7.2.2 Alternative uses of hops

7.2.2 Alternative uses of hops

For alternative applications, not only the cones but also the rest of the hop plant can be used. The inner, wooden parts of the hop bine, for instance, are known as shives or shoves. They have excellent insulation properties and mechanical strength, which makes them well suited as a material for insulation. They can also be turned into molded parts for such applications as automotive door panels. To date, however, no such applications exist on a large scale. As for cones, the antimicrobial properties of their bitter acids are of special interest for alternative uses. Even in catalytic quantities (0.001 to 0.1% by weight), they reveal their antimicrobial and preservative effectiveness, in ascending strength from iso-alpha acids, to alpha acids, to beta acids polar (Figure 7.6).

Figure 7.6: Sequence of antimicrobial activity of iso-alpha acids, alpha acids, and beta acids, as well as their effectiveness

The more non-polar a molecule is, the greater is its antimicrobial effectiveness. The bitter substances destroy the pH gradient on the cell membranes of gram-positive bacteria, which prevents the bacteria from absorbing nutrients and causes them to die. Iso-alpha acids inhibit inflammatory processes and have positive effects on fat and sugar metabolisms. In beer, they even protect against Helicobacter pylori, a type of bacterium that can trigger stomach cancer. Beta acids are effective against the growth of gram-positive bacteria such as listeria and clostridia; and they can inhibit the tuberculosis-causing pathogen Mycobacterium tuberculosis. Because of these properties, hop bitter substances can be used as natural biocides wherever bacteria must be kept in check. In the sugar and ethanol industries, beta acids have already become a successful substitute for formalin. Other possible uses of the antimicrobial properties of hops are as preservatives in the food industry (fish, meat, and dairy products) or as antibiotics in animal nutrition, as well as for sanitizing biohazardous waste (sewage sludge, compost) and for the elimination of mold infestations. They can also be used as odor and hygiene improvements in litter and for the control of allergens. It is certainly conceivable that the use of hops in these applications will increase in the future. Therefore, developing hops with an increase in beta acids is also a breeding objective in Hüll. The current record in beta-acid is at about 20%. There is even a breeding line that produces only beta and no alpha acids. This variety is used for tea.

Because hops contain a large number of polyphenolic substances, they are also of interest for applications in health, wellness, nutritional supplements and functional foods. Hops can have a polyphenol content of up to 8%, which puts them into the group of very polyphenol-rich plants. Polyphenols are generally considered beneficial because they are antioxidants and can trap free radicals. Substances in hops with very high antioxidative potential include oligomeric proanthocyanidins (up to 1.3%), glycosidically bound quercetin (up to 0.2%), and kaempferol (up to 0.2%). Anti-inflammatory multifidols, too, are significant compounds in hops. Their name derives from the tropical plant Jatropha multifida, which exudes a milky latex sap that contains these compounds. Finally, hops contain trace amounts of prenylated flavonoids such as 8-prenylnaringenin, which is one of the strongest phytoestrogens. Therefore, hops have a mild estrogenic effect. Of all the hop polyphenols, however, xanthohumol has received the most public attention. Scientific work on this polyphenol has exploded, which has led to the European Food Safety Authority (EFSA) of the European Union to recognize the health-promoting effects of xanthohumol. This means that xanthohumol can now be marketed with health claims for applications in food supplements and functional foods. Comprehensive information about the history of xanthohumol and its effects can be found on the homepage of T.A. XAN Development S.A.M. (https://www.xan.com). The benefits of xanthohumol cover a broad spectrum (Figure 7.7), but its most important aspect, no doubt, is its anticarcinogen effect. During the brewing process, prenylated flavonoid is constantly being transformed (Figure 7.7). During the wort boil, xanthohumol is isomerized to iso-xanthohumol, and dimethylxanthohumol, to 8- and 6-prenylnaringenin. Therefore, desmethyl-xanthohumol cannot be found in beer. On the other hand, concentrations of prenylated naringenins are significantly higher in beer than in hops.

Figure 7.7: Effects of xanthohumol and its transformations in the brewing process The estrogenic effect of 8-prenylnaringenin (8-PN) stems from the fact that the structure of this substance is similar to that of the female sex hormone 17-beta-estradiol.