Postharvest application of polyamines influence ripening related changes and ameliorate chilling stress in carambola during cold storage

Ahmad, Azhane (2018) Postharvest application of polyamines influence ripening related changes and ameliorate chilling stress in carambola during cold storage. PhD thesis, University of Nottingham.

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Malaysian carambola (Averrhoa carambola L.) B10 variety is one of the promising exotic tropical fruit traded in the global market. The alarming demand for carambola was stimulated by its unique shape and flavour, increasing health consciousness and great potential in fresh-cut industry. Nevertheless, carambola is a highly perishable commodity that greatly impairs its postharvest quality and long term storability. Therefore, investigations were carried out to verify the potential of putrescine (PUT), spermidine (SPD) and spermine (SPM) as a postharvest dip treatment for maintaining quality, reducing chilling injury (CI) and extending the storage life of carambola.

Carambola at Index II was dipped in different concentrations (0.0, 0.1, 1.0 and 2.0 mM) of PUT, SPD and SPM, and then stored at 3oC (±0.5), with 85-90% RH. Physicochemical changes and fruit quality attributes were made at harvest, 7 day intervals for 28 days of cold storage plus 6 days at 22±1oC for shelf life. PUT treatment effectively lowered the weight loss, maintained peel color (L*, C*, ho), retained higher firmness, reduced the rate of respiration and ethylene emission, suppressed the degradation of soluble solid content (SSC) and titrable acidity (TA) throughout shelf life. Moreover, PUT-treated fruit substantially suppressed the advancement of dominant softening enzymes in carambola such as β-galactosidase (β-gal), polygalacturonase (PG) and pectin methylesterase (PME). The softening enzymes activity trends in PUT-treated fruit were concomitant with less apparent changes in flesh firmness.

Accordingly, the applied PUT treatment significantly reduced CI symptoms in carambola. Lipid peroxidation levels (MDA) and membrane leakage activity were declined in fruit treated with PAs, and the reduction was more distinct in fruit treated with PUT. This study demonstrates that the influence of PUT on postharvest quality and protection of cell membrane against chilling damage was more profound at the highest concentration (2.0 mM). Ascorbic acid (AA), total antioxidant (TAA) and total phenolic contents (TPC) were enhanced to greater levels in PAs-treated fruit, while control fruit experienced significant losses of these bioactive compounds throughout chilling storage. Highest SPM concentration (2.0 mM) exhibited the best results on increasing TAA through an increment of TPC. On the other hand, AA content was increased with the lower concentration of SPD (1.0 mM).

Exogenously supplied PUT induced tremendous endogenous PAs accumulation in carambola tissue, particularly free PUT and SPD concentrations. Such responses suggest that PUT may stabilize and protect cellular membrane integrity against chilling stress. In general, the increment of endogenous PAs with PUT treatment induced stress tolerance mechanisms in carambola during cold storage. An attempt to identify unknown genes sequence of SAMDC, ADC, ACS and ACO in carambola was carried out. In line with this, an efficient extraction protocol of RNA isolation from carambola mesocarp tissue was optimized. CODEHOP features were exploited to design degenerate oligonucleotide primers and RT-PCR approach was utilized to attest degenerate primer specificity. Phylogenetic trees revealed the sequenced products of SAMDC, ADC, ACS and ACO in carambola exhibited close evolutionary relationship with protein sequences present in muskmelon, peach, tobacco and sweet oranges respectively.

These present findings throw light on the potential of PAs particularly PUT at a dose of 2.0 mM for 5 min could be an effective means for maintaining postharvest quality and protection against CI, with a net increase in shelf-life of B10 carambola.

Item Type: Thesis (University of Nottingham only) (PhD)
Supervisors: Ali, Asgar
Chin, Chiew Foan
Keywords: polyamines, carambola, postharvest quality, potential of putrescine
Subjects: S Agriculture > SB Plant culture
Faculties/Schools: University of Nottingham, Malaysia > Faculty of Science and Engineering — Science > School of Biosciences
Item ID: 47441
Depositing User: AHMAD, AZHANE
Date Deposited: 22 Apr 2020 15:40
Last Modified: 06 May 2020 08:32

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