Morphogenesis, volume and number of hop (Humulus lupulus L.) glandular trichomes, and their influence on alpha-acid accumulation in fresh bracts of hop cones

Abstract

The ESEM investigations revealed the morphogenesis of peltate glandular trichomes, which was divided into five phases. In phase one, new peltate glandular trichomes were initiated; in phase two, they were differentiated; in phase three trichomes grew vigorously; in phase four they were determined; in the fifth and final phase they came to maturity. Volume of glandular trichome during the different phases of morphogenesis varied from 0.25´10 -2 mm 3 in phase 1, to 1.95´10 -2 mm 3 in phase 5. More glandular trichomes are placed on the base of the adaxial side of bracts (average 7 mm -2 ) than on the base of abaxial side (average 5.8 mm -2 ). In this research, positive Spearman's rank order correlations were found between the average number of glandular trichomes and content of a-acids as well as between the average volume of glandular trichomes and content of a-acids.

Changes in the composition of hop secondary metabolites induced by high hydrostatic pressure

“…The contents of α and β acids (Saaz, Agnus, Vital), prenylflavonoid xanthohumol (Agnus, Vital) and DMX (Vital) for dried hops and pressurized homogenates, fresh and 12 months old, are summarized in Table . The data show that HPP homogenates retain more secondary metabolites than dried hops despite the fact that some losses of lupulin grains in dried hops can occur during drying as a result of mechanical shaking and disintegration of hop cones . The data show relatively large annual differences in the content of α and β acids and prenylflavonoids as a result of differing weather conditions during the growing season.…”

Empiric mathematical model for predicting the content of alpha-acids in hop (Humulus lupulus L.) cv. Aurora

“…This is also possible to explain with results of Pavlovič et al (2012), according to them, rainfall quantity from June 18 to July 22 shows the highest correlation with alpha-acid contents and impact of rainfall begins to decline after July 29. However, in time after July 29, the formation of glandular trichomes starts and the positive Spearman’s rank correlations were found between the average number of glandular trichomes and the content of alpha-acids (r s  = 0.90; p<0.05) and also between the average volume of glandular trichomes and content of alpha-acids (r s  = 0.97; p<0.05) (Srečec et al 2011). …”

Italian hop germplasm: Characterization of wild Humulus lupulus L. genotypes from Northern Italy by means of phytochemical, morphological traits and multivariate data analysis

“…Hop strobiles, and hop leaves to a very lesser extent, display a substantial density of hop glandular trichomes (lupulin), mostly located in the outer lower surface of bracteoles and in the whole surface of the female perianth (Kavalier et al, 2011;Srecec et al, 2011). These glands store an unique and complex pool of secondary metabolites biosynthesized in the foliar mesophyll, comprising both prenylflavonoids (e.g., xanthohumol), prenylphloroglucinols (known as bitter ␣-and ␤-acids, prevailing in bitter hops) and a volatile terpenic fraction (prevailing in aromatic or finishing hops) that confers a characteristic fragrance, extremely valuable in the brewing process (Kishimoto et al, 2006;Wang et al, 2008;Zanoli and Zavatti, 2008;Srecec et al, 2012).…”