The ozone exposure frequency was designed on a weekly basis , where fruit with and without coatings were exposed to ozone at frequency of once , twice , three or four times during a cold storage period .

Fruit physical quality attributes and chemical analysis were carried out and then the data was analysed using Genstat version 18 . ‘ Gem ’ fruit treated with moringa CMC ( 1 %) that were exposed to ozone of two times at 7d , 14d ; 7d , 21d ; 14d , 21d , and three times at 0d , 7d , 14d ; 0d , 7d , 21d ; 7d , 14d , 21d had significantly lower mass loss ( 3.25 ± 1.2 %), electrical conductivity ( 3.5 ± 0.9 m . mohs / cm ) and respiration rate ( 160 ± 36 mg / kg / h ), ethylene accumulation ( 3.5 ± 1.2 mg / kg / h ) compared to the untreated control with respective values of ( 7.8 ± 1.4 %), ( 11.3 ± 1.3 m . mohs / cm ), ( 220 ± 29 mg / kg / h ), ( 11.8 ± 1.8 mg / kg / h ). The same treatment had higher values for firmness ( 80.0 ± 6.25 N ) and phytochemical characteristics , mainly D-mannoheptulose ( 5.67 ± 0.6 g / kg . against 1.206 g / kg ), and the volatile hexanal ( 834 ± 95 µ g / l against 672 ± 63 µ g / l ).

In conclusion , intermittent ozone treatment together with edible coating could enhance postharvest fruit quality and reduce uneven ripening in ‘ Gem ’ fruit during storage , if ozone is applied at optimum dose and using adequate storage conditions : ( low temperature ( 5 ° C ) and high relative humidity ( 90-95 %).

INTRODUCTION Avocado ( Persea americana , Mill .) is an extremely perishable fruit , with a very high metabolic rate , resultant in a short postharvest life of about three to five weeks when stored under optimum conditions ( Yahia & Gonzalez-Aguilar , 1998 ).

The postharvest storage life of avocado fruit is limited by its climacteric-ripening pattern which exhibits high ethylene accumulation , stimulating faster ripening as result of the high rate of respiration ( Blakey et al ., 2012 ). Avocado fruit are also considered to have a high postharvest mass loss , and this is mostly due to moisture loss through transpiration , which has been shown to contribute about 90 % of the total fruit mass loss ( Cutting & Wolstenholme , 1992 ).

Fruit and vegetables after harvest are still alive , in which transpiration , respiration , and other metabolic processes continue during

the postharvest period . All these biological processes can lead to quality losses , due to external and internal factors . During the postharvest period , fruit exposure to ethylene may occur advertently in storage or transit from atmosphere pollution as a byproduct of human industrial activities ( Chang & Bleecker , 2004 ) or from ethylene produced by adjacent plant products .

In fruits and vegetables a strong correlation between storage life and ethylene atmospheric concentration has been found , in which ethylene levels higher than 0.10 μll−1 would cause important quality loss ( Wills & Warton , 2000 ) leading to shortening of the shelf-life by acceleration of the ripening and senescence processes .

These accelerated metabolic processes depend on a number of variables , the most important being fruit sensitivity to ethylene , duration of exposure , ethylene concentration , atmospheric composition , and temperature ( Saltveit , 1999 ). To reduce adverse effects of ethylene on vegetable and fruit quality the level of ethylene concentrations should be kept below the threshold depending on tissue sensitivity in storage areas ( Wills & Warton , 2000 ).

Furthermore , there are postharvest treatments and technologies in practice that are used in delaying and / or inhibiting ethylene production as well as removing ethylene under controlled atmospheric condition . Globally , in avocado fruit industries , there have been challenges of fruit softening on arrival to long distance markets , so this has posed a desperate need to find a solution that would remove ethylene accumulation during cold storage .

Previously , there have been different methods used by industry in order to increase fruit shelf life , 1-Methylcyclopropene ( 1MCP ), potassium permanganate has been used to reduce ethylene accumulation . However , due to safety concerns by some countries in using chemical based treatment , the avocado industry has gradually begun to abandon these chemicals to avoid rejections due to residual maximum limits ( RMLs ) being exceeded .

Ozone is a naturally produced , three oxygen atomic molecule used in postharvest fruit treatments . The use of ozone for ethylene degradation in air has been well documented ( Dickson et al ., 1992 ). The physicochemical characteristics of O3 in terms of solubility in water and reactivity makes it useful in the food industry for food preservation and equipment sterilisation ( disinfectant and sanitiser ) and promoting shelf-life extension ( Suslow , 2004 ).

Ozone has been listed as a GRAS ( generally recognised as safe ) material by the Food and Drug Administration ( FDA ) ( 2001 )

and approved for use during food processing ( raw and processed fruit and vegetables ), and for treatment and storage , both in gas or aqueous phases . Edible coatings are ecologically friendly substitutes applied on fresh produce to reduce water transfer , gaseous exchange and oxidation processes ( Dhall , 2013 ).

Among edible coatings , CMC have been reported on avocado fruit ( Maftoonazad & Ramaswamy , 2005 ). Tesfay & Magwaza ( 2017 ) has reported ‘ Fuerte ’ and ‘ Hass ’ avocado fruit coated with moringa + 1 % CMC had lower rates of respiration , higher values of firmness compared with the uncoated control In this experiment , it investigated the efficacy of intermittent application of ozones in reducing the fruit sensitivity towards ethylene by slowing down its accumulation greater than threshhold amount ; and ozone compatibility with edible coatings in maintaining fruit quality .

STUDY MATERIALS AND METHODS Fruits were collected from Westfalia fruit Merenesky packhouse in Howick , South Africa . ‘ Gem ’ avocado cultivar was used for the experiment , 840 fruit were assigned for two levels of coating ( control , CMC 1 %+ Moringa leaf ) treatments . The fruits were equally divided , each group had 420 fruit , and the two groups were then exposed to ozone treatments during cold storage .

Ozone application times ( 0.25 ppm ) was for 12 h ( 0d , 7d , 14d , 21d ) and its matrix . Each treatment set had 60 fruits with 3 replications , there were 20 fruit per replication . The storage room was set at 5.5 ° C for 21 days and afterwards fruits were moved to ambient condition for ripening and evaluated on the fruit shelf life to each treatments .

FRUIT PHYSICAL AND BIOCHEMICAL PARAMETERS WERE MEASURED Fruit ethylene production was measured with an F-950 handheld ethylene analyser ( Felix Instruments QC Applied Food Sciences ) using fixed volume mode which samples 15ml from the headspace and sampling was taken every seven days ( Blakey et al . 2012 ). Each fruit was sealed in a 1l jar for 15 min , the readings recorded as a rate of ethylene in ppm .

Fruit CO ₂ production measurement

Fruit CO ₂ production was measured with an environmental gas monitor ( EGM-1 , PP Systems , Hitchin , UK ) every seven days ( Blakey et al . 2012 ). Each fruit was sealed in a 1l jar for 10 min , after which the headspace

CO ₂ concentration was determined and the results calculated as a rate of CO2 production ( mg kg−1 FW h −1 ), taking into

account fruit mass , headspace and ambient room CO ₂ concentration .

Fruit firmness measurement Fruit firmness was determined every seven days during cold storage and shelflife using a handheld firmness tester ( Bareiss , Germany ). Two readings , on a scale of 100 ( hard , unripe ) to < 60 ( ready to eat ), were taken at the equatorial region of the fruit on opposite sides . Firmness readings with 100 representing hard , unripe fruit and 60 soft , ripe fruit ( Standard ISO 7619 , International Organisation for Standardisation ).

Electrical conductivity ( EC ) The electrolytes conductivity from mesocarp tissue leakage was determined using a multirange conductivity meter ( HI 9033 , Hanna Instruments , Johannesburg , South Africa ) ( Venkatarayappa et al ., 1984 ), with slight modification . Briefly , a mesocarp plug was taken from the cut-half of each fruit at the distal end , between the seed and the mesocarp . A disc of 11mm thickness ( 2.0 – 2.5 g ) was cut from this plug , rinsed three times in distilled water and placed in a boiling tube containing 25ml distilled water . The tubes were then shaken for 3 h and the solution was ready for the EC analysis . The EC of each tube was recorded before and after boiling , the electrolyte leakage calculated as the EC according to the following formula :

Where EC = electrical conductivity ; ECi = initial reading ; ECf = final reading ; n = number of samples .

Carbohydrate determination Freeze-dried mesocarp powder ( 0.10 g ) was mixed with 10 ml 80 % ( v / v ) ethanol and homogenised for 1 min . Thereafter , the mixture was incubated in an 80 ° C in a water bath for 60min to extract the soluble sugars . Subsequently , the mixture was stored at 4 ° C overnight to facilitate release of soluble sugars . The mixture then centrifuged at 12000g for 15 min at 4 ° C , the supernatant was filtered through glass wool and the filtrate was taken to dryness in a GenVac ( model EZ2.3 , GenVac LTD , Ipswich , England ). Dried samples were resuspended in 2ml ultra-pure water , filtered through a 0.45 μm nylon filter into HPLC vial , and sugars were analysed according to Liu et al . ( 1999 ), using an isocratic HPLC system equipped with a refractive index