Experiments on Extended ControlledAtmosphere Storage of HeidiMango: 19981 2S.A. Oosthuyse and M.C. DoddIHortResearch SA, P. O. Box 3849, Tzaneen 08502Transfresh Africa, P.D. Box 87, Howard Place 7450

ABSTRACTHeidi mangoes were harvested at the recommended stage of maturation. Following the commercial packlinetreatment, the fruits were placed in cool-storage at 9.SC, a temperature which usually causes chilling injury. After3 days, some of the fruits were placed under controlled atmosphere storage. Two differing atmospheres wereevaluated (Atmos. A - similar C02 and 02 concentrations; Atmos. B - high C02 and low 02 concentration).Conventional storage and controlled atmosphere storage occurred in the same cool-storage room. After a further18 days, all of the fruits were removed from their storage environments and were placed in a well ventilatedlaboratory at 20C to ripen fully. Quality evaluation was performed on a fruit when it attained the firm-ripe stage.Both atmospheres reduced the manifestation of disease. Atmos. B reduced the incidence surface scald (lowtemperature damage to the skin). Ground skin colouration and taste were slightly elevated by atmosphere storage.Total soluble solids content was greater following storage under Atmos. A. Differences in skin corking (russet),lenticel damage incidence, internal disorder incidence or pH in relation to treatment were not apparent. The resultsconfirm a benefit of controlled atmosphere storage for Heidi mango.

UITTREKSELHeidi-mangoes is op die korrekte stadium van volwassenheid gepluk. Nadat die vrugte die pakhuisbehandeling gekryhet, is dit in 'n koelkamer teen 9.SC, 'n temperatuur wat gewoonlik koueskade veroorsaak, geberg. Na drie dae issommige vrugte in gekontroleerde atmosfeer (toestande) geberg. Twee verskillende atmosfere is getoets (Atmos. A- gelykwaardige C02 en 02 konsentrasies; Atmos. B - hoog C02 en laag 02 konsentrasie). Konvensionele bergingen gekontroleerde atmosfeer berging het in dieselfde koelkamer voorgekom. Na 'n verdere 18 dae is al die vrugteuit hul bergingsplekke verwyder en in 'n goedgeventileerde laboratorium by 20C geplaas om ten volle ryp te word.Kwaliteitsbeoordeling is gedoen toe die vrugte in 'n ferm-rypstadium was. Beide atmosfere het die manifesstasie vansiektes verminder. Atmos. B het die voorkoms van oppervlaktebrand verminder (lae temperatuur-skade aan dieskil). Verkleuring en smaak is effens verhoog deur atmosferiese berging. Die totale oplosbare vaste inhoud was groteronder Atmos. A-berging. Verskille in lentiselskade, interne problem voorkoms of pH met betrekking tot behandelingwas nie ynsigbaar nie. Die resultate bevestig die voordeel van gekontroleerde atmosferiese berging virHeidi-mangoes.

Heidi mangoes develop skin and pulp injury whenplaced in cool-storage for prolonged periods. The pulpbecomes brown and the skin develops darkened indenta-tions which are referred to as surface scald (Fig. 1).

In a previous study (Oosthuyse, 1997), no benefit ofcontrolled atmosphere storage of Heidi mangoes harvestedat an advanced stage of maturation was found. The out-turnof good quality fruits was generally poor. However, whenfruits were harvested at the conventional maturation stage,atmosphere storage reduced the incidence of surface scald,pulp browning and internal breakdown, and enhanced shelf-life and taste. The out-turn of good quality fruits was rela-tively good. The fruits were stored at 12.Se.

The aim of the present study was to confirm the priorbenefits of controlled atmosphere storage found, and toassess atmosphere storage at 9.SC, a temperature whichusually causes surface scald.

Fig. I Suiface scald on Heidi fruits which often occurs asa result of low temperature storage.

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Fig. 2 Differences in disease manifestation in relation totreatment. Bars headed by differing letters differ signifi-cantly (P<O.05).

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Fig. 3 Differences in scald severity in relation to treatment.Bars headed by differing letters differ significantly

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Fig. 4 Differences in ground skin colouration in relation totreatment. Bars headed by differing letters differ signifi-cantly (P<O.05).

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Fig. 5 Differences in taste in relation to treatment. Barsheaded by differing leiters differ significantly (P<O.05).

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Fig. 6 Differences in total soluble solids content in relationto treatment. Bars headed by differing letters differ signifi-cantly (P<O.05).

ISO Heidi fruits were harvested from an orchard in theTzaneen region. Average degree of pulp colouration was 0.2(± 0.1; Heidi pulp colouration chart). The fruits were sub-jected to the commercially adopted packline treatment [fruitrespectively washed in a I % soap solution (ByProx), dippedin hot-water at 50C for 5 minutes, dipped in prochloraz (180ml Omega/lOOl H20) for 20 seconds, and hand waxed withTAG], and were placed in cool-storage at 9.5C for threedays [storage under normal atmosphere for three days priorto storage under atmosphere was done to effect commercialrepresentation, i.e., pre-storage at a packhouse, followed byrefrigerated trucking to Cape Town harbour, followed bycool-storage until ship loading when controlled atmospherestorage would commence]. After this period, 50 randomlyselected fruits were placed in air containing C02 and 02 atsimilar concentrations (Atmos. A), and 50 randomly se-lected fruits were placed in air containing C02 at a highconcentration relative to that of 02 (Atmos. B). The remain-ing fruits were stored in normal air (controls). All of the

fruits were placed in cool-storage [in a cool-storage room,the fruit under atmosphere being in especially designedTransfresh bins] for a further 18 days, after which they wereplaced, under normal atmosphere, in a well ventilated labo-ratory maintained at 20C (±1C) to continue ripening. Duringthe latter period, the stage of ripening of each fruit wasassessed daily with a densimeter (Heinrich Bareiss,Oberdischingen, Germany). Each fruit was evaluated whenit was firm-ripe (densimeter reading of less than 60 andgreater than 40).

The Completely Randomised Design, (comprising 50single fruit replicates of three treatments), was employed.

Fruit evaluation on ripening comprised the following:

Skin corking (russet) in each fruit was rated accordingits severeness. A rating of 0 was given if symptoms wereabsent, a rating of 1 if symptoms were present but werelocalised to a small portion of the fruit's surface, a rating of2 if approximately 1/3 of the fruit's surface showed symp-toms, a rating of 3 if 2/3 of the fruit's surface was affected,or a rating of 4 if the entire fruit's surface was visiblyaffected.

Skin colour in each fruit was rated. A rating of 0 wasgiven when signs of skin colouration were absent, a ratingof 1 if a transition to a lighter green was apparent, a ratingof 2 if regions of the skin had become yellow but the totalarea which was yellow was less than the total area whichwas green, a rating of 3 if regions of the skin had becomeyellow and the total area which was yellow exceeded thetotal area which was green, or a rating of 4 if the skin wascompletely yellow. The skin area covered with red-blushwas not considered.

Disease manifestation in each fruit was rated accordingits severeness. A rating of 0 was given if a fruit was diseasefree, a rating of 1 if symptoms were present but werelocalised to a small portion of the fruit's surface, a rating of2 if approximately 1/3 of the fruit's surface showed symp-toms, a rating of 3 if 2/3 of the fruit's surface was affected,or a rating of 4 if the entire fruit's surface was visiblydiseased.

Lenticel damage and surface scald were rated by ap-proximating the percentage of the skin surface over whichsymptoms could be seen. The percentages designated wereeither 0, 25, 50, 75 or 100.

To assess internal quality in each fruit, each was first cutthrough twice; longitudinally along the flattened margins ofthe seed. In each fruit, juice from the cheeks thus obtainedwas evaluated by measuring its pH (Mettler Toledo 120 pHmeter) and total soluble solids content (Euromex RF 0232hand held refractometer), and by assessing its taste.

Taste was rated. A rating of 1 was given if taste wasdeemed appealing, a rating of 0 if taste was deemed satis-factory but not appealing, or a rating of -1 if taste wasdeemed unsatisfactory.

Physiological disorder manifestation in each fruit wasrated as was disease manifestation, except that the degree towhich the mesocarp as opposed to the exocarp (skin) wasaffected, was taken into account.

The date were subjected to non-parametric analysis ofvariance (Kruskal Wallis).

Disease manifestation was markedly reduced by atmos-phere storage (Fig. 2). Storage under Atmos. B reduced theseverity of surface scald (Fig. 3). No apparent effect onsurface scald was found following storage under Atmos. A.Ground skin colouration was slightly elevated by atmos-phere storage (Fig. 4). Taste was markedly elevated byatmosphere storage (Fig. 5). Storage under Atmos. A gaverise to a slight elevation in total soluble solids content (Fig.6). Differences in skin corking (russet type symptom), len-tice! damage incidence or physiological disorder incidencein relation to treatment were not apparent. The incidence ofthese disorders was acceptably low (10% of fruits affected;data not shown). Differences in pH in relation to treatmentwere not apparent (data not shown).

Atmosphere storage reduced surface scald and the extentof disease manifestation, and increased skin colouration,taste, and total soluble solids content. These results are inagreement with those found in a previous study wherereductions in surface scald and increases in taste wereobserved (Oosthuyse, 1997).

O'Hare, and Prasad (1993) specifically associated thealleviation of chilling injury symptoms to atmospheres hav-ing elevated concentrations of C02. In th.eir study, reduced02 concentrations had no significant effect on chilling in-jury. The results of the current study are consistent withthose of these workers.

An enhancement in taste following atmosphere storagehas also been found in fig (Turk et ai., 1994), apple (Jank-ovic and Drobnjak, 1992), kiwifruit (Sawada et ai., 1993)and plum (Ben and Gaweda, 1992).

The fungistatic effect of controlled atmosphere storageof fruits has often been documented, and is generally as-cribed to the action of the high C02 concentrations (Ertanet ai., 1990; Skrzynski, 1990; Ben-Arie et ai., 1991; Brashet ai., 1992; Sugar, et ai., 1994).

In view of the beneficial results obtained in storing Heidimangoes under atmosphere, semi-commercial adoption forexport to Europe might be considered. A storage tempera-ture of 11C is recommended in view of the results ofprevious research aimed at ascertaining the optimum cool-storage temperature for this cultivar (unpublished).

Thanks are due to Transfresh Africa for the provision ofequipment and for sponsoring this study. This study was notsponsored by the South African Mango Growers' Associa-tion.

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Marilyn Mango in France with TECTROLTEKAt the by TransFresh Africa, Controlled Atmosphere Specialists