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Cell wall compositional differences between mealy and non-mealy ‘Forelle’ pear (Pyrus communis L.)
Thesis (PhD(Agric) (Horticulture))--University of Stellenbosch, 2011.
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| Format: | Thesis |
| Language: | English |
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Stellenbosch : University of Stellenbosch
2011
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| _version_ | 1867613935752970241 |
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| access_status_str | Open Access |
| author | Crouch, Elke Monika |
| author2 | Huysamer, Marius |
| author_browse | Crouch, Elke Monika Huysamer, Marius |
| author_facet | Huysamer, Marius Crouch, Elke Monika |
| author_sort | Crouch, Elke Monika |
| collection | Thesis |
| dc_rights_str_mv | University of Stellenbosch |
| description | Thesis (PhD(Agric) (Horticulture))--University of Stellenbosch, 2011. |
| format | Thesis |
| id | oai:scholar.sun.ac.za:10019.1/6746 |
| institution | Stellenbosch University (South Africa) |
| language | English |
| last_indexed | 2026-06-10T12:44:03.396Z |
| license_str | Other — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from SUNScholar — Stellenbosch University Repository |
| publishDate | 2011 |
| publishDateRange | 2011 |
| publishDateSort | 2011 |
| publisher | Stellenbosch : University of Stellenbosch |
| publisherStr | Stellenbosch : University of Stellenbosch |
| record_format | dspace |
| source_str | SUNScholar — Stellenbosch University Repository |
| spelling | oai:scholar.sun.ac.za:10019.1/6746 Cell wall compositional differences between mealy and non-mealy ‘Forelle’ pear (Pyrus communis L.) Crouch, Elke Monika Huysamer, Marius Holcroft, Deirdre University of Stellenbosch. Faculty of AgriSciences. Dept. of Horticulture. Plant cell walls Pyrus communis L. Dissertations -- Horticulture Theses -- Horticulture Forelle pears -- Texture Thesis (PhD(Agric) (Horticulture))--University of Stellenbosch, 2011. Includes bibliography. ENGLISH ABSTRACT: Mealiness, a soft, dry textural disorder of ‘Forelle’ pear (Pyrus communis L.), is a problem for the South African fruit export industry. Soft, dry textural disorders seem to be related to changes in cell wall breakdown. The aim of this work was, therefore, to investigate the occurrence of mealiness‐associated changes in the cell wall and elucidate the mechanism by which mealiness occurs in ‘Forelle’ pear, as well as to characterise cell wall changes occurring during normal ripening. Mealy ‘Forelle’ tissues had significantly lower total galacturonic acids associated with the middle lamella (water‐ and CDTA‐soluble fractions). The water‐soluble pectin of mealy tissues was depolymerised at an earlier stage of ripening. The widespread disintegration of cell‐to‐cell adhesion in mealy cell walls only, suggests that the middle lamella and the plasmodesmata are more broken down. In mealy ‘Forelle’ tissues there was no indication of less broken down high molecular weight polyuronides in the CDTA fraction, normally associated with these dry, soft textures. The pectins from mealy tissues were more broken down and both mealy and non‐mealy tissue polyuronides depolymerised. Furthermore, there was a lack of light toluidine staining in the larger air spaces, which would indicate such water‐insoluble pectins. These data suggest that the formation of high molecular weight pectate gels is unlikely in mealy ‘Forelle’ pear. The slight increase in the galactose content in mealy tissues in CDTA‐ and Na2CO3‐soluble fractions and slight decrease in the 1 M KOH glycan fraction during later stages of ripening (6+11, 9+7, 9+11; weeks at ‐0.5°C plus days at 15°C) may indicate that galactose loosely interlinked into the glycan fraction broke down sooner for mealy tissues. This didn’t increase molecular size profiles in the CDTA fraction. Arabinose content was slightly higher in the 4 M KOH fraction and slightly lower in mealy tissues of water‐ and CDTA fractions. This did not influence the molecular weight of the glycans compared to those in the nonmealy tissues. ‘Forelle’ data therefore seem to be more congruent with a decrease in intercellular adhesion as the mechanism by which mealiness occurs, rather than the formation of high molecular weight pectins taking up the cellular fluid. ‘Forelle’ pear water‐soluble pectin content increases with increased ripening. High amounts of watersoluble pectin and low amounts of Na2CO3‐soluble pectin suggests that solubilisation of rhamnogalacturonan‐I pectins must have taken place during early ripening (at a fruit firmness of > 4.7 kg (7.9mm tip). Galactose and glucose in the pectin fraction dramatically decreased after fruit ripened to a firmness of 4.5 kg, whereafter they remained unchanged. This was also the period in which fruit softened the most and the biggest increase in pectin water‐solubility occurred. It is not known whether these events are coincidental, or linked causally. Rhamnose and arabinose extractability increased in the water fraction and xylose, fucose and mannose increased in glycan fractions with ripening. The biggest changes in polyuronide solubilisation and depolymerisation occurred in water‐ and CDTA fractions between storage and ripening durations of 3+7 (4.7 kg) and 6+4 (2.7 kg). AFRIKAANSE OPSOMMING: Melerigheid, ʼn sagte droë tekstuur afwyking van ‘Forelle’ pere (Pyrus communis L.), is ʼn probleem vir die Suid Afrikaanse vrugte uitvoerbedryf. Sagte, droë tekstuur afwykings blyk betrekking te hê op selwandafbraak veranderinge. Die doel van die studie was dus om die melerigheid‐geassosieerde veranderinge in die selwand te ondersoek, sowel as om vas te stel wat die meganisme betrokke is by melerigheid ontwikkeling in ‘Forelle’ pere. Die selwand veranderinge gedurende normale rypwording is ook gekarakteriseer. Melerige ‘Forelle’ weefsel het betekenisvol laer totale galakturoonsuur wat geassosieer is met die middellamella (water‐ en CDTA‐oplosbare fraksies). Die water‐oplosbare pektien van melerige weefsel was op ʼn vroeër stadium van rypwording gedepolimeriseer. Die wydverspreide disintegrasie van sel‐tot‐sel adhesie, slegs in melerige selwande, dui aan dat die middellamella en die plasmodesmata meer afgebreek is. Daar is geen indikasie van hoë molekulêre massa poliuroniedes in die CDTA fraksie van melerige ‘Forelle’ weefsel, wat gewoonlik geassosieer word met droë, sagte teksture nie. Die pektiene van melerige weefsel was meer afgebreek en melerige en nie‐melerige weefsel se poliurone was gedepolimeriseer. Daar was ook geen ligte toluïdien verkleuring in die groter intersellulêre lugruimtes nie, wat ʼn aanduiding sou wees van wateronoplosbare pektiene. Hierdie data dui dus aan dat die vorming van hoë molekulêre pektien jel in melerige ‘Forelle’ pere onwaarskynlik is. Die klein toename in galaktose inhoud in die CDTA‐ en Na2CO3‐ oplosbare fraksies en ʼn klein afname in 1 M KOH glikaan fraksie tydens latere rypheidstadiums (6+11, 9+7, 9+11; weke by ‐0.5°C plus dae by 15°C), kan beteken dat los verweefde galaktose in die glikaan fraksie vroeër afgebreek het in melerige weefsels. Die molekulêre grootte profiel is nie verander in die CDTA fraksie nie. Arabinose inhoud was bietjie hoër in die 4 M KOH fraksie en bietjie laer in melerige weefsel van die water‐ en CDTA fraksies. Die molekulêre massa van die glikane was klaarblyklik onbeïnvloed hierdeur. ‘Forelle’ data blyk dus meer saam te stem met die meganisme waar ʼn vermindering in intersellulêre adhesie ʼn rol speel in melerigheid, eerder as die meganisme waar hoë molekulêre pektien selvloeistowwe bind. ‘Forelle’ peer water‐oplosbare pektieninhoud neem toe met toenemende rypheid. Hoë vlakke wateroplosbare pektien en lae vlakke Na2CO3‐oplosbare pektien stel voor dat die oplossing van rhamnogalakturonan‐I pektiene gedurende vroeë rypwording moes plaasgevind het (by ʼn fermheid van > 4.7 kg (7.9mm punt). Galaktose en glukose in die pektienfraksie het drasties verminder nadat vrugte tot ʼn fermheid van 4.5 kg ryp geword het, waarna hul onveranderd gebly het. Dit was ook die periode waarin vrugte die meeste sag geword het en die grootste toename in poliuronied wateroplosbaarheid gevind is. Dit is nie bekend of die gebeure toevallig of oorsaaklik verbind is nie. Rhamnose en arabinose ekstraheerbaarheid het vermeerder in die water fraksies, en xylose, fukose en mannose het vermeerder in die glikaan fraksies gedurende rypwording. Die grootste verandering in oplosbaarheid en depolimerisasie het plaasgevind in die water‐ en CDTA fraksies tussen opberging en rypwordingsperiodes van 3+7 (4.7 kg) en 6+4 (2.7 kg). Doctoral 2011-02-28T14:17:57Z 2011-03-14T08:37:21Z 2011-02-28T14:17:57Z 2011-03-14T08:37:21Z 2011-03 Thesis http://hdl.handle.net/10019.1/6746 en University of Stellenbosch 159 p. : ill. application/pdf Stellenbosch : University of Stellenbosch |
| spellingShingle | Plant cell walls Pyrus communis L. Dissertations -- Horticulture Theses -- Horticulture Forelle pears -- Texture Crouch, Elke Monika Cell wall compositional differences between mealy and non-mealy ‘Forelle’ pear (Pyrus communis L.) |
| title | Cell wall compositional differences between mealy and non-mealy ‘Forelle’ pear (Pyrus communis L.) |
| title_full | Cell wall compositional differences between mealy and non-mealy ‘Forelle’ pear (Pyrus communis L.) |
| title_fullStr | Cell wall compositional differences between mealy and non-mealy ‘Forelle’ pear (Pyrus communis L.) |
| title_full_unstemmed | Cell wall compositional differences between mealy and non-mealy ‘Forelle’ pear (Pyrus communis L.) |
| title_short | Cell wall compositional differences between mealy and non-mealy ‘Forelle’ pear (Pyrus communis L.) |
| title_sort | cell wall compositional differences between mealy and non mealy forelle pear pyrus communis l |
| topic | Plant cell walls Pyrus communis L. Dissertations -- Horticulture Theses -- Horticulture Forelle pears -- Texture |
| url | http://hdl.handle.net/10019.1/6746 |
| work_keys_str_mv | AT crouchelkemonika cellwallcompositionaldifferencesbetweenmealyandnonmealyforellepearpyruscommunisl |