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Efficacy of enhanced freshness formulation as a novel postharvest treatment for gold kiwifruit (actinidia chinensis)

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When exporting kiwifruit, the main limiting factors are excessive fruit softening and fungal decay. Furthermore, exposing kiwifruits to low temperatures induces the mechanisms involved in the softening process. In addition, kiwifruit become much more susceptible to fungal decay as they soften, which exacerbates deterioration of kiwifruit during transit. Fruit firmness is an important criterion for the market value of kiwifruit and storage life for the wholesale and retail trade. Therefore, loss in firmness is a serious problem resulting in postharvest and economic losses. Given that cold storage alone is not enough to optimise firmness retention of kiwifruit, the current study aimed to investigate the capacity of enhanced freshness formulation (EFF) to reduce kiwifruit softening. Kiwifruits were subjected to eight weeks of storage at 0 °C and 90 % relative humidity, followed by one week at ambient storage. The efficacy of EFF to regulate the mechanisms behind the softening process such as cell wall degradation, membrane deterioration and fungal infection was evaluated. Furthermore, the efficacy of EFF to preserve bioactive compounds was also evaluated to assess the effect of this treatment on these highly appreciated quality attributes. The first study evaluated the efficacy of EFF to delay softening of kiwifruit harvested at both the mid and late maturity stage. The influence of EFF on cell wall polysaccharides (CWPs) and cell wall degrading enzymes (CWDEs) was assessed. The findings showed that EFF optimised firmness retention of kiwifruit by preserving CWPs through the suppression of CWDEs which are responsible for initiating fruit softening. Furthermore, EFF maintained fruit quality and marketability, characterised by significantly lower mass loss, total soluble solids and higher titratable acidity. The second study examined the capacity of EFF to inhibit the excessive production of reactive oxygen species (ROS) which induce membrane damage, resulting in softening and senescence. EFF treatment effectively delayed the progression of kiwifruit senescence by reducing membrane deterioration and the accumulation of ROS. The mechanism by which EFF reduced membrane damage caused by ROS was attributed to its capacity to enhance the activities of antioxidant enzymes involved in neutralising ROS and suppressing Phospholipase D which destroys membrane integrity, resulting in improved storability of treated fruit. The third study assessed the efficacy of EFF to inhibit the fungal growth of Botrytis cinerea, which one of the major postharvest pathogens of kiwifruit that contribute to excessive softening. The findings show that EFF effectively suppressed the fungal growth of Botrytis cinerea in a dose -dependent manner. The results demonstrate that EFF can serve as a potential disease control strategy for kiwifruit at the postharvest stage. The mechanism by which EFF suppressed fungal decay can be attributed to the treatment’s capacity to induce disease resistance against Botrytis cinerea, by enhancing the synthesis of secondary metabolites and the action of defence-related enzymes, thus conferring greater protection against pathogen attack. The fourth study investigated the ability of EFF to retain the antioxidant quality of kiwifruit during prolonged storage. The bioactive compounds of EFF-treated kiwifruits were effectively maintained throughout the storage period. The findings of the present study further revealed that the mechanism by which EFF optimises antioxidant retention is due to its ability to regulate enzymes involved in the synthesis and oxidation of bioactive compounds. Despite the positive results, further research on transcriptome analysis is needed to elucidate how EFF regulates softening and antioxidant enzymes.


Doctoral Degree. University of KwaZulu-Natal, Pietermaritzburg.