# Possibility of Using Fermented Curly Kale Juice to Manufacture Feta-Type Cheese
## 3 Results and Discussion
### Milk Clotting Ability of Fermented Curly Kale Juice
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Type of Sample** & **Duration** & **Gel Time** & **Phase Angle** & **G\({}^{\prime}\)** & **G\({}^{\prime\prime}\)** & **Turbiscan** \\  & **of Study** & & **Value** & **G\({}^{\prime}\)** & **G\({}^{\prime\prime}\)** & **Stability Index** \\ \hline Milk with rennet & 90 min & 1800 s/6 min & 32.51 & 0.12 & 0.08 & 23.6 \\ Milk with rennet and fermented curly & 90 min & 1200 s/4 min & 34.82 & 0.10 & 0.07 & 21.4 \\  & kale juice & 21 h & 39900 s/665 min & 43.28 & 0.16 & 0.15 & 20.6 \\ \hline \multicolumn{7}{c}{G\({}^{\prime}\)—storage modulus; G\({}^{\prime\prime}\)—loss modulus.} \\ \end{tabular}
\end{table} 
Table 1: Effect of addition of rennet and curly kale juice on the rheological parameters of cheese curds. Figure 2: _Cont._The Turbiscan Stability Index (TSI) is given in Table 1. The TSI value refers to stability and varies from 0 to 100. The closer to 100, the more unstable the cheese curd is. TSI is a very valuable parameter used to monitor the destabilization kinetics of systems such as cheese curds, which has been previously used to analyze changes in high-protein yoghurts during fermentation [27]. It is worth noting that, according to the TSI methodology, the sample containing milk and fermented curly kale juice was the most stable during the coagulation; cheese curds obtained with rennet and rennet with fermented curly kale juice were less stable. However, the reaction time for the latter was 90 min. The TSI values recorded for the samples containing milk with rennet and rennet with fermented curly kale juice after 90 min proved that the curd formation was faster than in the sample containing only fermented curly kale juice. The highest TSI was recorded for the curd obtained with milk and rennet, moderate TSI was found for the sample containing milk with rennet and fermented curly kale juice and the lowest value was noted for the sample obtained with milk and fermented curly kale juice. Changes in The Physico-Chemical Composition and Microbial Population in Feta-Type Cheese during Ripening  
Ripening is an example of a process of complex biofilm maturation, in which biochemical and microbiological changes take place in the curd mostly through the metabolism of residual lactose, lactate and citrate besides proteolysis and lipolysis [28]. Table 2 demonstrates changes in the physico-chemical parameters during the ripening of Feta-type cheese. A strong interaction was observed between the ripening time and the lactose concentration and pH value. The part of lactose maintained in the cheese after curd cutting was catabolized by the starter culture during the ripening period. Thus, after 16 weeks of maturation, no lactose content was detected in the Feta-type cheese, while \(2.41\pm 0.11\%\) of this carbohydrate was determined before ripening. Our finding is in agreement with previous studies that reported significant reduction in the lactose concentration during ripening [29]. The pH value in the 16-week-old cheese significantly decreased to \(5.3\pm 0.05\), which was due to the metabolism of LAB as in the case of lactose. Similar findings were reported by [PERSON] et al. [30], who found that pH of Feta-type cheese supplemented with _Lactobacillus_ strains was around 5.19-5.3. Previous studies have reported absorption of water in high-pH cheeses (>5.2). This may be also related to the fact that amino acids are released during cheese ripening, thereby increasing the pH value [31]. The protein content decreased during storage from 25.69 \(\pm\) 0.33 to 19.61 \(\pm\) 0.97% of fw. The reduction in the protein content may have been a consequence  
Figure 2: Evolution of backscattering spectra during curd coagulation for milk with rennet (**a**), milk with rennet and fermented juice (**b**) and milk with fermented curly kale juice (**c**). of diffusion of compounds from the cheese curd to the brine during ripening. Studies conducted by [PERSON] et al. [32] and [PERSON] et al. [33] reported a similar trend for ripened cheese.