Red colour development and loss in pear fruit

Steyn, Willem J. (2003-03)

Thesis (PhD (Agric))--University of Stellenbosch, 2003.

Thesis

ENGLISH ABSTRACT: Downgrading of fruit due to insufficient red colour has limited the profitability of lucrative blushed pear cultivars (Pyrus communis L.). In 'Rosemarie', poor fruit colour has been ascribed to pre-harvest red colour loss during periods of high temperature. The regulation of colour development in pears has not been studied and, in addition, little is known about anthocyanin degradation in attached fruit. Changes in colour were recorded and phenylalanine ammonia-lyase (PAL) and UDPGalactose: flavonoid-3-0-glycosyltransferase (UFGT) activities assessed in response to cold fronts and during fruit development in order to establish the regulation of colour development in red and blushed pear cultivars. Best red colour was generally attained a month or more before harvest whereafter red colour faded towards harvest. Unlike in some other fruits, UFGT activity apparently did not limit colour development whereas fading of red colour towards harvest might relate to decreasing PAL activity. 'Rosemarie' colour fluctuated considerably, increasing with cold fronts and decreasing during intermittent warmer periods, while red colour was more stable in other cultivars. PAL and UFGT activities in 'Rosemarie' increased in response to low temperatures, but were unaffected in 'Bon Rouge'. We concluded that anthocyanin synthesis in 'Rosemarie' requires low temperatures while colour development in 'Bon Rouge' and probably also other cultivars is primarily regulated by endogenous factors. Detached pome fruit were used to study temperature and light effects on anthocyanin degradation and fruit colour and to assess the modifying effect of anthocyanin concentration on colour loss. Anthocyanin degradation and red colour loss increased linearly between 10°C and 30°C. Irradiation further increased the rate of degradation and colour loss. The rate of colour loss depended on anthocyanin concentration, being much faster in fruit with high compared to fruit with low pigment levels. This was ascribed to the exponential relationship between anthocyanin concentration and hue at high pigment levels and the linear relationship at lower pigment levels. Anthocyanin degradation and pre-harvest red colour loss in 'Rosemarie' was quantitatively confirmed and corresponded with a warm period during fruit development. Based on these data, we attributed the susceptibility of 'Rosemarie' to pre-harvest colour loss to low anthocyanin concentrations in its peel that allow the visualisation of net anthocyanin degradation at high temperatures. Overhead evaporative cooling (EG) as measure to improve red colour in blushed pears was evaluated. 'Rosemarie' fruit that received pulsed EG applications from two weeks before harvest at air temperatures exceeding 28°G were redder than control fruit at harvest. EG had no effect on 'Forelle' colour. Though EG could be used to improve 'Rosemarie' fruit colour in warm production areas, its effect was relatively small compared to colour change in response to temperature. Lastly, we assessed the photoprotective function of anthocyanin in pear peel. Photoinhibition was evident in exposed faces of pears under natural conditions. The extent of photoinhibition increased with decreasing redness of peel and was maintained after photoinhibitory treatment. Although anthocyanin was apparently able to afford photoprotection at 40oG, we argued against this as a general function. There were indications that photoprotection was associated, but not necessarily due to light attenuation by anthocyanin.

AFRIKAANSE OPSOMMING: Afgradering van vrugte vanweë onvoldoende rooi kleur beperk die winsgewendheid van blospeercultivars (Pyrus communis L.). In die geval van 'Rosemarie' word swak kleur toegeskryf aan vooroes rooikleurverlies gedurende warm periodes. Die regulering van kleurontwikkelling in pere is nog nie ondersoek nie terwyl min bekend is oor antosianiendegradasie aan die boom. Om die regulering van kleurontwikkelling in rooi- en blospeercultivars vas te stel, is veranderinge in kleur en in die aktiwiteit van fenielalanien ammonia-liase (FAL) en UDPGalaktose: flavonoied-3-o-glikosieltransferase (UFGT) gemeet gedurende vrugontwikkelling en in reaksie op koue fronte. Pere was op hul rooiste 'n maand of langer voor oes. Hierna het rooi kleur afgeneem tot met oes. Anders as in sommige ander vrugsoorte het UFGT aktiwiteit nie kleurontwikkeling beperk nie. Die afname in rooi kleur tot met oes mag egter verband hou met 'n gelyktydige afname in FAL aktiwiteit. 'Rosemarie' kleur het aansienlik gefluktueer in reaksie op temperatuur. Rooi kleur het toegeneem met koue fronte en afgeneem in die warmer periodes tussen fronte. Rooi kleur was meer stabiel en klaarblyklik minder afhanlik van lae temperature in ander peercultivars. Die noodsaaklikheid van lae temperature vir kleurontwikkelling in 'Rosemarie' is bevestig deur 'n toename in ensiemaktiwiteit in reaksie op koue fronte. Lae temperature het geen effek gehad op ensiemaktiwiteit in 'Bon Rouge' nie. Appels en pere is gebruik om die effek van temperatuur en lig op antosianiendegradasie en vrugkleur te ondersoek. Die modifiserende effek van antosianienkonsentrasie op kleurverlies is ook ondersoek. Antosianiendegradasie en rooi kleurverlies het lineêr toegeneem tussen 10° en 30°C. Beligting het degradasie en kleurverlies verder versnel. Die tempo van kleurverlies was afhanklik van antosianienkonsentrasie. Kleurverlies was aansienlik vinniger in vrugte met hoë pigmentvlakke, in vergelyking met vrugte met lae pigmentvlakke vanweë die eksponensiële verwantskap tussen antosianienkonsentrasie en kleurskakeringswaardes (hue values) by hoë pigmentvlakke en die lineêre verwantskap by lae pigmentvlakke. Antosianiendegradasie en vooroes rooikleurverlies in 'Rosemarie' is kwantitatief bevestig en het saamgeval met 'n warm periode tydens vrugontwikkelling. Gebaseer op hierdie data is die gevoeligheid van 'Rosemarie' vir vooroes rooikleurverlies toegeskryf aan lae antosianienkonsentrasies wat die sigbaarheid van netto antosianiendegradasie by hoë temperature verhoog. Die gebruik van oorhoofse evaporatiewe verkoeling (EG) om rooi kleur van blospere te verbeter is ge-evalueer. 'Rosemarie' vrugte wat evaporatief verkoel is bo 28°G vanaf twee weke voor oes, was rooier as kontrole vrugte by oes. 'Forelle' kleur het nie gereageer op EG nie. Die effek van EG op vrugkleur was relatief klein in vergelyking met die effek van temperatuur. AI kan EG 'Rosemarie' kleur verbeter in warm produksiestreke sou dit meer effektief wees om 'Rosemarie' se verbouing te beperk tot koeler klimaatstreke. Laastens is die vermoë van antosianien om peerskil teen fotoinhibisie te beskerm ondersoek. Fotoinhibisie was aanwesig in vrugskil wat direk blootgestel was aan sonlig in die boord. Die omvang van fotoinhibisie het toegeneem met 'n afname in rooi pigmentasie van vrugskil. Die verband tussen skilkleur en fotoinhibisie was steeds aanwesig na blootstelling aan ligstres by 10° en 400G. Ons het egter geredeneer teen 'n algemene funksie vir antosianien in fotobeskerming by hoë temperature. Verder was daar aanduidings dat, alhoewel geassossieer met rooi skilkleur, beskerming teen ligstres nie noodwendig te wyte was aan antosianien nie.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/53569
This item appears in the following collections: