Temperatures. Air Storage of Broccoli Florets at Various. Hidemi IZUMI,* Alley E. WATADA and Willard DOUGLAS. Horticultural Crops Quality Laboratory, ...
Food Sci. Technol. Int. Toky'o, 3 ( I ), 34-40, 1 997
Controlled Atmosphere and Subsequent Air Storage of Broccoli Florets at Various
Temperatures Hidemi IZUMI,* Alley E. WATADA and Willard DOUGLAS Horticultural Crops Quality Laboratory, Beltsville Agricultural
Research Center, Agricu!tural Research Service, U.S. Department of
Agriculture, Beltsville, MD 20 705, USA
Received June 17, 1996 The physiology and quality of 'Greenbelt' broccoli florets (Brassica oleracea L. italica) were monitored during
CA storage in 0.5% 02 and 10% C02 at O and 5'C and in 1% 02 and 10% C02 at 10"C and subsequent air storage at the same temperature. The CA reduced respiration, weight loss, and decay at all temperatures, yellowing and L-ascorbic acid loss at 5 and 10'C, and ethylene production and microbial growth at 10'C. Upon transfer of the florets to air following CA storage for 4, 3, and I weeks at O, 5, and 10'C, respectively, respiration rate increased initially
and then remained constant. Ethylene production continually increased. Decay, microbial count, odor, color, and L-ascorbic acid content remained essentially unchanged for a few days after the samples were transferred to air regardless of temperature.
Keywords:
broccoli florets, controlled atmosphere, aeration, respiration, microbial population, hue angle, ascorbic acid
The controlled atmosphere (CA) or modified atmosphere (MA) storage of broccoli florets stored at 10'C or less, has
been reported to reduce respiration (Forney et al, 1989; Bastrash et al, 1993), weight or moisture loss (Forney et al, 1989; Barth et al, 1993a; Bastrash et a/, 1993), ascorbic acid
loss (Barth et a/, 1993a) and the growth of microorganisms (Berrang et al., 1990), and delay chlorophyll loss or yellowing
1990; Yamashita, 1996). In this study, we initially determined the effects of CA on broccoli florets stored at O, 5, and lO'C. The additional
temperatures were included, because, although O'C is the recommended storage temperature (Hardenburg et al, 1986), broccoli florets are sometimes held at higher temperatures. The concentrations of 02 and C02 differed with temperature
(Barth et a/., 1993a; Bastrash et al., 1993). In these studies the
and were selected on the basis of earlier findings (Izumi et al,
florets were kept in an atmosphere recommended for broccoli heads (Saltveit, 1989) at a single temperature. Our earlier study indicated that 0.5% 02 Or lO% C02 at O and 5'C, and 1%
1 996). Subsequently, we determined the residual effects of CA
02 or 10% C02 at 10'C seemed to be recommended for the
production, decay, off-odor, L-ascorbic acid, and microbial
storage of broccoli fiorets based on respiration rate, color changes and the development of decay or off-odor (Izumi et al, 1996). The combination ofdecreased 02 and elevated C02
population.
generally is more beneficial in maintaining quality than using
on florets when transferred to air at the same temperature.
Attributes measured included respiration rate, ethylene
Materials and Methods Plant materials Heads of 'Greenbelt' broccoli were
either low 02 or high C02 independently (Lebermann et al.,
obtalned from the Wholesale Distribution Center in Jessup,
1968a).
MD and washed with water. Florets (~~10g each) were
The residual effects of CA or MA during the air storage of
broccoli florets are not known. The exposure of broccoli
separated with a knife from the heads. CA storage Florets ( 1 50 g) were placed on a screen
heads to air for 2 to 4 days after CA storage resulted in the
10cated above 100 ml of distilled water in a 2-/ glass jar. Three
dissipation of any off-odor and/or off-flavor (Kasmire et al.,
replicated samples were stored at O, 5, and 10'C under a continuous stream of air or CA at lO, 20, and 40 ml/min, respectively. The CA conditions of 0.5% 02 and 10% C02 at O and 5'C and l% 02 and lO% C02 at lO'C, with the balance being N2' which were selected on the basis of our earlier
1974; Lipton & Harris, 1974; Wang & Hruschka, 1977) and the restoration of the pH values of fresh heads and that of color and texture of the heads after cooking (Leberrnann et al, 1968b). It is unknown how closely the florets will behave of the overall quality of broccoli florets stored in air after CA
findings (lzumi et al, 1996). Oxygen and C02 contents of the inlet and outlet streams of
treatments would be useful in order to maximize the success-
each jar were monitored every 8 h using 02 and C02 analyzers
ful use of CA technology and possibly lower the storage cost
(Model S-3A/1 and Model CD-3A; Ametek, Pittsburgh, PA, USA, respectively) and the average of 3 measurements/day
like the heads when transferred from CA to air. Knowledge
by operating the CA equipment less (Bartsch & Blanpied,
was used for the data analysis. Ethylene levels In 5 ml aliquot ' Present address: Faculty of Biology-Oriented Science and Technology, Klnkl
University. Uchita~ho, Naga-gun, Wakayama 649-64, Japan.
of gas samples taken from each jar were measured with a GC
(Model AGC-21 l; Carle, Tulsa. OK. USA) equipped with a
Broccoli Stored in CA and Subsequent Air
35
Incidence of soft rot and brownlng, development of off-odor, and total microbial CFU of broccoli florets stored in air or CAa) at O, 5, and
Table 1.
Storage temp. Days m storage Treatment
Soft rotb)
('C)
O
26
Air
IO
27
14
Raw
Cooked
i O'C .
Log*o CFU/gd)
33.4
23.7
1 .O
O
7.2
O
O
0.7
O
6.5
NS
NS
NS
CA 5
Browningb)
Odorc)
Air
73,7
5 1 .9
0.7
l .O
8. l
CA
16,7
37.5
0.3
O
7.5
**
NS
NS
NS
NS
Air
91,5
33.9
3.3
4.0
7.8
CA
l 1,9
20.4
1 .O
6.4
**
NS
NS
a) O.5% 02+ IO% C02 at O and 5'C; 1% 02+10% C02 at lO'C. Number of Injured florets x 100. Number of observed florets c) Rated on a scale of O to 4, wlth O-normal and 4=severely objectionable. b)
d) LogloCFU/g on initial day was 3.4. NS, * **: Nonsignificant or significant at p~0.05 or 0.01, respectively.
flame ionization detector. Subsamples of florets were initially taken and at scheduled
Results and Discussion
tlme periods during storage for the determlnation of decay, odor, microbial count, weight, color, and L-ascorbic acid
development of soft rot at all three temperatures and the browning of cut surfaces at O'C (Table l). High C02 Or the combination of a low 02 and high C02 atmosphere has been
content.
Incidences of soft rot and browning of cut surfaces are expressed as the percentage of the total number of florets with
defects in each jar. The odor of fresh and cooked fiorets (microwaved for 2 min) were rated on a scale of O to 4, with
0=normal and 4=severely objectionable. The total microbial population on the surface of 10 g samples were determined as previously described (lzumi & Watada, 1994). The microbial
population is expressed as loglo colony-forming units (CFU)/g sample. The color of the central part of 5 florets was measured wlth
a chromameter (Model CR-300; Minolta, Osaka) with a I cm aperture and the results are expressed as hue angle (tan~1b*/ a*) values. The L-ascorbic acid content in 3 g floral tissues
was determined using a HPLC equipped with a Polymer Laboratories column (Model PLRP-S 100A) and electrochemical detector (Model 400; EG&G, Princeton, NJ, USA)
Controlled atmosphere storage CA suppressed the
shown to delay the development of soft rot or mold of broccoli (Lipton & Harris, 1974; Aharoni et al, 1985; Makhlouf et al, 1989a). Aharoni et al (1985) reported that the suppression of rot development in florets under CA was mainly related to the effect of high C02 Of lO% or more in retarding the senescence process in the host tissues, thereby
maintaining its natural resistance to decay. CA conditions have also been shown to suppress the postharvest decay of fruits and vegetables due to the suppresslon of the pathogenic
growth of bacteria and fungi (El-Goorani & Sommer, 1981). In our study, CA reduced the total aerobic microbial CFU (p ~0.05) only at 10'C (Table l), but the decay was reduced at all temperatures. The population of gram-positive organisms such as lactic acid bacteria, which is favored in CA or MA (Brackett, 1989), seemed not to affect the development of decay in CA stored broccoli. A slight or no off-odor was emitted by the fresh or cooked
as previously described (Izumi & Watada, 1995). A ir storage following CA treatment Broccoli florets were stored in CA as previously described for 4, 3, and l
florets during storage in air or CA at O or 5'C (Table l). At
weeks at O, 5, and lO'C, respectively, and then placed In an air
persisted after cooking. Samples in CA at 10'C had a
atmosphere at the same temperature. The three replicated
moderate amount of off-odor, which slightly decreased with cooking. The off-odor produced by florets held in air and CA
samples were stored for 7 days in air at the same fiow rates as
10'C, the off-odor noted with fiorets held in air on day 14
monltored, and evaluations of decay, odor, microbial count, color, and L-ascorbic acid content of the subsamples were
was probably enhanced by decay. The weight loss was significantly (p~0.05) Iower with samples from the CA than from air storage at all temperatures, except for the first sampling day at O'C, and the
made at scheduled dates, as already described for the CA
difference was greater at the higher storage temperatures (Fig.
storage experiments. Statistica/ analysts Statistically significant differences
1). Some of the weight loss could be due to loss of carbon from respiration. The total carbon loss, calculated using the
the CA storage at each temperature.
Oxygen, C02, and ethylene levels of each sample were
(p~~0.05) between treatments were determined for the CA
average rate ofC02 production (Fig. 4), was I I to 19% ofthe
effects data on each sampling day in the CA storage experiments using an analysis of variance, and the standard error of
total weight loss at all temperatures (data not shown), which
individual means was presented in the figures. Duncan's multiple range test was used to separate the means of
at 5'C (Forney et al., 1989). The calculated carbon loss was 34, 58, and 73% Iower with florets in CA than in air at O, 5, and lO'C, respectively. The greater weight loss by samples in air may also be due to the more advanced stages of senescence in air than in CA, which was readily apparent at the higher
tabulated data and residual effects data in the air storage
experiments following CA.
is similar to that noted with broccoli heads stored for 21 days
H. IzUMI et al.
36
8
8
o'c
~ ~ ~
5
5'c O Air
6
e CA
~04 ~ ,1
4
/~/
tL()
-. -~'~
~2
/
2
/
o
O 5 10 15 20 25 30 O 5
o
10
15 20 25 30 O 4 8 12 16
DayS in storage Fig. 1. Weight loss of broccoll fiorets during storage in air or CA at O, 5.
and IO'=C. CA: 0.5% 02+ lO% C02 at O and 5'C; I% 02+ lO% C02 at IO'C. Vertical
lines represent SE. SE bars not shown when within symbols.
1 40
1 40
o'c
10'C
1:1)/e 1 20 1 20 (u ~L] ~: clj
(L,
*
~ I OO ~C:
1 oo
O Air
O CA
80
O 5 10 1520 25 30 O 5 10 15 2025 30 O Days in storage
Fig. 2.
Hue angle (tan~1b'/a') value ofbroccoli florets durlng storage in air or CA at O, 5, and IO'C.
at lO'C.
Vertical lines represent SE. SE bars not shown when wlthin symbols.
temperatures. Green color, as expressed as hue angle, was retained for florets held in CA at all temperatures, whereas it decreased
4 8 12 16
80
CA: 0.5% O,+10% CO, at O and 5'C; I% 0=+ lO% CO,
decreasing hue angle. A significant negative correlation (p~:
0.01) was found between ethylene production and the hue angle values of florets held at all temperatures (-0.94) (data
2). CA or MA has been shown to delay the yellowing of
not shown). The L-ascorbic acid content of fiorets decreased at all
broccoli florefs stored at 4'C (Bastrash et al, 1993), lO'C
temperatures, with the decrease being significantly (p ~ 0.05)
(Barth et al, 1993a), 15'C (Hirata et a/, 1995), 20'C (Barth et
greater in air than in CA after day 1 3 at 5'C and after day 7
al, 1993b; Abe et al, 1995), and 25'C (Makhlouf et al., 1989b). Abe et al ( 1995) reported that ethyl alcohol or acetaldehyde delayed yellowing and decreased ethylene production of broccoli fiorets as well as a high C02 atmosphere. Chlorophyll degradation was closely correlated to
at lO'C, but not at O'C (Fig. 3). Weichmann (1986) reported that the reduced 02 and elevated C02 effect on L-ascorbic acid
ethylene production ofthe broccoli floral tissues (Aharoni et
(Barth et al., 1993a) or 0.5% 02 and 20% C02 at 15'C (Hirata
with florets in air on day 27 at 5'C and after day 7 at lO'C (Fig.
content was dependent on commodity and storage temperature. L-Ascorbic acid has been shown to be retained in packaged broccoli florets under 8% 02 and lO% C02 at lO'C
al, 1985; Makhlouf et a/., 1989b), especially from the
et al, 1995), but the ascorbate oxidase and peroxidase
reproductive structures, stamens and pistil (Tian et al, 1994).
activities did not differ between packaged and unpackaged broccoli (Barth et al, 1993a). L-Ascorbic acid loss has been attrlbuted to several enzymes, including ascorbate oxidase,
In our study, we also noted that ethylene production increased with increased loss of color as indicated by the
Broccoli Stored in CA and Subsequent Air
37 1 40
1 40
o'c
'~, ~J]
C vf~*~
10'C
5'c
1 20
1 20
\\,\\/
\\
~C 1 oo HH
\~' 1~
~\
1 oo
\r'\
\~\ \~
80
U
/ ,
rr~_J
eo
~~
40
o (J
'\.r~ 60
40
e Air
,7]
20
~
80
~
20
o CA
o
o
O 5 10 15 20 25 30 O 5 10 15 2025 30
o
4
8
12
16
Days in storage 0.5% 02+ lO% C02 at O and 5'C; l% 02+ lO% C02 at lO'C.
Fig. 3. L-Ascorbic acid content ofbroccoll florets during storage In air or CA at O, 5, and lO'C. CA:
Vertical lines represent SE. SE bars not shown when within symbols.
30
35 30
~~~Qcc~co
~f' 2 5 +1
20
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15
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ct~cipcocc;oco
c~eerpt~'ee
ii+~~!If ' t " ~!~""w"be
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05
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20
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of)~i\~ 5 1In o+t()7 1 ~:e 5 20 25 30 o 5 1 o 1 5 20 25 30 fit O'c rDt~~~~~.= irT
