Cold Link Africa January / February 2023 | Page 31

TECHNICAL

INCORPORATING COLD CHAIN

sugars among the treatments ( Figs . 6 and 7 ). For instance , D-mannoheptulose which is a dominant soluble sugar in avocado fruit significantly decreased with storage period from average of 15 g / kg at the beginning of the experiment to less than 6-7 g / kg upon ripening . At the end of the storage period , control fruit had the lowest concentration of D-mannoheptulose . Avocado fruit is known to produce the two dominant C7 sugars , D-mannoheptulose and perseitol and they also produce hexoses as the relatively smaller amount . It is also reported that D-mannoheptulose is known to delay the onset of ripening or else improves fruit shelf life . The treated fruit retained these C7 sugars as compared to control . Tesfay and Magwaza ( 2017 ) who observed a decrease in the content of C7 sugar in avocado fruit during ripening reported a similar trend .

Fig . 6 . Effect of ozone on mesocarp D-Mannoheptulose for coated as well as uncoated fruit during storage time . Vertical bars represent standard error of the mean value ( n = 5 ). The SE refers to the standard deviation of each measured values from the mean value .

Fig . 7 . Effect of ozone on mesocarp perseitol for coated as well as uncoated fruit during storage time . Vertical bars represent standard error of the mean value ( n = 5 ). The SE refers to the standard deviation of each measured value from the mean value .

Fruit volatiles Two volatiles were analysed , the concentrations significantly changed during postharvest . The hexanal displayed a declining pattern . Where as the pentanal was increasing over the storage time , but its concentration was significantly higher in a fruit coated with ozone treatments than control fruit ( Figs . 8 and 9 ). There is a clear correlation observed with fruit maturity and ripening that hexanal had high concentration at early stages and the amount decreases as the fruit ripening and over-matures .

This finding can also give a good insight of hexanal volatiles , an aldehyde that could play a vital role if it can be applied exogenously to delay ripening . This has left a room to further investigate how this volatile affects fruit quality . On the contrary the pentanal displayed an increasing trend with fruit ripening and maturity . Obenland et al . ( 2012 ) also reported similar result that pentanal increases during avocado fruit maturity and the concentration can have an influence in fruit flavor .

Fig . 8 . Effect of ozone on mesocarp hexanal for coated as well as uncoated fruit during storage time . Vertical bars represent standard error of the mean value ( n = 5 ). The SE refers to the standard deviation of each measured values from the mean value .

Fig . 9 . Effect of ozone on mesocarp pentanal for coated as well as uncoated fruit during storage time . Vertical bars represent standard error of the mean value ( n = 5 ). The SE refers to the standard deviation of each measured values from the mean value .

Aldehydes and alcohols such as hexanal , trans-2-hexenal and cis-3-hexen-1-ol are important for the green , unripe notes in strawberry aroma . Their concentrations are also cultivar and ripeness dependent ( Jetti et al ., 2007 ). Our findings are also in agreement with El-Mageed ( 2007 ) that ethanol , ( Z ) -3-hexanol and ( E ) -2-hexenal , the most abundant volatiles in whole green and ripe “ Fuerte ” avocados ( Persea Americana Mill ), declined with ripening , while overripe fruit had the highest ester concentration ( El- Mageed , 2007 ).

Pereira ( 2010 ) reported that the most abundant volatiles present in the headspace of unripe , diced “ Simmonds ” avocado were sesquiterpenes and hexanal , whereas the amounts of these compounds was greatly reduced by ripening . During maturation time of avocados cv . “ Hass ” the concentration of hexanal , ( E ) -2-hexenal and 2,4-hexadienal greatly declined in amount , while acetaldehyde , methyl acetate , pentanal , and β-myrcene were at higher concentrations in mature fruit and may also have contributed to the overall flavor ( Obenland et al ., 2012 ).

IN CONCLUSION The combined treatments edible coating and ozone enhance fruit quality . The treatments improve the physical appearance and membrane structures ,

reduced moisture loss , reduced respiration and ethylene accumulation than control fruit . Since the treatments are natural and leaves no residues , introduction of edible products and ozone can be invaluable material for postharvest fruit treatments by fruit industries .

It needs to be noted that although consumption of fruits is regarded as its nutritional and has health benefits , nowadays consumers are raising a concern on safety issues towards what they consume . Accordingly , using chemicals by fruit industries impose pressure to comply with safety regulations , our research therefore reports on potential use of edible coating and ozone gas that are safe and long lasting . This perhaps boosts our fruit industries ’ global competitiveness in supplying quality fruit .

ACKNOWLEDGMENTS This research was supported by the South African

Avocado Growers ’ Association ( SAAGA ).

The authors are grateful to Mr Lynton Freese

and Mr Sipho Sekhune , Westfalia packhouse in

Howick , KwaZulu-Natal , South Africa for providing

fruit for entire research . And we are also very

grateful to Mr Edward Erasmus , production

manager from OzoneUV for generously supplying the Ozone generator equipment . CLA

Introduction of edible products and ozone can be invaluable material for postharvest fruit treatments

ARTICLE AUTHORS AND IMAGE CREDITS Samson Zeray Tesfay , Lembe Samukelo Magwaza , Asanda Mditshwa . Discipline of Horticultural Science , School of Agricultural , Earth and Environmental Sciences , University of KwaZulu-Natal & Discipline of Crop Science , School of Agricultural , Earth and Environmental Sciences , University of KwaZuluNatal .