Hop Leaves as an Alternative Source of Health-Active Compounds: Effect of Genotype and Drying Conditions

Abstract

In hop cultivation, one-third of the crop is a valuable product (hop cones), and two-thirds is unexploited biomass, consisting mainly of leaves and stems, which, in a circular economy approach, can be recovered and, once stabilized, supplied to industrial sectors, such as cosmetics, pharmaceuticals and phytotherapy, with high added value. In this regard, this study aimed to investigate the effects of two different drying methods: oven drying (OD) at 45 °C and freeze-drying (FD), on the overall nutraceutical profile (i.e., total phenols, total flavans and total thiols), pigment content (i.e., carotenoids and chlorophylls) and the antioxidant potential of leaves from five different Humulus lupulus varieties grown in central Italy. Moreover, attenuated total reflectance infrared (ATR-FTIR) spectroscopy was applied to dried leaf powders to study the influence of both the variety and treatment on their molecular fingerprints. The spectral data were then analyzed by principal component analysis (PCA), which was able to group the samples mainly based on the applied treatment. Considering the overall phytochemical profile, FD appeared to be the most suitable drying method, while OD provided higher carotenoid retention, depending on the genotype considered. Finally, unsupervised chemometric tools (i.e., PCA and hierarchical clustering) revealed that the two main clusters contained subclusters based on the drying treatment applied; these subgroups were related to the susceptibility of the variety to the drying conditions studied.

Hop Extract Anti-Inflammatory Effect on Human Chondrocytes Is Potentiated When Encapsulated in Rapeseed Lecithin Nanoliposomes

“…It has been shown that several active molecules detected in hop may be considered for their antioxidant and/or antimicrobial activities. Among these compounds, prenylated polyphenols were shown to have many biological activities that might be useful for human health [ 27 , 28 , 31 , 41 ].…”

“…Hop plants ( Humulus lupulus L.) are cultivated for the brewing industry, where only female cones are considered valuable products due to the presence of bitter acids [ 27 ]. In the end, two-thirds of the plant (mainly leaves and stems) is unexploited, whereas the whole plant is known to contain a wide range of active biomolecules, such as anti-inflammatory compounds [ 28 , 29 ]. The valorization of other hop plant parts, such as leaves, might represent a real opportunity to improve OA [ 28 , 30 ], since hop compounds have already shown their efficacy in reducing inflammation in other pathologies [ 31 , 32 , 33 , 34 ].…”

“…In the end, two-thirds of the plant (mainly leaves and stems) is unexploited, whereas the whole plant is known to contain a wide range of active biomolecules, such as anti-inflammatory compounds [ 28 , 29 ]. The valorization of other hop plant parts, such as leaves, might represent a real opportunity to improve OA [ 28 , 30 ], since hop compounds have already shown their efficacy in reducing inflammation in other pathologies [ 31 , 32 , 33 , 34 ]. Furthermore, the valorization of hop leaves, considered an agricultural by-product and currently discarded as organic waste, might serve territorial bioeconomic purposes.…”

Antioxidants in Hops: Bioavailability, Health Effects and Perspectives for New Products

“…They take into account the studies regarding the antioxidant effects of hops’ components, correlated with the consumer’s desire to have products of natural origin. Moreover, in addition to hops fruits, the use of hops leaves with a high antioxidants content is also considered [ 85 ]. Of course, most of the new products benefit not only from the antioxidant effect, but also from other positive actions of the existing substances in hops, with convergent effects.…”

Hops Germplasm: Phytochemical Characterization of Wild Humulus lupulus of Central and Northern Italy

“…Regarding the polyphenolic component, in recent years, studies have shown the effectiveness of using hop extracts against some chronic-degenerative diseases, such as cancer and metabolic syndrome [9]. This perspective has prompted some researchers to investigate the use of agricultural waste from the hop harvest as a source of secondary metabolites for use in industries other than brewing, such as food, cosmetics, and pharmaceuticals [10]. Hop is a very widespread species in the wild state in Central and Northern Italy, but its cultivation is not strongly developed.…”