## 1 Introduction  
Fruit juices are an important part of the diet of both adults and children, as well as people with special dietary needs. They are a source of valuable vitamins, antioxidants and minerals [1]. However, they also contain a significant amount of energy and sugars (in apple juice on average 45 kcal, and 9.6 g in 100 g, respectively), similar to sweetened beverages [2]. When comparing the average energy and sugars content in one portion of apple juice (250 mL) to the reference intake presented in Regulation of the European Parliament and of the Council [3], which are 2000 kcal and 90 g, respectively, it is evident that while the energy intake connected with this consumption is relatively low (5.6% of the reference intake), sugars intake is much higher, and reaches even more than 20% of the reference intake. Nowadays, consumers becoming more and more aware of the impact of diet on physical fitness and health, reluctantly reach for fruit juices despite their obvious taste and nutritional values. While consumption of whole apples can improve vascular function, decrease systolic BP and reduce cholesterol levels, clear apple juice has been associated with adverse effects, most likely due to its high fructose and low fibre content [4; 5]. According to [PERSON] and [PERSON] [2] the accepted guidelines recommending the consumption of 5 portions of fruit and vegetables per day should not include fruit juices. It has been shown that although consuming a significant amount of whole fruit results in a reduced or neutral risk of diabetes, drinking large amounts of fruit juices may lead to an increased risk of type 2 diabetes [2; 6]. One glass of fruit juice contains much more sugar than one piece of fruit. Moreover, many nutrients, such as fiber, pectin, proteins and free amino acids, are found in juices in much smaller quantities or not at all [7]. A study presented by [PERSON] et al. [8], which compared whole oranges (2.5% fiber) to orange juice (fiber free) and whole grapes (1.3% fiber) to grape juice (fiber free) confirmed that whole fruit provided more satiety than juice, and the return of appetite was delayed. With oranges, and previously reported with apples, there was a significantly smaller insulin response to fruit than to juice and less postabsorptive fall in plasma glucose. According to [PERSON] et al. [6] relatively high glycemic load values of fruit juices along with reduced levels of beneficial nutrients through juicing processes (for example, the glycemic load values per serving are 6.2 for raw oranges and 13.4 for orange juice, and fibre levels per serving are 3.1 g and 0.5 g, respectively), may explain the positive associations between fruit juice consumption and risk of type 2 diabetes. According to former World Health Organisation (WHO) guidelines, a glass of juice could be treated as one of five portions of fruit and vegetables recommended for consumption during the day, but current official guidelines do not include juices in the list [9; 10]. Among fruit juices, cloudy versions have gained an increased market value, due to their sensory and nutritional qualities [11]. They contain valuable ingredients, which are normally rejected during clear juice processing (especially clarification) [5]. That is why special attention should be paid to the possibilities to increase cloudy juice consumption (instead of clear juices), and methods which could be used for the reduction of sugar content in these juices. In the current study, we propose a novel sustainable approach for the production of low-sugar cloudy apple-cranberry juice, in which it is possible to utilize the retenstate coming from cloudy juice ultrafiltration (UF) or diafiltration (DF). Such an approach to obtain a low sugar juice fraction was firstly proposed and patented by Black and Bray [12]. Sugar separation processes involve ultrafiltration, nanofiltration and optionally reverse osmosis.