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Pereira, O.R.;  Santos, G.;  Sousa, M.J. Humulus lupulus L. By-Products. Encyclopedia. Available online: https://encyclopedia.pub/entry/39028 (accessed on 11 May 2024).
Pereira OR,  Santos G,  Sousa MJ. Humulus lupulus L. By-Products. Encyclopedia. Available at: https://encyclopedia.pub/entry/39028. Accessed May 11, 2024.
Pereira, Olívia R., Gleiciara Santos, Maria João Sousa. "Humulus lupulus L. By-Products" Encyclopedia, https://encyclopedia.pub/entry/39028 (accessed May 11, 2024).
Pereira, O.R.,  Santos, G., & Sousa, M.J. (2022, December 21). Humulus lupulus L. By-Products. In Encyclopedia. https://encyclopedia.pub/entry/39028
Pereira, Olívia R., et al. "Humulus lupulus L. By-Products." Encyclopedia. Web. 21 December, 2022.
Humulus lupulus L. By-Products
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This entry is adapted from the peer-reviewed paper 10.3390/cosmetics9060139

Hops (Humulus lupulus L.) are known worldwide as a raw material in beer production due their flavor and preservative values. The beneficial properties of the plant have been mostly associated with the female hop inflorescences (cones), which is also the part used in the brewing industry. However, some studies indicate the presence of compounds associated with health benefits in the vegetative parts of hops or small-caliber cones, which discarded in hop collection. Moreover, large quantities of by-products remain in the forms of spent grains and spent hops/hot trub and are produced by breweries raising environmental and economic sustainability concerns.

Humulus lupulus L. hop cosmetic waste valorization

1. Introduction

The Humulus lupulus L. (hop) plant is dioecious (i.e., the male and female flowers usually develop on separate plants); occasional fertile monoecious individual plants have been reported. For brewing beer, viable seeds are undesirable; therefore, only female plants are grown in hops fields to prevent pollination. Female plants are propagated vegetatively, and male plants are culled if plants are grown from seeds. Under natural conditions, the flowers are wind pollinated and the female inflorescence develops to form a strobile (or cone). The strobiles of the female plants are able to develop the lupulin glands that secrete a fine yellow resinous powder. These glands secrete predominantly bitter acids and essential oils, the constituents of which include prenylflavonoids [1][2].
In Europe, there is evidence of the use of H. lupulus since prehistoric times. The ancient Romans employed its leaves and inflorescences in some food preparations as well as in textiles and cosmetic products [2]. Afterwards, the use of hop rapidly increased in the Middle Ages, presumably because of their developed utilization in the brewing process. Cultivation of hop began in the mid-ninth century AC in Germany, then spread throughout the Central Europe [3].
According to the latest Food and Agriculture Organization (FAO) estimates, the global area devoted to hop cultivation was around 65,500 ha in 2019, with a production that exceeded 130,000 tons. The European continent contributed decisively to this production, with a volume of almost 68,000 tons, representing 52% of the world hops production [4].
Hop plants are grown almost exclusively for the brewing industry, in which the resins and essential oils from female cones are used for aroma [5]. Female hop flowers, also known as cones or hops, are primarily used in brewing beer; most of the bitter flavor and characteristic zesty beer aromas arise from hop cones added at various points during wort boiling, secondary fermentation, and the aging process [6]. At harvest, one-third is valuable product (hop cones) and two-thirds is leftover biomass, consisting primarily of leaves, stems, and unremoved hop cones [7].
However, the plant has been well-known for its beneficial properties for human health since ancient times. This is due to the plethora of its bioactive compounds (bitter acids, prenyl chalcones, polyphenols, terpenoids, etc.), which are mainly associated with the female inflorescences [8]. On addition to the application in the brewing industry, hop have for a long time been used for various medicinal purposes [9][10]. The beneficial effects of hop polyphenols in various chronic diseases, such as insomnia, inflammation, diabetes, as well as in menopause and as antifungal, have been scientifically proven in many studies [11][12]. In recent years, the antioxidant and anti-inflammatory activities of hop extracts have attracted attention and have been widely studied [9][13].

2. By-Products of H. lupulus

Millions of tons of residues are produced in the brewing process. On other hand, large amounts of vegetal material such as leaves, stems, and small-caliber cones are discarded in the harvest process. The recovery or extraction of high-value bioactive compounds from the by-products or non-used parts of H. lupulus in the brewing industry has been a strategy emphasized by the recent literature in order to solve this ecological and economical issue [14][15][16]. In fact, the by-products and parts of the plant discarded in the hops harvest are a source of potential nutritional and pharmacological compounds that could be used as functional and cosmetic ingredients [17]. The traditional methods using organic solvents have concerns related to the environment and also related to health. Still, new eco-friendly extraction methods should be developed to increase the yield and the selectivity of the compounds [14]. Natural, deep eutectic solvents and emerging extraction technologies such as ultrasound-assisted, microwave-assisted, pressurized liquid, and supercritical fluid extraction are emerging solutions to the sustainable extraction and isolation of natural compounds [2][18].
Many components of the hop by-products of interest are proteins, carbohydrates, fiber, phenolic compounds, vitamins, or minerals that have been explored for applications in the food industry [14][16] but less so for the development of skin care products.

2.1. Brewery By-Products

Generally, in beer production, chemical and biochemical reactions occur and the process involves the main stages of malting, mashing, lautering, boiling, fermenting, conditioning, filtering, and bottling [14]. During this process, spent grains, spent hops/hot trub, and spent yeast are produced, constituting the main marketable by-products with potential interest for the food, pharmaceutical, cosmetics, agriculture, and chemical industries.
Spent brewer’s grain is formed after the malt mashing process, and in some brewing regimens, some residues of hops are introduced during mashing. Spent brewer’s grain is the main solid brewery by-product (accounting for approx. 85% of all residues) which can be used wet and dry as direct animal feed or for further preparation of silage, both used specially for cattle but also for poultry, pigs, goats, and as fish food [14], and less frequently, it is used in human food [19]. Even so, large amounts of spent brewer’s grain are discarded despite it being rich in valuable compounds such as proteins (more than 20%), fiber, lipids and fatty acids, carbohydrates, polyphenols (mainly hidroxycinnamic acids), and minerals. In addition to that, it enhances aroma-binding properties and has gelling, emulsifying, and film-forming properties [19].
Approximately 85% of the hops constituents used by beer production become spent hop material. The hot trub are insoluble sediments formed during the wort boiling process [14].
These hops by-products (spent hops or hot trub) have been used as a fertilizer due to the high nitrogen content, as a low-grade fuel, and for animal feed when mixed with spent grain [20].
Although currently the possible markets for spent hops are restricted, hops constitute a by-product rich in interesting compounds such as proteins, lipids, polyphenols, minerals, flavors, carbohydrates, and organic acids [21].
Spent yeast is the second largest by-product from the brewing industry and is obtained after filtration or centrifuging. Originally applied as baker’s yeast, currently it is used as fertilizer and as a feedstock for fuel and industrial ethanol production and mixed with spent brewers’ grain as a feed material [22].
The chemical composition of spent yeast includes carbohydrates, free amino acids, ash, vitamins and minerals, and fatty acids; it also constitutes an excellent source of high-quality protein [22].

2.2. Non-Recovered Parts of H. lupulus

As only the hop cones have been used in the beer making industry, hop leaves are an agricultural by-product currently discarded as waste (like the stems and small-caliber cones that are discarded in the hop harvest process) [6].
Leaf sampling from wild-growing hop plants is a far simpler task than collecting cones, which are located up to 10 m off the ground in heavily wooded and overgrown areas and are only present late in the growing season. Additionally, male hop plants do not generate cones. Hop leaves are composed of flavanol glycosides (quercetin and kaempferol derivatives) ranging in total concentration from 0.28% to 2.77% dw (quercetin-3-O-rutinoside equivalents), although the total values are highly dependent on the phenological development stage, sampling date, and physical location [6]. The work of Macchioni et al. [4] showed the presence of significant quantities of soluble polyphenolic compounds and antioxidant pigments in the non-phenolic fraction of hop leaves.
Herbal products and/or it active compounds have been used has ingredients for cosmetic formulations. Recent scientific studies confirm the use of hop extracts for treating acne, loose skin, stretch marks, and sagging, preventing skin ageing and as hair cosmetics. As previous described, hop cones but also other parts of the plant or brewery by-products have been described as enriched in antioxidant, anti-inflammatory and anti-microbial compounds, being these properties crucial for skincare formulations. Other properties such as antioxidant protective effects in keratinocytes models, in vitro and cellular tyrosinase inhibition, intracellular melanin inhibition as well antiodor and antiacne effect.

References

  1. Committee on Herbal Medicinal Products Assessment report on Humulus lupulus L., flos. Eur. Med. Agency 2014, 44, 1–38.
  2. Astray, G.; Gullón, P.; Gullón, B.; Munekata, P.E.S.; Lorenzo, J.M. Humulus lupulus L. as a natural source of functional biomolecules. Appl. Sci. 2020, 10, 5074.
  3. Santagostini, L.; Caporali, E.; Giuliani, C.; Bottoni, M.; Ascrizzi, R.; Araneo, S.R.; Papini, A.; Flamini, G.; Fico, G. Humulus lupulus L. cv. Cascade grown in Northern Italy: Morphological and phytochemical characterization. Plant Biosyst. 2020, 154, 316–325.
  4. Macchioni, V.; Picchi, V. Hop Leaves as an Alternative Source of Health-Active Compounds: Effect of Genotype and Drying Conditions. Plants 2022, 11, 99.
  5. Almaguer, C.; Schönberger, C.; Gastl, M.; Arendt, E.K.; Becker, T. Humulus lupulus—A story that begs to be told. A review. J. Inst. Brew. 2014, 120, 289–314.
  6. Mccallum, J.L.; Nabuurs, M.H.; Gallant, S.T.; Kirby, C.W.; Mills, A.A.S. Phytochemical Characterization of Wild Hops (Humulus lupulus ssp. lupuloides) Germplasm Resources from the Maritimes Region of Canada. Front. Plant Sci. 2019, 10, 1438.
  7. Hrnčič, M.K.; Španinger, E.; Košir, I.J.; Knez, Ž.; Bren, U. Hop compounds: Extraction techniques, chemical analyses, antioxidative, antimicrobial, and anticarcinogenic effects. Nutrients 2019, 11, 257.
  8. Muzykiewicz, A.; Nowak, A.; Zielonka-brzezicka, J.; Duchnik, W.; Klimowicz, A. Comparison of antioxidant activity of extracts of hop leaves harvested in different years. Herba Pol. 2019, 65, 1–9.
  9. Zugravu, C.; Bohiltea, R.; Salmen, T.; Pogurschi, E. Antioxidants in Hops: Bioavailability, Health Effects and Perspectives for New Products. Antioxidants 2022, 11, 241.
  10. Liu, M.; Hansen, P.E.; Wang, G.; Qiu, L.; Dong, J.; Yin, H.; Qian, Z.; Yang, M.; Miao, J. Pharmacological profile of xanthohumol, a prenylated flavonoid from hops (Humulus lupulus). Molecules 2015, 20, 754–779.
  11. Inui, T.; Okumura, K.; Matsui, H.; Hosoya, T.; Kumazawa, S. Effect of harvest time on some In Vitro functional properties of hop polyphenols. Food Chem. 2017, 225, 69–76.
  12. Yan, Y.-F.; Wu, T.-L.; Du, S.-S. The Antifungal Mechanism of Isoxanthohumol from H. lupulus Linn. Int. J. Mol. Sci. 2021, 22, 10853.
  13. Wu, C.N.; Sun, L.C.; Chu, Y.L.; Yu, R.C.; Hsieh, C.W.; Hsu, H.Y.; Hsu, F.C.; Cheng, K.C. Bioactive compounds with anti-oxidative and anti-inflammatory activities of hop extracts. Food Chem. 2020, 330, 127244.
  14. Fărcaş, A.C.; Socaci, S.A.; Mudura, E.; Dulf, F.V.; Vodnar, D.C.; Tofană, M.; Salanță, L.C. Exploitation of Brewing Industry Wastes to Produce Functional Ingredients. Brew. Technol. 2017, 13, 137–156.
  15. Kerby, C.; Vriesekoop, F. An Overview of the Utilisation of Brewery By-Products as Generated by British Craft Breweries. Beverages 2017, 3, 24.
  16. Rachwał, K.; Waśko, A.; Gustaw, K.; Polak-berecka, M. Utilization of brewery wastes in food industry. PeerJ 2020, 8, e9427.
  17. del Río, J.C.; Prinsen, P.; Gutiérrez, A. Chemical composition of lipids in brewer’s spent grain: A promising source of valuable phytochemicals. J. Cereal Sci. 2013, 58, 248–254.
  18. Olivares-Galván, S.; Marina, M.L.; García, M.C. Extraction of valuable compounds from brewing residues: Malt rootlets, spent hops, and spent yeast. Trends Food Sci. Technol. 2022, 127, 181–197.
  19. Jackowski, M.; Niedźwiecki, Ł.; Jagiełło, K.; Uchańska, O.; Trusek, A. Brewer’s spent grains—valuable beer industry by-product. Biomolecules 2020, 10, 1669.
  20. Habschied, K.; Krstanovi, V.; Karlovi, A.; Juri, A. By-Products in the Malting and Brewing Industries—Re-Usage Possibilities. Fermentation 2020, 6, 82.
  21. Bravi, E.; De Francesco, G.; Sileoni, V.; Perretti, G.; Galgano, F.; Marconi, O. Brewing by-product upcycling potential: Nutritionally valuable compounds and antioxidant activity evaluation. Antioxidants 2021, 10, 165.
  22. Mussatto, S.I. Brewer’s spent grain: A valuable feedstock for industrial applications. J. Sci. Food Agric. 2014, 94, 1264–1275.
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Subjects: Plant Sciences
Contributors MDPI registered users' name will be linked to their SciProfiles pages. To register with us, please refer to https://encyclopedia.pub/register :
Olívia R. Pereira
,
Gleiciara Santos
,
Maria João Sousa
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Revisions: 2 times (View History)
Update Date: 22 Dec 2022
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