USE OF THE MEMBRANE SYSTEM FOR LONG-TERM CA STORAGE OFCABBAGE

Y. Garfcpy1, G.S.V. Raghavan1, and R. Theriault2

Agricultural Engineering Department, Macdonald College ofMcGill University, Ste-Anne-de-Bellevue, QuebecH9X ICO; andResearch Station, Research Branch, Agriculture Canada, St-Jean-sur-Richelieu, Quebec J3B 6Z8.

Contribution no. J-958, received 5 January 1984, accepted 30 July 1984

Gariepy, Y., G.S.V.Raghavan, andR. Theriault. 1984. Use of themembrane system for long-term CAstorageof cabbage. Can. Agric. Eng. 26: 105-109.

In the first part of theexperiment, the suitability of the silicone membrane system for controlled atmosphere (CA)storage of Winter Green cabbages (Brassica oleracea var. capitata) was studied using small experimental chambers.Inthesecond part, three different CA starting techniques were evaluated using acabbage cultivar imported from Florida.In eachcase, there wasa control with the product stored under regular atmosphere (RA) at the sametemperature. Thesilicone membrane system maintained CAconditions of 3.5-5%C02and1.5-3%02, where 5%and3%, respectively,were expected. After 198 days of storage, total mass loss was 14% under CAcompared to 40% under RA. The threemethods used to achieve the CA conditions did not have any significant effect on the storability of cabbages, but allmaintained 3-4% C02 and 2-3% 02 while 5% and 3%, respectively, were expected. In both experiments, cabbagesstored under CA showed better retentionof their green color, fresher appearance, firmer texture and lower total masslosses compared to those stored under RA.

Dans un premier temps, on etudie la possibility de r6aliser efficacement, dansde petites unites experimentales, l'entre-posage sous atmosphere contr616e (CA) de choux (Brassica oleracea var. capitata), avec le systeme de membrane ausiliconeen utilisant le cultivarWinterGreen produit localement. Dans un deuxiemetemps, trois techniques differentesde demarrage de l'atmosphere controlee sontevalu6es avecdes chouximported dont le cultivarn'etait pas connu. Dansles deux cas, des lots de choux entreposes sous atmosphere normale (RA) dans la meme chambre froide servent detemoins. Le systemede membrane au silicone a permis de maintenir des conditions CA de 3.5-5% de C02 et 1.5-3%d'02 alorsqu'on visait 5 et 3%, respectivement. Apres 198jours d'entreposage, les pertesde massestotalesetaientde14% sous CA comparativement a 40% sous RA. Les trois techniques de demarrage du CA n'ont produit aucun effetsignificatif sur la qualite des choux entrepos^s; les conditions de CA de 3-4% de C02 et 2-3% d'02 ont ete obtenuesalorsqu'on visait5 et 3% respectivement. Danslesdeuxexperiences, unecouleurplusverte, une apparence plus fraicheet une texture plus ferme caract6risaient les choux entreposes sous CA comparativementa ceux entreposes sous RA.

Under Canadian weather conditions

vegetable production is usually limited toone crop per year. For most vegetables,the harvest takes place during the periodextending from early August to late October. In most cases, the product is soldreadily after the harvest or stored for ashort period of time in conventional refrigerated room. To sustain the supply forthe remaining months of the year, Canadian consumers and food processors haveto rely on expensive greenhouse production and imports. Considering the presentday fuel costs it becomes economicallyfeasible and essential to develop long-termstorage systems that will reduce this typeof dependency. The ideal long-term storage system should have the ability to provide low temperature, high relative humidity and optimum gas composition inorder to minimize the metabolic activityof the stored commodity. Under theseconditions the stored product is expectedto maintain its freshness and nutritionalquality for a much longer period of time.Characteristic advantages of such a system as compared with the commonly usedrefrigerated room are: (i) reduction of therespiration rate (RR), (ii) reduction of the

transpiration rate, (iii) reduction of theacidity losses, (iv) preservation of thechlorophyll levels, (v) retardation of thepectic hydrolytic changes, (vi) reductionof the volatile compounds, and (vii) reduction of the bacterial infestations (Bohl-ing and Hansen 1977; Smock 1979).

Long-term CA storage of cabbage wasfound advantageous by many authors.Among those, van den Berg and Lentz(1966) reported that Mammoth Red Rockand Penn State Ballhead cabbage storedfor 8 mo in CA of 5% C02 and 3% 02 withonly 25% and 30% trimming losses, respectively. Furry et al. (1981) have suggested 8-mo storage at 0-1 °C in high relative humidity (97%) and CA of 5% C02,2.5% 02, with the remaining atmospheremade of N2and traces of other gases. Theyalso stress the need to reduce the ethyleneinside the storage room in order to minimize its effect on the stored produce. Gee-son et al. (1980) and Isenberg (1979) havealso recommended CA long-term storagefor cabbage.

There are many ways to provide the desired gas composition in the storage environment, each having its own characteristics and advantages over the other

CANADIAN AGRICULTURAL ENGINEERING, VOL. 26, NO. 2, WINTER 1984

systems. They can be classified into threemajor groups: (i) the 02 control systems,such as the catalytic burners, hypobaricstorages and liquid nitrogen atmospheregenerators; (ii) the C02 control systems,such as the C02-scrubbers; and (iii) the so-called membrane systems. The ProducePackage, Marcellin and the Atmolysairsystems are examples of the latter category.

Recently, commercial long-term CAvegetable storage facilities have been introduced on the Canadian market. Raghavan et al. (1984) have demonstrated thatWinter Green cabbage grown in Quebecstored very well for 7 mo at 1-1.5°C undera CA of 5-6% C02,2-3% 02,92% N2andtraces of other gases. The total mass loss,including storage and trimming loss, wasless than 10% in the CA room comparedto more than 30% in the refrigerated roomoperating concurrently at 0-0.5°C. In thiscommercial trial, the CA was maintainedin the storage room with an Atmopile designed by Atmolysair. This unit uses thesemi-permeable membrane developed byMarcellin and Leteinturier (1966, 1967).The membrane is an elastomer of silicone

which has the ability to exchange gases at

105

different rates according to their chemicaland physical properties. For instance, at apressure of 100 kPa its permeability to C02is 1750 L/(daym2), with a selectivity of5.5 for the ratio of C02:02 and 2.5 for theratio of C02:C2H4.

It should be pointed out that the resultsquantifying the effect of different methodsof CA establishment in the storage facilityon the storability of agricultural productsare not available in the literature. There

fore, it is important that this aspect bequantified in order to obtain valuable recommendations.

The objectives of this study were: (1)To assess the suitability of the siliconemembrane system for CA storage of cabbage using small experimental chambers.(2) To compare the effect of different CAstarting methods on the storability of cabbage.

MATERIALS AND METHODS

Membrane Storage SystemIn the experimental chambers the CA

composition was achieved and maintainedby means of the silicone membrane system. Two types of chambers were designed. The first type, used for determining the suitability of the membranesystem, was made of clear plexiglass (9mm thick) and is shown in Fig. 1. Thesilicone membrane was fixed on one side

of the chamber and its area was selected

as 225 cm2according to the procedures described by Raghavan et al. (1982). Figure2 shows the second type of chamber designed for studying different techniques ofestablishing CA conditions. It was madewith a section of 0.25-m diameter PVC

pipe. A soft rubber gasket was installedbetween the lid and the cylinder to ensuregood airtightness. A 36-cm2 siliconemembrane window was installed on the lid

of each chamber to attain and maintain the

desired CA composition. This chamberwas easier to manipulate and seal than thefirst type.

The two experiments were conducted ina RA cold room operating at 1.5°C and80-90% relative humidity.

Parameters Recorded

Temperature, relative humidity and CAcomposition were monitored on a regularbasis. The air temperature was measuredwith thermocouples while the relative humidity was measured with a Lufft hygrometer model AB62B. For the completeduration of the experiment, the CA composition (C02, 02, N2 and C2H4) was analyzed on a weekly basis with a gas chro-matograph and the output was recordedwith a programmable reporting integrator.

106

SILICONE

MEMBRANE

ACCESS TUBE

ACCESS TUBE

GAS SAMPLING UNIT

THERMOCOUPLE

All measurements

are in mm

Figure 1. Experimental chamber usedto studythe suitability of the silicone membrane systemfor CA storage of cabbage.

THREADED ROD

6.4 mm diameter

CLEAR PLEXIGLASS LID

6 mm thick

ACCESS TUBE

SEPTUM FOR GASSAMPLING

SILICONE MEMBRANE

Figure 2. Experimental chamber used to compare CA initiation techniques for cabbage storage.

Storage and trimming losses wereassessed at the end of the storage period.The trimming operation consisted of removing all the maids and undesirableleaves (dessicated, rotted or blemished),and the discolored end of the stem. Thevisual criteria selected to assess the final

quality of the stored produce were color,amount of leaf abscission, molding, rotting, and leaf and root regrowth.

Considering the CA chamber as a closedsystem in which all the gas exchange occurs across the membrane window, it ispossible to estimate the RR and respirationquotient (RQ) of the stored product withsimple numerical procedures. The parameters required for the mathematical modelare mainly the partial pressure of the different gases involved in the respiratoryprocessandthe diffusion characteristics ofthe silicone membrane.

Experimental ProcedureSuitability ofthe membrane systemfor CAstorage of cabbage. The silicone membrane system was tested on four chambersof the first type specially designed for CAcondition of 5% C02, 3% 02 and 92% N2.Four similar but unsealed chambers were

used for RA condition (0.03% C02, 21%02 and 78% N2).

The required quantity of Winter Greencabbage (harvested in October 1981) wasobtained from a local producer. On 1 Dec.1981, the cabbages were selected at random from a pile, cleaned, weighed andplaced in their respective chamber (around57 kg per chamber). The CA chamberswere then carefully closed and the experiment started. The experiment was endedafter 198 days of storage. Storage andtrimming losses were then assessed andcompared.

CANADIAN AGRICULTURAL ENGINEERING, VOL. 26, NO. 2, WINTER 1984

Taste panel tests were conducted toevaluate and compare the appearance, thetexture, the flavor and the overall acceptance of trimmed cabbage from RA and CAwith fresh market cabbage. The rawshredded cabbage samples were assessedwith the Hedonic scale which ranges from1, liked extremely, to 9, disliked extremely.Effect ofCA starting methods on the storability of cabbage. The experiment wasconducted to assess and compare the effect of three different CA starting methodson the storability of cabbage. The cabbages imported from Florida were boughtfrom a local wholesale dealer. Unfortu

nately, it was not possible to identify thecultivar. The 12 CA chambers were de

signed to maintain a CA composition of5% C02, 3% 02 and 92% N2. The experiment was started on 21 Apr. 1982 andended after 159 days in RA and 265 daysin CA, using the procedures described inthe previous experiment.

The CA inside the CA chambers were

established as follows: (i) Treatment no.1:Four chambers filled with 7-8 kg ofcoldcabbage heads (1.5°C) were flushed witha gas mixture of 5% C02, 3% 02 and 92%N2. This method established the CA almost instantaneously, (ii) Treatment no.2: Cold cabbage heads were placed intofour chambers, without any specific intervention. This resulted in slow establish

ment of the desired CA since the RR of

the cabbage is low at 1.5°C (1750 kJ/tonne-day), (iii) Treatment no. 3: Fourchambers filled with cabbage were kept ata temperature of 20°C until the averageC02 level reached 5%. The chambers werethen transferred into the cold room. This

technique provided a fast establishment ofthe CA since the RR of cabbage at 20°C(11 670 kJ/tonne-day) is much greaterthan at 1.5°C.

In addition to the above treatments, fourchambers filled with cabbage were exposed to the ambient air (normal air composition) prevailing in the cold room.These were considered as controls.

RESULTS AND DISCUSSIONS

Air Temperature and Relative Humidity

The cold room temperature, set at1.5°C, normally fluctuated between 0 and3°C. However, the air temperature insidethe experimental chambers was not affected by these variations and ranged from1.5-1.7°C. The RH recorded in the cold

room ranged between 80 and 90% whilelevels close to saturation were monitoredinside the CA chambers.

CA Progression in the ExperimentalChambers

In the four CA chambers containingWinter Green cabbage, the first experiment, the C02 contents rose to 5-6% (Fig.3) during the first 20 days of the experiment and graduallydropped to 3-4% during the next 15days. Then the C02 slowlyincreased to 5% during the remaining period of the experiment. The 02 contentsdropped steadily in the chambers from21% to 3% within 20 days from the startand gradually decreased to 1.5-2% overthe remaining period.

In the second experiment (Figs. 4 and5), the flushing method used to initiate the

CA-treatment no. 1 led to onset concentrations of 3.0% C02 and 6.0% 02. Insufficient air mixing and improper gas flowcontrol were the two reasons for the CAnot reaching the desired level of 5% C02and 3% 02. The method used to start CA-treatment no. 2 promoted self establishment of the CA in the chambers as it iscommonly practiced with the membranesystem. In all the chambers, the C02 peaksoccurred after 15 days of storage andranged between 4 and 5%. The progression of the C02 and 02 followed a trendcharacteristic of the silicone membrane

window system. CA-treatment no. 3 wasdesigned for a fastbuild up of the CA in

20 40 60 80 100 120

TIME , days

Figure 3. C02 and 02 concentration curves obtained from the suitability of the membranesystem experiment.

10 -

zo

<cr

UJ4

— TREATMENT 1

— TREATMENT 2

TREATMENT 3

0 20 40 60 80 100 120 HO 160 180 200 220 240 260TIME . days

Figure 4. C02 concentration curve obtained under each treatment in the experiment comparingdifferent CA starting techniques.

CANADIAN AGRICULTURAL ENGINEERING, VOL. 26, NO. 2, WINTER 1984 107

TREATMENT 1

TREATMENT 2

TREATMENT 3

J. J. J. J.

120 K0 160 160 200 220 240 260

TIME , days

Figure5. 02 concentration curve obtained undereach treatment in the experiment comparingdifferent CA starting techniques.

ing gas compositions. It was further observed that the average RR of cabbagestored under CA was 2.5 mg C02/(kg-h).This is close to 40% of that in RA at thesame temperature as reported by Porritt(1975) and U.S. Department of Agriculture (1977).

Excluding the first 10 days of storage,the calculated RQ of the Winter Greencabbage varied from 0.75 to 0.95. The experiment with imported cabbage showdRQ values varying between 0.5 and 1.2.

Visual Quality and Disorder Assessment

In both experiments, the final visualqualityof the cabbagewasexcellent in the

10

o

<

ui4

CA chambers compared to its counterpartin the RA chambers. In particular, the CAWinter Green cabbage showed better colorretention and no leaf abscission. At the end

of the second experiment, the RA imported cabbage had a yellowish color andsuffered from extensive molding and rotting, while CA cabbage showed little yellowing and browning of the outsideleaves, and little superficial molding androtting. Only a few CA cabbage heads suffered from browning and softening of theinner tissues.

Mass Losses

Storage, trimming and total mass losseswere assessed and the overall results areshown in Tables I and II. In the experiment with Winter Green cabbage, the lowstorage mass loss observed in both RA andCA can be attributed to the high RH levelsin all the chambers. The total mass lossobtained for Winter Green cabbage storedin CA was significantly (0.05 level) lowerthan that in RA demonstrating the beneficial effect of CA for long-term storage.

With the imported cabbage cultivar, thehigher RA storage mass loss was due toextensive molding and rotting. The totalmass loss of the cabbage stored under RAwas significantly greater than for cabbagestored in CA. However, the different CAstartingtechniquestested did not showanysignificant differences in total mass lossesat the 0.05 level.

Sensory EvaluationA taste panel test was performed to

assess and compare the quality of WinterGreen cabbage stored in RA and CA, with

TREATMENT

TREATMENT

TREATMENT

^-«-—zrzz*

Jim

240 260

the experimental chambers. The C02peaked three days after the beginning ofthe experiment, whereas 02 contentsreached their equilibrium level within 15days. Afterwards, theevolutionof the C02and 02 followed a trend characteristic ofthe silicone membrane window system.

In both experiments, the C02 and 02levels obtained were below the designedvalues of 5 and 3%, respectively. The twopossible reasons that can explain the under-designed values are the inaccurate estimates of the RR under CA and that theprocedures to calculate the membraneareado not consider the amount of 02 consumed by the stored commodity but onlythe C02 produced.

As shown in Fig. 6, large variations inC2H4 concentrationswere measuredby thechromatographic analysis. The major factorresponsible forthesevariations wasthelow sensitivity of the instrument. In bothexperiments, the C2H4 contents rapidlyrose to 2-3 ppm within the first month ofstorageand then slowly increased to an average of 4 ppm for the remainder of theexperiment. These C2H4 levels did not affectthequalityof theproductsinceno disorders associated with its presence wereobserved.

Respiration Rate and Respiratory Quotient

Large fluctuations of RR and RQ wereobserved during the establishment of theCA, and they were associated with thechanging gas composition. Reasons to explain this specific behavior are unknownand more investigations are required toassess the RR and RQ changes with vary

Figure 6. C2H4 concentration curve obtained under each treatment inthe experiment comparingdifferent CA starting techniques.

108CANADIANAGRICULTURALENGINEERING, VOL. 26, NO. 2, WINTER 1984

TABLE I. MASS LOSS DATA OF WINTER GREEN CABBAGE AFTER 198DAYS OF STORAGE

Initial Storage Trim Total

mass loss loss loss

Treatment (kg) (%) (%) (%)

Controlled

atmosphere 57.21 2.3a 11.7c U.Oe

Regularatmosphere 58.04 3.5b 36.64 40.1/

a-f Means withthe same letter are not significantly different atthe0.05level.

TABLE H. MASS LOSS DATA OF IMPORTED CABBAGE AFTER 159 DAYS OF STORAGEUNDER RA AND 265 DAYS UNDER CA

Initial Storage Trim Total

mass loss loss loss

Treatment (kg) (%) (%) (%)

CA-1 6.67 1.2a 13.8c 15.0a"

CA-2 7.00 0.9a 19.1c 20.0a1

CA-3 7.36 0.9a 14.0c 14.9a*

RA 14.63 U.Ob 24.6c 38.6c

a-e Means with the same letter are not significantiy different at the 0.05 level.

TABLE HI. MEANS SCORE OBTAINED FROM THE SENSORY ASSESSMENT OF THE WINTERGREEN CABBAGE COMPARED TO THE FRESH MARKET CABBAGE

Cabbage Appearance Texture Flavor Overall

sample score score score acceptance

Controlled

atmosphere 3.5a 3.1c 3.0c 3.2*

Regularatmosphere 4.1b 4.8d 4.9/ 4.9/i

Fresh market

cabbage 2.8a 3.1c 3.8c,/ 3.6*

a-g Means with the same letterarenot significantly different at the 0.05 level.

the fresh market cabbage (unknown cultivar) available at the end of spring. Fromthe results shown in Table III, it was evident that Winter Green cabbage stored for7 mo under CA was comparable in desirability to fresh market product, while RAcabbage was not.

RECOMMENDATIONS

From this study, it can be recommendedthat

(1) The silicone membrane system is suitable for long-term CA storage of cabbagesince it maintained CA of 3.5-5% C02,

1.5-3% 02,92-95% N2and traces ofothergases, with no external intervention.(2) The management method used to establish the CA in long-term storage facilities using the membrane system is not ascritical as commonly expected. No specialCA starting method is necessary.(3) Ethylene scrubbers are not requiredwith the membrane system, since the ethylene is removed from the CA storageroom by diffusion. In the experiments, thelevels reached were around 4 ppm and didnot affect the product quality since no leafabscission was observed on the CA stored

cabbage.

CANADIAN AGRICULTURAL ENGINEERING, VOL. 26, NO. 2, WINTER 1984

ACKNOWLEDGMENTS

The authors are grateful to NRC and Agriculture Canada for the financial assistancethrough their ERDAF program. They furtherthank Mr. R. Plasse for his assistance in this

study.

REFERENCES

BOHLING, H. and H. Hansen. 1977. Storageof white storage cabbage (Brassica olera-cerea var. capitata) in controlled atmosphere. Acta Hortic. 62: 49-54.

FURRY, R. B., F. M. R. ISENBERG, andM. C. JOHNSEN. 1981. Postharvest controlled atmosphere storage of cabbage.Search Agriculture, Cornell University.No.19, 1981.

GEESON, J. D. and K. M. BROWNE. 1980.Controlled atmosphere storage of winterwhite cabbage. Ann. Appl. Biol. 95: 267-272.

ISENBERG, F. M. R. 1979. CA storage ofvegetables. Hortic. Rev. 1: 337-394.

MARCELLIN, P. and J. LETEINTURIER.1966. Etude d'une installation de conservation de pommes en atmosphere contr616e.Inter. Inst. Refrig. Bui. Annexe 1966-1.Bologne, Italy.

MARCELLIN, P. and J. LETEINTURIER.1967. Premieres applications industriellesdes membranes de caoutchouc de silicone a

l'entreposage des pommes en atmospherecontrolee. Congr. Inter. Froid, Madrid,Spain. 1-9. Int. Inst, du Froid, Paris,France.

PORRITT, S. W. 1975. Entreposage des fruitset legumes. Agric. Can. Publ. 1532,Ottawa,Ont. 62 pp.

RAGHAVAN, G. S. V., S. TESSIER, N.CHAYET, E. R. NORRIS, and C. T.PHAN. 1982. Storage of vegetable in amembrane system. Trans. ASAE (Am. Soc.Agric. Eng.) 25: 433-436.

RAGHAVAN, G. S. V., Y. GARIEPY, R.THERIAULT, and A. LANSON. 1984.System for controlled atmosphere long-termcabbage storage. Int. J. Refrig. 7: 66-71.

U.S. DEPARTMENT OF AGRICULTURE.

1977. The commercial storage of fruits,vegetables and florist and nursery stocks.USDA, Washington, D.C. 301 pp.

VAN DEN BERG, L. and C. P. LENTZ.1966. High humidity storage of carrots andcabbage. Int. Inst. Refrig. Bull., Annexe1966-1, 355 pp.

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