Yearbook �03 55 Jaarboek �03

INTRODUCTIONIn the past the firmness of export avocadoswas maintained by reducing the storage tem-perature during transport. However, tem-perature control alone will not prevent rip-ening during a 28 day export period, espe-cially during the late season. Since 1996, con-trolled atmosphere (CA) became available inSouth Africa as an additional tool to reduceripening during storage. Due to the success

Semi-commercial evaluation ofSmartFresh� with South African

export avocados in static containers atthe Westfalia packhouse during 2002D Lemmer#, J Bezuidenhout*, S Sekhune*, P Ramokone*, L Letsoalo*,

T R Malumane#, P Chibi#, Y Nxundu# , M Hobson+ and F J Kruger#

#ARC-ITSC, Private Bag X11208, Nelspruit 1200, South Africa+ARC-ITSC � Merensky experimental farm

*Westfalia Estates, PO Box 14, Duiwelskloof 0835, South AfricaE-mail: danie@itsc.agric.za (or) frans@itsc.agric.za

ABSTRACTDuring the 2000 and 2001 seasons, intensive laboratory testing was done with 1-methylcyclopropene (1-MCP), an ethylene blocker on avocado fruit. All the major South Africancultivars were tested and aspects such as storage potential, respiration rate and fruit qualityupon ripening were covered. The results were extremely positive and the manufacturer (Rohm& Haas, USA) has subsequently registered the product in South Africa. During 2002, a tabletformulation of 1-MCP, SmartFreshTM, was tested under semi-commercial conditions on �Fuerte�and �Hass� at the Westfalia packhouse in Tzaneen. The product was applied in a static reefercontainer. SmartFresh TM was found to effectively inhibit the ripening process of �Hass� and�Fuerte� under the semi-commercial conditions described above. The inhibition of ripening wasmore intense in �Fuerte� than in �Hass�. Furthermore, the inhibition of ripening was more in-tense in the smaller count 18 fruit than in the bigger count 10-12 fruit. The increase in storagelife was found to be comparable to that attained with control atmosphere storage (CA) whenSmartFreshTM was applied at the optimum dosage. The most appropriate packhouse baseddosage regime for all sized fruit was determined and commercial application commenced dur-ing 2003.

of this method, virtually all avocados are cur-rently exported under CA. This method cer-tainly improved the chances of landing a hardfruit in Europe and extended the harvestingwindow. Cold storage and CA both delay theripening process by slowing down the me-tabolism of the fruit.

During the 2000 � 2001 seasons, the ARC-ITSC has been evaluating the effectiveness ofSmartFreshTM, a product containing an ethyl-

South African Avocado Growers' Association Yearbook. 2003. 26:55-64

Jaarboek �03 56 Yearbook �03

ene inhibitor, 1-methyl cyclopropene (1-MCP),on avocados (Lemmer et al., 2002). The tri-als were done in the laboratory using all themajor export cultivars and covered aspectssuch as storage potential, respiration rate andfruit quality upon ripening.

The main conclusions drawn from the ini-tial laboratory based trials were:� SmartFreshTM slows down the ripening

process of avocado under export simula-tion conditions.

� The ripening retarding effect is more in-tense on slow metabolizing CV�s such asRyan compared to CV�s with a faster me-tabolism such as Hass.

� SmartFreshTM can be applied over a widerange of concentrations and a dosage ef-fect exists.

� SmartFreshTM can be applied at the tem-perature the fruit are to be exported at.

� Storage potential of SmartFreshTM treatedfruit is comparable to CA fruit.

� SmartFreshTM suppresses respiration rate toa greater extent than CA.

� SmartFreshTM reduces grey pulp underlaboratory conditions.

� The storage period is not to be over ex-tended as this may increase the incidenceof fungal pathology.Due to the extremely positive results, the

manufacturer (Rohm & Haas, USA) has regis-tered the product on avocados in South Af-rica.

During 2002, a tablet formulation,SmartFreshTM, was tested under semi-com-mercial conditions on �Fuerte� and �Hass� atthe Westfalia packhouse in Tzaneen. Theproduct was applied under packhouse con-ditions in a static reefer container. The re-search aimed to determine suitable applica-tion periods and optimum dosage regimes for�Fuerte� and �Hass�avocado fruit.

MATERIAL AND METHODSFruitIn the case of �Fuerte� count 18 (211 � 235 g )and count 10 (366 � 450 g) fruit were used. In

the case of �Hass� count 18 and count 12 (306� 365 g) fruit were used. Freshly harvestedand packed export fruit were sampled for thetrials.

TreatmentsTaking the previous results into considera-tion, it was decided to include twoSmartFreshTM concentrations (300 ppb and500 ppb) and to treat the fruit for 16 hours.On packhouse management request, an 8hour regime was also included in one of thetrials. In all cases, the SmartFreshTM treatedfruit were compared with untreated controlfruit from the same batch.

SmartfreshTM treated fruit were also com-pared with CA stored fruit (CO2 = 6% and O2=4%). A flow-through CA system (consistingof a 100 L drum connected to gas regulatorsand a CA control board) was installed in aWestfalia cold room for this purpose.

Treatment application and storageTwo 58m3 reefer shipping containers wereparked at Westfalia packhouse for the dura-tion of the 2002 season. One container wasair-tightened and used for treating the fruitwhile the second was used for cool storage.

A total number of 11 container loads weretreated during the season. �Fuerte� fruit weretreated on 18 April, 25 April, 5 June, 23 July,24 July, 31 July, 2 August. �Hass� fruit weretreated on 5 June, 23 July, 24 July, 2 August,26 August, 27 August, 28 August, 29 Augustand 30 August. During the first two trials, ex-port fruit samples (3 boxes per size) wereplaced in the center of 20 pallets. The rest ofthe pallets consisted of local market fruit. Theaim of the experiment was to establishwhether the 1-MCP gas diffused evenlythrough the container from the point of re-lease at the door. After the application pe-riod of 16 hours, the doors and the vents wereopened. The pallets were removed and 10 ofthe pallets were replaced with pallets contain-ing control untreated samples. The palletswere placed in the same order, from the con-

Yearbook �03 57 Jaarboek �03

denser side towards the door of the container.The fruit were stored inside the container withthe vents 15% open to simulate the exportperiod to Europe. After a 28 days storageperiod at the SAAGA prescribed temperatureregime, the fruit were ripened at 18oC andevaluated.

During the remaining 9 trials, the treatmentcontainer was filled with bulk bins contain-ing local market fruit. Two sets of export fruitsamples (three boxes of each count) wereplaced near the condenser and door, on topof the bulk bins. After treatment, the samplefruit were removed from the pallets andstored in the second empty container.

Evaluation criteriaIndividual fruit were comprehensively evalu-ated as they ripened. This was done by theapplication of moderate finger pressure to thefruit on a daily basis. Densimeter readingswere also taken upon evaluation to ensurethat the fruit were cut within similar firm-ness ranges. Fruit ripening was expressedas the mean number of days until the fruitripened and a longitudinal ripening profilewas composed.

The following criteria were includedwhen evaluating the fruit upon ripening:� No. of days to ripen� Bruising� Black cold damage� Lenticel damage� Dusky browning� Grey pulp� Pulpspot� Vascular browning� Anthracnose� Stem-end rot.

The physiological and pathological dis-orders were scored on a scale of 1 � 3 where1 depicted a mild and 3 a severe disorder.

RESULTS AND DISCUSSIONFigure 1 is a representation of the effect thatSmartFreshTM has on the external colour of�Hass� fruit. This photograph was taken upon

removal from a 28 day cold storage period inone of the experiments during which certainlogistical problems were encountered. Thecontrol fruit has started turning black duringstorage, while the SmartFreshTM treated fruitremained green. This visually exemplifies theripening inhibition properties of SmartFreshTM.

Figure 2 demonstrates the effect of palletposition within the container during the ap-plication and storage period on the ripeningof �Fuerte� count 18 fruit. Pallet position didnot make a difference. This indicates thatSmartfreshTM diffused effectively through thecontainer.

Figure 1. SmartFreshTM slows down thedegreening of �Hass� fruit during coldstorage. This photograph was takendirectly after storage, during one of thetrials where logistical problems caused thecontrol fruit to ripen prematurely.

Figure 2. Mean number of days required to ripen count18 �Fuerte� fruit treated and stored in different palletpositions within the container. The fruit were treatedon 25 April with 300 ppb SmartFreshTM for 16 hoursbefore being stored with untreated samples for 28 daysat 7oC. Bars marked with the same symbol are notsignificantly different (Student t-test, P>0.05).

Jaarboek �03 58 Yearbook �03

The number of days required toripen �Fuerte� fruit during the vari-ous trials, is displayed in Figure 3.Treatment with SmartFreshTM led toa significant increase in the averagenumber of days to ripen, through-out the season. This was true for thecount 18 and count 10 fruit. How-ever, the inhibition of ripening wasmore pronounced in the smallercount 18 fruit than in the bigger count10 fruit. When comparing the 300ppb and 500 ppb treatments, it is clearthat the higher concentration ofSmartfreshTM more drastically inhib-ited ripening than the lower concen-tration. Nevertheless, the effect at-tained with the 300 ppb treatmentwas still satisfactory.

During the treatment carried outon 25 April, the packhouse capacitywas overloaded. Due to insufficientstorage space, the treatment pallets

were stored in side halls of the load-ing zones, with no temperature con-trol. Furthermore, only one forkliftwas available which had to be sharedwith the packhouse and oil-factory.For this reason, the palletelised fruitstood outside in the sun for severalhours. Regardless of these sub-opti-mal conditions, the 300 ppb treatmentwas still able to retain storage poten-tial. This is a very promising observa-tion, indicating that SmartFresh TM willhave a buffering effect against tem-perature related hick-ups in the coldchain.

The number of days until ripe re-corded for �Hass� fruit is shown in Fig-ure 4. A trend similar to �Fuerte� wasobserved. However, the Hass fruit,especially the bigger count 12 fruit,reacted less favourably than �Fuerte�to the SmartFreshTM treatment. Thismight be contributed to the highermetablic rate of �Hass� fruit. The gen-

Figure 3. Mean number of days taken to ripen counts10 and 18 �Fuerte� fruit at 18oC. The fruit were treatedon the listed dates inside a 58 m3 refrigerated seafreight container with either 300 or 500 ppbSmartFreshTM for 16 hours, before being stored withuntreated samples for 28 days at the indicated exporttemperatures used at the time. Bars marked withthe same symbol are not significantly different. Thestatistics apply separately for each treatment dateand fruit count (Student t-test, P>0.05).

Figure 4. Mean number of days taken to ripen counts12 and 18 �Hass� fruit at 18oC. The fruit were treatedon the listed dates inside a 58 m3 refrigerated seafreight container with either 300 or 500 ppbSmartFreshTM for 16 hours, before being stored withuntreated samples for 28 days at the indicated exporttemperatures used at the time. Bars marked withthe same symbol are not significantly different. Thestatistics apply separately for each treatment dateand fruit count (Student t-test, P>0.05).

Yearbook �03 59 Jaarboek �03

eral effect was nonetheless acceptableand, as will be shown later, very similarto that attained with CA.

The percentage �Fuerte� fruit withgrey pulp is portrayed in Figure 5. Theuntreated fruit showed an increasingprevalence as the season progressedand this trend started earlier and to agreater extend in the bigger count 10fruit. It is promising to note that theSmartfreshTM treatments led to a signifi-cant decrease in the grey pulp inci-dence of, especially, the count 10 fruit.The reduction was more prominentand consistent in the higher dosagetreatments (500 ppb) of 24 July and 2August.

The incidence of grey pulp in �Hass�fruit is portrayed in Figure 6. The preva-lence of the disorder was too low todraw any conclusions.

The incidence of anthracnose in�Fuerte� is represented in Figure 7. As

the season progressed, the incidenceof the infection increased. It istherefore promising to note thatonly one SmartFreshTM treatment(count 10; treated on 31 July)showed a significantly higher inci-dence of anthracnose. We expectedthe lengthening of the storage periodto cause more anthracnose infec-tions.

A similar trend was noticed in�Hass� (Figure 8). Only one Smart-FreshTM treatment showed a signifi-cant increase in anthracnose infec-tion (count18; treated on 30 August).This treatment was done at thehigher dosage (500 ppb) and the rip-ening period was considerablylonger in this specific case. The in-tensity of the infection was also in-fluenced. With the control, all 16%of infected fruit scored 1. With theSmartFreshTM treatment, 16% of thefruit obtained a rating of 1, while

Figure 5. Percentage counts 10 and 18 �Fuerte� fruitwith grey pulp as recorded when the fruit ripened.The fruit were treated on the listed dates inside a58 m3 refrigerated sea freight container with either300 or 500 ppb SmartFreshTM for 16 hours, beforebeing stored with untreated samples for 28 days atthe SAAGA export temperatures used at the time.Bars marked with the same symbol are notsignificantly different. The statistics applyseparately for each treatment date and fruit count(χ 2-test, P<0.95).

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refrigerated sea freight container with either 300 or500 ppb SmartFreshTM for 16 hours, before being storedwith untreated samples for 28 days at the SAAGA exporttemperatures used at the time. Bars marked with thesame symbol are not significantly different. Thestatistics apply separately for each treatment date andfruit count (χ 2-test, P<0.95).

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Jaarboek �03 60 Yearbook �03

7.4% scored 2 and 3.7% scored 3. Caremust therefore be taken not to overextend the shelflife by using too higha dosage. This was also noticed in thelaboratory trials conducted during theprevious 2 seasons (Lemmer et al.,2002).

The percentage of �Fuerte� fruitwith stem-end rot is displayed in Fig-ure 9. The control fruit did not showa significant increase in infection to-wards the end of the season. However,the SmartfreshTM treatments did. Thisincrease was earlier and more promi-nent in the count 10 fruit and wasagain caused by the lengthening of thestorage period.

With �Hass�, the early season Smart-FreshTM treatment conducted on 5 June,led to a significant increase in stem-endrot (Figure 10). In this regard it mustbe mentioned that it is common to finda high incidence of stem-end rot in-fection at the beginning of the harvestwindow, when the fruit are still rela-tively immature. This is exacerbatedby further lengthening of the storageperiod. However, the severity of theinfection was not influenced.

The highest incidence of in stem-end rot in �Hass� was recorded duringthe late season (2 and 30 August) incount 12 fruit. These treatments wereboth done at the higher 500 ppb re-gime and at first glance may be as-cribed to the lengthening of the stor-age period. However, these two trialsalso showed the highest incidence oflenticel damage (Figure 11) andbruising (Figure 12). The pre-harvestquality of the fruit was obviously poor.

In Table 1, SmartFreshTM is com-pared with CA. Both methods inhib-ited ripening to a similar degree incount 12 Hass fruit during both theearly (Table 1a) and the late (Table 1b)season. During the early season, no

Figure 7. Percentage counts 10 and 18 �Fuerte�fruit with anthracnose, as recorded when the fruitripened. The fruit were treated on the listeddates inside a 58 m3 refrigerated sea freightcontainer with either 300 or 500 ppb SmartFreshTM

for 16 hours, before being stored with untreatedsamples for 28 days at the SAAGA exporttemperatures used at the time. Bars marked withthe same symbol are not significantly different.The statistics apply separately for each treatmentdate and fruit count (χ 2-test, P<0.95).

Figure 8. Percentage counts 12 and 18 �Hass� fruitwith anthracnose, as recorded when the fruit ripened.The fruit were treated on the listed dates inside a 58m3 refrigerated sea freight container with either 300or 500 ppb SmartFreshTM for 16 hours, before beingstored with untreated samples for 28 days at theSAAGA export temperatures used at the time. Barsmarked with the same symbol are not significantlydifferent. The statistics apply separately for eachtreatment date and fruit count (χ2-test, P<0.95).

Yearbook �03 61 Jaarboek �03

anthracnose occurred in any of thetreatments. However, during the lateseason both SmartfreshTM and CAcaused significant increases in the in-cidence of anthracnose infection.Both treatments also caused an in-crease in the incidence of stem-end-rot during the early season. Althoughthe interpretation of the late seasondata was confounded by discrepan-cies between the cold room and con-tainer data, a similar trend seemed toexist. As mentioned repeatedly, theobserved increase in pathological dis-orders can be contributed to thelengthening of the shelf-life period.This gives the infections more time todevelop under favourable conditions.

In Figure 13, the 8 hour exposureperiod is compared to the 16 hourtreatment period. Three Smart-FreshTM dosage regimes were used,namely 300 ppb, 400 ppb and 500 ppb.From the graph it is clear that the 8

hour regime was less effective than the16 hour regime. In case of count 12fruit, no significant increase was ob-tained at both the 300 ppb and 400 ppbconcentrations when treated for 8hours. Only the 500 ppb treatmentgave a significant increase in shelf lifewhen treated for 8 hours. In case ofthe smaller count 18 fruit, both the 400ppb and 500 ppb treatments were ef-fective when applied for 8 hours.

The above results infer that differ-ent concentrations of SmartFfreshTM isrequired for small and large fruit, whentreating the fruit for 8 hours. However,the relatively small volumes of count10 � 12 fruit packed makes this im-practical. Furthermore, the increaseddosage needed for the 8 hour regimewill have unnecessary cost implica-tions. As the 300 ppb/16 hour was ef-fective for both cultivars as well as for

Figure 9. Percentage counts 10 and 18 �Fuerte� fruitwith stem-end rot, as recorded when the fruit ripened.The fruit were treated on the listed dates inside a 58m3 refrigerated sea freight container with either 300or 500 ppb SmartFreshTM for 16 hours, before beingstored with untreated samples for 28 days at theSAAGA export temperatures used at the time. Barsmarked with the same symbol are not significantlydifferent. The statistics apply separately for eachtreatment date and count fruit (χ 2-test, P<0.95).

Figure 10. Percentage counts 12 and 18 �Hass� fruitwith stem-end rot, as recorded when the fruitripened. The fruit were treated on the listed datesinside a 58 m3 refrigerated sea freight containerwith either 300 or 500 ppb SmartFreshTM for 16hours, before being stored with untreated samplesfor 28 days at the SAAGA export temperatures usedat the time. Bars marked with the same symbolare not significantly different. The statistics applyseparately for each treatment date and count fruit(χ 2-test, P<0.95).

Jaarboek �03 62 Yearbook �03

small and large counts, this is obvi-ously the better recommendation.

Ad Hoc laboratory trials con-ducted during 2002In addition to the semi-commercialtrials described above, two labora-tory scaled trials were conductedduring 2002. The trials were con-ducted at Westfalia Estates using theequipment and procedures de-scribed by Lemmer et al. (2002).

A question often asked is: �Will itbe possible to treat avocado fruitin a cool truck while in transit toCape Town harbour?� This impli-cates a longer exposure periodsthan the above 16 hour recommen-dation. To answer this question, thefruit were treated with 300 ppb forrespectively 16, 24 or 36 hours.The results are shown in Table 2.There was no difference betweenthe treatments in terms of thenumber of days to ripen (Table 2)or fruit quality (data not shown).This indicates that the lengthenedtreatment period had no negativeeffect.

The second experiment aimedto determine what effect a delaybetween packing and treating hason storage potential of the fruit. Todo this, �Hass� fruit were treatedwith 300 ppb SmartFreshTM for 8hours directly after harvest as wellas after 3 and 7 days. The resultsare shown in Table 3. When ap-plied 3 days after harvest, theSmartFreshTM treatment was as ef-fective as when applied directlyafter harvest. When applied 7 daysafter harvest, the treatment wasslightly less effective and it led toincreased pathological disorders(data not shown) which is undesir-able.

Figure 11. The percentage counts 12 and 18 �Hass�with lenticel damage, as recorded upon removalfrom cold storage. The fruit were treated on thelisted dates inside a 58 m3 refrigerated sea freightcontainer with either 300 or 500 ppb SmartFreshTM

for 16 hours, before being stored with untreatedsamples for 28 days at the SAAGA exporttemperatures used at the time. Bars marked withthe same symbol are not significantly different. Thestatistics apply separately for each treatment dateand count fruit (χ2-test, P<0.95).

Figure 12. Percentage bruised counts 10 and 18 �Hass�fruit, as recorded when the fruit ripened. The fruitwere treated on the listed dates inside a 58 m3

refrigerated sea freight container with either 300 or500 ppb SmartFreshTM for 16 hours, before beingstored with untreated samples for 28 days at theSAAGA export temperatures used at the time. Barsmarked with the same symbol are not significantlydifferent. The statistics apply separately for eachtreatment date and count fruit (χ2-test, P<0.95).

Yearbook �03 63 Jaarboek �03

SUMMARY AND RECOMMENDA-TIONSPrevention of soft landings� SmartFresh TM effectively inhib-ited the ripening process of �Hass� and�Fuerte� under bigger volume semi-commercial conditions.� The increase in storage life is com-parable to CA when SmartfreshTM isapplied at optimum dosage.� The inhibition of ripening is moreintense in �Fuerte� compared to �Hass�.� The inhibition of ripening is moreintense in the smaller Count 18 fruitcompared to bigger Count 10-12 fruit.

Physiological disorders� SmartfreshTM reduced the inci-dence of grey pulp during certain tri-als.� The reduction was greater at the500 ppb concentration than at the 300ppb concentration.

Figure 13. Mean number of days taken to ripencounts 12 and 18 �Hass� fruit at 18oC. The fruit weretreated inside a container with either 300, 400 or500 ppb SmartFreshTM for 8 or 16 hours, before beingstored with untreated samples for 28 days at therecommended export temperature. Bars markedwith the same symbol are not significantlydifferent. The statistics apply separately for eachtreatment date and fruit count (Student t-test,P>0.05).

Table 1. Comparison of the effect of CA and SmartFreshTM on count 12 �Hass� fruit in terms ofthe number of days to ripen and the incidence of pathological disorders recorded during theearly (a) and late (b) season.

Jaarboek �03 64 Yearbook �03

Table 3. The effect that a postharvestdelay before the SmartFreshTM applicationhas on the number of days to ripen �Hass�count 18 fruit. The fruit were treatedinside with 300ppb SmartFreshTM inside a100 l plastic container for 16 hours, eitherdirectly after harvest or after a 3 or 7 daydelay, before being stored with untreatedsamples for 28 days at the recommendedexport temperature, inside a 58m3 seafreight container. Values marked with thesame symbol are not significantlydifferent (Student t-test, P>0.05).

� The reduction was most noticeable in big-ger sized fruit, especially at the end of theseason when the incidence of grey pulpwas at its highest.

Pathological disorders� In both SmartfreshTM treated and CA stored

fruit the lengthening in days to ripen doesnot influence anthracnose infection inci-dence in the early season.

� During the late season, increased anthra-cnose infection incidence sometimes oc-curred in both SmartfreshTM treated and CAstored fruit.

� Lengthening of ripening period sometimesled to an increase incidence of stem-endrot in both CA and SmartfreshTM treatedfruit. This was more prominent at the endof the season.

� The increased incidence of pathological

Table 2. Number of days to ripen count 18�Hass� fruit treated with 300ppbSmartFreshTM inside a 100l plasticcontainer for 16, 24 or 36 hours, beforebeing stored with untreated samples for 28days at the recommended exporttemperatures, inside the 58m3 sea freightcontainer. Values marked with the samesymbol are not significantly different(Student t-test, P>0.05).

disorders associated with the lengthenedshelf life is exacerbated by the pre-harvestquality of the fruit.

Dosage and treatment period� At this stage, it is recommended that

packhouses apply SmartFresh TM to �Fuerte�and Hass fruit at a concentration of 300ppb for a period of 16 hours.

� The SmartfreshTM is most effective whenapplied within 3 days after harvest.

LITERATURE CITEDLEMMER, D., KRUGER, F.J., MALUMANE, T.R.

& NXUDU, Y. 2002. 1-Methyl cyclopropene:an alternative for controlled atmospherestorage of South African export avocados.Journal of the South African AvocadoGrowers� Association, 25: 28-39.