## 3 Results
### Selectivity of Ultrafiltration and Diafiltration  
Both the determination of particular physicochemical properties, and the analysis of FTIR spectra, does not give the full overview about the progress of the membrane processing and the characteristics of the obtained products. Additionally, for these purposes, the selectivity of UF and DF was described, based on recovery factor \(R\) (Table 3). R of individual compounds (TSS, TS, Glu, Fru, TPC, TA) after UF was at the same level (0.76-0.77), while for NSS it was lower (0.72). This means that the applied membrane was selective for juice compounds, sugars (TS, Glu, Fru) were transmitted together with acids (TA) and polyphenols (TPC), while the transmission of other non-sugar soluble compounds to the permeate was higher. However, the obtained juice contained insoluble phase, fibre and high molecular weight solids (including pectins) of potential health-promoting properties, coming from ACJ. According to [PERSON] et al. [47] unclarified apple juice contains soluble pectin with a molecular weight distribution centered around 100 kDa. Other authors [15] used UF to separate apple pectin on the basis that 68% of the pectin have a molecular weights over 300 kDa whereas a minority has a molecular weight below 5 kDa. Thus, 15 kDa membrane used in the current work should reject the majority of pectin present in ACJ. [PERSON] et al. [35] presented lower rejection (17.7-26.6%) of TPC after UF of orange juice, but membranes of higher MWCO were used (50 and 100 kDa MWCO)  
It has to be emphasized, that although in general UF membranes are not a barrier for glucose and fructose (the size of pores is bigger than the size of molecules), during the process not every molecule of sugars had a possibility to contact the membrane, due to the fact that the process was performed in a dynamic mode (the flow of feed/retentate was perpendicular to the membrane). Figure 4: Discrimination of apple-cranberry cloudy juice samples before and after membrane processing based on hierarchical cluster analysis (HCA) of FTIR spectra (B). After DF, the recovery factor \(R\) of TSS, TS, Glu, Fru, TPC and TA was lower than after UF (0.58-0.64), which resulted from longer processing and the \"washout\" effect due to water addition. Moreover, some differentiation of values for individual components could be observed. The recovery of polyphenols (TPC) was lower than of TSS, acids (TA) and sugars (TS). According to a previously published work [24], UF can be applied for the separation of polyphenols from sugars present in apple juice. Under optimum operating UF conditions (1 kDa MWCO, TMP 4 bar, temperature 30 \({}^{\circ}\)C, feed flow rate 1-1.8 L/min, pH 3 and 10 \({}^{\circ}\)Brix), 70% of polyphenols were transmitted to the permeate, while only approx. 20% of the sugar was present in that stream. Thus, it was a similar effect as observed during DF in the current work, of higher transmission of polyphenols than sugars. This effect is not favorable from the point of view of the aim of the current work. As was discussed above, polyphenols with their natural antioxidant ability, if possible, should be retained in the proposed products, provided that the addition of some antioxidants will prevent them the from the oxidative and post oxidative transformations. On the contrary to UF, after DF the recovery of NSS was higher than of other compounds. In the patent published by Black and Bray [12], dealing with membrane hybrid processing of fruit juices to obtain low-sugar juice, the subsequent nanofiltration (NF) step after UF is proposed, in which acids (including ascorbic acid), minerals, and other water-soluble components transmitted to permeate during UF, can be separated from sugars. As was presented by [PERSON] et al. [48], [PERSON] et al. [49], and [PERSON] et al. [50], phenolic compounds can be separated from sugars by the adequate NF membrane, rejecting phenolic compounds and transmitting sugars. Then, NF retentate could be included in the final product for these compounds retrieval.