Beer As a Source of Hop Prenylated Flavonoids, Compounds with Antioxidant, Chemoprotective and Phytoestrogen Activity

BEER AS A SOURCE OF HOP PRENYLATED FLAVONOIDS, COMPOUNDS WITH ANTIOXIDANT, CHEMOPROTECTIVE AND PHYTOESTROGEN ACTIVITY Dana Urminská*1 and Nora Jedináková2 Address(es): Doc. RNDr. Dana Urminská, CSc., 1Slovak University of Agriculture, Faculty of Biotechnology and Food Sciences, Department of Biochemistry and Biotechnology, Trieda Andreja Hlinku 2, 949 76 Nitra-Chrenová, Slovakia, phone number: +421 37 641 4696. *Corresponding author: [email protected] https://doi.org/10.15414/jmbfs.4426 ARTICLE INFO ABSTRACT Received 4. 3. 2021 Beer is an alcoholic beverage consumed worldwide, which is given its typical taste by the presence of hops. Hops contain an array Revised 1. 6. 2021 technologically important substances, which are primarily represented by hop resins (humulones, lupulones, humulinones, hulupones, Accepted 1. 6. 2021 etc.), essential oils (humulene, myrcene, etc.) and tannins (phenolic compounds quercetin, catechin, etc.). In addition to their sensory Published 1. 8. 2021 properties, these molecules contribute to the biological and colloidal stability of beer with their antiseptic and antioxidant properties. Recently, an increased attention has been given to prenylated hop flavonoids, particularly xanthohumol, isoxanthohumol and 8- prenylnaringenin. Xanthohumol is a prenylated chalcone that exhibit antioxidant, anticancer and chemoprotective effects. Its only source Regular article in human nutrition is beer, nevertheless a large part of xanthohumol from hops is isomerized by heat to isoxanthohumol and desmethylxanthohumol, from which a racemic mixture of 6- and 8-prenylnaringenins is formed during the beer production. Xanthohumol is also converted to isoxanthohumol by digestion, leading to the formation of 8-prenylnaringenin that is being catalyzed by the enzymes of the intestinal microorganisms as well as liver enzymes. This substance is currently considered to be the most effective natural phytoestrogen. Keywords: hops, xanthohumol, isoxanthohumol, prenylated flavonoids INTRODUCTION by a high antioxidant activity, even stronger than resveratrol present in wine. The content of xanthohumol in dry hops may oscillate around 1%, while the amount Beer is a global traditional fermented beverage containing carbohydrates, typical of 8-prenylnaringenin is about ten times lower. An analytical complication lies in organic acids, vitamins, proteins and in particular hop substances. the fact that the exact concentration of each of these substances is difficult to be The most popular type of beer in the world is the bottom-fermented beer, which determined due to their isomerization. During the heat treatment, xanthohumol is is produced mainly by the brewer's yeast Saccharomyces pastorianus and the isomerized to isoxanthohumol, while desmethylxanthohumol is isomerized to a fermentation process takes place at temperatures ranging from 3.3 to 10 °C. The racemic mixture of 6- and 8-prenylnaringenins. second type is the top-fermented beer, which is fermented with the help of the Xanthohumol itself was not identified until 1957 and its favorable yeast Saccharomyces cerevisiae at temperatures from 20 to 24 °C. In comparison pharmacological properties, particularly its antioxidant, anti-inflammatory, to other alcoholic beverages, classic beer has a higher nutritional value, mainly antimicrobial, antiplasmodial and anticancer characteristics were not described because of the presence of extracted substances from barley, flavor molecules until the 1990s. from hops, as well as a relatively high content of minerals and nutrients such as The total content of biologically beneficial substances also depends on the actual calcium, sodium, potassium, and magnesium. In addition, by using malt, and processing of the common hops into their final form used in brewing. Hops can especially hops, beer is enriched with naturally occurring antioxidants - phenolic be used in the form of dried heads, hop pellets, extracts or isoextracts. Currently, compounds. the newest and most innovative method of processing hops lies in the use of Antioxidants are substances that are present in foods and food products in lower liquid nitrogen, during which lupulin is extracted, containing most of the bitter concentrations when compared to oxidizable substrates, and act to cease or and aromatic substances. inhibit the oxidation process of such substrates. In beer, these compounds There are several methods to determine the content of prenylated flavonoids in originate from malt (70%) and hops (30%). During the brewing and fermentation hops or beer, based mainly on the principle of liquid chromatography. At present, process, hops release three main metabolites into the beverage, namely bitter liquid chromatography combined with tandem mass spectrometry are considered acids, prenylated chalcones and essential oils. to be the most suitable. Common hops (Humulus lupulus L.) are botanically classified into the Rosidae subclass, the Fabidae group, the Rosales order and the Cannabaceae family. BEER Several available varieties may be used for the brewing industry, which provide the beer with different flavors and aromas. Breweries use female cones Beer as a fermented beverage has a very long history (8000 years), while the exclusively, as these contain glandular trichomes located in the lupulin glands. basic brewing methods have not changed significantly. A more sophisticated and These glands are considered to be the centre for the biosynthesis of secondary efficient method of beer production was introduced only in the period of the metabolites such as terpenoids, prenylated flavonoids, phenolic compounds, industrial revolution (Guido, 2019). Following water and tea, beer is the third essential oils, resins and bitter acids. While all metabolites exhibit a certain most frequently consumed drink in the world. Currently, the popularity of small biological activity, when it comes to the antioxidant potential and health benefits, craft breweries or home brewing is increasing, which is gradually outpacing the the most interesting are prenylated chalcones, containing α- and β-unsaturated demand for commercially brewed beer (Matanjević et al., 2019). ketones. Beer is an alcoholic beverage produced using yeast and three raw materials, Prenylated hop chalcones include xanthohumol, desmethylxanthohumol, which are water, malt and hops. The main steps of the beer production process xanthogalenol and isoxanthohumol, 6-prenylnaringenin, 8-prenylnaringenin and include the preparation of malt and its milling, wiping, mashing, lautering, wort 8-geranylnaringenin. Out of these, xanthohumol stands out, as it is characterized boiling, wort clarification, fermentation, storage and filtration. The basic 1 J Microbiol Biotech Food Sci / Urminská and Jedináková 2021 : 11 (1) e4426 qualitative characterization of beer is divided by Gonzales-Viejo et al. (2016) iron (Punčochářová et al., 2019). Novotný (2019) explains that calcium and into a visual and a sensory one. The primary attribute that consumers rate is magnesium ions are involved in accelerating the isomerization of bitter visual, which includes the color of the beer, the overall appearance, the volume substances, besides being essential for the yeast metabolism and interacting with and stability of the foam, or the clarity of the beer. The sensory attributes malt phosphates, thereby lowering the pH of the mash. Chlorides accentuate the comprise the perception and drinkability of beer, including the content of alcohol malty character and fullness of beer, while in turn, sulphates promote the taste of and carbon dioxide, aroma, mouthfeel, bitterness, or the presence of unpleasant hops. According to Kunatha (2012), iron provides beer with an undesirable tastes in beer. flavor and is responsible for slowing down the fermentation processes. Micro- The color, turbidity and fermentation process are all taken into account when and macroelements that are irreplaceable for yeasts should come from malt and classifying beer into individual categories. The color of beer is generally hops, and not from the water. determined by the color of the malt, which depends on the color of the grain. Barley is most often used for malting because of its high ratio of starch to protein, Eventually, barley grain acquires color during the malt production and roasting while the husks of the grain are responsible for typical malt flavors. Other cereals due to the Maillard reaction or caramelization (Lukinac et al., 2019). Thus, beer may be used as well, such as wheat, oats, rye, sorghum or millet, which, can take on a vast array of shades of yellow, red, brown to black. Depending on following malting, can serve not only for brewing purposes, but also for the the brewer's yeast used and the fermentation temperature, three main categories production of distillates, or in other sectors of the food industry (MacLeod et al., may be distinguished: 2016). Within non-traditional malts, an increased attention has been paid to sorghum and • bottom-fermented beers (lagers), millet malt, as they have a significantly higher lysine content and a better protein • top-fermented beers (ALEs), digestibility than conventional cereal malts. However, the malting of sorghum • spontaneously fermented beers (Ebienfa et al., 2015). leads to the release of hydrogen cyanide, which must be removed in the form of gaseous cyanide by drying the malt at a temperature above 30 °C. These raw According to Nešpor et al. (2019) specific features of bottom-fermented beers materials are also more susceptible

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