Lingonberry fruits are a rich source of dietary micronutrients and bioactive compounds, including vitamins, polyphenols, and minerals. Polyphenolics, such as flavonoids, polyphenolic acids, anthocyanins, procyanidins, organic acids, vitamins (A, B1, B2, B3, and C), potassium, calcium, magnesium, and phosphorous, have been found in lingonberries
[3,6,17][3][6][17]. However, there is some variation between the content and profile of the phenolics in lingonberry fruit, depending on the region they grow in, cultivar, growing environment, ripening stage, weather, soil conditions, and extraction methods. The total phenolics content in wild lingonberry growing in Alaska was in the range of 624.4 mg/100 g FW
[18], while lingonberry grown in the forests in central Poland had total phenolics in the range of 582–760 mg/100 g FW for the ethanol-water extract and 436–636 mg/100 g FW for the water extract
[19]. The solubility of phenolics is higher in alcohols; thus, for the ethanol-water extract, higher results were obtained
[19]. The mean concentration of the phenolic compounds in cultivated lingonberries grown in a research plot in Oregon (United States) was estimated at 566 mg/100 g (range 431–660 mg/100 g FW)
[16]. Significantly lower results (360–410 mg/100 g FW) were reported for various lingonberry extracts grown in the southern Labrador area in Canada
[20]. In cultivated lingonberries (US), the total anthocyanin (ACN) content ranged from 27.4 to 52.6 mg/100 g, depending on the cultivar
[16], while total anthocyanins in wild fruits were in the range of 33–47 mg/100 g FW in Poland
[19] and 77.5 mg/100 g FW for berries grown in Finland
[21]. The highest ACN concentration accumulated in lingonberry from Alaska (194.6 mg/100 g FW)
[18]. The total flavonoids content in wild lingonberry from Poland ranged from 522–647 μmol/100 g FW for the ethanol-water extract and 255–353 μmol/100 g FW for the water extract (Poland)
[19]. Proanthocyanidins (PAC) exhibited the highest levels in wild Alaskan lingonberry (278.8 mg/100 g FW), which was comparable to the PAC content of the same species in Finland (260 mg/100 g FW)
[18,22][18][22]. Anthocyanin glycosides, the pigments responsible for the blue and red colors in berries, are the most abundant phenolic compounds in lingonberries. Wild Alaskan lingonberry displayed only cyanidin glycosides as the dominant anthocyanin, with non-detectable levels of peonidins
[18]. The higher relative content of cyanidin glycosides was linked to geographical and environmental factors in the northernmost latitudes of Finland
[22]. Cyanidin-3-galactoside constitutes approximately 82.5% of all anthocyanin compounds in wild lingonberries, while cyanidin-3-arabinoside and cyanidin-3-glucoside are present in smaller amounts
[6,17][6][17]. Individual anthocyanin content in cultivated lingonberries were 79% for cyanidin-3-galactoside, 10% for cyanidin-3-glucoside, and 11% for cyanidin-3-arabinoside
[16]. The polyphenolic and anthocyanin contents in wild berry fruits are generally higher than in cultivated fruits. Wild berries exposed to environmental stress enhance their defenses by producing an increased number of polyphenolics, which protects plants from external agents
[23]. The content of the particular classes of compounds in lingonberries depends on the location and type (wild/cultivated), as shown in . Within the group of phenolic acids, derivatives of ferulic acid, coumaric acid, caffeoylquinic acid, and benzoic acid were found in lingonberry fruit
[6,17][6][17]. Moreover, flavonols, such as quercetin and its glycosylated derivatives, and two flavanols identified as catechin and epicatechin, were identified in the fruits
[6]. In the aqueous extract from the fruit, the flavanol contents ranged between 30 and 36%, and the relative contents of the flavonol glycosides were in the range of 7–9%. Among the quercetin glycosides identified, quercetin-3-O-galactoside, quercetin-3-O-glucoside, quercetin rutinoside, quercetin pentosides, quercetin-3-O-rhamnoside, and quercetin-3-O-(4″-(3-hydroxy-3-methylglutaryl))-α-rhamnoside were described
[1,17,24][1][17][24]. Additionally, kaempferol glycosides, such as kaempferol hexoside, kaempferol rutinoside, kaempferol pentoside, and kaempferol-3-O-rhamnoside, were also identified in lingonberry fruit
[1,17,24][1][17][24]. Dimeric B-type and A-type, and trimeric proanthocyanidins type A, represent approximately 23% of the total polyphenols
[6]. Wild Alaskan lingonberry exhibited a higher percentage of B-type dimers (16.5%) and trimers (12.8%) than A-type analogs (7.8 and 2.6%, respectively)
[18]. Hydroxycinnamic acids represent the less abundant group of phenolic compounds in the lingonberry fruit. Their relative content was in the range of 2–3%
[24]. In processed lingonberry extract, p-coumaric acid was the predominant hydroxycinnamic acid, followed by caffeic and ferulic acid. Other phenolic acids represented in the lower amount are esters of caffeic acid, chlorogenic, and crypto-chlorogenic acid. The 4-glucosides of p-coumaric and caffeic acids were also detected in a lingonberry extract
[1]. Triterpenoids, lingonberry secondary metabolites, are another group of compounds with beneficial health effects. Szakiel et al. (2012) identified the main triterpenoid compounds occurring in lingonberry fruits. The quantitative determination of individual triterpenoids showed that the two isomeric acids, oleanolic and ursolic, were the most abundant compounds, comprising 70–73% of all triterpenoids in the fruit. The main lingonberry triterpenoid profile, identified by GC–MS/FID, consisted of α-amyrin, β-amyrin, betulin, campesterol, cycloartanol, erythrodiol, fern-7-en-3β-ol, friedelin, lupeol, sitosterol, stigmasterol, stigmasta-3,5-dien-7-one, swert-9(11)-en-3β-ol, taraxasterol, urs-12-en-29-al, uvaol, oleanolic acid, and ursolic acid
[4].