Effect of fruit canopy position, harvest maturity and storage duration on post-harvest mealiness development of ‘Forelle’ pears (Pyrus communis L.)

Cronje, Rudolph John (2019-12)

Thesis (MScAgric)--Stellenbosch University, 2019.

Thesis

ENGLISH ABSTRACT: Preliminary studies indicated a link between fruit canopy position and higher total soluble solids (TSS), respectively, and mealiness development during ripening of ‘Forelle’ pear. In this study this link is further explored to establish whether different parts of the canopy result in differences in maturity and ripening rates which affect mealiness incidence after ripening post-harvest. This study also investigates whether mealiness incidence is related to the micro-climactic differences within the canopy. Mealy textured pears were in general bigger sized fruit associated with higher TSS, lower titratable acid (TA), a redder blush colour, yellower background colour, and lower firmness after a period of ripening. Mealy fruit were also associated with a lower juice area and juice mass that were measured using a confined compression method. Mealiness incidence was the highest for red blushed outer canopy ‘Forelle’ pears associated with the highest exposure to sunlight, coupled with the highest fruit surface temperatures and vapour pressure deficit. The shading of outer canopy pears reduced mealiness incidence significantly, compared to that of sun-exposed outer canopy pears, which could be an indication that direct exposure to full sunlight coupled with high fruit temperatures for most part of the day could be one of the determining factors in ‘Forelle’ mealiness development. However, not all outer canopy fruit developed a mealy texture and therefore another unidentified tree factor might also play a role. The ripening rate developed earlier for outer canopy pears (earlier loss of firmness and an earlier transition to a more yellow ground colour) compared to intermediate and shaded inner canopy pears for both seasons, irrespective of harvest maturity. This is an indication that outer canopy fruit are in a more advanced stage of maturity than the other fruit positions. Fruit harvested at post-commercial maturity seems to be more susceptible to mealiness development. Highest mealiness incidence was observed after 8 weeks of cold storage at - 0.5 °C with 4, 7 and 11 days of ripening at 20 °C (8w RA + 4, 7 and 11d SL), while mealiness decreased with prolonged cold storage. Mealiness does however, not seem to be directly linked to ethylene production rate.

AFRIKAANSE OPSOMMING: Voorlopige studies dui op ’n ooreenkoms tussen die effek van boomposisie van ‘Forelle’ pere, hoër totale opgeloste vastestowwe (TOV) en die ontwikkeling van melerigheid gedurende die proses van rypwording. In hierdie studie is die verband verder getoets om vas te stel of vrugte van verskillende boomposisies tot verskillende ryphede met gevolglike verskille in melerigheid tydens die na-oes periode lei. Verder het die studie gepoog om vas te stel of hierdie verskille moontlik gekoppel kan word aan mikro-klimaat verskille van vrugte op verskillende boomposisies. Pere met ‘n melerige tekstuur was oor die algemeen groter, tesame met hoër totale opgeloste vastestowwe (TOV), laer titreerbare sure (TS), rooier bloskleur, geler agtergrond kleur en laer fermheid na ‘n periode van na-oes rypwording. Melerigheid was ook geassosieer met ‘n laer sap area en sap gewig wat verkry was deur die begrensde kompressie metode. Die voorkoms van melerigheid was die hoogste vir die rooier bloskleur ‘Forelle’ pere wat geassosieer is met die hoogste persentasie blootstelling aan maksimum sonlig tesame met die hoogste vrugoppervlaktemperatuur- en dampdruk verskille. Wanneer buitevrugte beskadu was, het die voorkoms van melerigheid betekenisvol afgeneem in vergelyking met díe van sonblootgestelde buitevrugte. Dit kan daarop dui dat direkte blootstelling aan vol sonlig tesame met hoë vrugtemperature vir die grootste gedeelte van die dag, een van die deurslaggewende faktore kan wees in die ontwikkeling van ‘Forelle’ melerigheid. Nie alle buitevrugte het egter ‘n melerige tekstuur ontwikkel nie, wat kan dui op ‘n onbekende boomfaktor wat ook moontlik ‘n invloed kan uitoefen. Die buitevrugte ontwikkel vroeër rypheid ontwikkel (vroeër afname in fermheid en oorgang na ‘n geler agtergrondkleur) as die intermediêre- en binneste vrugposisies vir beide seisoene, ongeag die oesrypheid. Dit is ‘n aanduiding dat buite vrugte in ‘n meer gevorde rypheid stadium is as vrugte afkomstig van ander boomposisies. Vrugte wat na die optimale-kommersiële rypheid gepluk is, blyk om meer vatbaar te wees vir die ontwikkeling van melerigheid. Die hoogste voorkoms van melerigheid is waargeneem 8 weke na koelopberging by -0.5 oC, opgevolg deur 4, 7 en 11 dae van rypwording by 20 oC (8w RA + 4, 7 en 11d RL) terwyl melerigheid in meeste gevalle afgeneem het met ‘n verlengde periode van koelopberging. Die ontwikkeling van ‘Forelle’ melerigheid blyk ook nie direk gekoppel te wees aan die vlak van etileen produksie nie.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/107285
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