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Doctoral Degrees (Horticultural Science)

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Browsing Doctoral Degrees (Horticultural Science) by SDG "SDG12"

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    Efficacy of enhanced freshness formulation as a novel postharvest treatment for gold kiwifruit (actinidia chinensis) = Ukusebenza kahle kwendlela entsha ethuthukisiwe yokugcina i-Gold Kiwifruit (Actinidia chinensis) ifreshi emva kokuvunwa.
    (2023) Mthembu, Sisanda Sibusiso Luyanda.; Mditshwa, Asanda.; Magwaza, Lembe Samukelo.; Tesfay, Samson Zeray .
    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. Iqoqa. Izimo eziyizihibe eziphambili uma kuthunyelwa emazweni angaphandle i-kiwifruit ukuthamba okwedlulele kwezithelo kanye nokonakala ngokukhunta okubhebhethekiswa amazinga aphansi okushiwa ngesikhathi izithelo zisendleleni, Ukuthamba akwandisi nje kuphela ukudaleka kokonakala kepha kuholela nasekulahlekelweni ngokwezomnotho. Ukugcina izithelo ziqinile kubaluleke kakhulu ngokwamanani ezimakethe kanye nokuhlala zifreshi lapho zigcinwe khona. Kodwa-ke, izindlela ezijwayelekile zokugcina impahla endaweni enamakhaza azanele ekubhekaneni nalezi zinselelo. Ngakho-ke, lolu cwaningo luhlola ukusebenza kahle kwendlela eyaziwa nge-Enhanced Freshness Formulation (EFF) ekunciphiseni ukuthamba kwe-kiwifruit. Ama-kiwifruit agcinwa amasonto ayisishiyagalombili endaweni eyisibandisi emazingeni okushisa awu-0°C kanye nama-90% okuswakama okuhambisanayo. Kwalandeliswa ngesonto elilodwa ngaphansi kwesimo sokushisa esikahle. Lolu cwaningo luhlola ukuthi i-EFF inamthelela muni ekuthambisekeni kwezithelo, okuhlanganisa nokulimala kwezindonga zamaseli/kongwengwezi lwamaseli, ukuqina kongwengwezi, kanye nokutheleleka ngokukhunta. Okunye futhi, ucwaningo luhlola amandla e-EFF ekulondolozeni izinhlanganisela okuyizona ezinomthelela kokuphilayo, okuyikhona okubalulekile ekugcineni ikhwalithi yezithelo ingaguquki. Uhlangothi olulodwa locwaningo luhlola ukusebenza ngendlela efanele kwe-EFF ekudambiseni ukushesha kokuthamba kwe-kiwifruit evunwe maphakathi nesigaba sokuvuthwa kanye nevunwe uma sekuseduze kakhulu ukuthi avuthwe. Imiphumela iveza ukuthi i-EFF iyakwazi ukulondoloza ama-polysaccharide ongwengwezi lwamaseli ngokucindezela ama-enzyme alimaza ungwengwezi lwamaseli, ngaleyo ndlela kuthuthukiseke ukuqina kwezithelo kanye nekhwalithi yazo. Okunye futhi ukuthi izithelo okwasetshenziswa kuzo i-EFF zakhombisa ukunganciphi ubungako bazo kanye nomthamo odlekayo, kanti futhi nobumuncwana bazo banda okwathuthukisa ukudayiseka kwazo. Kwagxilwa futhi nasemandleni e-EFF ukunciphisa ukukhiqizeka kwe-reactive oxygen species (ROS) eyaziwa kakhulu ngokusheshisa ukuzwela kanye nokuthamba. Ukukwazi kwe-EFF ukuthiya i- Phospholipase D ibe ithuthukisa ukusebenza kwe-antioxidant enzyme kwanciphisa ukwakheka nokudaleka kwe-ROS kanye nokulimala kongwengwezi. Ngaleyo ndlela kwandiseka isikhathi okungagcinwa ngaso lezi zithelo. Okunye, ucwaningo luhlola ukusebenza kwe-EFF ekulwisaneni ne-Botrytis cinerea, okuyigciwane elivame ukuhlasela emva kokuvuna. I-EFF ikucindezela kakhulu ukukhula nokwanda kokukhunta ngenxa yokuthi ikwazi ukuthuthukisa ukulwisana nezifo ngokuhlanganisa okwaziwa nge-secondary metabolite kanye nokusebenza kwama-enzyme ahambisana nokuvikela. Okunye futhi, lolu cwaningo lwahlola umthelela we-EFF ekugcinekeni kwama-antioxidant ngesikhathi izithelo zisagcinwe isikhathi eside. Imiphumela iveza ukuthi i-EFF yakuthuthukisa kakhulu ukugcineka kwama-antioxidant ezithelweni ama-kiwifruit esetshenziswe kuzo ngokulawula ama-enzyme atholakala ekuhlanganisweni kwezinhlanganisela ezinomthelela kokuphilayo kanye nesimo esaziwa nge-oxidation lapho kwakheka khona i-oksijini eningi noma kulahleke i-hydrogen. Ekuphetheni, i-EFF ikhombisa ukuthi likhona ithemba lokuthi kungabhekwana nezinselelo eziphathelene nokuhanjiswa kwe-kiwifruit emazweni angaphandle ngokunciphisa ukuthamba kanye nokonakala kokukhunta, lokho okungathuthukisa ikhwalithi yezithelo kanye nokudayiseka kwazo. Lusadingeka olunye ucwaningo ukuze kuqondakale kahle ukusebenza kwamamolekhuli ekulawuleni ukuthamba kanye nama-antioxidant enzyme, kanye nokuthuthukisa ukusetshenziswa kwayo kulo mkhakha womkhiqizo.
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    Ethephon-induced changes in macadamia nuts: implications for dietary indicators, nutritional quality, and postharvest shelf life = Okulawula ukukhula kokwenziwa kwesihlahla okunomthelela emantongomaneni iMacademia: Isiphakamiso esimayelana nezinkombaluhlelo zokudla, izingabunjalo lomsoco nobude besikhathi sokuyigcina emva kwesivuno.
    (2024) Aruwajoye, Noluthando Noxolo.; Tesfay, Samson Zeray.; Mditshwa, Asanda.; Magwaza, Lembe Samukelo.
    The thriving macadamia nut industry, prized for its nutritional value, grapples with the challenge of inconsistent abscission seasons, leading to variable harvest times and increased operational costs. To address this, the traditional application of ethephon induces uniform nut abscission and streamlines harvesting. However, it is crucial to investigate how ethephon impacts the nutritional quality and postharvest shelf life of macadamia nuts. This study focuses on the effect of ethephon on the postharvest quality of the ‘788’ and ‘Beaumont’ cultivars, comparing various categories: nuts that successfully abscised due to ethephon (ED), those manually picked from ethephon-treated trees (ET), nuts naturally dropped from control trees (CD), and those manually picked from control trees (CT). Guided by industryrecommended doses, Ethephon 480 SL® was administered using a Cima mist blower to facilitate nut abscission, specifically targeting physiologically mature nuts. The research explores the influence on fatty acids, dietary indicators, biochemical components, and polyphenol oxidase (PPO) activity. Various parameters, including total phenolics, flavonoids, antioxidant activities, sucrose, and total protein, were assessed across treatments using standardized procedures. samples were collected over a 72-day accelerated storage period. The study further assessed the effect of Ethephon on the physical attributes of macadamia during a 56-day accelerated storage, analyzing mass, diameter, colour (L*, a*, b*, and hue angle), and texture. Kernels were roasted at 125 °C for 15 minutes using a hot air oven dryer post drying and dehusking. Models were then developed to predict the firmness and colour parameters of macadamia nuts harvested with ethephon from the ‘788’ and ‘Beaumont’ cultivars based on drying days and storage conditions. The aim was to determine the minimal processing requirements for achieving satisfactory postharvest nut appearance. Input parameters considered included storage temperature, drying temperature, and storage days, vi while the resulting outputs were firmness and colour parameters (L*, a*, b*, and hue angle). The range of the input parameters spanned from -22℃ to 25℃ for storage temperature, 35 to 57℃ for drying temperature, and 0 to 70 days for storage duration. Significant changes were observed in the fatty acid profiles of macadamia nuts exposed to ethephon treatment. Notably, ethephon led to a substantial increase in stearic acid content, reaching 24,622 µg/g in (ED) after 72 days, compared to 16,764 µg/g in (CD), thereby impacting their nutritional quality. Conversely, ED nuts exhibited a reduction in unsaturated fatty acids (USFAs). Hierarchical clustering analysis identified strong correlations between ED and saturated fatty acids (SFAs) in both ‘Beaumont’ and ‘788’ cultivars, with coefficients of 0.78 and 0.80, respectively. This was accompanied by an increase in atherogenic indices, thrombogenic index, and saturation index, along with a decrease in the hypocholesterolemic/hypercholesterolemic ratio. Concurrently, a robust correlation (0.97) between sucrose and Polyphenol Oxidase (PPO) was observed in ‘Beaumont’, underscoring the influence of ethylene treatment. Notably, ED ‘Beaumont’ nuts exhibited the highest sucrose content at 18.63 mg/g, coupled with elevated PPO activity at 1.06 U g-L. For the physical attributes, ED exhibited a notable influence on the ‘Beaumont’ cultivar, particularly affecting parameters such as a*, b*, mass, and diameter. Conversely, in the ‘788’ cultivar, Principal Component Analysis (PCA) revealed that CD treatment held prominence, showing elevated values for firmness, a*, and b*. Furthermore, model development demonstrated significance, with high coefficients of determination ranging between 0.83 and 0.97. Notably, under reduced drying days and optimal storage temperature, the models predicted maximum L* values of 76.253 and 79.748 for the ‘788’ cultivar. This study provides a theoretical framework for identifying optimum set points crucial for the effective preservation of both the ‘788’ and ‘Beaumont’ varieties of macadamia nuts, particularly in preventing external discolouration. The proposed set points aim to enhance the quality and overall market value of these macadamia nut varieties. The overall findings offer a comprehensive perspective on the effects of ethephon application on macadamia nuts. Stakeholders, producers, and processors in the macadamia nut industry can leverage this research to make informed decisions that enhance overall efficiency and quality while ensuring optimal nutritional value and extended shelf life for macadamia nuts. Iqoqa. Imboni yokukhiqiza amantongomane abizwa ngemacadamia ibhekene nezinkinga ngenxa yezikhathi ezingenayo inhlalanjalo zokuwohloka kwamahlamvu ezihlahla eyenzeka noma yinini, okwenza isivuno singazinzi kahle futhi kunyuke nezindleko. Ukusetshenziswa komuthi i-ethephon kusiza ekutheni ukuwohloka kwamahlamvu ezihlahla kwenzeke ngesikhathi sonyaka esifanele, nokho umphumela walo muthi ezingeni lokudla nesikhathi sokugcinwa kwakho awaziwa. Lolu cwaningo lucubungula imiphumela ye-ethephon mayelana nezinga lokudla osekuvuniwe i-788 nezitshalo ezahlukene zeBeaumont. Izinhlobo ezahlukene zamantongomane, okufaka nalawo awiswe yi-ethephon, nathathwa ezihlahleni ezilashiwe, naziwele ngokwawo, kwahlolwa futhi kwaqhathaniswa. I-ethephon yasetshenziswa kulandelwa imigomo ebekiwe yezimboni, kubhekwa amantongomane asevuthiwe. Lolu cwaningo lwaluhlola isimuncwane esinafutha, izinkomba zokudla, amakhemikhali nepolyphenol oxidase (PPO). Amasampula ocwaningo aqoqwa esikhathini esiyizinsuku ezingama-72 sokugcinwa kwawo, ukucubungula izinto ezibonakalayo njengesisindo, umnqamulankaba, umbala kanye nobunjalobotho. Imifanekisomumo iqagule ukuzinza nemibala emihle ngezikhathi ezinzima namazinga okugcineka kokudla, ukuhlonza nokugcina isikalo esibekiwe. Inguquko ekwakhekeni kwamfutha yabonakala yenzeka, amantongomane afakwe i-ethephon akhombisa ukwenyuka kwesimuncwane esigcwele amafutha nokuncipha kwesimuncwane esinamafutha angagcwele. Kwatholakala ubudlelwane obuqinile phakathi kokusetshenziswa kwe-ethephon kanye nesimuncwane samafutha aphelele. Kwatholakala kunokwenyuka kwesakhi sikashukela kamoba noma webhithrudi kanye noksebenza kwe-PPO emantongomaneni eBeaumont alashwe kusetshenziswa i-ethephon. Ukuhlaziya okukhulu kocwaningo kwaveza imiphumela ehlukile ngokwakheka kwesitshalo ngasinye esasicwaningwa. Indlela ecwaninga ukukhula yaveza ukwenyuka kwesibalo, esasifinyelela phezulu emibaleni ngendlela eyayilindekile. Indlela yokubheka ukuzinza yayibaluleke kakhulu ezitshalweni ze-788. Lolu cwaningo luza nomhlahlandela mayelana nokugcinwa kwamantongomane emacadamia, ukuthuthukiswa kwezinga kanye namanani okudayisa. Abathintekayo bangasebenzisa le miphumela yocwaningo ukuthuthukisa indlela yokusebenza kahle, izinga, kanye nokukwazi ukugcina ukudla isikhathi eside futhi kuqinisekiswe nokuthi ukudla kunomsoco odingekayo.