Isa Bertling | University of KwaZulu-Natal (original) (raw)

Papers by Isa Bertling

Australian Journal of Botany, 2012

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International Journal of Postharvest Technology and Innovation, 2012

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Ripening of avocado fruit is variable, being more rapid with increasing maturity, and within a co... more Ripening of avocado fruit is variable, being more rapid with increasing maturity, and within a consignment. In- ternal quality is often also variable. In order to understand the drivers behind the variability in fruit ripening and quality characteristics, the known ripening enzymes pectin methylesterase (PME), polygalacturonase (PG) and cellulase were studied during the ripening phase. Together with these enzymes, changes in ethylene and carbon dioxide evolution were monitored. Fruit was sourced from two climatic zones, Tzaneen and Howick, and across the season to evaluate the infl uence of maturity, which was estimated through measurement of moisture content. Ripening followed the ethylene climacteric, with more mature fruit ripening faster. Total proteins tended to follow the same pattern, but where initial concentration was high, a decline was not noted towards softening, while if low at harvest, proteins decreased towards softening. It is suggested that this is related to energy...

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A three year study considered the effects of production location, maturity, storage temperature, ... more A three year study considered the effects of production location, maturity, storage temperature, modified atmosphere (MA) storage and a cold chain break on avocado ripening physiology. The aim of this study was to better understand post-harvest avocado physiology to enable improved post-harvest management to maintain fruit quality longer. Focus was placed on sugars, ripening enzymes, respiration, ethylene production and water relations. The seven carbon sugars, mannoheptulose and perseitol, were confirmed as the predominant sugars and possible energy source of avocado fruit. The six carbon sugars – glucose, fructose and sucrose – were not present in sufficient quantities nor do their trends suggest that they are used as an energy source. The seven carbon sugars are present in low concentrations in the mesocarp and need to be preserved during cold storage to enable proper ripening. The activity of three enzymes (cellulase, polygalacturonase and pectin methylesterase) was measured dur...

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Acta Horticulturae, 2011

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Journal of Horticultural Science and Biotechnology

A better understanding of the post-harvest physiology of avocado (Persea americana Mill.) fruit i... more A better understanding of the post-harvest physiology of avocado (Persea americana Mill.) fruit is required to improve the post-harvest management of the crop. Two heptoses, D-mannoheptulose and perseitol, occur in unusually high concentrations in avocado tissues and are thought to be important in fruit ripening. We determined changes in the concentrations and relationships between individual sugars, total soluble proteins, and oil during fruit ripening. ‘Hass’ fruit were harvested from cool and warm sub-tropical areas in South Africa three-times during a single season. Dry matter increased during the season at both locations. For fruit from the cool sub-tropical climate, D-mannoheptulose and perseitol concentrations declined rapidly from 15.9 mg g-1 dry weight (DW) and 7.9 mg g-1 DW to 2.1 mg g-1 DW and 0.6 mg g-1 DW, respectively, 13 d after harvest. Overall concentrations of glucose and fructose were negligible at harvest and increased to 1.4 mg g-1 DW and 0.8 mg g-1 DW, respecti...

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Acta Agriculturae Scandinavica, Section B - Soil & Plant Science, 2013

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The potential involvement of C7 sugars as antioxidants in various avocado tissues was tested. Tot... more The potential involvement of C7 sugars as antioxidants in various avocado tissues was tested. Total antioxidant activity was found to be similar in leaf, exocarp and seed tissue; however, the concentration of total antioxidants in mesocarp tissue was lower than in other tissues at all three sampling dates. The various tissues examined had different predominant antioxidant systems; while leaf tissue contained high concentrations of anthocyanins, ascorbic acid was found to be the main antioxidant in the seed as well as the rind tissue. In mesocarp tissue, however, C7 sugars, and particularly mannoheptulose, played the major antioxidant role. As levels of both C7 sugars declined signifi cantly as harvest maturity was approached, the reduction in C7 sugars could be related to deteriora- tion in post-harvest quality. Therefore, management practises should be established to increase the concentration of these sugars in the mesocarp prior to harvesting.

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The effect of isoprenoid growth regulators on avocado (Persea americana Mill. cv Hass) fruit grow... more The effect of isoprenoid growth regulators on avocado (Persea americana Mill. cv Hass) fruit growth and mesocarp 3-hydroxy-3- methylglutaryl coenzyme A reductase (HMCR) activity was inves- tigated during the course of fruit ontogeny. Both normal and small- fruit phenotypes were used to probe the interaction between the end products of isoprenoid biosynthesis and the activity of HMCR in the metabolic

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I All Africa Horticultural Congress, 2011

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Southern Forests: a Journal of Forest Science, 2013

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Ripening of avocado fruit is variable, being more rapid with increasing maturity, and within a co... more Ripening of avocado fruit is variable, being more rapid with increasing maturity, and within a consignment. In- ternal quality is often also variable. In order to understand the drivers behind the variability in fruit ripening and quality characteristics, the known ripening enzymes pectin methylesterase (PME), polygalacturonase (PG) and cellulase were studied during the ripening phase. Together with these enzymes, changes

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Journal of Horticultural Science and Biotechnology

A better understanding of the post-harvest physiology of avocado (Persea americana Mill.) fruit i... more A better understanding of the post-harvest physiology of avocado (Persea americana Mill.) fruit is required to improve the post-harvest management of the crop. Two heptoses, D-mannoheptulose and perseitol, occur in unusually high concentrations in avocado tissues and are thought to be important in fruit ripening. We determined changes in the concentrations and relationships between individual sugars, total soluble proteins, and oil during fruit ripening. ‘Hass’ fruit were harvested from cool and warm sub-tropical areas in South Africa three-times during a single season. Dry matter increased during the season at both locations. For fruit from the cool sub-tropical climate, D-mannoheptulose and perseitol concentrations declined rapidly from 15.9 mg g-1 dry weight (DW) and 7.9 mg g-1 DW to 2.1 mg g-1 DW and 0.6 mg g-1 DW, respectively, 13 d after harvest. Overall concentrations of glucose and fructose were negligible at harvest and increased to 1.4 mg g-1 DW and 0.8 mg g-1 DW, respecti...

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Journal of Horticultural Science and Biotechnology

The export of avocado (Persea americana Mill.) fruit into foreign markets has become a high prior... more The export of avocado (Persea americana Mill.) fruit into foreign markets has become a high priority for the South African industry due to increased competition in the European market. Some of these countries require phytosanitary treatment before access is granted. Cold disinfestation is the only suitable phytosanitary treatment available for avocado, but the fruit are generally considered to be sensitive to temperatures below approx. 5ºC. Phytosanitary disinfestation of South African avocados of acceptable fruit quality has been achieved by maintaining the pulp temperature below 2ºC for 28 d, but the effect on ripening physiology has not been determined. The effect of cold storage at 1ºC (air delivery temperature) on 'Hass' avocados with or without modified humidity packaging (MHP) for 28 d was examined. Compared to a conventional storage temperature of 5.5ºC for 28 d, fruit stored at 1ºC had significantly reduced rates of respiration and ethylene production, less softenin...

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Acta horticulturae

The South African avocado industry is export-based, with the majority of fruit exported to Europe... more The South African avocado industry is export-based, with the majority of fruit exported to Europe. Fruit are cold-stored for a minimum of 28 days with a number of handling points in the cold chain. These breaks in the cold chain are thought to increase postharvest losses but have not been quantified. Fruit (‘Hass’) were harvested from Howick and subjected to a 9-h break in cold storage at 5, 10 or 20 days, or a delay of 24 h before cold storage to simulate shipping conditions from South Africa to Europe. Fruit were stored at 1 or 5.5°C for 28 days. After the storage period respiration, ethylene production, firmness, and fruit mass were measured and fruit quality assessed. Fruit only showed significant differences (P=0.05) in the physiological parameters on the first day after removal from cold storage, but fruit quality was severely reduced by breaking the cold chain. Storage temperature also had a significant effect on fruit quality. Storage at 5.5°C resulted in only having between...

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The effect of postharvest silicon dips on the concentration of total antioxidants, total phenolic... more The effect of postharvest silicon dips on the concentration of total antioxidants, total phenolics, and malondialdehyde, as well as the susceptibility to chilling injury of lemon fruit rind was studied. Fruit from two orchards were soaked into different silicon concentrations (0, 50, 150, and 250 mg/L K 2 SiO 3) for 30 min and thereafter stored at -0.5 or 2°C for 28 days with weekly evaluation of chilling injury and total flavedo antioxidants. Total antioxidants were determined using three assays, the ferric reducing antioxidant power (FRAP), the 1,1-diphenyl-2-picrylhydrazyl (DPPH), and the 2,2'-azino-bis-3-ethylbenzothiazoline-6-sulphonic acid (ABTS) assay. Silicon concentration in the flavedo was determined using Scanning Electron Microscope (SEM). Significant differences in endogenous silicon as well as chilling susceptibility between fruits from the two sources were observed. Fruit stored at -0.5°C was less chilling susceptible compared with fruit stored at 2°C. However, th...

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Postharvest Biology and Technology, 2009

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South African Journal of Plant and Soil, 2014

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Australian Journal of Botany, 2012

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International Journal of Postharvest Technology and Innovation, 2012

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Ripening of avocado fruit is variable, being more rapid with increasing maturity, and within a co... more Ripening of avocado fruit is variable, being more rapid with increasing maturity, and within a consignment. In- ternal quality is often also variable. In order to understand the drivers behind the variability in fruit ripening and quality characteristics, the known ripening enzymes pectin methylesterase (PME), polygalacturonase (PG) and cellulase were studied during the ripening phase. Together with these enzymes, changes in ethylene and carbon dioxide evolution were monitored. Fruit was sourced from two climatic zones, Tzaneen and Howick, and across the season to evaluate the infl uence of maturity, which was estimated through measurement of moisture content. Ripening followed the ethylene climacteric, with more mature fruit ripening faster. Total proteins tended to follow the same pattern, but where initial concentration was high, a decline was not noted towards softening, while if low at harvest, proteins decreased towards softening. It is suggested that this is related to energy...

Bookmarks Related papers MentionsView impact

A three year study considered the effects of production location, maturity, storage temperature, ... more A three year study considered the effects of production location, maturity, storage temperature, modified atmosphere (MA) storage and a cold chain break on avocado ripening physiology. The aim of this study was to better understand post-harvest avocado physiology to enable improved post-harvest management to maintain fruit quality longer. Focus was placed on sugars, ripening enzymes, respiration, ethylene production and water relations. The seven carbon sugars, mannoheptulose and perseitol, were confirmed as the predominant sugars and possible energy source of avocado fruit. The six carbon sugars – glucose, fructose and sucrose – were not present in sufficient quantities nor do their trends suggest that they are used as an energy source. The seven carbon sugars are present in low concentrations in the mesocarp and need to be preserved during cold storage to enable proper ripening. The activity of three enzymes (cellulase, polygalacturonase and pectin methylesterase) was measured dur...

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Acta Horticulturae, 2011

Bookmarks Related papers MentionsView impact

Journal of Horticultural Science and Biotechnology

A better understanding of the post-harvest physiology of avocado (Persea americana Mill.) fruit i... more A better understanding of the post-harvest physiology of avocado (Persea americana Mill.) fruit is required to improve the post-harvest management of the crop. Two heptoses, D-mannoheptulose and perseitol, occur in unusually high concentrations in avocado tissues and are thought to be important in fruit ripening. We determined changes in the concentrations and relationships between individual sugars, total soluble proteins, and oil during fruit ripening. ‘Hass’ fruit were harvested from cool and warm sub-tropical areas in South Africa three-times during a single season. Dry matter increased during the season at both locations. For fruit from the cool sub-tropical climate, D-mannoheptulose and perseitol concentrations declined rapidly from 15.9 mg g-1 dry weight (DW) and 7.9 mg g-1 DW to 2.1 mg g-1 DW and 0.6 mg g-1 DW, respectively, 13 d after harvest. Overall concentrations of glucose and fructose were negligible at harvest and increased to 1.4 mg g-1 DW and 0.8 mg g-1 DW, respecti...

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Bookmarks Related papers MentionsView impact

Acta Agriculturae Scandinavica, Section B - Soil & Plant Science, 2013

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The potential involvement of C7 sugars as antioxidants in various avocado tissues was tested. Tot... more The potential involvement of C7 sugars as antioxidants in various avocado tissues was tested. Total antioxidant activity was found to be similar in leaf, exocarp and seed tissue; however, the concentration of total antioxidants in mesocarp tissue was lower than in other tissues at all three sampling dates. The various tissues examined had different predominant antioxidant systems; while leaf tissue contained high concentrations of anthocyanins, ascorbic acid was found to be the main antioxidant in the seed as well as the rind tissue. In mesocarp tissue, however, C7 sugars, and particularly mannoheptulose, played the major antioxidant role. As levels of both C7 sugars declined signifi cantly as harvest maturity was approached, the reduction in C7 sugars could be related to deteriora- tion in post-harvest quality. Therefore, management practises should be established to increase the concentration of these sugars in the mesocarp prior to harvesting.

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The effect of isoprenoid growth regulators on avocado (Persea americana Mill. cv Hass) fruit grow... more The effect of isoprenoid growth regulators on avocado (Persea americana Mill. cv Hass) fruit growth and mesocarp 3-hydroxy-3- methylglutaryl coenzyme A reductase (HMCR) activity was inves- tigated during the course of fruit ontogeny. Both normal and small- fruit phenotypes were used to probe the interaction between the end products of isoprenoid biosynthesis and the activity of HMCR in the metabolic

Bookmarks Related papers MentionsView impact

I All Africa Horticultural Congress, 2011

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Southern Forests: a Journal of Forest Science, 2013

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Ripening of avocado fruit is variable, being more rapid with increasing maturity, and within a co... more Ripening of avocado fruit is variable, being more rapid with increasing maturity, and within a consignment. In- ternal quality is often also variable. In order to understand the drivers behind the variability in fruit ripening and quality characteristics, the known ripening enzymes pectin methylesterase (PME), polygalacturonase (PG) and cellulase were studied during the ripening phase. Together with these enzymes, changes

Bookmarks Related papers MentionsView impact

Journal of Horticultural Science and Biotechnology

A better understanding of the post-harvest physiology of avocado (Persea americana Mill.) fruit i... more A better understanding of the post-harvest physiology of avocado (Persea americana Mill.) fruit is required to improve the post-harvest management of the crop. Two heptoses, D-mannoheptulose and perseitol, occur in unusually high concentrations in avocado tissues and are thought to be important in fruit ripening. We determined changes in the concentrations and relationships between individual sugars, total soluble proteins, and oil during fruit ripening. ‘Hass’ fruit were harvested from cool and warm sub-tropical areas in South Africa three-times during a single season. Dry matter increased during the season at both locations. For fruit from the cool sub-tropical climate, D-mannoheptulose and perseitol concentrations declined rapidly from 15.9 mg g-1 dry weight (DW) and 7.9 mg g-1 DW to 2.1 mg g-1 DW and 0.6 mg g-1 DW, respectively, 13 d after harvest. Overall concentrations of glucose and fructose were negligible at harvest and increased to 1.4 mg g-1 DW and 0.8 mg g-1 DW, respecti...

Bookmarks Related papers MentionsView impact

Journal of Horticultural Science and Biotechnology

The export of avocado (Persea americana Mill.) fruit into foreign markets has become a high prior... more The export of avocado (Persea americana Mill.) fruit into foreign markets has become a high priority for the South African industry due to increased competition in the European market. Some of these countries require phytosanitary treatment before access is granted. Cold disinfestation is the only suitable phytosanitary treatment available for avocado, but the fruit are generally considered to be sensitive to temperatures below approx. 5ºC. Phytosanitary disinfestation of South African avocados of acceptable fruit quality has been achieved by maintaining the pulp temperature below 2ºC for 28 d, but the effect on ripening physiology has not been determined. The effect of cold storage at 1ºC (air delivery temperature) on 'Hass' avocados with or without modified humidity packaging (MHP) for 28 d was examined. Compared to a conventional storage temperature of 5.5ºC for 28 d, fruit stored at 1ºC had significantly reduced rates of respiration and ethylene production, less softenin...

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Acta horticulturae

The South African avocado industry is export-based, with the majority of fruit exported to Europe... more The South African avocado industry is export-based, with the majority of fruit exported to Europe. Fruit are cold-stored for a minimum of 28 days with a number of handling points in the cold chain. These breaks in the cold chain are thought to increase postharvest losses but have not been quantified. Fruit (‘Hass’) were harvested from Howick and subjected to a 9-h break in cold storage at 5, 10 or 20 days, or a delay of 24 h before cold storage to simulate shipping conditions from South Africa to Europe. Fruit were stored at 1 or 5.5°C for 28 days. After the storage period respiration, ethylene production, firmness, and fruit mass were measured and fruit quality assessed. Fruit only showed significant differences (P=0.05) in the physiological parameters on the first day after removal from cold storage, but fruit quality was severely reduced by breaking the cold chain. Storage temperature also had a significant effect on fruit quality. Storage at 5.5°C resulted in only having between...

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The effect of postharvest silicon dips on the concentration of total antioxidants, total phenolic... more The effect of postharvest silicon dips on the concentration of total antioxidants, total phenolics, and malondialdehyde, as well as the susceptibility to chilling injury of lemon fruit rind was studied. Fruit from two orchards were soaked into different silicon concentrations (0, 50, 150, and 250 mg/L K 2 SiO 3) for 30 min and thereafter stored at -0.5 or 2°C for 28 days with weekly evaluation of chilling injury and total flavedo antioxidants. Total antioxidants were determined using three assays, the ferric reducing antioxidant power (FRAP), the 1,1-diphenyl-2-picrylhydrazyl (DPPH), and the 2,2'-azino-bis-3-ethylbenzothiazoline-6-sulphonic acid (ABTS) assay. Silicon concentration in the flavedo was determined using Scanning Electron Microscope (SEM). Significant differences in endogenous silicon as well as chilling susceptibility between fruits from the two sources were observed. Fruit stored at -0.5°C was less chilling susceptible compared with fruit stored at 2°C. However, th...

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Postharvest Biology and Technology, 2009

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South African Journal of Plant and Soil, 2014

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Bookmarks Related papers MentionsView impact