Content uploaded by Roberto Ruggeri
Author content
All content in this area was uploaded by Roberto Ruggeri on Oct 13, 2020
Content may be subject to copyright.
agronomy
Article
Beyond Beer: Hop Shoot Production and
Nutritional Composition under Mediterranean
Climatic Conditions
Francesco Rossini 1, Giuseppe Virga 2, Paolo Loreti 1, Maria Elena Provenzano 1,*,
Pier Paolo Danieli 1and Roberto Ruggeri 1, *
1Department of Agriculture and Forest Sciences (DAFNE), University of Tuscia, Via San Camillo de Lellis,
01100 Viterbo, Italy; rossini@unitus.it (F.R.); loreti@unitus.it (P.L.); danieli@unitus.it (P.P.D.)
2Research Consortium for the Development of Innovative Agro-environmental Systems (CoRiSSIA),
Via della Libertà203, 90143 Palermo, Italy; giuseppe.virga@corissia.it
*Correspondence: provenzano.mariaelena@gmail.com (M.E.P.); r.ruggeri@unitus.it (R.R.);
Tel.: +39-0761-357561 (R.R.)
Received: 21 September 2020; Accepted: 7 October 2020; Published: 11 October 2020
Abstract:
For hop growers, surplus shoots are generally a useless by-product of cultivation.
Conversely, they may represent a valuable resource due to rising interest towards healthy and
traditional foods. A field trial was carried out in Central Italy to characterize shoot production
(number of emerged shoots, shoot fresh weight, marketable shoot yield, and shoot diameter) of
three commercial hop cultivars (Cascade, Challenger, and Hallertauer Magnum) and to survey
shoot proximate composition (ash, ether extract, crude protein, and crude fiber). Green shoots were
harvested when they were from 20 to 40 cm in length. The results from two years showed that there
was significant difference among the varieties and between growing seasons, both for yield traits and
for nutritional composition. H. Magnum showed the highest marketable shoot yield (152 g per plant,
two-year mean), while Cascade had the best proximate composition. The number of emerged shoots
per plant varied from 62.5 of Cascade to 84.3 of H. Magnum over a two-year average. Marketable
shoot yield showed a positive relationship with number of shoots and average shoot fresh weight,
while no significant correlation was found with shoot diameter. Hop shoots proved to be a low-fat
food (ether extract from 2 to 6% dry matter (DM)) with high protein (from 22 to 30% DM) and fiber
content (from 10 to 16% DM).
Keywords:
hop; Humulus lupulus L.; shoot yield; proximate composition; Cascade; Challenger;
Hallertauer Magnum
1. Introduction
Hop (Humulus lupulus L.) is a dioecious perennial climbing plant, and it is known mainly for its
use in the brewing industry.
Even though hop can grow between 35 and 50
◦
latitude in both hemispheres, commercial
production is traditionally limited to moist and temperate regions like central Europe and the Pacific
Northwestern United States [
1
–
3
]. In 2018, the world’s top hop-producing countries were USA,
Germany, and China; however, the USA and all European countries together shared about 88% of
world production [4].
While hop today is mainly grown for its female inflorescence (commonly known as cone but
formally defined as strobilus), it actually has a long history of being used for various medicinal,
household, and culinary purposes [
5
,
6
]. Similarly to asparagus, young hop shoots are eaten in spring,
which is one of the oldest and traditional uses of the plant [
7
]. Hop shoots are a delicate vegetable
Agronomy 2020,10, 1547; doi:10.3390/agronomy10101547 www.mdpi.com/journal/agronomy
Agronomy 2020,10, 1547 2 of 13
greatly sought after in most European countries [
8
]. In the Mediterranean region, foraging for wild hop
shoots is quite popular, thus different ways to cook them have been originated [
9
–
11
]. After boiling,
young shoots have low fat content (<0.2 g/100 g), energy value (25 kcal/100 g), and sodium content
(<40 g/100 g), whereas they are a good source of dietary fiber and vitamin B9 [
12
–
14
]. Moreover, wild
hop shoots have less than 67 mg/100 g of oxalic acid and high vitamin C levels (about 40 mg/100 g),
and thus they are a potential source of new functional ingredients in developing new foodstuffs [
14
].
Fresh green shoots have a short shelf life, so they should be consumed shortly or processed to store
them safely for a longer period (e.g., pickled hop shoots).
Developing wild edible plants through cultivation may be a winning strategy to meet the demand
of niche markets [15–17] and to limit overharvesting and loss of biodiversity [18–20].
Regardless of this commercial, nutritional, and conservation value, yield potential and nutritional
characteristics of wild edible plants are not yet fully explored, particularly in the Mediterranean
region [21].
Regarding shoot production in hops, many young shoots emerge from the mature overwintering
rootstock in early spring (Figure 1). Bine selection (from two to six per hill) and training are two
critical agronomic practices to optimize cone yield [
8
]. For growers and brewers, surplus shoots are a
worthless product of the hopyard, but for gastronomes they are among the world’s most expensive
vegetables. Their remarkable commercial value is due to limited availability (a few days in spring) and
the onerous harvest. Additionally, in a study conducted in Northern Italy, results pointed out that wild
hop shoots represent a new source of flavonols and can be incorporated in the diet as a functional food
or applied in the nutraceutical ambit [
22
]. Moreover, in Slovenia, white shoots from cultivated hop
were found to be better antioxidants than hop cones and leaves, without any problems of pesticide
residues [
23
]. Finally, use of young shoots as vegetables may represent a valuable additional source of
income for hop growers.
Agronomy 2020, 10, x FOR PEER REVIEW 3 of 19
incorporated in the diet as a functional food or applied in the nutraceutical ambit [22]. Moreover,
in Slovenia, white shoots from cultivated hop were found to be better antioxidants than hop cones
and leaves, without any problems of pesticide residues [23]. Finally, use of young shoots as
vegetables may represent a valuable additional source of income for hop growers.
Recently, proliferation of microbreweries in countries that were not typical hop producers (such
as those around the Mediterranean basin) has led to (i) an increasing trend in the consumption of
special beers and (ii) a growing interest in hop cultivation. In these new growing areas, very
limited knowledge is available on cultivated hop, though this species often belongs to local
spontaneous flora. Furthermore, while many studies have been conducted to investigate factors
affecting cone yield and quality [24–27], information is scarce on shoot production and
nutritional composition. According to our best knowledge, few studies aiming to characterize
shoot yield under Mediterranean climatic condition were conducted on wild hop [12,17,28] and
only one on cultivated hop [7]. This latter study was conducted on young plants (2- and 3-year-
old rootstocks), thus making necessary a further investigation to understand rootstock growth
over time.
The aim of the present study was to accurately characterize the shoot yield gathered from
cultivation of three commercial hop varieties in two subsequent years, under Mediterranean
climatic conditions.
Additionally, we surveyed shoot proximate composition to provide novel data for a nutritional
evaluation of the crop. Results from this study can help hop growers to better exploit the
economic potential of the hopyard, taking into account alternative uses of this versatile crop.
Figure 1. Hop shoots emerging from a rootstock.
Agronomy 2020,10, 1547 3 of 13
Recently, proliferation of microbreweries in countries that were not typical hop producers (such
as those around the Mediterranean basin) has led to (i) an increasing trend in the consumption of
special beers and (ii) a growing interest in hop cultivation. In these new growing areas, very limited
knowledge is available on cultivated hop, though this species often belongs to local spontaneous flora.
Furthermore, while many studies have been conducted to investigate factors affecting cone yield and
quality [
24
–
27
], information is scarce on shoot production and nutritional composition. According
to our best knowledge, few studies aiming to characterize shoot yield under Mediterranean climatic
condition were conducted on wild hop [
12
,
17
,
28
] and only one on cultivated hop [
7
]. This latter
study was conducted on young plants (2- and 3-year-old rootstocks), thus making necessary a further
investigation to understand rootstock growth over time.
The aim of the present study was to accurately characterize the shoot yield gathered from cultivation
of three commercial hop varieties in two subsequent years, under Mediterranean climatic conditions.
Additionally, we surveyed shoot proximate composition to provide novel data for a nutritional
evaluation of the crop. Results from this study can help hop growers to better exploit the economic
potential of the hopyard, taking into account alternative uses of this versatile crop.
2. Materials and Methods
2.1. Location, Experimental Design, and Hopyard Management
Field trials were carried out in Viterbo (42
◦
26
0
N, 12
◦
04
0
E, altitude 310 m above sea level) in
2017 and 2018 growing seasons. The site has a typical Mediterranean climate, with mean annual air
temperature of about 14.5
◦
C and total annual rainfall of 790 mm. For both years, weather data were
retrieved from the meteorological station located within 200 m from the experimental site, and they are
reported in Figure 2.
Agronomy 2020, 10, x FOR PEER REVIEW 5 of 19
Figure 2. Monthly mean maximum (Tmax), mean minimum (Tmin), and average (Tavg) air
temperature and rainfall during 2017 and 2018 growing seasons, as retrieved from the weather
station of the experimental farm of the University of Tuscia, Viterbo (Italy).
Table 1. List of hop cultivars used for the experiment, their harvest time, brewing use, and origin.
Cultivar Harvest Time Brewing Use Origin
Cascade M Dual purpose US
Challenger L Dual purpose UK
Hallertauer Magnum L Bittering Germany
Harvest time: M = medium; L = late.
2.3. Field Measurements
Shoots of all cultivars were harvested after completion of bine training. At harvest time, young
shoots generally had 5 or 6 nodes completely differentiated, and they were from 20 to 40 cm in
length. To avoid border effects, only shoots from the three central rootstocks in each plot were
used to assess marketable yield per plant (number of shoots and their fresh weight). Fresh shoots
from each rootstock were counted, labeled, cut at the marketable length of 20 cm, and weighed.
The average fresh shoot weight was determined by dividing the total fresh weight of shoots by
their number. A sub-sample of 10 shoots per replication was randomly chosen for determination
of single fresh weight and diameter. Shoot diameter was measured in the median portion of
shoots using a digital caliper.
2.4. Laboratory Analysis
Figure 2.
Monthly mean maximum (Tmax), mean minimum (Tmin), and average (Tavg) air temperature
and rainfall during 2017 and 2018 growing seasons, as retrieved from the weather station of the
experimental farm of the University of Tuscia, Viterbo (Italy).
Agronomy 2020,10, 1547 4 of 13
The experimental design was a randomized complete block with three replicates; treatments were
varieties. The hopyard was constructed in the spring of 2011 using a standard high trellis system with
a finished height of 8 m. Aircraft cable was used for trellis wires. The soil was tilled with a moldboard
plow, tilled again with a rotary tiller, and then planted with two hop rhizomes per hill (hereafter
referred to as plants) on 13 April 2011. Plants were distanced 1.5 m apart, and rows were spaced at
1.8 m. Each plot consisted of five consecutive plants. All varieties were planted in 2011. A rate of
150 kg ha
−1
of K
2
O was applied before soil tillage and 80 kg ha
−1
of P
2
O
5
at planting time, while N
was yearly split in two rates of 50 and 50 kg ha
−1
for spring (late March–early April) and late spring
(May–June) applications. The hopyard was not irrigated before shoot collection. Each year, rows were
trained with two plastic strings per plant, with two to four of the most vigorous bines trained per
string. During each growing season, weeds, pests, and pathogens were chemically controlled.
2.2. Plant Materials
Female plants of the three following cultivars were used: Cascade, Challenger, and Hallertauer
Magnum (hereafter referred to as H. Magnum). The varieties were selected from a wider list to include
a different range of earliness, origin, and brewing quality traits.
Their origin, indicative harvest time, and brewing use are reported in Table 1.
Table 1. List of hop cultivars used for the experiment, their harvest time, brewing use, and origin.
Cultivar Harvest Time Brewing Use Origin
Cascade M Dual purpose US
Challenger L Dual purpose UK
Hallertauer Magnum L Bittering Germany
Harvest time: M =medium; L =late.
2.3. Field Measurements
Shoots of all cultivars were harvested after completion of bine training. At harvest time, young
shoots generally had 5 or 6 nodes completely differentiated, and they were from 20 to 40 cm in length.
To avoid border effects, only shoots from the three central rootstocks in each plot were used to assess
marketable yield per plant (number of shoots and their fresh weight). Fresh shoots from each rootstock
were counted, labeled, cut at the marketable length of 20 cm, and weighed. The average fresh shoot
weight was determined by dividing the total fresh weight of shoots by their number. A sub-sample of
10 shoots per replication was randomly chosen for determination of single fresh weight and diameter.
Shoot diameter was measured in the median portion of shoots using a digital caliper.
2.4. Laboratory Analysis
The proximate composition of hop shoots was determined for the different cultivars. All analytical
determinations were performed twice. Gravimetric measurements were carried out by using a PE160
analytical scale (Mettler Toledo S.p.A., Novate Milanese, Italy). The dry matter content (DM) of the
samples was determined according to the AOAC method n. 934.01 [
24
]. Gravimetric determination
of ash content (ASH) was obtained after sample incineration by a muffle furnace model VISM 96
(Vismara s.r.l., Trezzano sul Naviglio, Italy) (AOAC method n. 942.05) [
24
]. Crude protein (CP) was
assessed through the Kjeldahl method (AOAC method n. 978.04), and ether extract (EE) was obtained
by Soxhlet extraction (AOAC method n. 920.39) [
24
]. Crude fiber (CF) was estimated through the
Weende method (AOAC method n. 978.10) by boiling a 1 g sample aliquot for 45 min in 100 mL of
H
2
SO
4
0.26 N, followed by a forty-five minutes extraction in 100 mL boiling NaOH (0.31 M) in an
ANKOM 200 Fiber Analyzer (ANKOM Technology, Macedon, NY, USA) [
24
]. All compositional data
were expressed as percent on dry matter (%DM).
Agronomy 2020,10, 1547 5 of 13
2.5. Statistical Analysis
Data were subjected to analysis of variance (ANOVA) using R 3.4.4 software [
25
] in order to test the
main effects of year, cultivar, and their interaction. Significantly different means were separated at the
0.05 probability level by the Fisher’s least significant differences test. Simple linear regression analysis
was carried out to investigate the relationship between number of shoots and the other variables (e.g.,
shoot yield, fresh shoot weight, and shoot diameter).
3. Results
3.1. Shoot Yield Characterization
The number of emerged shoots was not affected by cultivar
×
year interaction, whereas ANOVA
showed a significant cultivar (p=0.026) and year (p=7.49
×
10
−5
) effect (Tables 2and 3). In 2017,
the number of shoots picked up per plant ranged from 37.3 of Challenger to 74 of Cascade, with an
average of 51.7 shoots per plant. In 2018, the average number of shoots was 89.8 per plant, varying
from 81.3 of Cascade to 94.7 of H. Magnum. The two-year average showed H. Magnum to be the best
performing cultivar, producing 84.3 shoots per plant, while Cascade and Challenger reached a similar
result (62.5 and 65.3 shoots per plant, respectively).
Table 2.
Number of shoots before training, average shoot weight (FW), average shoot weight (DW),
marketable shoot yield (FW), and shoot diameter. Year
×
cultivar interaction. Means
±
standard error.
Year Cultivar Emerged Shoots
(no. plant−1)
Shoot FW
(g)
Shoot DW
(g)
Marketable Shoot Yield
(g plant−1)
Shoot Diameter
(mm)
2017 Cascade 43.67 ±3.38 2.04 ±1.14 0.30 ±0.018 90.08 ±12.31 2.10 ±0.07
Challenger 37.33 ±10.87 1.48 ±0.06 0.18 ±0.009 56.56 ±19.04 1.25 ±0.03
H. Magnum 74.00 ±7.94 2.77 ±0.02 0.29 ±0.003 205.21 ±23.76 1.91 ±0.05
2018 Cascade 81.33 ±3.38 1.02 ±0.03 0.08 ±0.003 82.74 ±1.21 1.16 ±0.01
Challenger 93.33 ±4.98 0.92 ±0.07 0.08 ±0.007 86.26 ±7.37 1.40 ±0.02
H. Magnum 94.67 ±8.21 1.04 ±0.07 0.09 ±0.007 99.08 ±12.90 1.65 ±0.07
ANOVA signif. ns *** *** *** ***
LSD (p<0.05) - 0.25 0.03 0.25 0.16
FW: fresh weight; DW: dry weight; ANOVA signif. codes: 0 ‘***’ 0.001; ns: not significant.
Table 3.
Number of shoots before training, average shoot weight (FW), average shoot weight
(DW), marketable shoot yield (FW), and shoot diameter. Cultivar and year mean values.
Means ±standard error.
Treatments Emerged Shoots
(no. plant−1)
Shoot FW
(g)
Shoot DW
(g)
Marketable Shoot Yield
(g plant−1)
Shoot Diameter
(mm)
Cultivar
Cascade 62.50 ±8.69 1.53 ±0.24 0.19 ±0.048 86.41 ±5.77 1.63 ±0.21
Challenger 65.33 ±13.62 1.20 ±0.13 0.13 ±0.024 71.41 ±11.29 1.32 ±0.04
H. Magnum 84.33 ±6.89 1.91 ±0.39 0.19 ±0.045 152.15 ±26.63 1.78 ±0.07
ANOVA signif. * *** *** *** ***
LSD (p<0.05) 16.17 0.18 0.02 34.18 0.12
Year
2017 51.67 ±6.93 2.10 ±0.19 0.26 ±0.019 117.28 ±24.42 1.75 ±0.13
2018 89.78 ±3.62 0.99 ±0.04 0.08 ±0.004 89.36 ±4.97 1.40 ±0.07
ANOVA signif. *** *** *** * ***
FW: fresh weight; DW: dry weight; ANOVA signif. codes: 0 ‘***’ 0.001 ‘*’ 0.05.
As shown in Table 2, a significant cultivar
×
year interaction (p=0.0001) was found for average
fresh shoot weight, which ranged from 0.92 g for Challenger in 2018 to 2.77 of H. Magnum in 2017.
All cultivars showed a significant decrease in average shoot weight, moving from 2017 to 2018.
Specifically, shoot weight was lower by 50% for cultivar (cv) Cascade (2.04 vs. 1.02 g), 38% for
Challenger (1.48 vs. 0.92 g), and 62% for H. Magnum (2.77 vs. 1.04 g). Despite this, the two-year
Agronomy 2020,10, 1547 6 of 13
average showed that H. Magnum was the top performing cultivars for this trait (1.91 g, Table 3),
followed by Cascade (1.53 g) and Challenger (1.20 g).
A significant cultivar
×
year interaction was also detected for marketable shoot yield (p=0.0035,
Table 2).
Shoot yield was not significantly different over the two-year period, except for H. Magnum,
whose yield was 52% lower in 2018 than in 2017 (Table 2). The top yielding variety was H. Magnum
(about 152 g per plant), while Cascade and Challenger showed similar yields: 86 and 71 g per plant,
respectively (Table 3).
Cultivar
×
year interaction significantly affected shoot diameter (p=3.72
×
10
−6
, Table 2),
which ranged from 1.16 to 2.10 mm for Cascade in 2018 and 2017, respectively. Cascade and H.
Magnum showed a significant decrease in shoot diameter moving from 2017 to 2018 (
−
45 and
−
14%, respectively), while Challenger, in the same period, weakly increased shoot diameter (+12%,
not significant).
3.2. Relationship among Shoot Traits
Figure 3shows the relationship between marketable shoot yield and number of emerged shoots
(A), average fresh shoot weight (B), and shoot diameter (C) in the two growing seasons. Marketable
shoot yield was positively and significantly related with both number of shoots per plant and fresh
shoot weight in both years, whereas no relation was found with shoot diameter.
Agronomy 2020, 10, x FOR PEER REVIEW 9 of 19
Figure 3. Relationship between marketable shoot yield and (A) number of emerged shoots, (B)
average shoot fresh weight (FW), and shoot diameter (C) in two growing seasons. Signif. codes:
0 ‘***’ 0.001 ‘*’ 0.05; ns: not significant.
Figure 3.
Relationship between marketable shoot yield and (
A
) number of emerged shoots, (
B
) average
shoot fresh weight (FW), and shoot diameter (
C
) in two growing seasons. Signif. codes: 0 ‘***’ 0.001
‘*’ 0.05; ns: not significant.
Agronomy 2020,10, 1547 7 of 13
This was because shoot diameter was related neither with number of shoots nor with fresh shoot
weight (Figures 4and 5). Generally, fresh weight of single shoot was negatively related with number
of emerged shoots, even though this relation was significant only for Cascade (Figure 6).
Agronomy 2020, 10, x FOR PEER REVIEW 10 of 19
Figure 4. Relationship between average shoot fresh weight (FW) and shoot diameter of (A)
Cascade, (B) Challenger, and (C) H. Magnum in two growing seasons. ns: not significant.
Figure 4.
Relationship between average shoot fresh weight (FW) and shoot diameter of (
A
) Cascade,
(B) Challenger, and (C) H. Magnum in two growing seasons. ns: not significant.
Agronomy 2020, 10, x FOR PEER REVIEW 10 of 19
Figure 4. Relationship between average shoot fresh weight (FW) and shoot diameter of (A)
Cascade, (B) Challenger, and (C) H. Magnum in two growing seasons. ns: not significant.
Figure 5.
Relationship between number of emerged shoots and shoot diameter in two growing seasons.
ns: not significant.
Agronomy 2020,10, 1547 8 of 13
Agronomy 2020, 10, x FOR PEER REVIEW 11 of 19
Figure 5. Relationship between number of emerged shoots and shoot diameter in two growing
seasons. ns: not significant.
Figure 6. Relationship between number of emerged shoots and averaged shoot fresh weight (FW)
of the three hop cultivars under study. Signif. codes: 0.01 ‘*’ 0.05; ns: not significant.
3.3. Proximate Composition
Proximate analysis and organic acid content of hop shoots are reported in Tables 4 and 5.
Generally, shoot moisture was significantly higher in 2018 than 2017. Significant cultivar × year
interaction was observed. Specifically, shoot moisture was significantly different among the three
varieties in 2017 (from 85.5% of Cascade to 89.4% of H. Magnum), while no statistical
difference was detected in 2018 (from 90.9% of H. Magnum to 91.9% of Cascade).
Ash content was not affected by cultivar × year interaction, whereas ANOVA showed significant
cultivar (p = 0.00096) and year (p = 2.75 × 10−9) effect. In 2017, ash content of the shoots ranged
from 10.6% DM in Challenger to 11.6% DM in Cascade, with an average of 11% DM. In 2018,
the average ash content was 8.3% DM, varying from 8.1% DM of Challenger to 8.7% DM of
Cascade. The two-year average showed that Cascade shoots had the highest ash content (10.2%
DM), while H. Magnum and Challenger showed a similar result (9.5 and 9.3% DM,
respectively).
Both EE and CF were affected by cultivar × year interaction (p = 1.63 × 10−7 and 5.12 × 10−6,
respectively), whereas ANOVA showed significant cultivar (p = 0.0005) and year (p = 7.32 ×
10−5) effect for the CP content. Overall, EE and CF were significantly higher in 2017 than in
2018, whereas CP showed an opposite trend (+16% DM in 2018, averaged over cultivars).
H. Magnum had an EE significantly higher than the other two varieties in both years, followed by
Challenger and then Cascade. Crude proteins ranged from 21.6% DM for Challenger in 2017 to
30% DM for H. Magnum and Cascade in 2018. Both the latter cultivars, averaged over years, had
Figure 6.
Relationship between number of emerged shoots and averaged shoot fresh weight (FW) of
the three hop cultivars under study. Signif. codes: 0.01 ‘*’ 0.05; ns: not significant.
3.3. Proximate Composition
Proximate analysis and organic acid content of hop shoots are reported in Tables 4and 5.
Table 4.
Moisture and proximate composition of hop shoots. Year
×
cultivar interaction. Means
±
standard error.
Year Cultivar Moisture
(%)
Ash
(% DM)
EE
(% DM)
CP
(% DM)
CF
(% DM)
2017 Cascade 85.5 ±0.1 11.64 ±0.21 3.88 ±0.07 27.04 ±0.46 16.48 ±0.06
Challenger 87.6 ±0.4 10.56 ±0.25 4.03 ±0.04 21.56 ±0.14 14.15 ±0.08
H. Magnum 89.4 ±0.6 10.73 ±0.28 6.30 ±0.12 26.75 ±0.83 12.23 ±0.34
2018 Cascade 91.9 ±0.05 8.71 ±0.18 1.71 ±0.02 30.01 ±0.14 11.27 ±0.28
Challenger 91.4 ±0.05 8.10 ±0.14 2.05 ±0.02 27.38 ±1.50 10.36 ±0.15
H. Magnum 90.9 ±0.05 8.17 ±0.07 2.61 ±0.02 30.00 ±0.44 11.26 ±0.28
ANOVA signif. ** ns *** ns ***
LSD (p<0.05) 1.06 - 0.20 - 0.66
Moisture =100
−
DM%; ASH =crude ash; EE =ether extract; CP =crude protein; CF =crude fiber. DM =dry
matter; ANOVA signif. codes: 0 ‘***’ 0.001 ‘**’ 0.01; ns: not significant.
Table 5.
Moisture and proximate composition of hop shoots. Cultivar and year mean values. Means
±
standard error.
Treatments Moisture
(%)
Ash
(% DM)
EE
(% DM)
CP
(% DM)
CF
(% DM)
Cultivar
Cascade 88.68 ±1.83 10.18 ±0.67 2.79 ±0.49 28.52 ±0.70 13.88 ±1.17
Challenger 89.48 ±1.09 9.33 ±0.56 3.04 ±0.44 24.47 ±1.47 12.26 ±0.85
H. Magnum 90.13 ±0.49 9.45 ±0.59 4.45 ±0.83 28.37 ±0.84 11.75 ±0.29
ANOVA signif. * *** *** *** ***
LSD (p<0.05) 0.87 0.37 0.14 1.70 0.46
Year
2017 87.50 ±0.74 10.98 ±0.21 4.73 ±0.39 25.11 ±0.93 14.29 ±0.62
2018 91.35 ±0.18 8.33 ±0.12 2.12 ±0.13 29.13 ±0.63 10.96 ±0.19
ANOVA signif. *** *** *** *** ***
Moisture =100
−
DM%; ASH =crude ash; EE =ether extract; CP =crude protein; CF =crude fiber. DM =dry
matter; ANOVA signif. codes: 0 ‘***’ 0.001 ‘*’ 0.05.
Agronomy 2020,10, 1547 9 of 13
Generally, shoot moisture was significantly higher in 2018 than 2017. Significant cultivar
×
year
interaction was observed. Specifically, shoot moisture was significantly different among the three
varieties in 2017 (from 85.5% of Cascade to 89.4% of H. Magnum), while no statistical difference was
detected in 2018 (from 90.9% of H. Magnum to 91.9% of Cascade).
Ash content was not affected by cultivar
×
year interaction, whereas ANOVA showed significant
cultivar (p=0.00096) and year (p=2.75
×
10
−9
) effect. In 2017, ash content of the shoots ranged from
10.6% DM in Challenger to 11.6% DM in Cascade, with an average of 11% DM. In 2018, the average
ash content was 8.3% DM, varying from 8.1% DM of Challenger to 8.7% DM of Cascade. The two-year
average showed that Cascade shoots had the highest ash content (10.2% DM), while H. Magnum and
Challenger showed a similar result (9.5 and 9.3% DM, respectively).
Both EE and CF were affected by cultivar
×
year interaction (p=1.63
×
10
−7
and 5.12
×
10
−6
,
respectively), whereas ANOVA showed significant cultivar (p=0.0005) and year (p=7.32
×
10
−5
)
effect for the CP content. Overall, EE and CF were significantly higher in 2017 than in 2018, whereas
CP showed an opposite trend (+16% DM in 2018, averaged over cultivars).
H. Magnum had an EE significantly higher than the other two varieties in both years, followed by
Challenger and then Cascade. Crude proteins ranged from 21.6% DM for Challenger in 2017 to 30%
DM for H. Magnum and Cascade in 2018. Both the latter cultivars, averaged over years, had a similar
CP content (28% DM), significantly higher than that of Challenger (24% DM). Cascade showed the
highest crude fiber percentage in 2017, followed by Challenger and H. Magnum, whereas in 2018 H.
Magnum and Cascade reached a similar fiber content (11.3% DM), significantly higher than that of
Challenger (10.4% DM).
4. Discussion
4.1. Shoot Production
Comparing results obtained from the present study with those reported by Ruggeri et al. [
7
] that
sampled the same plants but younger (2 and 3 years old), we can obtain interesting information about
rootstock growth in the Mediterranean environment. Cascade and H. Magnum increased the average
number of emerged shoots by 118% (28.7 vs. 62.5) and 260% (23.3 vs. 84.3), respectively, moving
from 2/3-year-old plants (2013 and 2014) to 6/7-year old plants (2017 and 2018). Challenger was not
present in that previous study. In the present study, H. Magnum was the top shoot producing cultivar,
whereas sampling younger plants, Ruggeri et al. [
7
] found Cascade to be the best performing variety.
The earlier sprouting, flowering, and maturing cultivar Cascade adapted to the Mediterranean climate
faster and better than the other two cultivars [
26
], and this may have caused an advantage for the
growth of rootstock in the early years.
As for average fresh weight of the single shoot, Cascade and H. Magnum increased their average
values by 17% (1.31 vs. 1.53 g) and 91% (1.00 vs. 1.91 g), respectively, moving from 2/3-year-old plants
(2013 and 2014) to 6/7-year-old plants (2017 and 2018). Moreover, we observed a marked reduction
of fresh shoot weight (
−
53%) moving from 2017 to 2018, while, in the same period, the number of
shoots per plant increased by 74%. In the previous study [
7
], we did not find this negative relationship
because the number of emerged shoots varied very little (7%, from 20.5 to 19), and average fresh
weight of the single shoot remained substantially unchanged (from 1.15 to 1.16 g). Our results are
in agreement with data recorded in other field experiments on Asparagus officinalis L. carried out in
southern Italy [
27
]. Conversely, average spear weight of wild asparagus (Asparagus acutifolius L.)
was found not to be affected by spear number [
15
]. We compare our results with those obtained on
asparagus because no characterization of shoot production was found in the literature for cultivated
hops. In our study, the mean weight of 20 cm shoots averaged over years (from 1.20 g of Challenger
to 1.91 g of H. Magnum) was in the range of that found by Molina [
28
] in Spain, collecting 15–30 cm
shoots from wild plants in three years and two sites (from 1.22 to 2.48 g). We expected a higher fresh
weight from cultivated hop; however, since the method of collection was very different, we can gather
Agronomy 2020,10, 1547 10 of 13
a simple indication from this comparison. In the study by Molina [
28
], wild shoots were collected in
different days from late March to May, thus causing less competition for rootstock reserves among
shoots and probably increasing the average single shoot weight.
The marketable yields gathered in our study (from 71 to 152 g per plant, 2-year mean) were
markedly higher than those recorded for white hop shoots harvested in Slovenia [23]. In more detail,
H. Magnum yielded 5.9 g DM per plant in Slovenia (3-year mean), while it produced 15 g DM per plant
(2-year mean) in the present study (152.15 g fresh weight (FW) per plant at 90.13% moisture). This can
be justified considering that white hop shoots are collected before they emerge from the soil, thus being
still fragile, shorter, and lighter than green hop shoots. In their study, [
23
] reported that each plant root
system had from 15 to 40 white shoots, with the mean fresh mass of each shoot approximately 1 g.
Looking at the variation over a longer time of the marketable shoot yield (from 2013–2014 to 2017–2018),
Cascade and H. Magnum increased production by 133% (37.14 g per plant vs. 86.41 g per plant) and
564% (23.3 g per plant vs. 84.3 g per plant), respectively. This enormous variation proves the excellent
adaptation of these two cultivars to the Mediterranean climate. As expected, and in agreement with
the previous study on younger plants, marketable yield was positively and significantly related to
number of emerged shoots [
7
]. In the present study, we also found a significant and positive relation
with the fresh weight of the single shoot that was not detected four years earlier [
7
]. Unexpectedly,
we did not find any relation between the fresh weight of the single shoot and its diameter. The reason
has to be searched in hop morphology because this species has bines with a hollow core between nodes.
This peculiarity makes the positive relationship normally existing between spear diameter and fresh
weight of A. officinalis [
29
] not applicable to hop. In fact, the hop shoots with a higher diameter are
often those with larger hollow core, while thinner ones are generally less hollow.
4.2. Proximate Composition
Moisture and proximate composition found in the present study is perfectly in the range shown
for wild hop shoots harvested in Spain [
30
], with the exception of fiber. Tard
í
o et al. [
30
] reported a
range of dietary fiber from 4.35 to 6.42% FW (from 30.5% to 44.9% DM) while, in our study, crude fiber
content, averaged over years, varied from 11.8% DM of H. Magnum to 13.9% DM of Cascade. It must
be noted that crude fiber is only one component of dietary fiber, primarily composed of cellulose and
lignin. In more detail, constituents of dietary fiber include cellulose, hemicelluloses, lignin, gums,
mucilage, oligosaccharides, pectin, and other associated minor substances [
31
]. For this reason, crude
fiber may grossly underestimate the actual dietary fiber content in foodstuff, but it can help in making
intra-study comparison, as in our case.
Shoot moisture was significantly higher in 2018 than 2017 (91.4 vs. 87.5%). This was probably due
to the different groundwater availability before and during shoot emergence. Rainfall amount from
February to April 2017 was 114 mm (
−
37% with respect to the long-term average), while in the same
period of 2018 it was more than double (328 mm). For the same reason, shoots picked in 2017 were more
fibrous than those harvested in 2018. Reduced water availability was already found to significantly
enhance fiber content in vegetables [
32
,
33
]. EE was also significantly higher in drought conditions of
2017 than the 2018 growing season. In this regard, it has to be said that various environmental stresses
may release a lipid-mediated signal. To mitigate such stresses, enhanced syntheses of lipids are often
observed in different plants [34].
Conversely, crude protein content increased in the 2018 rainy season as compared to the
2017 drought season. Previous studies have demonstrated that drought can decrease the protein
concentration of plant tissues, mainly for a decrease in nitrogen uptake from the soil [
35
,
36
]. The ash
content significantly decreased in the 2018 rainy season as compared with the 2017 drought season.
We actually expected an opposite trend, as a result of reduced nutrient availability and uptake in the
drought season [
37
]. However, heavy rainfall occurred before and during shoot emergence (+82%
with respect to the long-term average), which may have caused a significant soil nutrient leaching,
only partially replaced by nitrogen fertilization.
Agronomy 2020,10, 1547 11 of 13
A significant year effect on proximate composition of wild hop shoots was also reported by Garc
í
a
Herrera [12] in Spain, but the author did not describe the weather pattern of the two years.
5. Conclusions
In the present study, all traits investigated (number of emerged shoots, shoot fresh and dry weight,
marketable shoot yield, shoot diameter, moisture, ash, ether extract, crude protein, and crude fiber
content) were significantly affected by genotype and year.
Marketable shoot yield was positively correlated with shoot number and fresh weight, whereas
no correlation was found with shoot diameter. Averaged over the two years, H. Magnum was the top
performing cultivar for all traits analyzed of shoot production, while Cascade and Challenger showed
similar results.
As for nutritional composition, hop shoots are confirmed to have low lipid content and to be a
good source of proteins and fiber. From this point of view, Cascade seems to be the cultivar with the
better-quality traits.
These results, coupled with those on shoot and cone yield reported in previous studies [
7
,
26
],
suggest that Cascade and H. Magnum adapt well to the Mediterranean climatic condition and could
represent the best choice for new hopyard establishment in those environments.
Further studies should deeper investigate the chemical composition of hop shoots deriving from
different commercial varieties (organic acid content, flavonols, vitamins, and antioxidant properties) in
order to better understand and assess their potential benefits for human health.
Cone production and quality in different growing environments should be also characterized.
Author Contributions:
Conceptualization, F.R., P.L., and R.R.; methodology, P.P.D., P.L., and R.R.; formal analysis,
F.R., M.E.P., and G.V.; investigation, F.R., P.L., and R.R.; resources, F.R., R.R., P.L., and P.P.D.; data curation, R.R.;
writing—original draft preparation, R.R.; writing—review and editing, R.R., F.R., P.P.D., P.L., M.E.P., and G.V.;
supervision, F.R. All authors have read and agreed to the published version of the manuscript.
Funding: This research received no external funding.
Acknowledgments:
The authors wish to acknowledge Albino Balletti (Department of Agriculture and Forest
Sciences, DAFNE, University of Tuscia) for the technical support provided.
Conflicts of Interest: The authors declare no conflict of interest.
References
1.
Haunold, A. Hop Production, Breeding, and Variety Development in Various Countries. J. Am. Soc. Brew.
Chem. 1981,39, 27–34. [CrossRef]
2.
Mahaffee, W.F.; Pethybridge, S. The genus Humulus. In Compendium of Hop Diseases and Pests; Mahaffee, W.F.,
Pethybridge, S., Gent, D.H., Eds.; The American Phytopatological Society: St. Paul, MN, USA, 2009; pp. 1–5.
3.
Turner, S.F.; Benedict, C.A.; Darby, H.; Hoagland, L.A.; Simonson, P.; Robert Sirrine, J.; Murphy, K.M.
Challenges and opportunities for organic hop production in the United States. Agron. J.
2011
,103, 1645–1654.
[CrossRef]
4.
FAOSTAT Production Quantities of Hops by Country. 2018. Available online: http://www.fao.org/faostat/en/
#data/QC/visualize (accessed on 3 October 2020).
5.
Bocquet, L.; Sahpaz, S.; Hilbert, J.L.; Rambaud, C.; Rivi
è
re, C. Humulus lupulus L., a Very Popular Beer
Ingredient and Medicinal Plant: Overview of Its Phytochemistry, Its Bioactivity, and Its Biotechnology.
Phytochem. Rev. 2018,17, 1047–1090. [CrossRef]
6.
Small, E.; Catling, P.M. Canadian Medicinal Crops; NRC Research Press: Ottawa, ON, Canada, 1999;
ISBN 0-660-17534-7.
7.
Ruggeri, R.; Loreti, P.; Rossini, F. Exploring the potential of hop as a dual purpose crop in the Mediterranean
environment: Shoot and cone yield from nine commercial cultivars. Eur. J. Agron.
2018
,93, 11–17. [CrossRef]
8. Neve, R.A. Hops; Chapman & Hal: London, UK, 1991; ISBN 9789401053754.
Agronomy 2020,10, 1547 12 of 13
9.
di Tizio, A.; Luczaj, L.J.; Quave, C.L.; Redzic, S.; Pieroni, A. Traditional food and herbal uses of wild plants in
the ancient South-Slavic diaspora of Mundimitar/Montemitro (Southern Italy). J. Ethnobiol. Ethnomed.
2012
,
8, 1–10. [CrossRef]
10.
Hadjichambis, A.C.; Paraskeva-hadjichambi, D.; Della, A.; Elena Giusti, M.; Pasquale, C.D.E.; Lenzarini, C.;
Censorii, E.; Reyes Gonzales-Tejero, M.; Patricia Sanchez-Rojas, C.; Ramiro-gutierrez, J.M.; et al. Wild and
semi-domesticated food plant consumption in seven circum-Mediterranean areas. Int. J. Food Sci. Nutr.
2008
,
59, 383–414. [CrossRef]
11.
Tardio, J.; Pardo-de-Santayana, M.; Morales, R. Ethnobotanical review of wild edible plants in Spain. Bot. J.
Linn. Soc. 2006,152, 27–71. [CrossRef]
12.
Garc
í
a Herrera, P. Plantas Silvestres de Consumo Tradicional en España: Caracterizaci
ó
n de su Valor
Nutricional y Estimaci
ó
n de su Actividad Antif
ú
ngica. Ph.D. Thesis, Universidad Complutense de Madrid,
Madrid, Spain, 2014.
13.
Morales G
ó
mez, P. Vegetales Silvestres de uso Alimentario: Determinaci
ó
n de Compuestos Bioactivos y
Valoraci
ó
n de la Capacidad Antioxidante. Ph.D. Thesis, Universidad Complutense de Madrid, Madrid
Spain, 2011.
14.
Sanchez-Mata, M.C.; Cabrera Loera, R.D.; Morales, P.; Fernandez-Ruiz, V.; Camara, M.; Diez Marqu
é
s, C.;
Pardo-de-Santayana, M.; Tardio, J. Wild vegetables of the Mediterranean area as valuable sources of bioactive
compounds. Genet. Resour. Crop Evol. 2012,59, 431–443. [CrossRef]
15.
Benincasa, P.; Tei, F.; Rosati, A. Plant density and genotype effects on wild asparagus (Asparagus acutifolius L.)
spear yield and quality. HortScience 2007,42, 1163–1166. [CrossRef]
16.
D’Antuono, L.F.; Lovato, A. Germination trials and domestication potential of three native species with
edible sprouts: Ruscus aculeatus L., Tamus communis L. and Smilax aspera L. Acta Hortic.
2003
,598, 211–218.
[CrossRef]
17.
Molina, M.; Pardo-de-Santayana, M.; Tard
í
o, J. Natural Production and Cultivation of Mediterranean Wild
Edibles. In Mediterranean Wild Edible Plants; S
á
nchez-Mata, M.D.C., Tard
í
o, J., Eds.; Springer: New York, NY,
USA, 2016; pp. 81–107. ISBN 978-1-4939-3329-7.
18. Kling, J. Protecting medicine’s wild pharmacy. Nat. Plants 2016,2. [CrossRef] [PubMed]
19.
Ceccanti, C.; Landi, M.; Benvenuti, S.; Pardossi, A.; Guidi, L. Mediterranean Wild Edible Plants: Weeds or
“New functional crops”? Molecules 2018,23, 2299. [CrossRef] [PubMed]
20.
Scarici, E.; Ruggeri, R.; Provenzano, M.E.; Rossini, F. Germination and performance of seven native
wildflowers in the Mediterranean landscape plantings. Ital. J. Agron. 2018,13, 163–171. [CrossRef]
21.
Molina, M.; Tard
í
o, J.; Aceituno-mata, L.; Morales, R.; Reyes-garc
í
a, V.; Pardo-de-santayana, M. Weeds
and Food Diversity: Natural Yield Assessment and Future Alternatives for Traditionally Consumed Wild
Vegetables. J. Ethnobiol. 2014,34, 44–67. [CrossRef]
22.
Maietti, A.; Brighenti, V.; Bonetti, G.; Tedeschi, P.; Prencipe, F.P.; Benvenuti, S.; Brandolini, V.; Pellati, F.
Metabolite profiling of flavonols and
in vitro
antioxidant activity of young shoots of wild Humulus lupulus L.
(hop). J. Pharm. Biomed. Anal. 2017,142, 28–34. [CrossRef]
23.
Vidmar, M.; ˇ
Ceh, B.; Demšar, L.; Ulrih, N.P. White Hop Shoot Production in Slovenia: Total Phenolic,
Microelement and Pesticide Residue Content in Five Commercial Cultivars. Food Technol. Biotechnol.
2019
,
57, 525–534. [CrossRef]
24.
AOAC. Official Methods of Analysis, 17th ed.; The Association of Official Analytical Chemists: Gaithersburg,
MD, USA, 2000.
25. R Core Team. R: A Language and Environment for Statistical Computing; R Core Team: Vienna, Austria, 2006.
26.
Rossini, F.; Loreti, P.; Provenzano, M.E.; De Santis, D.; Ruggeri, R. Agronomic performance and beer quality
assessment of twenty hop cultivars grown in central Italy. Ital. J. Agron. 2016,11. [CrossRef]
27.
Caruso, G.; Villari, G.; Borrelli, C.; Russo, G. Effects of crop method and harvest seasons on yield and quality
of green asparagus under tunnel in southern italy. Adv. Hortic. Sci. 2012,26, 51–58.
28.
Molina, M. Producci
ó
n y Abundancia Natural de Verduras de Hoja, Esp
á
rragos y Frutos Carnosos Silvestres
de uso Tradicional en España. Ph.D. Thesis, Universidad Autónoma de Madrid, Madrid, Spain, 2014.
29.
Siomos, A.S. The quality of asparagus as affected by preharvest factors. Sci. Hortic.
2018
,233, 510–519.
[CrossRef]
Agronomy 2020,10, 1547 13 of 13
30.
Tard
í
o, J.; S
á
nchez-Mata, M.D.C.; Morales, R.; Molina, M.; D
í
ez-Marqu
é
s, C.; Pardo-de-Santayana, M.; Cruz
Matallana-Gonz
á
lez, M.; Ruiz-Rodr
í
guez, B.M.; S
á
nchez-Mata, D.; Torija-Isasa, M.E.; et al. Ethnobotanical
and Food Composition Monographs of Selected Mediterranean Wild Edible Plants. In Mediterranean Wild
Edible Plants—Ethnobotany and Food Composition Tables; S
á
nchez-Mata, M.D.C., Tard
í
o, J., Eds.; Springer:
New York, NY, USA, 2016; p. 478.
31.
Dai, F.J.; Chau, C.F. Classification and regulatory perspectives of dietary fiber. J. Food Drug Anal.
2017
,25,
37–42. [CrossRef]
32.
Sarker, U.; Oba, S. Drought stress enhances nutritional and bioactive compounds, phenolic acids and
antioxidant capacity of Amaranthus leafy vegetable. BMC Plant Biol. 2018,18. [CrossRef] [PubMed]
33.
Osuagwu, G.G.E.; Edeoga, H.O. The effect of water stress (drought) on the proximate composition of the
leaves of Ocimum gratissimum (L) and Gongronema latifolium (Benth). Int. J. Med. Arom. Plants
2013
,3, 293–299.
[CrossRef]
34.
Okazaki, Y.; Saito, K. Roles of lipids as signaling molecules and mitigators during stress response in plants.
Plant J. 2014,79, 584–596. [CrossRef] [PubMed]
35.
Ruggeri, R.; Primi, R.; Danieli, P.P.; Ronchi, B.; Rossini, F. Effects of seeding date and seeding rate on yield,
proximate composition and total tannins content of two Kabuli chickpea cultivars. Ital. J. Agron.
2017
,12.
[CrossRef]
36.
Bista, D.R.; Heckathorn, S.A.; Jayawardena, D.M.; Mishra, S.; Boldt, J.K. Effects of drought on nutrient uptake
and the levels of nutrient-uptake proteins in roots of drought-sensitive and -tolerant grasses. Plants
2018
,
7, 28. [CrossRef]
37.
Zewdie, S.; Olsson, M.; Fetene, M. Effect of drought/irrigation on proximate composition and carbohydrate
content of two enset [Ensete ventricosum (Welw.) Cheesman] clones. SINET Ethiop. J. Sci.
2011
,31, 81–88.
[CrossRef]
©
2020 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access
article distributed under the terms and conditions of the Creative Commons Attribution
(CC BY) license (http://creativecommons.org/licenses/by/4.0/).