysis of polysaccharides and the formation of exopolysaccharide. Therefore, simple carbohydrates, uronic acids and fermentable sugars may show slight increases or variable rates of decrease from one analysis stage to another, as a result of the balance created between these biochemical  
Figure 4: Variation in carbohydrate content: reducing simple carbohydrates and fermentable sugars (**a**) and reducing and fermentable uronic acids (**b**) in fermented apple (_Malus domestica_) samples in different brine solutions. The values on the same line marked with different letters are different in a statistically significant manner (\(p<0.05\)).  
processes. Additionally, the leaching of soluble compounds into the brine solution is an important factor influencing the levels of sugars and uronic acids in the pulp of pickled apples [31].