Postharvest Biology and Technology 41 (2006) 307–316
Quality changes of intact and sliced fennel storedunder different atmospheres
Vıctor H. Escalona, Encarna Aguayo, Francisco Artes ∗
Postharvest and Refrigeration Group, Department of Food Engineering, Technical University of Cartagena,Paseo Alfonso XIII, 48. 30203 Cartagena, Murcia, Spain
Received 28 June 2005; accepted 9 April 2006
bstract
The effect of atmospheres of 5 kPa O2 + 5 kPa CO2, 5 kPa O2 + 15 kPa CO2, and 21 kPa O2 + 0 kPa CO2 (as a control) on the metabolicctivity and quality of intact and sliced ‘Orion’ fennel was studied. Under these atmospheres, intact bulbs were stored for 28 days at 5 ◦Collowed by 3 days at 15 ◦C and 60–70% RH in air while sliced fennel was stored under the same atmospheres for 14 days at 5 ◦C. In bothntact bulbs and sliced fennel respiration rates, ethylene production, microbial counts (only for slices), colour, sugar and organic acid contents,nd chemical and sensory attributes were evaluated. By using a controlled atmosphere (CA) with low O2, the respiration rates and ethyleneroduction decreased by more than 50% compared to air. This reduction of the metabolic activity was more substantial for intact bulbs than
liced fennel. CA with 5 kPa O2 delayed the quality loss of slices and fennel bulbs. After 3 weeks of storage, intact bulbs stored in 5 kPa2 + 15 kPa CO2 suffered physiological damage developing as a brown spot. Using a CA of 5 kPa O2 + 15 kPa CO2 led to the best quality in
liced fennel. However, the recommended atmosphere for intact fennel was 5 kPa O2 + 5 kPa CO2.2006 Elsevier B.V. All rights reserved.
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eywords: Respiration rate; Ethylene production; Microbial and sensory qu
. Introduction
An increasing demand for fennel from European countriesuch as Germany, Italy, The Netherlands and United King-om has resulted an expansion of the cultivated area into thepanish Mediterranean coast. In the south-east of Spain thearvest season for fennel extends from December to March,ith a yield of about 30–35 t ha−1 (Pico, 2001). Fennel bulbs
re harvested when they have an equatorial diameter greaterhan 6 cm, ensuring that the bulbs are firm, white, sweet, andithout injuries.Usually fennel bulbs are not cold-stored for a long time,
eing harvested according to market demand. However, com-ercial storage can reach 2 weeks at 0–1 ◦C and 95% RH.
he major postharvest loses of fennel under high humid-
ty and low temperature conditions are due to weight lossnd decay associated with bacteria (Erwinia carotovora and
seudomonas spp.) and moulds (Botrytis cinerea and Sclero-inia sclerotiorum) (Snowdon, 1991; Namesny, 1993; Pico,001).
Browning on the butt end cut zone of fennel bulbs andn the cut surfaces of fresh-cut fennel is the most importantause of deterioration during cold storage and distributionAlbenzio et al., 1998; Escalona et al., 2005a,b). Low O2 andigh CO2 levels in controlled atmospheres (CA) or modifiedtmosphere packaging (MAP) can reduce browning of fennelulbs after 2 weeks of storage at 0 and 5 ◦C (Artes et al.,002a,b).
During minimal fresh processing for preparing ready-to-at fruit and vegetables, tissues suffer damage mainly byutting, which increases their rate of deterioration. For keep-ng quality and extending shelf life, these products muste maintained throughout the cold chain in the range of
–5 ◦C (Huxsoll and Bolin, 1989; Varoquaux and Wiley,994; Ahvenainen, 1996). MAP at 0–5 ◦C with 1–8 kPa O2nd 5–20 kPa CO2 might be a beneficial tool for maintaininguality of these kinds of vegetables because these conditions
educe water loss, respiration rate and ethylene production,nhibit browning and some physiological disorders and retard
icrobial growth and decay (Varoquaux and Wiley, 1994;atada et al., 1996; Gorny, 1997; Artes et al., 1999a). Under
hese conditions senescent browning in fresh-cut lettuce waselayed due to a reduced production of phenolic compoundsLopez-Galvez et al., 1996). For fresh-cut vegetables, most ofhich fall into the low-acid category (pH 5.8–6.0), the highumidity and the extension of the cut surfaces can providedeal conditions for the growth of microorganisms (Brackett,987).
Previously, other authors have found it difficult to createminimally processed fresh product from fennel largely due
o its susceptibility to enzymatic browning (Albenzio et al.,998). Minimally processed fennel should be considered asnew product and thus has received little attention in the
cientific literature (Escalona et al., 2005a,b).The purpose of this work was to determine the effect of
ow O2 combined with moderate to high CO2 levels on theespiration rate and ethylene production of intact bulbs andliced fennel at 5 ◦C (usual commercial temperature). Sev-ral chemical and sensory parameters were monitored duringhilling storage and retail sale.
. Materials and methods
.1. Preparation of fennel bulbs
‘Orion’ fennel (Foeniculum vulgare var. dulce) was field-rown in Torre Pacheco (Murcia, Spain) in the Mediterraneanoast of Spain. Bulbs were hand-harvested on 8th Febru-ry, and selected in the field, eliminating the soiled andecayed external leaves. Four to five stalks 10 cm long wereaintained per bulb, transported to the laboratory (40 km)
nd stored at 0 ◦C. The next morning, bulbs were carefullynspected, selecting only those that were free from defectsnd with similar appearance. The average weight of bulbselected was 312 ± 16 g (mean ± S.E.), with equatorial andongitudinal diameters of 8.0 ± 0.2 and 7.6 ± 0.3 cm, respec-ively. In the clean room at 7 ◦C, bulbs were washed in aolution of 50 mg L−1 NaOCl (pH 7.5) at 5 ◦C for 1 min.
.2. Minimal fresh processing of fennel
Minimal processing was conducted in a disinfected coldoom at 7 ◦C. Bulbs selected for processing were cut inlices approximately 0.8 cm thick using a commercial cut-ing machine (Hallde RG-100, Sweden). Immediately afterutting, the slices were immersed in a 100 mg L−1 NaOClolution at 5 ◦C and pH 7.5 for 1 min and then drained.
.3. Experimental set-up
The treatment gas mixtures of 5 kPa O2 + 5 kPa CO2,kPa O2 + 15 kPa CO2 and 21 kPa O2 + 0 kPa CO2 (as a
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nd Technology 41 (2006) 307–316
ontrol) were selected based on results of our previousxperiments (Artes et al., 2002a,b; Escalona et al., 2005a,b).o simulate commercial practice, the maximum cold storageeriod requirement for intact bulbs and sliced fennel weretored for 28 and 14 days at 5 ◦C, respectively. Afterold storage, intact bulbs were maintained at 15 ◦C and0–70% RH in air for 3 days to simulate a retail saleeriod.
.4. Respiration rate and ethylene production
Samples of 3–4 intact bulbs and 400 g of sliced fennelere put into 2.6 and 1.5 L glass jars, respectively. For eachas mixture, five jars were connected to a flushing panelith a flow rate of 1–2 L h−1 humidified to 95% RH. The gasixture was composed of a gas-mixing panel (Flowboard,avis, CA, USA). The jars were closed and the initial head
pace composition (O2, CO2 and N2) was monitored using a.5 mL gas sample which was injected into a gas chromato-raph (GC) (Shimadzu GC-14B, Tokyo, Japan) equippedith a thermal conductivity detector. The C2H4 productionas measured with a GC (Hewlett Packard 5730A, Philadel-hia, PA, USA) equipped with a flame ionisation detectorn a 1 mL gas sample. The headspaces were analysed again–4 h later. The measurements were conducted periodicallyuring the storage period. Between measurements, thears were continuously flushed with the respective gas
ixture.
.5. Microbiological analysis
In order to determine microbial growth on sliced fenneln days 0 (production day) and 14, three random samplesere taken. Three jars per treatment were analysed in each
valuation period. A 30 g sample of slices was blended with70 mL of sterile peptone buffered water (Merck Darmstadt,ermany) for 1 min into a sterile stomacher bag (Model 400ags 6141, London, UK) by using a Masticator (Sewardedical, London, UK). Serial dilutions were prepared
n 9 mL PPS. From each dilution, 1 mL aliquots wereseptically pipetted for bacteria microflora and 0.1 mL foreasts and moulds. The following media and incubationonditions were used: plate count agar (MERCK Darmstadt,ermany) incubated for mesophilic and psychrophilic
erobic bacteria, incubated at 32 ◦C for 48 h and at 7 ◦Cor 7 days, respectively, and Rose Bengal Chloramphenicolgar base (MERCK Darmstadt, Germany) for yeasts andoulds by spread, 5 days at 22 ◦C. Duplicates were made
or each dilution (Pascual and Calderon, 2000). Microbialounts were reported as log10 colony forming units per gample (log cfu g−1). Microbial quality of the product wasvaluated according to the Spanish legislation for minimally
resh processed vegetables (RD 3484/2000, 2001), whereaximum microbial counts are 7 log cfu g−1 for aerobic
acteria, and 5 and 3 log cfu g−1 for yeasts and moulds,espectively.
Colour changes were measured with a tristimulus col-rimeter (Minolta CR-300, Ramsey, NJ, USA) with an 8 mmiameter of viewing aperture, using a white plate as referenceY = 94.3; x = 0.3142; y = 0.3211, standard CIE illuminant, 2◦bserver). Colour was expressed as L*, a*, b*, hue angleH◦ = tan−1 b*/a*) and chroma [(a*2 + b*2)1/2]. Measurementf bulb colour was conducted at six points on the equatorialxis and additionally at three points on the butt end cut zonef the bulbs on days 0 and 28 of storage a 5 ◦C and after 3ays at 15 ◦C in air. The butt end cut zone is the most sensi-ive to enzymatic browning (Artes et al., 2002a; Escalona etl., 2004). The colour of sliced fennel was measured on eachlice taken randomly, 30 per jar (Escalona et al., 2005a).
.7. Sugar and organic acid contents
After each evaluation, juice samples (20 mL) were frozent −70 ◦C. At the end of storage, samples were thawednd centrifuged (Sigma 1-13 model, Osterode, Germany) at0,468 × gn for 10 min. The supernatent was filtered twice,rstly by using a 0.45 �m pore size filter (Nylon Filter Mediaith Polypropylene Housing, Whatman, Clifton, NJ, USA)
nd secondly with a Sep-Pack Cartridge filter (C-18 Car-ridges Waters, Taunton, Ireland). The extracts were anal-sed on by HPLC (Merck Hitachi, Darmstadt, Germany) asescribed by Melgarejo et al. (2000). Sugar composition wasetermined by HPLC equipped with a refractive index detec-or (Hitachi, L-7490 model, Tokyo, Japan) and a Lichrospher50-4 NH2 column (Lichrospher, 5 �m, 100 NH2, Merck,armstadt, Germany). A 20 �L extract sample was injectedsing a mobile phase of 85:15 acetonitrile: water (Merck,ermany) at a 1.5 mL min−1 flow.Organic acids were analysed in 10 �L aliquots with a
on-polar derivatives Lichrospher column (RP-Select B,�m, Merck, Darmstadt, Germany). The mobile phase
0.3 mL min−1) was a combination of water and methanol99:1, v/v) with a buffer of 50 mM phosphate di-hydrogenotassium with H2SO4 (pH 3). Samples were read at 210 nmith a UV–vis dectector (Hitachi, L-7400, Tokyo, Japan).uantification of samples was determined by comparison
o authentic standards (Sigma–Aldrich Chemie, Steinheim,ermany). Values were expressed in g per 100 mL of juice.
.8. Sensory evaluations
At the beginning and at the end of cold storage and afterhe retail sale period (bulbs only), an informal panel of fiveeople (3 men and 2 women, aged 25–55), familiar with theensory properties of fennel, evaluated appearance, aromand texture. A nine-point scale to record their perceptions of
ppearance where 1: inedible, 3: poor, 5: fair, 7: good, and 9:xcellent was used. Aroma and texture were scored based on aimilar scale, where 1: complete lacking or soft, 5: moderate,nd 9: full characteristic or fresh, respectively (adapted from
t
iw
nd Technology 41 (2006) 307–316 309
ader et al., 1973). Browning on the butt end cut zone of theulbs and on cut slices was determined subjectively for eachepetition using the scale 1: none; 2: slight, 3: moderate, 4:evere; and 5: very severe. Both 4 and 5 indicate that slicesere commercially unacceptable (Escalona et al., 2005a).
.9. Statistical analysis
A completely randomised design with five replicates perreatment, where each glass jar constituted a replicate, waserformed. To determine the effect of storage time (at harvest,fter cold storage and after retail sale) and gas mixture (5 kPa2 + 5 kPa CO2; 5 kPa O2 + 15 kPa CO2; 21 kPa O2 + 0 kPaO2) a two-way ANOVA (P < 0.05, 0.01, 0.001) was carriedut. Mean values were compared by the LSD multiple rangeest to identify significant differences among treatments andignificant interactions between factors.
. Results and discussion
.1. Respiration rates
After 4 days at 5 ◦C, the respiration rates of bulbs storedn air (18 mg CO2 kg−1 h−1) was higher than those in 5 kPa
2 + 5 or 15 kPa CO2 (7–11 mg CO2 kg−1 h−1). During coldtorage, control bulbs showed a larger reduction in their res-iration rate (Fig. 1A). CA-stored bulbs from either treatmenthowed a relatively constant respiration rate throughout 28ays at 5 ◦C. The respiration rate at 5 ◦C was significantlyeduced when O2 levels decreased from 21 to 5 kPa. TheO2 level of 15 kPa stimulated the respiration rate as com-ared to a CA of 5 kPa CO2. This could be due to ‘Orion’ennel bulbs stored under high CO2 level showing a physio-ogical disorder (‘brown spot’) on the external leaves startingt the third week of storage. However, the respiration rate ofClio’ fennel bulbs at 0 ◦C was reduced when in a CA of 5 kPa
2, the CO2 level increased from 5 to 20 kPa (Artes et al.,002a). In fennel bulbs stored at 0 ◦C in air, a low to moderateonclimacteric respiratory behaviour with a respiration ratef 8–9 mg CO2 kg−1 h−1 was found (Escalona et al., 2004).
Respiration rates of control fennel slices were about 25%igher than under 5 kPa O2 + 15 kPa CO2, and 100% com-ared to 5 kPa O2 + 5 kPa CO2. After 3 days of cold stor-ge, the rates were 25.3 mg CO2 kg−1 h−1 for control, 12.6nd 20 mg CO2 kg−1 h−1 for 5 kPa O2 + 5 or 15 kPa CO2,espectively (Fig. 1B). Therefore, the slices in a CA of5 kPa CO2 had higher respiration rates than in a CA ofkPa CO2, although they maintained lower rates than inir. Furthermore, in contrast to results in intact bulbs, underCA of 15 kPa CO2, no physiological disorders on fennel
lices were found. This was probably due to lesser storage
ime.
After minimal fresh processing the respiration ratencreased around 25% compared to intact bulbs. This rateas slightly higher than the lower limit of the range between
310 V.H. Escalona et al. / Postharvest Biology and Technology 41 (2006) 307–316
Fig. 1. Respiration rates of intact bulbs (A) and slices of fennel (B) underdifferent atmospheres for 27 and 13 days at 5 ◦C, respectively. The symbolsaC
1acpthbowri(d2(ptcfcOa
Fig. 2. Ethylene production of intact bulbs (A) and slices of fennel (B) indaC
3
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a(aekbphysiological disorders.
re the average value for 5 replicates and bars ± S.E. (�) 21 kPa O2 + 0 kPaO2; (�) 5 kPa O2 + 5 kPa CO2; (�) 5 kPa O2 + 15 kPa CO2).
.2- and seven-fold cited for this kind of produce (Cantwellnd Suslow, 2002; Aguayo et al., 2004), depending on theultivars, maturity stage, O2 and CO2 levels, water vapourressure, presence of inhibitors, severity of wounding, andemperature. Therefore, the sliced cut did not seriouslyarm the fennel tissues as recommended for processing ofulbs. According to previous reports, the respiration ratesf diced fennel and intact bulbs for 13 days at 0 ◦C in airere 11–17 mg CO2 kg−1 h−1 and 9–14 mg CO2 kg−1 h−1,
espectively. For this reason, the effect of cutting resultedn CO2 production 50% higher than that of the intact bulbsEscalona et al., 2005a). Fennel slices showed a slightecrease in respiration when in air storage with rates of4–20 mg kg−1 h−1 at 5 ◦C and 16–14 mg kg−1 h−1 at 0 ◦CEscalona et al., 2005b). No other studies on minimal freshrocessing of fennel have been published so far. Never-heless, an increased respiration rate of diced onion in airompared to 5 kPa O2 + 0 kPa CO2 after 4 days at 4 ◦C wasound (Blanchard et al., 1996). On the other hand, fresh-
ut carrot showed a decreased respiration rate under 0.5 kPa2 + 10 kPa CO2 of about 55% at 0 ◦C, 65% at 5 ◦C and 75%
t 10 ◦C compared to air (Izumi et al., 1996).ti
ifferent atmospheres for 27 and 13 days at 5 ◦C, respectively. The symbolsre the average value for 5 replicates and bars ± S.E. (�) 21 kPa O2 + 0 kPaO2; (�) 5 kPa O2 + 5 kPa CO2; (�) 5 kPa O2 + 15 kPa CO2).
.2. Ethylene production
Intact bulbs under air and CA showed a decrease in ethy-ene production until day 17 of storage (Fig. 2A). At the endf the experiment, the ethylene production slightly rose in allreatments due to the start of decay on the bulb stalks. Afterdays at 5 ◦C, the bulbs reached a production rate of 0.9 �L2H4 kg−1 h−1 in air and 0.7 and 0.5 �L C2H4 kg−1 h−1 inCA of 5 kPa O2 combined with 5 and 15 kPa CO2, respec-
ively. Therefore, under both CA conditions, the metabolicctivity of bulbs was reduced 50% compared to that in air. InOrion’ fennel bulbs an ethylene production of 0.2–0.5 mL2H4 kg−1 h−1 at 0 ◦C was found (Escalona et al., 2004).
Low O2 levels reduced ethylene synthesis of vegetablesnd high CO2 levels delayed sensitivity of bulbs to ethyleneSaltveit, 2003). Consequently, low O2 and high CO2 levelsre interesting for storage of intact fennel because very highthylene could negatively affect their quality. Therefore, anowledge of respiration rates and ethylene production mighte a useful tool to predict rate of decay and development of
The ethylene production of the sliced fennel decreasedhroughout storage, particularly during the first 6 days, show-ng a similar behaviour to that of the respiration rate (Fig. 2B).
V.H. Escalona et al. / Postharvest Biology and Technology 41 (2006) 307–316 311
Table 1Mesophilic, psychrophilic, yeast, and mould counts in fennel slices at day 0 and after 14 days at 5 ◦C under different atmospheres
Treatments Mesophilic Psychrophilic Yeast Mould
Initial 5.2 ± 0.3 5.2 ± 0.4 ≤2.0 2.2 ± 0.2
After 14 days at 5 ◦C21 kPa O2 + 0 kPa CO2 8.9 ± 0.1 8.9 ± 0.2 ≤2.0 ≤2.0
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5 kPa O2 + 5 kPa CO2 8.8 ± 0.25 kPa O2 + 15 kPa CO2 9.3 ± 0.2
ata are mean values of three replicates and are expressed as log cfu g−1 ±
thylene production decreased when CO2 increased from 0o 15 kPa, reaching on day 3 a rate of 0.9, 0.63 and 0.47 �L
2H4 kg−1 h−1 under air, 5 kPa O2 + 5 kPa CO2 and 5 kPa2 + 15 kPa CO2, respectively.Fennel slices had a similar ethylene production to that
f intact bulbs until day 5 of cold storage. Subsequentlyhe ethylene production of the slices continued decreasingess than for the intact bulbs. This behaviour was unex-ected because after cutting, ethylene production commonlyncreases (Varoquaux and Wiley, 1994; Ahvenainen, 1996;antwell and Suslow, 2002). However, these results confirmur previous report on diced fennel at 0 ◦C (Escalona et al.,005a) and also those with sliced tomato at 2 ◦C (Artes etl., 1999b) and pears (Rosen and Kader, 1989). Izumi et al.1996), found that the ethylene production of fresh-cut carrotas lower than 0.1 �L kg−1 h−1 in air and in a CA of 0.5 kPa2 + 10 kPa CO2.
.3. Microbiological quality
Results for aerobic mesophilic and psychrophilic bacte-ia counts were similar to each other and increased duringhe cold storage period of 14 days from 5.2 log cfu g−1 atay 0 to 8.6–9.3 log cfu g−1 in all gas mixtures (Table 1).he bacterial counts were higher than the mesophilic maxi-um limit (7 log cfu g−1) prescribed by the Spanish standard
RD 3484/2000, 2001) and than the psychrophilic limit oflog cfu g−1 (Debevere, 1996). After 14 days at 0 ◦C, fen-el dices in an MAP of 11–13 kPa O2 + 9–12 kPa CO2 hadesophilic counts of 5.3–5.4 log cfu g−1 (Escalona et al.,
005a). Similar to this work, mesophilic and psychrophilicounts in diced onion increased from 4 log cfu g−1 at day 0o 8 log cfu g−1 after 14 days at 4 ◦C under 2 kPa O2 + 0 orkPa CO2 and air (Blanchard et al., 1996). However, foriced onion, the psychrophilic count decreased slightly inkPa O2 + 10 kPa CO2 due to the antimicrobial activity ofigh CO2 levels (Kader et al., 1989). Barriga et al. (1991),ound a significant increase of mesophilic and psychrophilicrowth on fresh-cut lettuce from 4 to 7 log cfu g−1 after 12ays at 4 ◦C in 3 kPa O2 + 3 or 5 kPa CO2 and air. Theseacteria counts slightly decreased in 3 kPa O2 + 10 kPa CO2t 4 ◦C. Nguyen-The and Carlin (1994) reported mesophilic
ounts in fresh-cut vegetables from 3 to 6 log cfu g−1 afterrocessing and from 3 to 9 log cfu g−1 after cold storage.
Additionally, in spinach leaves stored under a CA of.8 kPa O2 combined with 0 or 10 kPa CO2 at 5 ◦C, the
ftdc
.6 ± 0.2 ≤2.0 ≤2.0
.2 ± 0.3 ≤2.0 ≤2.0
esophilic and psychrophilic growth decreased in com-arison with air atmosphere. In low O2 alone or combinedith high CO2 levels at 5 ◦C, the bacterial counts decreasedetween 10- and 100-fold compared to air. However,hese atmospheres did not have any effect at 10 ◦C (Babicnd Watada, 1996). Nguyen-The and Carlin (1994), alsoeported that an increased CO2 level delayed the microbialrowth on chicory leaves at 2 and 6 ◦C, but not at 10 ◦C.he aerobic bacterial counts on fresh-cut celery were–7.7 log cfu g−1 after 14 days in MAP at 2 ◦C (Robbs etl., 1996). After 15 days at 4 ◦C, celery sticks stored underAP of 6 kPa O2 + 7 kPa CO2 showed a fresh quality better
han air reaching mesophilic and psychrotrophic counts of.9 and 1.6 log cfu g−1, respectively compared to 3.3 and.6 log cfu g−1 in air (Gomez and Artes, 2005).
In all gas mixtures, fennel slices registered a yeastnd mould growth (2.0–2.2 log cfu g−1) substantially lowerhan the Spanish legal limit (5 log cfu g−1 for yeasts andlog cfu g−1 for moulds). Similar mould and yeast countsave been reported in sliced fennel (Escalona et al., 2005a),iced onion (Blanchard et al., 1996) and diced kohlrabiEscalona et al., 2003). In contrast, Barriga et al. (1991) foundhat 3 kPa O2 + 10 kPa CO2 did not depress the yeast growthn cut lettuce.
.4. Colour change
In all intact bulb treatments a decrease in lightness (L*)f the external leaves from 80.4 (at harvest) to 77.7–78.9fter cold storage was found (data not shown). A significantnteraction between time and atmosphere factors (P < 0.05)as observed. An unexpected increase in L* values waseasured after the retail sale period in comparison with
8 days of storage in all gas mixtures. Significant changesn b*, chroma and hue angle values were found at harvest,fter cold storage and after retail sale. These colour differ-nces were affected by the increase in temperature duringhe retail sale period. Therefore, the colour values on exter-al leaves obtained by using a colorimeter were not a goodndicator of fennel bulbs as browning does not affect theeaves.
A significant interaction between time and atmosphere
actors (P < 0.001) was found for all colour parameters onhe butt end cut zone of the bulbs (Table 2). Browning wasemonstrated by darkening (decrease in L*), an increase inhroma values and a hue angle change toward red colours.
312 V.H. Escalona et al. / Postharvest Biology and Technology 41 (2006) 307–316
Table 2Colour changes of the butt end cut zone of ‘Orion’ fennel bulbs at harvest and after 28 days at 5 ◦C under different atmospheres followed by 3 days at 15 ◦C inair
Time (3.33)*** (0.27)** (1.52)*** (1.51)*** (1.82)***
Atmosphere ns ns (1.87)*** (1.85)*** (2.23)***
Time × atmosphere ns ns (2.64)*** (2.62)*** (3.15)***
L
*
TbnOadwb
eiOd
TCf
T
2
2
L
SD values are in parentheses, Probability: ns, not significant.** Significant at P < 0.05.** Significant at P < 0.001.
he colour changes were larger for control bulbs than foroth CA treatments. However, the CA-stored bulbs showedo colour changes compared to colour at harvest. Under 5 kPa2 + 5 kPa CO2, the bulbs showed less browning than that
t harvest. After the retail sale period, both CA treatmentselayed colour changes on the butt end cut zone of the bulbs,ith the treatment of 5 kPa O2 + 5 kPa CO2 performing theest. This result agrees with that reported previously by Artes
a(s
able 4hanges in fructose, mannose, glucose, sucrose levels and in glucose:fructose ratio of
ollowed by 3 days at 15 ◦C in air
ime (days) Atmosphere Fructose Ma
0 1.91 0.16
8 21 kPa O2 + 0 kPa CO2 1.44 0.145 kPa O2 + 5 kPa CO2 1.79 0.155 kPa O2 + 15 kPa CO2 1.44 0.16
8 + 3 21 kPa O2 + 0 kPa CO2 1.90 0.265 kPa O2 + 5 kPa CO2 1.78 0.195 kPa O2 + 15 kPa CO2 1.99 0.20
Time ns nsAtmosphere ns (0.0Time × atmosphere ns ns
SD values are in parentheses. Probability: ns. not significant. The mean values (n** Significant at P < 0.05.
t al. (2002a,b). In chicory, where a red colouration is the mostmportant disorder on the butt end cut zone, a CA of 10 kPa
2 + 10 kPa CO2 prevents the development of the red coloururing 21 days at 5 ◦C (Vanstreels et al., 2002).
*
The lightness (L ) of fennel slices diminished during stor-ge at 5 ◦C for 14 days irrespective of atmosphere treatmentTable 3). A significant interaction between time and atmo-phere factors (P < 0.001) was detected increasing the chroma
‘Orion’ fennel bulbs throughout 28 days at 5 ◦C under different atmospheres
nnose Glucose Sucrose Glucose/fructose
1.46 0.30 0.76
1.06 0.26 0.741.03 0.36 0.580.90 0.20 0.63
1.05 0.18 0.561.28 0.13 0.721.12 0.10 0.56
ns (0.10)** ns8)** ns ns ns
ns ns ns
= 5) are g per 100 mL juice.
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nd decreasing the hue angle values on control slices. AA of 5 kPa O2 + 15 kPa CO2 was found to be the best toelay browning on fennel slices. Escalona et al. (2005a) alsoeported that MAP of 11–13 kPa O2 + 9–12 kPa CO2 reducedrowning on the cut zones of fennel dices for while at 0 ◦Cor 14 days.
.5. Sugar contents
Fructose and glucose were the predominant sugars in fen-el bulbs with an initial level of 1.91 and 1.46 g 100 mL−1,espectively (Table 4). These sugars did not register signifi-ant differences after cold storage and the retail sale period.owever, sucrose content significantly decreased after retail
ale in all gas mixtures. Probably the reduction of sucroseas related to the increased respiration rate caused by theigher temperature during this period. The sucrose consump-ion could maintain the fructose and glucose levels in thelycolysis pathway.
The initial mannose content (0.16 g 100 mL−1) was main-ained for 28 days at 5 ◦C and slightly increased after the retailale due to the weight loss (Table 4). The glucose:fructoseatio was lower than one, indicating a higher synthesis inpposition to glucose.
Fennel slices had no change in fructose and mannose con-ents for 14 days at 5 ◦C (Table 5). Fructose is the mostmportant sugar and respiratory metabolic substrate of fennel.owever, glucose and mainly sucrose could be the sources
o generate new fructose for maintaining the energy require-ents of the cells. For that reason, glucose and sucrose
ontents decreased during storage in all gas mixtures. Thelices also showed a glucose:fructose ratio lower than one, asn the intact bulbs. Similar results were previously reported iniced fennel stored 14 days at 5 ◦C (Escalona et al., 2005a).eimdal et al. (1995), found that the sugar content in shred-ed iceberg lettuce slightly declined after 10 days at 5 ◦Cnder MAP. The glucose and fructose contents decreasedbout 10–17% and 6–17%, respectively. Lopez-Galvez et
l. (1997), reported similar results in fresh-cut romaine let-uce stored in MAP. The reduction of total sugar content wasrom 2.1 to 1.7 g/100 g after 15 days at 5 ◦C. According tolanchard et al. (1996), the sucrose loss found in diced onion
t
rb
able 5hanges in fructose, mannose, glucose, sucrose levels and glucose:fructose ratio of ‘
ime (days) Atmosphere Fructose Man
0 1.91 0.16
4 21 kPa O2 + 0 kPa CO2 1.46 0.135 kPa O2 + 5 kPa CO2 1.06 0.165 kPa O2 + 15 kPa CO2 1.12 0.10
Time ns nsAtmosphere ns nsTime × atmosphere ns ns
SD values are in parentheses. Probability: ns, not significant. The mean values (n* Significant at P < 0.01.
** Significant at P < 0.001.
nd Technology 41 (2006) 307–316 313
nder air and 2 kPa O2 alone during 12 days at 4 ◦C coulde due to hydrolysis of sucrose toward glucose and fruc-ose. Under 2 kPa O2 + 10 kPa CO2, the hydrolysis of sucroseas delayed because the respiration rate of diced onion was
educed.
.6. Organic acid contents
Oxalic acid was the main organic acid of fennel bulbs withn amount of 30.4 mg per 100 mL−1 juice at harvest (Table 6).his value was higher than that reported by Souci et al. (1986)f 5 mg per 100 g fresh weight although our results werexpressed per fresh juice. After cold storage and the retailale period, the oxalic acid decreased to 11.56–14.81 mger 100 mL−1 juice, independent of the gas mixtures. Theseesults agree with the reduction of malic acid content in greenomatoes after 4 weeks at 12 ◦C. The citric acid changesere different depending on cultivar. However, storage in
ir and 5 kPa O2 + 5 kPa CO2 had no effect on acid contentGoodenough et al., 1982).
Fennel slices showed a decrease in oxalic acid contentsfter cold storage (Table 6). A CA of 5 kPa O2 + 5 to 15 kPaO2 did not delay the oxalic acid loss following the sameattern as for sugar contents (Table 5). After cold storage,he oxalic acid content of slices was similar to that of intactulbs, possibly because the respiration rate in slices waswo-fold higher than in bulbs although their storage timeas half. Therefore, no clear influence of gas mixtures on
he oxalic acid consumption of fennel stored at 5 ◦C wasound.
.7. Decay and physiological disorders
At the end of cold storage, control bulbs developed bacte-ial soft-rot (Erwinia and Pseudomonas), gray mould (Botry-is cinerea), and watery rot (Sclerotinia spp.) on the end ofulb stalks. According to Snowdon (1991), these kinds ofecay are normal in fennel bulbs stored at chilling tempera-
ures.
During the retail sale period, the dehydration of the stalkseduced decay growth. The decay of control bulbs was helpedy the prolonged storage of 28 days at 5 ◦C.
Orion’ fennel slices throughout 14 days at 5 ◦C under different atmospheres
nose Glucose Sucrose Glucose/fructose
1.46 0.30 0.76
0.82 0.06 0.560.72 0.03 0.680.72 0.04 0.64
(0.71)* (0.20)*** nsns ns nsns ns ns
= 5) are g 100 mL−1 juice.
314 V.H. Escalona et al. / Postharvest Biology and Technology 41 (2006) 307–316
Table 6Changes in oxalic acid content of whole bulbs and slices of fennel throughout 28 days at 5 ◦C under different atmospheres followed by 3 days at 15 ◦C in airand troughout 14 days at 5 ◦C under different atmospheres
Time (days) Atmosphere Intact bulbs Slices
0 30.43 30.43
After cold storage 28 d 5 ◦C 14 d 5 ◦C28 21 kPa O2 + 0 kPa CO2 24.63 14.81
5 kPa O2 + 5 kPa CO2 9.97 11.565 kPa O2 + 15 kPa CO2 12.27 14.11
After retail sale period 28 d 5 ◦C + 3 d 15 ◦C21 kPa O2 + 0 kPa CO2 13.505 kPa O2 + 5 kPa CO2 11.975 kPa O2 + 15 kPa CO2 12.43
Time (12.20)*** (12.61)***
Atmosphere ns nsTime × atmosphere ns ns
L ues (n =*
isHbi(afssrwbdrs
iomwH1l
3
a
TCf
T
2
2
Af
*
SD values are in parentheses, probability: ns. not significant, the mean val** Significant at P < 0.001.
Browning on the butt end cut zone of the fennel bulbsncreased in all treatments. In air, browning was scored asevere after cold storage and retail sale periods (Table 7).owever, browning was delayed under CA conditions, thiseing more effective at 15 than 5 kPa CO2. A significantnteraction was found between time and atmosphere factorsP < 0.001), showing differences between evaluation periodsnd air compared to CA conditions. After 3 weeks of storage,ennel bulbs stored under 15 kPa CO2 showed little brownpots on the external leaves that affected around 10% of theurface. This disorder did not increase subsequently after theetail sale period. An MAP of 16–17 kPa O2 + 6–7 kPa CO2ithin baskets and 6–7 kPa O2 + 10 to 12 kPa CO2 within
ags inhibited browning of the butt end cut of fennel for 14ays at 0 ◦C. However, only the bag treatments showed aesidual effect for delaying browning at the end of the retailale period (Escalona et al., 2004).
sssi
able 7hanges in appearance, aroma texture, and browning on the butt end cut zone of ‘
ollowed by 3 days at 15 ◦C in air
ime (Days) Atmosphere Appearance
0 8.08 21 kPa O2 + 0 kPa CO2 5.0
5 kPa O2 + 5 kPa CO2 6.35 kPa O2 + 15 kPa CO2 5.5
8 + 3 21 kPa O2 + 0 kPa CO2 2.55 kPa O2 + 5 kPa CO2 6.05 kPa O2 + 15 kPa CO2 4.5
Time (0.94)***
Atmosphere (0.94)***
Time × atmosphere (1.63)***
ppearance scored on 1: inedible, 5: fair, and 9: excellent. Aroma and texture scorresh, respectively. Browning scored on 1: none; 3: moderate, and 5: very severe. L** Significant at P < 0.05.** Significant at P < 0.001.
5) are mg 100 mL−1 juice.
After cold storage, fennel slices showed neither physiolog-cal disorders nor decay in any treatment. However, browningn the cut was scored as severe (higher than the limit ofarketability) in control slices, but it was efficiently delayedhen the CO2 level increased from 5 to 15 kPa (Table 8).amza et al. (1996), found that after 16 days at 4 ◦C underkPa O2 + 10 kPa CO2 fresh-cut romaine lettuce showed
ower browning compared to air.
.8. Sensory attributes
After cold storage and retail sale periods, the appearancet harvest decreased in all treatments mainly in control bulbs
howing decay development (Table 7). At the end of the retailale, the bulbs stored under 5 kPa O2 + 15 kPa CO2 reached acore slightly lower than 5 due to little brown spots develop-ng on the external leaves. However, under 5 kPa O2 + 5 kPa
Orion’ fennel bulbs troughout 28 days at 5 ◦C under different atmospheres
Aroma Texture Browning
6.8 8.5 1.05.5 5.8 4.35.8 6.9 3.45.8 7.1 2.4
5.8 5.7 4.16.0 6.8 3.05.8 6.7 2.3
ns (0.74)*** (0.55)***
ns (0.41)** (0.55)***
ns ns (0.95)***
ed on 1: complete lacking or soft, 5: moderate, and 9: full characteristic orSD values are in parentheses, probability: ns, not significant.
V.H. Escalona et al. / Postharvest Biology and Technology 41 (2006) 307–316 315
Table 8Changes in appearance, aroma, texture, and browning of ‘Orion’ fennel slices troughout 14 days at 5 ◦C under different atmospheres
Time (days) Atmosphere Appearance Aroma Texture Browning
Appearance scored on 1: inedible, 5: fair, and 9: excellent. Aroma and texture scored on 1: omplete lacking or soft, 5: moderate, and 9: full characteristic orfresh, respectively. Browning scored on 1: none; 3: moderate, and 5: very severe. LSD values are in parentheses, probability: ns, not significant, significant atP*
Cfihd
s(so(
1baCaosoct
Cnd2C(iacft
daeOw1
twCatCtcr
4
4
5fmrB5s
4
5m5aid
A
< 0.01.** Significant at P < 0.001.
O2 a better appearance with a score higher than acceptableor consumption was found. The texture of the bulbs dimin-shed during cold storage although all treatments had a highumidity. The aroma did not show any significant changeuring the experiment.
After the retail sale, the bulbs kept in 5 kPa O2 + 5 kPa CO2howed the best sensory quality in texture and appearanceTable 7). In agreement with our previous results in bulbstored at 0 ◦C under CA after the retail sale period, browningf the butt end cut and external leaves was almost inhibitedArtes et al., 2002a).
The sensory quality of the fennel slices decreased after4 days at 5 ◦C, appearance being the attribute most affectedy cold storage (Table 8). The appearance scores reached 5.4nd 5.9 in slices from 5 kPa O2 combined with 5 or 15 kPaO2, respectively, but control slices had a low score. Theroma decreased from 6.8 to 2–3 in all gas mixtures. Ratingf the initial texture also was significantly reduced after coldtorage, although it was considered as good (about 7) with-ut significant differences between treatments. The texturehanges could be more related to the high relative humidityhan to O2 and CO2 levels.
It was previously reported that 11–13 kPa O2 + 9–12 kPaO2 resulted in slight browning on the surface of diced fen-el, although chemical, sensory, and microbial quality of theices were suitable for commercial purposes (Escalona et al.,005a). Additionally, an MAP with 2–6 kPa O2 + 10–20 kPaO2 at 0 and 5 ◦C maintained good quality of sliced fennel
Escalona et al., 2005b). However, our results for brown-ng development contrast with those reported by Albenzio etl. (1998), who considered enzymatic browning as the mainause of postharvest deterioration of minimally processedennel, probably due to different fennel cultivar sensitivitieso browning.
Shredded iceberg lettuce had a sensory quality thatecreased after 10 days at 5 ◦C maintaining a better appear-nce under 2 kPa O2 and 7 kPa CO2. Low O2 levels delayed
nzymatic browning because PPO showed a lower affinity for2 (Heimdal et al., 1994). The visual quality of diced onionas higher under 2 kPa O2 and 10–15 kPa CO2 than air after2 days at 4 ◦C (Blanchard et al., 1996). In other reports,
i0Sa
he visual quality of fresh-cut lettuce significantly decreasedhen the storage conditions were air or 3 kPa O2 + 0–5 kPaO2, but the appearance improved in 10 kPa CO2 (Barriga etl., 1991). According to Mateos et al. (1993), the phenol con-ent in cut lettuce decreased under air enriched with 20 kPaO2 after 10 and 20 days at 2.5 ◦C, probably due to a reduc-
ion of cytoplasmic pH and PAL activity. However, when theut lettuces were placed in air at 20 ◦C, the cytoplasmic pHecovered the normal value and PAL activity.
. Conclusions
.1. Fennel bulbs
The respiration rate of bulbs decreased under CA withkPa O2 compared to air. The increase of the CO2 level
rom 5 to 15 kPa raised the respiration of the bulbs. A gasixture with low O2 and moderate CO2 levels was more
ecommended for storage of bulbs up to 28 days at 5 ◦C.rowning on the butt end cut of the bulbs was delayed underkPa O2 combined with 5 or 15 kPa CO2. Fennel bulbs are
ensitive to 15 kPa CO2 level from the 3rd week at 5 ◦C.
.2. Fennel slices
Under CA conditions, the respiration rate of slices was0% lower than in air. CA with 5 kPa O2 could be recom-ended for keeping quality of sliced fennel up to 14 days at◦C combined with 5 or 15 kPa CO2. Under CA, chemicalnd sensory attributes of slices suffered minimal changes innitial values. Browning of the cutting zones was particularlyelayed under 5 kPa O2 + 15 kPa CO2.
cknowledgements
The authors are grateful to financial support of the Span-
sh Ministry for Education and Science, project AGL2004-8004/ALI, and to CEBAS-CSIC (Murcia) and FRUVEGoc. Coop. (Torre Pacheco, Murcia) for providing facilitiesnd fennel, respectively.
3 iology
R
A
A
A
A
A
A
A
B
B
B
B
C
D
E
E
E
E
G
G
G
H
H
H
H
I
K
K
L
L
M
M
N
N
P
P
R
R
R
S
S
S
V
V
Fresh-cut Refrigerated Fruits and Vegetables. Chapman and Hall, NewYork, pp. 226–268.
16 V.H. Escalona et al. / Postharvest B
eferences
guayo, E., Escalona, V.H., Artes, F., 2004. Metabolic behavior and qual-ity changes of whole and fresh processed melon. J. Food Sci. 69,148–155.
hvenainen, R., 1996. New approaches in improving the shelf life offresh-cut fruits and vegetables. Trends Food Sci. Technol. 7, 179–186.
lbenzio, M., Corbo, M.R., Sinigalia, M., 1998. Influenza del confezion-amento sulla shellife di ortaggi di IV gamma. Industrie Alimentaria37, 150–341.
rtes, F., Martınez, J.A., Marın, J.G., 1999a. Quality changes in mini-mally processed ‘Romaine’ lettuce as affected by several treatments.In: Hagg, M., Avenhainen, R., Evers, A.M., Tiikkala, K. (Eds.), Agri-Food Quality. II. Quality Management of Fruits and Vegetables. TheRoyal Society of Chemistry, London, pp. 115–118.
rackett, R.E., 1987. Microbial consequence of fresh-cut fruits and veg-etables. J. Food Qual. 10, 195–206.
antwell, M.I., Suslow, T.V., 2002. Postharvest handling systems: fresh-cut fruits and vegetables, In: Kader, A.A. (Ed.), Postharvest Tech-nology of Horticultural Crops, 3rd ed., Pub 3311, University ofCalifornia, Davis, pp. 445–463.
ebevere, J., 1996. Criteria en practische methoden voor de bepaling vande houdbaarhei dsdatum in the etikettering. In: Temmerman, G., Cre-mer, G., Thyssen, M., Devebere, J. (Eds.), Etikettering, Houdbaarheiden bewaring (voedingsmiddelen en recht 2). Die Keure, Brugge Bel-gium, pp. 37–64.
scalona, V.H., Aguayo, E., Artes, F., 2003. Quality and physiologicalchanges of fresh-cut kohlrabi. HortScience 38, 1148–1152.
scalona, V.H., Aguayo, E., Gomez, P., Artes, F., 2004. Modified atmo-sphere packaging inhibits browning in fennel. Lebensm-Wiss. Tech-nol. 37, 115–1121.
scalona, V.H., Aguayo, E., Artes, F., 2005a. Overall quality throughoutshelf life of minimally fresh processed fennel. J. Food Sci. 70, 13–17.
scalona, V.H., Artes-Hernandez, F., Artes, F., 2005b. Gas compositionand temperature affects quality of fresh processed fennel. HortScience40, 737–739.
oodenough, P.W., Tucker, G.A., Grierson, D., Thomas, T., 1982.Changes in colour, polygalacturonase, monosaccharides and organicacids during storage of tomatoes. Phytochemistry 21, 281–284.
orny, J.R., 1997. A summary of CA and MAP requirements and recom-mendations for fresh-cut (Fresh-cut) fruits and vegetables, in: Gorny,J.R., (Ed.), Fresh-Cut Fruits and Vegetables and MAP. CA‘97 Pro-ceedings 5. University of California, Davis, USA, pp. 30–-33.
eimdal, H., Kuhn, B.F., Poll, L., Larsen, L.M., 1995. Biochemicalchanges and sensory quality of shredded and MA-packaged iceberglettuce. J. Food Sci. 60, 1265–1268.
eimdal, H., Larsen, L.M., Poll, L., 1994. Characterization of polyphe-nol oxidase from photosynthetic and vascular lettuce tissues (Lactucasativa). J. Agric. Food Chem. 42, 1428–1433.
uxsoll, C.C., Bolin, H.R., 1989. Processing and distribution alterna-tives for fresh-cut fruits and vegetables. Food Technol. 43, 124–128.
zumi, H., Watada, A.E., Ko, N.P., Douglas, W., 1996. Controlled atmo-sphere storage of carrot slices, sticks and shreds. Postharvest Biol.Technol. 9, 165–172.
ader, A.A., Lipton, W.J., Morris, L.L., 1973. Systems for scoring qualityof harvested lettuce. HortScience 8, 408–409.
ader, A.A., Zagory, D., Kerbel, E.L., 1989. Modified atmosphere pack-aging of fruits and vegetables. Crit. Rev. Food Sci. 28, 1–27.
opez-Galvez, G., Salveit, M., Cantwell, M., 1996. The visual quality ofminimally processed lettuces stored in air or controlled atmospherewith emphasis on romaine and iceberg types. Postharvest Biol. Tech-nol. 8, 179–190.
opez-Galvez, G., Peiser, G., Nie, X., Cantwell, M., 1997. Qualitychanges in packaged salad products during storage. Z. Lebensm.Unters. FA. 205, 64–72.
ateos, M., Ke, D., Cantwell, M., Kader, A.A., 1993. Phenolicmetabolism and ethanolic fermentation of intact and cut lettuceexposed to CO2-enriched atmosphere. Postharvest Biol. Technol. 3,225–233.
elgarejo, P., Salazar, D.M., Artes, F., 2000. Organic acids and sugarcomposition of harvested pomegranate fruits. Eur. Food Res. Technol.211, 185–190.
amesny, A., 1993. Hinojo. In: Postrecoleccion de hortalizas. Edicionesde Horticultura S.L. I, pp. 257–262.
guyen-The, C., Carlin, F., 1994. The microbiology of fresh-cut freshfruits and vegetables. Crit. Rev. Food Sci. 34, 371–401.
ascual, M.R., Calderon, V., 2000. Microbiologıa Alimentaria:Metodologıa Analıtica para Alimentos y Bebidas, 2nd ed. Dıaz deSantos, Madrid, Spain, p. 441.
ico, B., 2001. Hinojo. In: Nuez, F., Yacer, G. (Eds.), La HorticulturaEspanola. Horticultura S.L., Tarragona, Espana, pp. 178–181.
eal Decreto 3484/2000, 2001. Boletın Oficial del Estado. Spain 11, pp.1435–1441.
obbs, P.G., Bartz, J.A., McFie, G., Hodge, N.C., 1996. Causes of decayof fresh-cut celery. J. Food Sci. 61, 444–448.
osen, J.C., Kader, A.A., 1989. Postharvest physiology and quality main-tenance of sliced pear and strawberry fruits. J. Food Sci. 54, 122–124.
altveit, M.E., 2003. Is it possible to find an optimal controlled atmo-sphere? Postharvest Biol. Technol. 27, 3–13.
nowdon, A.L., 1991. Colour atlas of post-harvest diseases and disor-ders of fruits and vegetables. Wolfe Publishing, vol. 2, vegetables,Aylesbury, UK.
ouci, S.W., Fachmann, W., Kraut, H., 1986. Food composition andnutrition tables. 3rd ed. Deutsche Forschungsanstalt fur Lebensmit-telchemie, Garching b. Munchen.
anstreels, E., Lammertyn, J., Verlinden, B.E., Gillis, N., Schenk,A., Nicolaı, B.M., 2002. Red discoloration of chicory under con-trolled atmosphere conditions. Postharvest Biol. Technol. 26, 313–322.
aroquaux, P., Wiley, R.C., 1994. Biological and biochemical changesin fresh-cut refrigerated fruits and vegetables. In: Wiley, R.C. (Ed.),
