Postharvest Biology and Technology 95 (2014) 50–59

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Postharvest Biology and Technology

journal homepage: www.elsevier.com/locate/postharvbio

Interaction of temperature control deficiencies and atmosphere

conditions during blueberry storage on quality outcomes
A.C. Paniagua, A.R. East ∗ , J.A. Heyes
Centre for Postharvest and Refrigeration Research, Massey University, Palmerston North, New Zealand

a r t i c l e i n f o a b s t r a c t

Article history: Southern hemisphere blueberry producers often export their products through extended supply chains
Received 19 December 2013 to Northern hemisphere consumers. During extended storage, small variations in temperature or atmo-
Accepted 12 April 2014 sphere concentrations may generate significant differences in final product quality. In addition, relatively
short delays in establishing cool storage temperatures may contribute to quality loss. In these experi-
Keywords: ments a full factorial analysis was done of the effects of three cooling delays (0, 12 or 24 h at 10 ◦ C), three
Rabbiteye
atmosphere concentrations (air, 10% CO2 + 2.5% O2 and 10% CO2 + 20% O2 ) and two storage temperatures
Highbush
(0 ◦ C and 4 ◦ C) which were assessed for their impact on final quality, measured as weight loss, firm-
Vaccinium ashei
Vaccinium corymbosum
ness and rot incidence. Two blueberry cultivars were studied: ‘Brigitta’, a highbush cultivar, and ‘Maru’,
Shipping conditions a rabbiteye. Delays in cooling had a small effect on final product weight, whereas variation in storage
temperature and atmosphere during simulated transport influenced both firmness and rot incidence.
Atmospheres with 10% CO2 reduced decay incidence, particularly at low oxygen concentration (2.5% O2 ),
although the latter conditions tended to soften fruit. In order to achieve optimal postharvest storage
for blueberries, minimising temperature variability in the supply chain is important, as is finding the
potentially cultivar-specific optimal combination of high CO2 and low O2 concentration that results in
simultaneously minimising rot incidence and induced softening.
© 2014 Elsevier B.V. All rights reserved.

1. Introduction 2004). Higher temperatures accelerate blueberry and pathogen

metabolism and are likely to increase moisture loss, leading to
Postharvest changes in blueberry quality are determined by higher decay, softening and weight loss during storage. Less than
diverse physiological, physical and pathological processes. Modes optimal temperatures can occur in real supply chains due to delays
of blueberry deterioration include decay, softening and shrivel in cooling immediately after harvest and as a result of poor cool
development. Fruit moisture loss has been found to have an impor- chain performance.
tant role in defining firmness changes of blueberries after harvest Cooling delays at high temperatures have previously been
(Paniagua et al., 2013b). Additionally, reduction of the saleable shown to decrease the postharvest life of blueberries during sub-
weight requires compensation through increased packing weight sequent storage (Ceponis and Cappellini, 1979, 1982; Jackson et al.,
resulting in reduced yield (punnets ha−1 ) of the crop. Although 1999; NeSmith et al., 2002; Paniagua et al., 2013a). Delay times
blueberries have been suggested to be climacteric (Perkins-Veazie, between harvest and cooling to storage temperature occur in prac-
2004), ethylene-related ripening changes have a minor influence on tice due to logistical constraints of transport, packing line and
their postharvest deterioration since they are fully ripe (full blue) at pre-cooling facilities. In some locations packing line constraint
harvest maturity with most of the cell wall modifications occurring delays are moderated by cooling the fruit initially to 10 ◦ C prior
before harvest (Vicente et al., 2007). to packing. The residual effect of cooling delays prior to storage is
Temperature is the most important environmental factor a function of the delay time and the temperature. Previous stud-
affecting blueberry quality after harvest. Fresh blueberries are ies have investigated ranges of delay times from 2 to 72 h (Ceponis
recommended to be stored at temperatures close to 0 ◦ C and and Cappellini, 1982) at temperatures ranging from 20 ◦ C (Ceponis
90–95% RH to obtain maximal postharvest life (Perkins-Veazie, and Cappellini, 1979) to 32 ◦ C (Tetteh et al., 2004) for rabbiteye and
highbush cultivars, while Jackson et al. (1999) investigated delays
at 12 ◦ C on lowbush blueberry. Quality loss symptoms report-
∗ Corresponding author. edly exacerbated by delays include increased decay incidence and
E-mail address: a.r.east@massey.ac.nz (A.R. East). weight loss and reduced fruit firmness after storage (Jackson et al.,

http://dx.doi.org/10.1016/j.postharvbio.2014.04.006
0925-5214/© 2014 Elsevier B.V. All rights reserved.
 A.C. Paniagua et al. / Postharvest Biology and Technology 95 (2014) 50–59 51

1999). Our previous work (Paniagua et al., 2013a) investigated temperature decreases CO2 and O2 solubility in aqueous solutions
effects of delays at pre-packing conditions (10 ◦ C) and found a (blueberry tissue) and will accelerate CO2 production and O2
delay-induced reduction in firmness after a further 2 weeks of stor- consumption by increasing the respiration rate. Hence the type of
age. temperature heterogeneity during the shipping period as reported
Non-ideal temperature conditions either temporally or spatially by Tanner and Amos (2003) could alter CA effects or alternatively
is a reality of real cool chain systems (Heap, 2006). The volumetric CA could influence the effects of temperature variations during
expansion of the global blueberry industry has resulted in the need shipping as observed by East et al. (2013) for apples.
to transport the crop in refrigerated sea freight containers. Spatial This research aimed to determine the magnitude of the interac-
temperature variation within a single refrigerated container has tions between delays in cooling, temperature variation in shipping
been reported to be as much as 4 ◦ C during fresh fruit shipment conditions and choice of atmosphere used in shipping on blueberry
(Tanner and Amos, 2003; Punt and Huysamer, 2005; Dodd and quality outcomes after a simulated shipping supply chain. These
Worthington-Smith, 2006; Dodd, 2013). It is not known whether questions were investigated over a single season by using one cul-
this type of temperature heterogeneity during shipping could con- tivar of both highbush and rabbiteye blueberries. Conducting such
stitute an important factor affecting final blueberry quality in an experiment not only establishes the potential of these factors
the marketplace. Previously, temperatures in the range of 0–5 ◦ C to influence quality outcomes, but also enables identification of
have not resulted in consistent differences on blueberry quality the postharvest factors on which to focus efforts in order to min-
attributes at the completion of storage (Table 1). Borecka and imise quality deterioration. This research contributes to the further
Pliszka (1985) reported increased incidence of decay and weight development and improvement of the blueberry export industry of
loss at the upper end of this range; Sanford et al. (1991) reported the Southern hemisphere to Northern hemisphere markets.
weight loss and firmness effects and Nunes et al. (2004) found
effects for decay only, while Forney et al. (1998) found no signif- 2. Materials and methods
icant difference on decay incidence, weight loss or firmness for a
3 ◦ C storage difference after 3 weeks storage. 2.1. Fruit material
Water loss from fresh produce is determined by the difference
in moisture content between the product and the surrounding air ‘Brigitta’ (Vaccinium corymbosum L.) and ‘Maru’ (Vaccinium ashei
(Wills et al., 2007). The capacity of air to retain water increases with Reade) blueberries were obtained from a commercial orchard
temperature, therefore, the partial pressure of water within fresh located near Hastings, Hawke’s Bay, New Zealand. Thirty-two kilo-
produce increases with higher product temperatures (Grierson and grams were collected from a single block with homogeneous plant
Wardowski, 1978). At the same water vapour partial pressure, the condition and common technical management (i.e. nutrition, irri-
RH decreases with increase in environmental temperature. As a gation, pruning and pest control) for each cultivar. Berries were
result increasing the temperature of a system (produce and envi- hand-harvested on the same day by farm pickers according to
ronment) without introducing water to the environment increases commercial practice and normal harvest index (i.e. 100% blue
the rate of the weight loss from produce, due to the resulting larger colouration). After picking, fruit were immediately moved to the
driving force (water vapour partial pressure difference) between farm packhouse and kept at 10 ◦ C for 4 h. Subsequently, fruit was
the product and the environment. transported at 18 ◦ C by car for 2 h to Massey University, Palmerston
In addition to temperature control, modern freight contain- North.
ers are able to control atmospheric composition (Brecht et al.,
2009). Controlled atmospheres of 8–15% CO2 and above 1% O2 are 2.2. Sample configuration
commonly used to extend the postharvest life of fresh blueber-
ries (Alsmairat et al., 2011). There are consistent reports of high Once at 20 ◦ C in the laboratory, fruit of each cultivar were ran-
CO2 concentrations delaying pathogen development in blueberries domised and hand-graded to eliminate major visual defects (e.g.
(Ceponis and Cappellini, 1985; Smittle and Miller, 1988; Beaudry peduncle, scars and cracks). For each cultivar, 182 samples of 140 g
et al., 1998; Harb and Streif, 2004, 2006). However, Fan (1993), of fruit (for 18 treatments by 5 measurement occasions in storage,
Kim et al. (1995) and Prange et al. (1995) all reported further decay replicated twice, plus 2 for initial measurement) were established
reduction effects when O2 was maintained below 10%. On the other in commercial vented polyethylene clamshells (T2907, Flight Plas-
hand, either increased CO2 concentrations or lower O2 can trig- tics, Auckland, New Zealand). Each sample comprised a sub-sample
ger physiological damage in blueberries leading to softening (Fan, of 22 fruit contained in a previously weighed cotton mesh bag
1993; Forney et al., 2003; Harb and Streif, 2004, 2006; Schotsmans of 10 cm × 10 cm. This sub-sample was identified at the initiation
et al., 2007) and off-flavour development (Forney et al., 2003; Harb of the experiment to remove potential for firmness measurement
and Streif, 2004, 2006; Krupa and Tomala, 2007), constituting an sampling bias from the clamshell after the storage period. Each
important risk for the export industry. However, using atmospheric sub-sample was identified, weighed and placed inside a clamshell
O2 concentrations (i.e. approx. 20%) has been suggested to reduce which was subsequently filled with additional fruit to reach 140 g
damage induced by high CO2 (Fan, 1993). Therefore, while high net. Clamshells were randomly allocated to treatments.
(8–15%) CO2 has been established as a storage life extending atmo-
sphere for blueberry, the recommended O2 concentrations to use in 2.3. Experimental design
combination are uncertain. Hence, evaluations of O2 concentration
effects on blueberry quality are still required to improve the use of A multifactorial design was created by the full combination of
CA. three factors (i.e. delay, atmosphere and temperature), defining a
While cooling delays, temperature management, and controlled total of 18 treatments (3 delays by 3 atmospheres by 2 temper-
atmospheres have all been identified as important factors that atures) which were conducted in 2 replicates. Delays in cooling
influence final blueberry quality outcomes, how these factors were conducted with open clamshells at one of three storage delay
interact to influence the three modes of blueberry product failure options (0, 12 or 24 h delay) at 10 ◦ C in a controlled tempera-
(loss of firmness, decay and weight loss) has not been investigated ture room, simulating normal prestorage periods for the blueberry
in detail. In particular it is possible that temperature management industry (NeSmith et al., 2005). Delay periods were applied with
deficiencies within the transportation system could influence open clamshells, to simulate the delay prior to packing in indus-
the effectiveness of the controlled atmosphere. Increased storage try, where fruit would be stored in bins or crates. Immediately
52 A.C. Paniagua et al. / Postharvest Biology and Technology 95 (2014) 50–59

Table 1
Previously reported effects of storage temperature (in the range of 0–5 ◦ C) on blueberry quality outcomes.

Storage Evaluation after storage Cultivar Reference

Temp (◦ C) Time (d) Decay (%) Weight loss (%) Firmness (N)

0 22 0.6 a 0.3 a NR ‘Herbert’ Borecka and

2 16.2 b 1.4 b (highbush) Pliszka (1985)
0 14 0a 5.3 a 28.9 a Wild genotype Sanford et al.
5 0.6 a 7.6 b 15.5 b (lowbush) (1991)
0 21 NS NS NS ‘Burlington’ Forney et al.
3 (highbush) (1998)
0 12 6† 1.8 a NR ‘Patriot’ Nunes et al.
5 8.5 † 2.4 b (highbush) (2004)
Different letters for the same experimental work indicate significant difference. NS, non-significant; NR, not reported/measured.
†
No statistical analysis reported for these data.

after completing the delay period, clamshells were closed and (34.20% and 66.24% glycerol for 90% at 0 ◦ C and 67% RH at 4 ◦ C,
placed in the storage environment of desired atmosphere and respectively).
temperature. Two storage temperatures were chosen: 0 ◦ C as rec- Temperature conditions during storage were maintained by
ommended for blueberries (Perkins-Veazie, 2004; Forney, 2009) having the experimental equipment located in 2 temperature-
and 4 ◦ C, given that this temperature range was reported by Tanner controlled rooms, at 0 ◦ C and 4 ◦ C, respectively. The relative
and Amos (2003) to occur within 40 foot refrigerated containers humidity of the rooms was adjusted and monitored during the
during extended marine shipments. Atmosphere conditions were experiment to match the desired RH setup inside the containers,
either air or one of two controlled atmospheres (10% CO2 + 2.5% in order to minimise any driving force for water vapour transport.
O2 or 10% CO2 + 20% O2 ), which are both within the range recom-
mended for blueberries (Ceponis and Cappellini, 1979, 1985; Fan,
1993; Harb and Streif, 2006). Fruit were maintained in the storage 2.5. Evaluation
environment for a maximum period of 6 weeks.
In order to represent the effect of potential container temper- Two samples of 140 g of fruit each were evaluated before
ature variability on relative humidity (RH) distribution within sea the storage delay period at the beginning of the experiment, to
freight containers, a specific RH was associated with each storage determine initial quality (week 0) for all the treatments. Fur-
temperature. Whereas 0 ◦ C and 90% RH are the optimum condi- ther evaluations of the treatments during storage were conducted
tions recommended for blueberry storage (Perkins-Veazie, 2004), weekly after an initial 2 weeks of storage, up to a total of 6 weeks
67% RH corresponds to the same water vapour partial pressure in by removing one sample from each container and conditioning it
the air when at 4 ◦ C (Talbot and Baird, 1991). for 1 h to room temperature (20 ◦ C) before measuring. The contain-
ers were immediately closed after each sampling to allow as soon
as practical recovery of the storage atmosphere. All samples were
2.4. Storage system eliminated after the evaluation process. Quality attributes eval-
uated were weight loss, firmness and rot incidence which were
Controlled atmosphere conditions were created by using a flow- assessed in this sequence.
through system which supplied the atmospheres from a mixer to
0.0135 m3 cylindrical (Øi = 160 mm) PVC containers. Food grade
gas supplies of oxygen (O2 ), carbon dioxide (CO2 ), nitrogen and 2.5.1. Weight loss
dry air were mixed into a continuous supply. Atmospheric mixes Weight loss was calculated as the percentage difference
were achieved to the desired proportion by regulating each gas between the initial and the final weight of the mesh bag containing
flow rate with a needle valve and measuring the resultant flow fruit, after the subtraction of the mesh bag weight. A digital balance
using a portable ADM 2000 gas flowmeter (Agilent Technologies, (PG503-S Mettler Toledo, Switzerland) of 0.001 g of precision was
Delaware, USA). The three different atmospheres were created used for this weight measurement.
before supplying to a manifold to split each gas mixture into 12
equal flows, one for each PVC container. Gas concentrations were
checked three times per week by sampling at the manifold and the 2.5.2. Firmness
PVC containers using 100 ␮L gastight syringes. Gas concentrations Fruit firmness was measured using a TA.XT Plus Texture Anal-
in the samples were assessed with a O2 /CO2 analyser equipped with yser (Stable Micro Systems Ltd., UK) equipped with a 5 kg load
an O2 electrode (Citicell C/S type, City Technology Ltd., London, cell (following Chiabrando et al., 2009), and a 25 mm diameter
UK) in series with a miniature infrared CO2 transducer (Analyti- flat end cylindrical aluminium probe (ASAE, 2003). Firmness was
cal Development Company, Hoddesdon, UK), with O2 -free N2 as assessed for each blueberry from within the mesh bag using a
carrier gas. non-destructive compression test, simulating a very gentle squeeze
Thirty-six PVC containers were used in total, with five clamshells with the fingers. Each blueberry was compressed 1 mm (following
of each cultivar within each container. Each atmosphere was Ferraz et al., 2001a; Saftner et al., 2008), equatorially (following
supplied continuously to the containers using a flow rate of Donahue and Work, 1998), using a test speed of 0.8 mm s−1 (fol-
50 mL min−1 . This flow rate resulted in a 12 h delay being required lowing Chiabrando et al., 2009), a pre-test speed of 1.6 mm s−1 ,
to completely establish the desired atmospheres within the PVC and a trigger force of 0.5 mN. The peak force (N) necessary to
containers, initially and after any fruit sampling. The gas mixtures achieve the target distance was recorded (following Schotsmans
were humidified by bubbling them through a glycerol solution et al., 2007; Saftner et al., 2008; Chiabrando et al., 2009). A flat
before each container, with the liquid volume maintained by metal ring of 10 mm internal diameter, 35 mm external diameter
replacing water evaporated weekly. Two glycerol solutions of dif- and 1 mm height was fixed above the centre of the platform to
ferent concentration were used to create the desired RH conditions support blueberries during measurement.
 A.C. Paniagua et al. / Postharvest Biology and Technology 95 (2014) 50–59 53

2.5.3. Rot incidence experiments which maintained high RH conditions together with
Rot incidence was determined by isolating and weighing from low temperature.
each sample all fruit showing fungal mycelium development, juice
leakage or collapse as a symptom of decay. The total weight of rot- 3.1.1. Effects of cooling delays on weight loss
ten fruit was related to the total weight of the fruit contained in the Cooling delays at 10 ◦ C (simulating packing temperature)
clamshell and expressed as percentage of rot incidence. increased the total weight loss of blueberries over the subsequent
storage period. Regardless of the delay duration (i.e. 12 or 24 h),
cooling delay led to 0.4% and 0.6% more total weight loss after stor-
2.6. Statistical methods age for ‘Brigitta’ (Table 2) and ‘Maru’ (Table 3), respectively. On the
other hand, the rate of weight loss during the subsequent storage
The data set was analysed by testing the effect of each fac- was not affected by the cooling delay times, in either cultivar. The
tor (delay, temperature, atmosphere, and evaluation time as fixed extended weight loss as a result of extending cooling delays is an
effects, replicates as random effects) and their interaction on each expected consequence of higher temperatures resulting in larger
quality attribute using ANOVA on untransformed data. Differences water vapour partial pressure differences (Talbot and Baird, 1991).
between means were assessed by using Tukey’s HSD (Honest signif- Longer delay time increases the exposure of the product to these
icant difference) test. Significant differences were considered at 5%. high weight loss periods.
Both cultivars were analysed independently as two different trials Previously both Ferraz et al. (2001b) and Tetteh et al. (2004)
although they shared methodologies and storage systems. Regres- found that different temperature/time delay combinations applied
sion analysis was performed on weight loss data of each replication to blueberries modified the total weight loss after subsequent stor-
to obtain a linear slope representing the rate of weight loss and age, but not the rate of weight loss during storage. Likewise, when
analysed with the same statistical methods. delays have included intermediate temperatures representative
of packing conditions (10–12 ◦ C), they have also led to increased
total weight loss after storage (Jackson et al., 1999; Paniagua et al.,
3. Results and discussion 2013a). The results obtained in this study are in agreement, in that
total weight loss of blueberries after storage increased as delay
3.1. Weight loss duration increased from 0 to 12 h, without altering the rate of
weight loss within storage.
Weight loss data analysis was conducted on both means and
slopes, representing total weight loss (%) and weight loss rate
(%/week), respectively. Storage time was found not to have a sig- 3.1.2. Effect of storage temperature on weight loss
nificant interaction with the experiment factors for mean weight The increased storage temperature of 4 ◦ C (and 67% RH) consis-
loss. There were also no interactions between experimental fac- tently resulted in an increased rate of weight loss and consequently
tors on the results; hence the results for each factor are discussed more weight loss at the end of storage, in comparison to 0 ◦ C (and
independently. 90% RH). This result is expected due to the increase in vapour par-
Weight loss obtained during the storage period was lower than tial pressure difference between the fruit and the environment
expected in the blueberry export industry (Paniagiua, personal that is created at 4 ◦ C and 67% RH. However, mathematical cal-
communication). After 3 weeks of storage, the total weight loss culation of the change in partial pressure difference between the
was 0.9% for both ‘Brigitta’ and ‘Maru’ (data not shown). By the two conditions results in a 4.4 times increase at 4 ◦ C, whereas the
end of the storage period (6 weeks) the total weight loss for both observed rate difference is 1.7–2.3 times. The difference between
varieties reached just 1.3%. The blueberry industry considers 5–7% observed results and the mathematical calculation is caused by
of fresh weight as the maximum acceptable weight loss during the additional barrier to water vapour transport provided by the
2–3 weeks of containerised marine export (at 0 ◦ C and 90–95% clamshell packaging that results in localised increased RH within
RH), with this difference being calculated between after packing the clamshell. In this system weight loss from the fruit is governed
and post container opening measurements. The differences in total by the water vapour partial pressure difference between the fruit
weight loss between this experimental data and common indus- and the environment inside the clamshell, with the external envi-
try values could be explained by logistical differences between the ronment influencing the rate of weight loss from the inside of the
processes. Industrial practice contains some less controlled addi- clamshell to the external environment.
tional factors between weight measurements which could increase
blueberry weight loss during the period, such as 2 h of forced air 3.1.3. Effect of controlled atmosphere on weight loss
cooling (to rapidly cool to 0 ◦ C), 1–3 d of preshipping storage (also Controlled atmosphere (CA) did not consistently influence blue-
at 0 ◦ C and 90–95% RH), the container loading process and the time berry weight loss during storage. There were no differences in total
required for container condition establishment. These additional weight loss among the atmospheres tested for ‘Brigitta’ (Table 2),
supply chain factors, not included in this experiment, may increase whereas for ‘Maru’ fruit kept in low O2 (2.5%) atmosphere gener-
blueberry weight loss during industrial shipping to higher values ated slightly higher total weight loss after storage than the other
than those observed in this study. atmospheres (Table 3). Previous studies have reported no effects
Previously reported weight loss for blueberries observed exper- of storage atmosphere on weight loss of blueberries (Smittle and
imentally is highly variable, because of varying experimental Miller, 1988; Schotsmans et al., 2007; Duarte et al., 2009), agreeing
conditions. For instance, Borecka and Pliszka (1985) obtained just with the results for ‘Brigitta’. The additional weight loss observed
0.3% of weight loss after storing highbush ‘Herbert’ blueberries at for cv. Maru kept at low oxygen atmosphere (2.5% O2 ) may be asso-
0 ◦ C and high RH (i.e. inside sealed plastic bags) for 22 d, whereas ciated with accelerated tissue metabolism due to anaerobiosis. Park
Forney et al. (1998) found that highbush blueberries (‘Burlington’) et al. (1994) demonstrated that storing tomatoes in anaerobic con-
decreased their weight by 1% after 21 d at 3 ◦ C and 85–95% RH. On ditions can lead to increased weight loss due to increased sugar
the other hand, when lowbush blueberries were stored for 14 d at loss and accelerated senescence. Fermentation has been reported
0 ◦ C or 5 ◦ C with no RH regulation, the total weight loss was 5.3% to occur consistently at O2 concentrations below 1% in blueber-
and 7.6%, respectively (Sanford et al., 1991). The weight loss mag- ries (Ceponis and Cappellini, 1985), though symptoms associated to
nitudes obtained in this research agree with the results from other anaerobiosis have been detected at 2% O2 in some cases (Fan, 1993).
54 A.C. Paniagua et al. / Postharvest Biology and Technology 95 (2014) 50–59

Table 2
Quality changes of ‘Brigitta’ blueberries over 6 weeks of storage as influenced by delay duration at 10 ◦ C, storage temperature, and atmosphere. Honest significant difference
(HSD) values and letter are used to report differences within factors. n, number of independent measurements; ns, not significant.

Factor Value Weight loss Firmness (N) Rot incidence (%)

Total (%) Rate (%/week) 4 weeks 5 weeks 6 weeks

Delay 0h 0.83 a 0.11 1.57 0.17 1.57 1.97

12 h 1.19 b 0.15 1.59 0.32 1.91 0.94
24 h 1.18 b 0.15 1.59 0.00 1.62 2.46
HSD 0.11 ns ns ns ns ns
n 60 12 1200 12 12 12

Temperature 0 ◦C 0.93 a 0.10 a 1.58 a 0.08 0.66 a 0.98 a

4 ◦C 1.20 b 0.17 b 1.69 b 0.25 2.74 b 2.59 b
HSD 0.08 0.05 0.03 ns 1.38 1.32
n 90 18 1800 18 18 18

Atmosphere Air 1.04 0.16 1.54 a 0.29 2.83 3.53 a

20% O2 + 10% CO2 1.12 0.12 1.62 b 0.07 1.46 1.39 b
2.5% O2 + 10% CO2 1.04 0.13 1.60 b 0.14 0.81 0.44 b
HSD ns ns 0.04 ns ns 1.95
n 60 12 1200 12 12 12

Temperature × atmosphere ns ns ns ns ns
0 ◦ C × air 1.52 bc
0 ◦ C × 20% O2 + 10% CO2 1.50 b
0 ◦ C × 2.5% O2 + 10% CO2 1.41 a
4 ◦ C × air 1.56 c
4 ◦ C × 20% O2 + 10% CO2 1.73 d
4 ◦ C × 2.5% O2 + 10% CO2 1.78 d
HSD 0.05
n 600

Gas threshold levels associated with fermentation in blueberries in sensory evaluated firmness during storage when weight loss
vary among species and cultivars (Pesis, 2005). of blueberries was lower than 1%. Similarly, Forney et al. (1998)
reported firming of ‘Burlington’ blueberries by up to 80% simultane-
ously with 1–2% weight loss; Duarte et al. (2009) found 40% firming
3.2. Firmness coinciding with approximately 0.5% weight loss; and Chiabrando
and Giacalone (2011) found ‘Lateblue’ to firm by 40% coincident
Storage time was found not to have a significant interaction with 2.5% weight loss. This study and each of the 3 aforementioned
with the experiment factors for firmness. An interaction was signifi- papers used a different firmness assessment method, suggesting
cant between temperature and atmosphere for ‘Brigitta’. Results for that the observation of firming is not an artefact of methodology.
each factor are first discussed independently, with the interaction Previously the authors’ own research found weight loss to have a
discussed at the end of the section. causal effect on firmness changes of blueberries (Paniagua et al.,
Fruit firmness increased in all the atmospheres and both tem- 2013b). Opposing firmness outcomes were obtained in different
peratures during the storage of both cultivars compared to the weight loss ranges where blueberry firming occurred consistently
initial condition of the fruit (p < 0.05), reaching maximum values with low levels of weight loss (0.22–1.34%) whereas softening was
at week 5 or 6 depending on storage factors (Fig. 1). ‘Brigitta’ and observed with higher weight loss (Paniagua et al., 2013b). Given
‘Maru’ were 63% and 44% firmer on average at week 6 in com- that the total weight loss for both varieties reached only 1.3%, then
parison to the beginning of the storage. The results of this work it is not surprising that a firming of blueberries was observed in this
are in agreement with Miller et al. (1993) who obtained increases work.

Table 3
Quality changes of ‘Maru’ blueberries over 6 weeks of storage as influenced by delay duration at 10 ◦ C, storage temperature, and atmosphere. No interaction terms were
significant. Honest significant difference (HSD) values and letter are used to report differences within factors. n, number of independent measurements; ns, not significant.

Factor Value Weight loss Firmness (N) Rot incidence (%)

Total (%) Rate (%/week) 4 weeks 5 weeks 6 weeks

Delay 0h 0.61 a 0.14 1.55 0.95 0.28 5.09

12 h 1.17 b 0.17 1.59 0.19 1.66 2.10
24 h 1.24 b 0.14 1.58 0.63 1.56 3.97
HSD 0.09 ns ns ns ns ns
n 60 12 1200 12 12 12

Temperature 0 ◦C 0.79 a 0.09 a 1.38 b 0.00 a 0.00 a 0.35 a

4 ◦C 1.23 b 0.21 b 1.76 a 1.18 b 2.33 b 7.08 b
HSD 0.06 0.04 0.03 0.87 1.50 2.20
n 90 18 1800 18 18 18

Atmosphere Air 0.97 a 0.13 1.69 a 1.04 2.34 6.04 a

20% O2 + 10% CO2 0.96 a 0.14 1.66 a 0.53 0.56 3.30 ab
2.5% O2 + 10% CO2 1.10 b 0.18 1.36 b 0.19 0.60 1.81 b
HSD 0.09 ns 0.05 ns ns 3.25
n 60 12 1200 12 12 12
 A.C. Paniagua et al. / Postharvest Biology and Technology 95 (2014) 50–59 55

Fig. 1. Firmness of ‘Brigitta’ (a–c) and ‘Maru’ (d–f) blueberries during storage, as affected by temperature and storage atmosphere. Error bars represent least significant
difference as determined by Tukey’s test (P < 0.05, n = 120 fruit).

3.2.1. Effect of cooling delays on firmness in comparison to air at 4 ◦ C (Table 2). However at 0 ◦ C, the 2.5%
Delays in cooling prior to storage had no influence on firm- O2 + 10% CO2 atmosphere resulted in softer fruit than the other two
ness outcomes after storage. Previously, when delayed cooling at atmospheres. Atmosphere effects were more consistent for ‘Maru’,
10 ◦ C was evaluated for ‘Maru’ blueberries, a residual effect on with the 2.5% O2 + 10% CO2 atmosphere consistently resulting in
firmness caused by 20 h delay was found after 2 weeks storage softer fruit in comparison to the two other atmospheres across
(Paniagua et al., 2013a), although in that trial firmness reduced both temperatures. Reported firmness behaviour for ‘Brigitta’
significantly in storage. Consequently, for this experiment it could blueberries exposed to commercially relevant CO2 concentrations
have been expected that a 24 h delay at 10 ◦ C would affect firmness. has not been consistent, which could be in part related to different
It seems possible that the particular firming response obtained in instrumental techniques used to measure firmness. ‘Brigitta’ were
this experiment could be masking the cooling delay effect on blue- softer, as measured with a durometer, when stored in 6–15% CO2
berry firmness reduction during storage. (combined with 6–15% O2 ) than in air after 8 weeks (Alsmairat
et al., 2011), and CA comprising 10% CO2 + 5% O2 decreased
3.2.2. Storage temperature ‘Brigitta’ firmness (measured as puncture test) compared to air
Because total weight loss was restricted in our experiments to storage after 7 week storage (Duarte et al., 2009). Contrastingly,
less than 1.5%, increased temperature resulted in firmer blueber- the compression firmness of ‘Brigitta’ blueberries was not affected
ries after storage. Firmness differences between temperatures of by 12% CO2 atmosphere compared with air during a storage period
13% for ‘Brigitta’ (Table 2) and 28% for ‘Maru’ (Table 3) were found. of 9 weeks (Forney et al., 1997).
A number of previous reports indicate that increased temperatures The observed different firmness responses between cultivars
lead to decreased firmness in fresh blueberries stored for periods agree with the high variability among blueberry genotypes for CA
ranging from 3 to 21 d (Sanford et al., 1991; Tetteh et al., 2004; outcomes reported in previous work. When Forney et al. (1997)
NeSmith et al., 2005; Nunez-Barrios et al., 2005), but these were stored five highbush blueberry cultivars in 12.5% CO2 during 9
always under conditions of higher total weight loss. However, a few weeks at a given O2 concentration, ‘Coville’ and ‘Reka’ blueberries
previous reports of increased blueberry firmness at higher tem- softened 23% and 41% after the period, respectively, whereas ‘Blue-
peratures exist. Bunemann et al. (1957) obtained higher sensory gold’, ‘Brigitta’ and ‘Burlington’ blueberries did not vary from their
firmness and skin toughness in blueberries stored at 10 ◦ C than at initial firmness. In other work, Alsmairat et al. (2011) compared
4.5 ◦ C, while Forney et al. (1998) found that storage at 3 ◦ C resulted the effect of atmospheres combining 6–19% CO2 with 2–15% O2
in more blueberry firming in comparison to 0 ◦ C. The temperature for 8 weeks on blueberry firmness obtaining a progressive firm-
effects on firmness in this trial are consistent with the low weight ness reduction as CO2 increased and O2 decreased for ‘Brigitta’,
loss conditions which are conducive to blueberry firming. ‘Jersey’, ‘Legacy’ and ‘Liberty’ blueberries, while the firmness of
‘Duke’, ‘Ozarkblue’ and ‘Toro’ blueberries was not clearly affected
3.2.3. Effect of controlled atmosphere on firmness by gas concentration. The skin of blueberries has been identified as
Atmosphere influenced the firmness of blueberries during stor- a major resistance to gas transfer (Cameron et al., 1994), whereas
age, although its effect varied depending on cultivar and storage the picking scar enhances the entry of gas into the fruit (Paul et al.,
temperature (Tables 2 and 3, Fig. 1). For ‘Brigitta’ increasing CO2 2012). Anatomical differences between blueberry cultivars such as
to 10% in either 2.5% or 20% oxygen resulted in increased firmness epidermal thickness (Makus and Morris, 1993), epicuticular wax
56 A.C. Paniagua et al. / Postharvest Biology and Technology 95 (2014) 50–59

configuration (Sapers et al., 1984) and stem scar diameter (Magee, conditions for 4 weeks (Harb and Streif, 2006). Consequently, the
1999) could influence CO2 and O2 diffusion into blueberry tissue, percentages of rot incidence obtained in this experiment are in
affecting internal gas concentrations and hence contributing to agreement with the decay range reported by similar earlier studies.
genotypic variability in response to atmospheric change. Most berries with decay presented one of two sets of symp-
CA resulted in higher firmness than air for ‘Brigitta’ blueberries toms: either a loose grey mycelium concentrated at the stem scar,
during storage in the present experiment, disagreeing with most of or a dense grey-green mycelium at the calyx scar, together with
the previous work that reports either no influence, or fermentation- an overall leaky appearance and sunken areas on the fruit epider-
induced softening (Fan, 1993; Forney et al., 2003; Harb and Streif, mis. These symptoms typically correspond to Botrytis cinerea and
2004, 2006; Schotsmans et al., 2007; Cantín et al., 2012). However, Alternaria sp. respectively, two of the most common postharvest
Prange et al. (1995) reported that lowbush blueberries were firmer fungi associated with blueberries (Caruso and Ramsdell, 1995; Anco
when kept at 0 ◦ C in 5–15% CO2 combined with 1–5% O2 CA than in and Ellis, 2011). These rot species originally inoculate in the field
air over 6 weeks storage. and proliferate in the postharvest chain due to the high contact
The firmness decrease observed for ‘Maru’ blueberries (in either between fruit and the ability of these fungi to grow under cold
temperature), and ‘Brigitta’ at 4 ◦ C in the low oxygen CA (2.5% storage conditions (Sommer, 1985).
O2 + 10% CO2 ) compared to air, may be associated with CO2 -induced
softening. Increased O2 appeared to have alleviated this effect in 3.3.1. Effect of cooling delays on rot incidence
the 20% O2 + 10% CO2 atmosphere. In a number of previous stud- Rot incidence of blueberries during storage was not influenced
ies, 10% CO2 has previously led to softer ‘Bluecrop’ (Fan, 1993) and by previous cooling delays at 10 ◦ C (Tables 2 and 3). These results
‘Burlington’ blueberries (Forney et al., 2003) in comparison to 0% contrast the findings of previous experiments evaluating the effects
CO2 atmospheres. Previously, Schotsmans et al. (2007) found stor- of cooling delays at 20–30 ◦ C where delayed cooling resulted in a
ing ‘Maru’ blueberries in 15% CO2 + 2.5% O2 resulted in softer fruit residual effect on blueberry rot incidence during storage (Ceponis
than air storage. The alleviation of softening at 10% CO2 by increased and Cappellini, 1979, 1982; Jackson et al., 1999). This is consistent
O2 observed in this work agrees with the work of Fan (1993), who with the observation that Botrytis cinerea requires temperatures of
found that CO2 -induced softening of ‘Bluecrop’ was triggered by at least 20 ◦ C and 15 ◦ C for spore germination and infection pro-
5–15% CO2 when combined with 1 and 2% O2 , but not when O2 was cesses respectively, and Alternaria sp. requires 20 ◦ C as a minimum
16.8%. Similarly, Harb and Streif (2006) found ‘Bluecrop’ to soften to germinate and infect fruits (Sommer, 1985; Caruso and Ramsdell,
less in 12% CO2 + 18% O2 in comparison to 12% CO2 + 2% O2 . 1995).
Fermentation induced by high CO2 is known to produce soften-
ing in blueberries during storage (Fan, 1993; Forney et al., 2003;
3.3.2. Effect of storage temperature on rot incidence
Schotsmans et al., 2007), although anaerobiosis threshold levels
Higher temperature (4 ◦ C in comparison to 0 ◦ C) resulted in more
vary between cultivars (Ehlenfeldt, 2002; Forney, 2009). The pos-
rot incidence from 5 weeks onwards for ‘Brigitta’ and after 4 weeks
itive effect of increased O2 reducing CO2 -related softening could
for ‘Maru’ (Tables 2 and 3, Fig. 2). Increase in rot incidence was 3 and
possibly be associated with an increase in the CO2 fermentation
20 fold, for ‘Brigitta’ and ‘Maru’ respectively, after 6 weeks storage.
trigger as O2 increases. This interaction between CO2 and O2 con-
The increase in rot incidence at higher storage temperatures
centrations for fermentation was demonstrated by Beaudry (1993)
is an expected consequence of both increased pathogen growth
for ‘Bluecrop’. Ceponis and Cappellini (1985) reported the detection
rate, and decreasing product resistance caused by accelerating fruit
of off-flavours attributed to fermentation in highbush blueberries
senescence (Barkai-Golan, 2001). Similar previous research within
kept in 10–15% CO2 + 2% O2 , while same CO2 concentrations did
the 0–5 ◦ C range has not been as consistent. For instance, ‘Her-
not generate off-flavours when combined with 20% O2 . Likewise,
bert’ rot incidence increased from 0.6% to 16.2% when maintained
Harb and Streif (2006) found that O2 concentrations of 2% or less
for 3 weeks at 2 ◦ C instead of 0 ◦ C (Borecka and Pliszka, 1985),
enhanced the off-flavours produced by CO2 in ‘Bluecrop’ and ‘Duke’.
whereas ‘Burlington’ developed equal decay levels after 6 weeks
Increased compression firmness obtained in this experiment in
when stored at either 0 ◦ C or 3 ◦ C (Forney et al., 1998).
10% CO2 at 0 ◦ C regardless of O2 concentration could indicate that
‘Brigitta’ blueberries did not undergo fermentation related soften-
ing during the storage conditions. This would agree with the results 3.3.3. Effect of controlled atmosphere on rot incidence
reported by Forney et al. (1997), suggesting that the fermentation Controlled atmosphere (CA) significantly decreased rot inci-
threshold for this cultivar would be at a lower O2 concentration. dence, with a tendency for fruit stored in air to develop the
highest decay from the appearance of the first rots at 4 weeks
3.3. Rot development (Tables 2 and 3, Fig. 2). After 6 weeks storage, the low oxygen
atmosphere (2.5% O2 + 10% CO2 ) significantly reduced rot incidence
Storage time was found to influence the significance of the for ‘Maru’ in comparison to air storage, while both CAs decreased
experiment factors on rot incidence. Consequently results were decay for ‘Brigitta’. For either cultivar, both CA atmospheres were
analysed at each storage period from the onset of initial visible indistinguishable despite the dramatic difference in O2 concentra-
decay symptoms (4 weeks). Results for each factor are discussed tion. The reduction of rot incidence in the CA provided in this work
independently. agrees with numerous studies demonstrating the efficacy of CO2
Visible decay was not observed irrespective of cooling delay in the range of 10–24% in reducing decay incidence of fresh blue-
period, storage temperature or atmosphere until after 4 weeks of berries (Ceponis and Cappellini, 1985; Fan, 1993; Harb and Streif,
storage for both cultivars. Maximum decay incidence reached 3.5% 2004, 2006). These results confirm the importance of using CA for
and 7% after 6 weeks for ‘Brigitta’ and ‘Maru’ cultivars, respec- blueberry marine exports (2–3 weeks) and long term storage up
tively. Factors such as amount of inoculum and cultivar sensitivity to 6 weeks in order to reduce decay incidence compared to air
influence expression of pathogenic fungi during cold storage refrigerated storage.
(Barkai-Golan, 2001). As a result the magnitude of rot incidence
obtained across previous similar studies has been highly variable. 3.4. Application of the results to real supply chains
For example, while Harb and Streif (2004) obtained 0.7% inci-
dence after cold storing ‘Duke’ for 5 weeks in air, the same authors When applying these results to the blueberry industry, the effect
reported rot incidence as high as 31% for ‘Bluecrop’ under the same of cooling delay at 10 ◦ C on weight loss obtained in this experiment
 A.C. Paniagua et al. / Postharvest Biology and Technology 95 (2014) 50–59 57

Fig. 2. Rot incidence of ‘Brigitta’ (a–c) and ‘Maru’ (d–f) blueberries during storage, as affected by temperature and storage atmosphere. Error bars represent least significant
difference as determined by Tukey’s test (P < 0.05, n = 6 clamshells).

could imply a relevant impact of extended packing periods on blue- Storage at 4 ◦ C also resulted in greater rot incidence than stor-
berry quality. The observed approximate 0.5% increase in weight age at 0 ◦ C. These differences of rot incidence obtained between 0 ◦ C
loss could constitute a serious risk of reaching shrivelling thresh- and 4 ◦ C storage indicate the potential negative impact of tempera-
old levels (5–8%) during the export period (2–3 weeks), assuming ture variability within a marine refrigerated container environment
that the additional factors along the commercial chain of blueber- on rot incidence of exported blueberries. Even though, in this case
ries which lead to increased weight loss remain. Similarly, since the generation of different decay levels occurred beyond the usual
total weight loss higher than 2% has been related to blueberry soft- shipping period of blueberries (2–3 weeks) in this experiment, the
ening (Paniagua et al., 2013b), this potential increase of weight loss risk for a potential expression of this difference earlier in the export
due to cooling delays could also lead to further quality reduction process or during the subsequent shelf life period seems to be high.
expressed as softening. Furthermore, a weight loss increase of 0.5% From container loading to display on the retail shelf exported blue-
during the supply chain would mean a loss of saleable weight for berries from Chile take approximately 3 weeks (North America),
blueberry exporters. On the other hand, it should be considered 4 weeks (Europe), or 6 weeks (Asia). The tolerance of blueberry
that the particular conditions of this experiment for the delay sim- importers for decay is zero in the marketplace, and therefore any
ulation led to similar total storage weight loss between 12 h and factor during the supply chain which enhances the development of
24 h delay. Consequently, improving packhouse logistics in order to rots has potential economic consequences. As such, the blueberry
reduce delay times at packing temperature below 12 h should effec- export industry could benefit from improved refrigerated trans-
tively reduce weight loss of blueberries, decreasing the risk of fruit port systems able to reduce temperature variability within marine
shrivelling and the loss of saleable weight during the postharvest containers.
chain. Otherwise the results obtained in this experiment indicate With the exception of ‘Brigitta’ at 4 ◦ C, application of the low O2 ,
that pre packing delays (up to 24 h at 10 ◦ C) do not lead to increased high CO2 atmosphere (2.5% O2 + 10% CO2 ) resulted in suppressed
decay or firmness loss during subsequent storage, which suggests firming in comparison to air or the alternative high O2 , high CO2
that there is little need to improve delays at 10 ◦ C and that invest- atmosphere. The potential alleviation of CO2 -induced softening
ment efforts should be focussed on other steps of the postharvest by increasing O2 concentrations agree with previous reports in
chain. which 16.8–20% O2 CA storage has decreased CO2 injury in blue-
While the potential for blueberry firming in situations where berries (Ceponis and Cappellini, 1985; Fan, 1993; Harb and Streif,
weight loss is low during storage has been confirmed, the possible 2004, 2006). However the same low oxygen, high carbon dioxide
causes leading to this increased firmness in the postharvest envi- atmospheres resulted in the best (although not significantly
ronment have not been addressed. The causal relationship between different) control of decay, resulting in a storage optimisation
moisture loss and firmness change previously found (Paniagua conflict between the firmness and decay modes of failure. As decay
et al., 2013b) emphasises the need to consider not only O2 and incidence is more unacceptable than firmness loss it would seem
CO2 concentration, but also the relative humidity established when that choice of low oxygen, high carbon dioxide atmosphere may
determining the effects of the atmosphere established on blueberry be the most appropriate option. Either way the conflicting benefits
storage (or transport) outcomes. Increased storage temperature of high and low O2 in combination with 10% CO2 for blueberries
(4 ◦ C instead of 0 ◦ C) also resulted in increased firmness outcomes observed in this work probably explains the lack of agreement in
in this work, a result that was also observed by Forney et al. (1998). choice of O2 conditions. Additionally, it is necessary to evaluate the
58 A.C. Paniagua et al. / Postharvest Biology and Technology 95 (2014) 50–59

interaction of gases across the main commercially grown cultivars Chiabrando, V., Giacalone, G., Rolle, L., 2009. Mechanical behaviour and quality traits
due to the high genotypic variability for O2 and CO2 fermentation of highbush blueberry during postharvest storage. J. Sci. Food Agric. 89, 989–992.
Chiabrando, V., Giacalone, G., 2011. Shelf-life extension of highbush blueberry using
thresholds and CO2 efficacy in suppressing decay. Future research 1-methylcyclopropene stored under air and controlled atmosphere. Food Chem.
should investigate the minimum O2 concentrations required to 126, 1812–1816.
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Donahue, D.W., Work, T.M., 1998. Sensory and textural evaluation of Maine wild
Sea fright export supply chains have a number of steps, includ- blueberries for the fresh pack market. J. Text. Stud. 29, 305–312.
ing time delay before removal of field heat, control of temperature Duarte, C., Guerra, M., Daniel, P., Camelo, A.L., Yommi, A., 2009. Quality changes of
highbush blueberries fruit stored in CA with different CO2 levels. J. Food Sci. 74,
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This work found that for blueberries, delays in cooling of up to 12 h native temperature control strategies for controlled atmosphere stored apples.
at 10 ◦ C are only likely to influence final product weight, whereas Int. J. Refrig. 36, 1109–1117.
Ehlenfeldt, M.K., 2002. Postharvest research and technology in Vaccinium. Acta Hort.
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