applied sciences Review Extraction, Identification, and Health Benefits of Anthocyanins in Blackcurrants (Ribes nigrum L.) Lei Cao 1, Yena Park 2, Sanggil Lee 3,* and Dae-Ok Kim 4,5,* 1 Institute of Marine Life Sciences, Pukyong National University, Busan 48513, Korea; [email protected] 2 Department of Smart Green Technology Engineering, Pukyong National University, Busan 48513, Korea; [email protected] 3 Department of Food Science and Nutrition, Pukyong National University, Busan 48513, Korea 4 Department of Food Science and Biotechnology, Kyung Hee University, Yongin 17104, Korea 5 Graduate School of Biotechnology and Institute of Life Science and Resources, Kyung Hee University, Yongin 17104, Korea * Correspondence: [email protected] (S.L.); [email protected] (D.-O.K.); Tel.: +82-051-629-5851 (S.L.); +82-31-201-2662 (D.-O.K.) Featured Application: The in-depth discussion on the extraction methods of anthocyanins from blackcurrants and the molecular mechanisms behind its health benefits improves the utilization of blackcurrant anthocyanins in academic and industrial fields. Abstract: The fruit of the blackcurrant (Ribes nigrum L.) is round-shaped, dark purple, bittersweet, and seed-containing edible berries. The blackcurrant has been used as a traditional medicine in both Asia and European countries. It is known as a rich source of antioxidants, largely due to its high content of phenolic compounds, especially anthocyanins. Studies on anthocyanins from blackcurrants have adopted different extraction methods and a panel of anthocyanins has been identified in them. Research on the health benefits of blackcurrant anthocyanins has also grown. Citation: Cao, L.; Park, Y.; Lee, S.; To present a general overview of research in blackcurrant anthocyanins, this review focuses on the Kim, D.-O. Extraction, Identification, extraction methods of anthocyanins from blackcurrants and the molecular mechanisms underlying and Health Benefits of Anthocyanins their health benefits. in Blackcurrants (Ribes nigrum L.). Appl. Sci. 2021, 11, 1863. https:// Keywords: blackcurrant; anthocyanins; extraction; identification; health benefits doi.org/10.3390/app11041863 Academic Editor: Claudio Medana Received: 30 January 2021 1. Introduction Accepted: 16 February 2021 The blackcurrant (Ribes nigrum L.) is a branched shrub with dark purple, bittersweet, Published: 20 February 2021 and seed-bearing berries that can grow to about 1 cm diameter [1]. All parts of the plant, including the fruits (skin, flesh, and seeds) and leaves, can be utilized. The fruit is often Publisher’s Note: MDPI stays neutral used to make dark violet dyes and can be eaten raw or in processed forms like juice, jams, with regard to jurisdictional claims in and jellies. Blackcurrant fruit waste has also been studied for its application in renewable published maps and institutional affil- hair dyes [2]. The leaves of the plant have been used as a flavor enhancer in soups due to iations. their strong scent. Oil extracted from the seeds is often used in cosmetics [3,4]. The fruits and leaves of the blackcurrant have a long history as a traditional medicine in both Asia and Europe [5,6]. Nowadays, blackcurrant extract capsules have been commercialized as a dietary supplement and marketed as an immunity booster. Copyright: © 2021 by the authors. Fresh blackcurrant fruit contains a variety of functional and bioactive compounds Licensee MDPI, Basel, Switzerland. such as soluble sugar, organic acid, diverse vitamins, multi-amino acids, diverse minerals, This article is an open access article elements, and unsaturated fatty acids [7–9]. One of the most studied groups of bioactive distributed under the terms and compounds in blackcurrants are anthocyanins. Anthocyanins exist not only in blackcurrant conditions of the Creative Commons berries but also in its seeds and leaves [10,11]. Attribution (CC BY) license (https:// The anthocyanin presents up to 2–4 g/kg of fresh weight in blackcurrants [12]. It creativecommons.org/licenses/by/ contributes to many sensorial properties, such as color, aroma, taste, and astringency. 4.0/). Appl. Sci. 2021, 11, 1863. https://doi.org/10.3390/app11041863 https://www.mdpi.com/journal/applsci Appl.Appl. Sci. Sci. 20212021, 11, 11, x, 1863FOR PEER REVIEW 2 2of of 14 14 basicThe chemical basic chemical structure structure of anthocyanins of anthocyanins is composed is composed of a sugar of conjugate a sugar conjugateand a phenolic and a aglyconphenolic [13]. aglycon Both are [13 known]. Both to are affect known the bioavailability to affect the bioavailability and metabolism and of anthocyanins metabolism of [14].anthocyanins The number [14 of]. articles The number studying of articles anthocyanins studying in anthocyaninsblackcurrants inhave blackcurrants increased con- have siderablyincreased over considerably the decades over (Figure the decades 1). Research (Figure has1). found Research that hasblackcurrant found that anthocyanins blackcurrant (BCA)anthocyanins exert a wide (BCA) range exert of abiological wide range functi of biologicalons including functions antioxidant, including anti-inflammation, antioxidant, anti- andinflammation, phytoestrogenic and phytoestrogenicactivities, as well activities,as an improvement as well as of an vision improvement and neuroprotective of vision and effectsneuroprotective [1,15]. Since effects the vast [1, 15majority]. Since of the studies vast majorityfocus on the of studies fruits of focus blackcurrants, on the fruits and of blackcurrantblackcurrants, fruits and contain blackcurrant a much higher fruits contain amount a of much anthocyanins higher amount than the of leaves anthocyanins [16], in thisthan review, the leaves “blackcurrants” [16], in this review,refers to “blackcurrants” the blackcurrant refers fruit, to unless the blackcurrant otherwise mentioned. fruit, unless otherwise mentioned. 150 117 100 74 50 40 37 4 2 0 0 5 0 5 0 2 01 -1995 -200 -201 -2 -20 6 91 16 011 19 199 2001-200 2006 2 20 FigureFigure 1. 1.TheThe number number of ofarticles articles retrieved retrieved on onPubM PubMeded using using searching searching terms terms “blackcurrant” “blackcurrant” and and “anthocyanins”“anthocyanins” over over different different periods. periods. AA variety variety of of extraction extraction methods methods have have been been applied applied to to blackcurrants blackcurrants for for anthocyanin anthocyanin extraction.extraction. However, However, it itis isdifficult difficult to to compar comparee the the extraction extraction yields yields among among different different meth- meth- odsods since since many many factors, factors, such such as as cultivars cultivars an andd storage storage conditions, conditions, have have an an impact impact on on the the anthocyaninanthocyanin yield yield [8,17]. [8,17 ].These These discrepancies discrepancies could could give give confusion confusion to to the the people people utilizing utilizing blackcurrantsblackcurrants in in academic academic and and industrial industrial fields. fields. Thus, Thus, this this review review analytically analytically organized organized thethe available available information information and and aimed aimed to to facilitate facilitate a abetter better understanding understanding regarding regarding BCA BCA extractionextraction methodologies, methodologies, as as well asas thethe health health benefits benefits and and related related molecular molecular mechanisms mecha- nismsof BCA. of BCA. With anWith emphasis an emphasis on the molecularon the molecular pathways pathways regulated regulated by BCA, by we BCA, wanted we to wantedmake anto in-depthmake an discussionin-depth discussion on the health-promoting on the health-promoting role of BCA. role of BCA. 2. Extraction Methods 2. Extraction Methods Solid-liquid extraction is a classic approach used to extract anthocyanins from plant Solid-liquid extraction is a classic approach used to extract anthocyanins from plant tissues, such as blackcurrants. The polarity of anthocyanins facilitates their dissolution into tissues, such as blackcurrants. The polarity of anthocyanins facilitates their dissolution polar solvents. Besides traditional solvent methods, new technologies have been tested into polar solvents. Besides traditional solvent methods, new technologies have been for a better extraction yield of anthocyanins. These unconventional technologies include tested for a better extraction yield of anthocyanins. These unconventional technologies microwave-assisted extraction, ultrasonic-assisted extraction, enzyme-assisted extraction, include microwave-assisted extraction, ultrasonic-assisted extraction, enzyme-assisted and pulsed electrical field extraction [18]. extraction, and pulsed electrical field extraction [18]. 2.1. Solvent Extraction for Blackcurrant Anthocyanins 2.1. Solvent Extraction for Blackcurrant Anthocyanins The polarity of the targeted compound is the most critical factor for extraction reagent choice.The polarity Given their of the polarity, targeted anthocyanins compound is are the usually most critical extracted factor by for methanol, extraction ethanol, rea- gentacetone, choice. and/or Given water their [polarity,19]. Ethanol anthocyani and methanolns are usually are more extracted efficient by at methanol, extracting etha- antho- nol,cyanins acetone, from and/or blackcurrants water [19]. than Ethanol water and [20 me].thanol A mixture are more of different efficient solvents at extracting showed an- a thocyaninsbetter extraction from blackcurrants ability than than