IJT - CIR - February 2024 - 8S

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International Journal of Toxicology 43(Supplement 1)
Table 2. Chemical and Physical Properties of Humulus Lupulus (Hops) Extract.
Property
Value
Physical Form
Color
Odor
Specific Gravity (@ 20oC)
Vapor Density (mmHg)
Melting Point (oC)
Water Solubility
Oil
Viscous liquida
Greenish-yellow-reddish brown
Yellow/orange to brown/greena
Harsh and bitter
Citrus, tropical fruit, stone fruit, pine, cedar, floral, spicy, herbal, earthy,
tobacco, onion/garlic and/or grassy
.883-.900
850-1100a
>1
40-60a
Negligible
Insolublea
aACO2 extract of dried cones manufactured for use as a food ingredient.
Preparation/Extraction
Humulus lupulus (hops). In general, when the strobiles are
harvested from Humulus lupulus (hops) bines for beer
production, the strobiles are immediately dried by forced
hot air, and are often pressed into dense cylindrical pellets, 5
to 8 mm in diameter and up to 25 mm long.17 The pelletization
reduces the overall surface area and therefore
reduces the rate of chemical oxidation/degradation, and
provides a more compact product for shipping. Not all
suppliers dry the strobiles; the strobiles may be harvested
fresh as whole, wet cones at the farm, and shipped for
immediate use within 36 h of harvest.23
Sometimes, hops are treated with sulfur dioxide to improve
the color and prevent change of active constituents.3
Methylene chloride is the most common solvent used for
the extraction of Humulus lupulus (hops) for beer brewing;
hexane and methanol are also employed.24 Typically, at least
95% of the available α-acids (source of the bitter flavorings)
can be extracted from fresh Humulus lupulus (hops) strobiles.
Methanol is the most efficient solvent for the extraction of
α-acids (approximately 25%), followed by methylene chloride
(approximately 20%) and hexane (approximately 18%).
Supercritical fluid extraction (SFE) with carbon dioxide is
also used to collect the extract for beer brewing.25-28 Another
modern method is pressurized fluid extraction (PFE), which is
employed for extracting different polyphenols.29-33 PFE has
been developed to extract bitter acids.
FDA regulations on the method of manufacture of
" modified hop extract, " as a food additive intended for use as a
flavoring agent in the brewing ofbeer, are provided in Table 3.
Six of the eight listed methods follow extraction with isomerization
of the extracted substance. The allowed solvents
include benzene, light petroleum spirits, methyl alcohol, nbutyl
alcohol, and ethyl acetate. [21CFR172.560]
In general, oils are extracted from Humulus lupulus (hops)
by steam distillation at 100°C.34
Humulus Lupulus (Hops) Extract. One manufacturer reported
that the method of manufacture of Humulus Lupulus (Hops)
Extract for use in cosmetics begins with extraction with water
and propylene glycol.35 The extract solution is then pressed,
clarified, and decontaminated. Further details were not
provided.
Another manufacturer reports that Humulus Lupulus
(Hops) Extract may be extracted with either a 50% volume
ethanol solution or a 50% volume butylene glycol solution.36
After the dried raw material (the flower head) is extracted with
the solution, the extract is filtered and concentrated. After
sedimentation, the filtrate is " adjusted " and packaged.
To manufacture a product mixture containing Humulus
Lupulus (Hops) Extract, dried whole strobiles of Humulus
lupulus (hops) are dispersed and solubilized with stirring in
caprylic/capric triglyceride.37 The solution is then filtered to
obtain the desired mixture.
Composition
Humulus lupulus (hops). The components of fresh and dried
Humulus lupulus (hops) strobiles/cones are listed in Table 4
and Table 5, respectivly.2,38 Analysis of dried food grade
Humulus lupulus (hops) strobiles grown for beer production
showed α-acids at 3.0 to 15.5% (w/w) and β-acids at 3.0 to
5.5% (w/w).23 Humulus lupulus (hops) bitter acids are
classified as either " α-acids " or " β-acids " that are, respectively,
di- or tri-prenylated phloroglucinol derivatives.
In addition, they each contain a 3-, 4-, 5-, or 6-carbon oxoalkyl
side chain.6,39 Historically, the α-acids were distinguished
because they precipitated from a crude extract of
hops with the addition of lead acetate. The β-acids, by
definition, would remain in solution. The α-acids, particularly
humulone (35 to 70% of total α-acids), cohumulone
(20 to 65%), and adhumulone (10 to 15%) are regarded as
the most important constituents determining the quality of
hops.6,39
Reference
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