Red fruit juices have long been popular in Europe, where the technology has been extensively developed for high-value-added fruits [1]. The documented phytochemical composition of red fruits is resulting in renewed global interest in industrial demand for these juices [2] since many red fruit juices, especially those that are naturally colorful, have high levels of antioxidants. Several researchers have studied the formation of consumers’ food quality expectations and sensory experiences as determinants of food acceptance ^[3][4][3,4]. Health issues can lead to the choice of red fruit juices and consequently to their approval and consumption [5]. Common fruits, such as berries, grapes, pomegranate, guava, sweetsop, persimmon, and plum, are rich in antioxidant phytochemicals ^[6][7][8][6,7,8] that have a protective role associated with their antioxidant activity since overproduction of oxidants (reactive oxygen species and reactive nitrogen species) in the human body is involved in the pathogenesis of many chronic diseases [9], for instance, cardiovascular diseases, diabetes, and cancers. Red fruit juice grains have been demonstrated to protect against developing these diseases ^[10][11][12][10,11,12].

2. Red Fruit Juices

The market for non-alcoholic beverages is growing because consumers prefer healthier beverages. Nowadays, red fruit juices are known for their health benefits due to their higher phenolic compounds concentration, namely in flavonoid and non-flavonoid compounds, and consequently high antioxidant activity. The main flavonoid compounds in red fruits are anthocyanins (cyanidin and other colorings of the skin, for example in red grape, delphinidin, peonidin, malvidin, pelargonidin, petunidin), flavanols (proanthocyanidins and catechins), flavonols (derivatives of rutin, quercetin, myricetin and kaempferol). For non-flavonoid compounds, the primary phenolic acids in red fruits are represented by hydroxylated derivatives of benzoic and hydroxycinnamic acid ^[13][14][14,15]. Within the red fruits used for the production of juices, pomegranate, red currant, blood orange, black currant, cherry, red raspberry, blackberry, strawberry, blueberry, elderberry, and grape berries are amongst the richest in anthocyanins—water-soluble pigments that contribute to the blue, purple, and red color in many fruits and their high antioxidant activity ^[15][16]. Numerous studies have shown that anthocyanins present various biological activities, including antioxidant, anti-inflammatory, antimicrobial, and anti-carcinogenic ^[16][17][18][17,18,19]. So, a high correlation has been demonstrated between antioxidant activity and total anthocyanin concentration of red fruit juices ^[19][20]. However, anthocyanin stability depends on the existence of methoxyl or a hydroxyl group in the anthocyanin structure, giving them more or less strength and thus impacting their bioavailability. For example, delphinidin-3-glucoside has three hydroxyl groups in its B ring, the most unstable anthocyanin, while malvidin-3-glucoside with more methoxyl groups is the most stable anthocyanin. Consequently, the biological activity of anthocyanins can also be influenced by glycosylation, making them more water soluble but less reactive to free radicals, subsequently decreasing their antioxidant activity ^[20][21]. For example, there is a motivation to produce red fruit beverages like grape juice or grape nectar for their important nutritional properties ^[21][22], such as antioxidant activity, due to the presence of phenolic compounds ^[22][23]. Grape juice is an unfermented beverage obtained from diluting grape pulp in water, with or without adding sugars and acids ^[23][24]. Nevertheless, the existing juice processing technology leads to significant losses of these compounds through heating degradation and poor extraction from fruit. Therefore, consumers demand fresh, unpasteurized juices. According to Yuste et al. ^[24][25], research into alternative juice processing technology has been stimulated to better preserve the properties of red fresh juices due to consumer demand for novel, natural, and fresh-like beverages that are both safe and have improved nutritional and sensory characteristics. Manea ^[25][26] observed that preserving red fruit juices at refrigeration temperature conserves anthocyanins and tannins. Elderberry juice presented a high concentration of anthocyanins, 0.84 g/L, and tannins, 3.22 g/L. Elderberry and grapes have anthocyanins in the skin; however, the skin and pulp ratio is lower in elderberry. Consequently, elderberry juice will be more concentrated in anthocyanins than grape juice (0.45 g/L). After three months of storage at refrigeration temperature, anthocyanin content decreased by 49.74% for grape juice and by 25.15% for the elderberry juice since in the elderberry juice, tannins were better preserved and acted as antioxidants and preservatives, inhibiting juice enzymes that contributed to the protection of the anthocyanins; therefore juice color and flavor were better maintained ^[25][26]. So, novel treatments such as high hydrostatic pressure, high-intensity pulsed electric fields, and ultrasound are alternative treatments to pasteurization to avoid the detrimental effects produced by high temperatures in the degradation of phenolic compounds as well as to be able to maintain the sensory quality attributes of the final product ^[26][27][27,28].

3. Composition of Red Fruit Juices

Grape nectar and beverages presented a different physicochemical composition to those from grape juice since they were obtained from a dilution of grape juice. Among the compounds that showed greater concentrations in grape juice are total soluble solids (16.2 °Brix), phenolic compounds, such as total polyphenol index (65.8), anthocyanins (283.7 mg/L) and color intensity (1.245), organic acids, namely tartaric acid (6.7 g/L) and malic acid (3.3 g/L). Grape nectar and beverage are characterized by a higher °Brix/titratable ratio, respectively 29.7 and 26.7 ^[22][23]. Red fruit juices’ phenolic composition, namely total phenolic compounds and total anthocyanins, ranged from 1234.27 mg GAE/L to 6361.89 mg GAE/L for red raspberry and elderberry, respectively, and the total anthocyanins went from 205.98 mgCGE/L to 4188.63 mgCGE/L, for strawberry and elderberry, respectively ^[19][20]. Total anthocyanins were the main phenolic compounds presented in elderberry juice (66%) or black currant juice (56%) ^[19][20]. The antioxidant activity of red fruit juices ranged from 4.07 to 62.14 μmol TE/mL for sweet cherry and elderberry, respectively ^[19][20], with elderberry juice being the one that has a higher concentration in total phenolic compounds, total anthocyanins and consequently higher antioxidant activity. Red fruit juices showed considerable variations in anthocyanin content and profile, as shown in Table 1. Some red fruit juices have low concentrations of anthocyanins, such as strawberry, red raspberry, and sweet cherry juice. In contrast, these flavonoid compounds are high in elderberry and black currant juice. Monomeric anthocyanins in red fruit juices were derivatives of cyanidin, delphinidin, pelargonidin, malvidin, and peonidin. So, it is evident that fluids produced with different red fruits, such as strawberry, raspberry, blueberry, black currant, and grapes, differ in the quantity and type of anthocyanins. The family of European Vitis vinifera vines is characterized by anthocyanins, which have only one glucose molecule. In contrast, non-vinifera vines such as Vitis labrusca or Vitis rotundafolia grapes and American hybrids have anthocyanins with two glucose molecules. Obón et al. ^[28][29], Lopes da Silva et al. ^[29][30], Jakobek et al. ^[19][20] and Stój et al. ^[30][31] determined in strawberry juices the existence of cyanidin 3-glucoside, pelargonidin 3-glucoside, and pelargonidin 3-rutinoside, the major anthocyanin in this juice being pelargonidin 3-glucoside (Table 1). The anthocyanin profile from red raspberry juices showed five anthocyanins, namely cyanidin 3-sophoroside, cyanidin 3-glucosyl-rutinoside, cyanidin 3-glucoside, pelargonidin 3-sophoroside, and cyanidin 3-rutinoside ^[28][30][31][29,31,32]. Blackcurrant juices are characterized by monomeric anthocyanins such as delphinidin 3-glucoside, delphinidin 3-rutinoside, cyanidin 3-glucoside, cyanidin 3-rutinoside, and delphinidin 3-rutinoside ^{[28][31][32][33]}[29,32,33,34]. Pelargonidin-3-glucoside and cyanidin-3-xylorutinoside were the main anthocyanins in strawberry and red currant juices. Those anthocyanins were not detected in raspberry and black currant juices, in which cyanidin-3-sophoroside as well as delphinidin-3-rutinoside and cyanidin-3-rutinoside were the main anthocyanins, respectively ^[30][31]. Blueberry juices anthocyanin profile studied by several authors ^{[28][31][34][35][36]}[29,32,35,36,37] showed fourteen different anthocyanins, namely dephinidin 3-galactoside, delphinidin 3-glucoside, cyanidin 3-galactoside, delphinidin 3-arabinoside, cyanidin 3-glucoside, petunidin 3-galactoside, cyanidin 3-arabinoside, petunidin 3-glucoside, peonidin 3-galactoside, petunidin 3-arabinoside, peonidin 3-glucoside, malvidin 3-galactoside, malvidin 3-glucoside, and malvidin 3-arabinoside (Table 1). Grape juice anthocyanins are mainly delphinidin 3-glucoside, cyanidin 3-glucoside, petunidin 3-glucoside, peonidin 3-glucoside and malvidin 3-glucoside ^[31][36][32,37]. According to Jakobek et al. ^[19][20], elderberry, blackberry, and sour cherry juice are characterized by cyanidin derivatives. In contrast, pelargonidin derivatives represent black currant juice by delphinidin, cyanidin derivatives, and strawberry juice. Table 1 shows that each red fruit juice possesses a unique anthocyanin profile. Although all red fruit juices are good sources of bioactive phytochemicals, elderberry and black currant juices stand out in higher anthocyanin concentrations and consequently have higher antioxidant activities ^[19][20].