Browsing by Author "Mditshwa, Asanda."

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Assessing gaseous ozone and edible coatings as postharvest treatments for mango (mangifera indica L.) fruit.
(2021) Bambalele, Nonjabulo Lynne.; Mditshwa, Asanda.; Magwaza, Lembe Samukelo.; Tesfay, Samson Zeray.
This research examines the potential of gaseous ozone and edible coatings in preserving postharvest quality and extending the shelf-life of ‘Keitt’ mango fruit. A critical review of the literature focused on the recent postharvest technologies used to preserve the quality of mango fruit. The prospects of using non-chemical postharvest treatments such as gaseous ozone and edible coatings were also reviewed. A screening study was conducted to determine the optimum ozone (O3) application time for effectively maintaining fruit quality and extending shelf-life. Mango fruit were intermittently exposed to gaseous ozone for twelve, twenty-four, thirty-six, or forty-eight hours, and the control fruit were untreated. Fruit were stored at 10℃ for twenty-one days and seven days shelf-life at ambient temperature. The findings showed that the O3 treatment should be applied at the pre-climacteric stage to achieve optimum results. Ozone treatment for 24 or 36 hours effectively maintained firmness and carotenoids content, delayed color changes, decay incidence, and mass loss. Therefore, an ozone exposure time of 24 and 36 hours was adopted for the study. These exposure times were incorporated into edible coatings (moringa leaf extract and carboxymethyl cellulose) for further investigation. The study on the effect of gaseous O3 incorporated with edible coatings on sensory attributes and physicochemical parameters showed that EC and EC + O3 (36 h) were more effective in delaying the ripening process and maintaining the postharvest quality. Overall, consumers preferred the fruit coated with EC due to its attractive color, smell, and sweetness. The study on the postharvest effect of gaseous O3 and EC on antioxidants and the biochemical properties of mango fruit is discussed in Chapter Five. The findings of this study demonstrated that the treatment combination of EC and gaseous O3 (36 h) effectively maintained antioxidants, membrane integrity and enhanced the quality of mango fruit during storage. The effect of gaseous O3 and EC on postharvest diseases of mango fruit, specifically Colletotrichum gloeosporioides (anthracnose) and Lasiodiplodia theobromae (stem-end rot), was also investigated. This study revealed that EC + O3 (24 h) effectively controlled stem-end rot and anthracnose in mango fruit. The treatment combination of EC and O3 (36 h) reduced the mycelial growth and disease incidence of Lasiodiplodia theobromae and Colletotrichum gloeosporioides. The study of EC and O3 in the volatile compounds of mango fruit is discussed in Chapter Seven. The fruit treated with EC had a high content of volatile compounds compared to other treatments. The treatment combination of EC + O3 (24 h) was not effective in maintaining the volatile compounds of mango fruit during storage. The findings of the current study suggest that EC + O3 (36 h) can be used as postharvest treatment of mango fruit. Additional research is required to gain more insights in understanding the EC+ O3 mode of action in maintaining volatile compounds and controlling mango postharvest diseases.
Effect of storage temperatures on the postharvest performance and sprouting of selected potato cultivars.
(2019) Ngceni, Xola.; Mditshwa, Asanda.; Magwaza, Lembe Samukelo.; Tesfay, Samson Zeray.
Sprouting, processing and nutritional quality of potato tubers are cultivar and storage dependent. Due to the extensive choice of potato cultivars currently available in South Africa, there is a limited information on their performance under the wide range of storage temperatures. This research investigated four objectives which were to: i) review the postharvest factors affecting the potato tuber quality; ii) investigate the effect of different storage temperatures on sprouting incidence and processing attributes of the selected potato cultivars; iii) determine the effect of different storage temperatures on nutritional quality parameters of selected potato cultivars; iv) develop prediction models using near infrared spectroscopy (NIRS) for determination of potato quality. In chapter 2, factors affecting postharvest quality of potato tubers were reviewed. It was observed that factors such as sprouting, mass loss, storage conditions and duration, and postharvest treatments have high influence on the postharvest quality of potato tubers. Sprouting was found to be the major cause of the high postharvest losses occurring in potato industry. Chapter 3 investigated the effect of storage temperatures on sprouting and processing attributes of potato tubers. The results clearly demonstrated that sprouting and processing attributes were both cultivar and storage dependent. For instance, sugars of some potato tubers were highly stimulated by cold storage whereas for sprouting it was vice-versa. The dry matter content and mass loss of potato cultivars slightly increased with storage time and temperature. In chapter 4, the effect of storage temperatures on the nutritional quality of potato tubers was investigated. In this chapter, the findings clearly proved that ascorbic acid and total phenolic content generally decreased while the antioxidant activity was increasing with storage time. Proteins in potato tuber varied based on storage temperature and cultivar. Chapter 5 sought to develop the predictive models for determination of the internal quality of potato tubers. Good models for ascorbic acid, mass loss and total phenolics for all the cultivars were developed. On the hand, poor models were developed for both sucrose and reducing sugars for all the cultivars.
Effects of edible coatings and moringa extracts on postharvest quality of papaya fruits.
(2018) Langa, Sabeliwe.; Tesfay, Samson Zeray.; Mditshwa, Asanda.
Carica papaya L., known as papaya is a member of the small family Caricaceae. It is an important fruit for both fresh and processed products. It is a good source of vitamin A, lycopene, polysaccharides and proteins. High consumption of papaya is known to contribute to the prevention of the chronic diseases such as cardiovascular disease. About 30-50% of the harvested papaya is reported to never reach the consumers due to postharvest spoilage. Postharvest spoilage can be attributed to the fact that it is perishable after harvesting. The level of spoilage depends on the management of pre-harvest (environment and cultural practices) and postharvest factors (handling, environmental conditions). The factors contribute largely to papaya quality deterioration by stimulating physiological/biochemical processes (respiration, transpiration) and microbial growth. Also, some of the factors affect papaya fruit quality at maturity stage, time of harvest and the harvest method. Various fungicides have been used to reduce postharvest spoilage. However, the negative effects on human health and the environment, accompanied with high costs, residues in plants has encouraged development of alternative approaches. The development of new natural preservatives and antimicrobials has increased as alternatives for fruit quality preservation. Edible coatings are amongst the natural methods of fruit quality preservation and protecting perishable food products from deterioration by retarding dehydration, suppressing respiration, improving textural quality, helping retain volatile flavour compounds and reducing microbial growth. The study evaluated the effect of edible coatings on papaya fruit quality, and antifungal activity of plant extracts against fungal pathogens that affect postharvest quality of fruits. In the first section of the study, Moringa oleifera extracts (leaf and seed) incorporated with chitosan and CMC (MLE+CH, MSE+CH, MLE+CMC and MSE+CMC) were used as an alternative for synthetic fungicides. The quality parameters were measured to observe the effect of treatments. The quality parameters that were assessed under cold and ambient storage conditions included pH, total titratable acidity, total soluble sugars, weight loss, firmness, peel colour, vitamin C, total flavonoids, total phenols, antioxidants and soluble sugars. Inhibitory effects of Moringa oleifera aqueous and ethanolic leaf and seed extracts (MLWE, MSWE, MLEE and MSEE) was evaluated in-vitro. Treatments applied (MLE+CH, MSE+CH, MLE+CMC and MSE+CMC) maintained papaya fruit quality compared to the control under both ambient and cold storage conditions. Treatment MSE+CMC showed better fruit quality maintenance compared to other treatments. MLWE, MSWE, MLEE and MSEE had relatively high inhibitory potential in all tested concentrations (10%, 20% and 30%) compared to the control treatment. A 100% mycelial growth inhibition in PDA agar amended with moringa extracted with ethanol was observed.
Efficacy of carboxymethyl cellulose and gum arabic edible coatings in combination with moringa leaf extract in improving postharvest quality of new avocado (Persea americana Mill.) cultivar, ‘Maluma’.
(2018) Kubheka, Sanele Fana.; Tesfay, Samson Zeray.; Magwaza, Lembe Samukelo.; Mditshwa, Asanda.
There is growing trend towards an increase in demand for environmental friendly and sustainable postharvest treatments for fresh horticultural produce. This trend is also coupled by the recent increase in demand for ‘organic’ fresh products. In response to these demands, fresh produce industry together with researchers in the postharvest biology and technology have identified polymers such as polysaccharides, proteins and waxes to develop what is known as edible coatings. Edible coatings have been successful in reducing mass loss, delaying senescence thus prolonging shelf life of fresh produce. In addition, edible coatings have proven to be excellent carriers of active ingredients such as colourants, antimicrobials which helps alleviate antimicrobials properties of coated produce. The application edible coatings can also provide relief to both producers and consumers as they are economical affordable compared to other techniques. This review looks at formulation of edible coatings with focused on maintenance of postharvest quality. Recent advances in application and their effect on phytochemicals and sensory properties is also discussed. Furthermore, this review makes recommendations that could of assistance in the future, whilst assisting in future research.
Efficacy of enhanced freshness formulation as a novel postharvest treatment for gold kiwifruit (actinidia chinensis)
(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.
Ethephon-induced changes in macadamia nuts: implications for dietary indicators, nutritional quality, and postharvest shelf life.
(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.
Evaluating the efficacy of formulations containing hexanal, moringa leaf extracts, and carboxy methylcellulose as postharvest treatments for fresh tomatoes (Solanum lycopersicum L.).
(2020) Mthembu, Sisanda Sibusiso Luyanda.; Tesfay, Samson Zeray.; Magwaza, Lembe Samukelo.; Mditshwa, Asanda.
Tomato fruit have a relatively short shelf life due to their highly perishable nature. This presents a challenge for long distance transportation of tomatoes. The use of non-refrigerated trucks (used by most commercial entities in South Africa) for transportation exacerbates the loss of fresh tomatoes. The adoption of low temperature storage units during transit is an expensive technology for farmers in developing countries. The application of postharvest treatments such as chemical treatments is used to reduce these losses. However, chemical treatments contain residues that negatively impact the environmental and human health. In addition, it causes off-flavours which negatively affects consumer acceptability and market value of tomatoes. The inefficiency of chemical treatments and the pressure experienced by producers to meet the increase in demand for fresh tomatoes without any hazardous residues by both consumers and regulatory agencies, encourages further research to investigate eco-friendly and sustainable treatments as an alternative to chemical treatments. The use of total soluble solids as a predictor of tomato quality does not provide an accurate description of internal biochemical changes. The use of accurate predictors such as sugar content and sweetness indices, provides a precise description of internal quality and estimation of shelf-life capacity. However, conventional measurements of these parameters are laborious. Thus, probing the use of a rapid and non-destructive technology (Vis/NIRS) to predict and determine sugar content and sweetness indices, in order to facilitate quality management and accurate grading of tomato produce along the supply chain. The research findings obtained in this present study, demonstrated the ability of the hexanal formulation and moringa based edible coating to optimise organoleptic quality and improve the nutritional quality of tomato fruit, harvested at different maturity stages. Vis/NIRS accurately predicted important internal quality parameters relating to the market value of tomatoes such as sugar content and sweetness indices. Results obtained by evaluating the effects of these treatments to extend shelf life and reduce losses of tomato show the potential of adopting these treatments to serve as an alternative to the currently used treatments in the tomato industry. The successful prediction and accurate determination of sugar content and sweetness indices using Vis/NIRS, has the potential to enable rapid and precise grading of tomato produce.
Integrated control of postharvest Fusarium solani of potatoes using UV-C irradiation and Moringa oleifera leaf extracts.
(2024) Buthelezi, Gcinokuhle.; Mbili, Nokwazi Carol.; Mditshwa, Asanda.
Potatoes are a source of food, income and important nutrients which are beneficial to human health. However, production of potato tuber may be hindered by postharvest losses, which reduce the quality and quantity of potatoes reaching consumers. Major losses of potatoes are caused by poor harvesting, sorting, cleaning, handling, and packing. Fusarium solani, a causal agent of dry rot disease that mainly affects potatoes occurs during storage as the pathogen invades the potato tuber through tissue injuries inflicted during lifting or grading. Fusarium dry rot has been mainly controlled by using chemicals. However, the frequent use of chemicals has been recently reported to enhance fungicide resistance to potato pathogens. Chemical fungicides also negatively affect human health and the environment, as they introduce residues in treated potatoes and soil. There is a need to investigate and develop sustainable agricultural strategies such as UV-C irradiation and plant extracts as alternative strategies which are human and environmentally friendly. Therefore, this research aimed to evaluate the effect of UVC irradiation and Moringa oleifera leaf extract, independently and their combined effect in controlling F. solani on potatoes in vitro and in vivo. The antifungal effects of UV-C irradiation against F. solani were evaluated in vitro and in vivo. UV-C treatment for 10 and 15 minutes at a 10 cm distance successfully inhibited the mycelial growth of F. solani by ≥ 50% at 7-day post-inoculation. The in vivo results showed that ‘Sifra’ potatoes treated with UV-C for 10 minutes and 15 minutes had a disease incidence ≤ 33%. The increase in the duration of UV-C exposure to potatoes lowered the disease incidence on potatoes. The scanning electron icrographs showed the breakage and shrinkage of the mycelia in vitro, and the disruption of spores in UVC -treated potatoes. Moringa leaf extracts were prepared and adjusted into different concentrations, MLE 1%, MLE 1.5%, MLE 2%, MLE 2.5%, and MLE 3%. These concentrations were evaluated for their efficacy against F. solani in vitro and in vivo. The findings demonstrated that MLE 1.5%, MLE 2.5%, and MLE 3% inhibited the mycelial growth of F. solani by ≥ 50% in vitro. The in vivo findings revealed that both MLE 2.5% and MLE 3% reduced incidence of dry rot in potatoes. The antifungal activity of moringa was increased at higher concentrations. The scanning electron micrographs showed mycelia distortion in samples treated with moringa and the disruption of F. solani spores on the treated potatoes. It also indicated the formation of biofilms in moringatreated potatoes. Furthermore, this study evaluated the effect of integrated control of F. solani using UVC and moringa leaf extracts. The in vitro results demonstrated that samples treated with MLE 2.5% and exposed to UV-C for 15 minutes inhibited the mycelial growth of F. solani by 100%. ‘Sifra’ potatoes exposed to UV-C for 15 minutes and treated with MLE 3% had the lowest disease incidence (8.33%). The scanning electron micrographs showed abnormal, shrinkage, disruption, aggregation and reduced hyphae length of mycelia in samples treated with both UV-C and MLE. Moreover, it indicated the formation of biofilms in UV and moringa-treated surfaces of potato wounds. These integrated treatments enhanced efficacy compared to the individual application of either treatment. UV-C can be integrated with moringa and be used as alternatives to synthetic fungicides to control dry rot of potatoes.
Investigating the effect of trellising and stem training methods on the horticultural performance of indeterminate tomatoes grown in dome shape tunnels.
(2020) Mngoma, Mlungisi Fihlane.; Magwaza, Lembe Samukelo.; Tesfay, Samson Zeray.; Sithole, Nkanyiso Justice.; Mditshwa, Asanda.; Magwaza, Shirly Tentile.
Growing of tomato in open field in South Africa is very challenging due to unfavorable environmental conditions, pests and diseases. This has resulted to an increased hydroponic production of tomatoes in protected cultivation. However, protected cultivation require many horticultural practices for optimum production. The first experiment of the study was conducted to evaluate the effect of different trellising methods namely, early layering, late layering and vertical trellising in response to leaf gas exchange and chlorophyll fluorescence of indeterminate tomato produced in tunnels. The second experiment was conducted to assess the effect of trellising method on growth, yield and quality parameters of indeterminate tomato. The third experiment investigated effects of different stem training methods namely, single stem, double stem and two plant per pot in line with growth, yield and physiological responses of indeterminate tomato grown in dome shape tunnels.The results of the first study showed that early and late layering increase photosynthetic rate (A), transpiration rate (T), the effective quantum efficiency of photosystem II photochemistry (ФPSII) and electron transportation rate (ETR) compare to vertical trellising. The second study revealed that early and later layering increase plant height, number of fruit and fruit mass compare to vertical trellising. However observed results showed no variation among trellising methods with quality parameters. The third experiment on leaf gas exchange results showed high photosynthetic rate (A) and stomatal conductance (gs) in single and two plants per pot stem. Single stem exhibited high plant height and stem diameter with double and two plants per pot stem. Single stem and double stem showed high number of fruits, and fruits mass compare to two plants per pot stem training. The study also showed high colour index, total soluble solids (TSS), titratable acids (TA), and BrimA with double stem and two plants per pot than single stem. Therefore, the presented results revealed that early and late layering trellising methods can be the best methods that can be used by resource-constrained farmers in dome shape tunnel to increase physiological efficiency, growth and yield. On the other hand double stem and two plants per pot training method can had a potential to improve yield and quality of indeterminate tomato grown in tunnel.
Non-destructive determination of pre-symptomatic biochemical markers for Peteca spot and evaluation of edible coatings for reducing the incidence of the disorder on ‘Eureka’ lemons
(2019) Mbhoni, Rikhotso Muriel.; Magwaza, Lembe Samukelo.; Tesfay, Samson Zeray.; Mditshwa, Asanda.
International markets that import citrus fruit from South Africa have imposed regulations that involve cold sterilization at low temperatures, which cause physiological disorders such as peteca spot in lemon. The aim of this study was to, non-destructively determine pre-symptomatic biochemical markers for Peteca spot and the evaluation of edible coatings for reducing the incidence of the disorder on ‘Eureka’ lemons. The first chapter is general background which introduces the key words and clearly outlines the aim and objectives of the study. The second chapter is review of literature, which motivated the three research chapters due to the gaps found. Presymptomatic biochemical markers that are related to peteca spot were evaluated in the third chapter. The Principal Component Analysis (PCA) was able to separate fruit harvested from the inside and outside canopy positions based on their susceptibility to the disorder. Fruit harvested in the inside canopy were more susceptible to peteca spot and these were correlated with physic-chemical properties, which were typically low in the inside canopy. The efficacy of carboxymethyl cellulose (CMC) and chitosan (CH) incorporated with moringa leaf extracts (M) edible coatings on reducing the incidence of peteca spot was also evaluated in the fourth chapter. Fruit harvested from inside and outside canopy positions were assigned to five coating treatments: control, M+CMC, CMC, CH and M+CH. The most effective coating treatment in reducing the susceptibility of ‘Eureka’ lemon to peteca spot was M+CMC followed by CMC and CH. The fifth chapter focused on, non-destructively predicting peteca spot using visible to near infrared spectroscopy (vis/NIRS). Presymptomatic biochemical markers that have been related to peteca spot were successfully predicted. Lastly, general discussions and conclusions were made in chapter six as well as recommendations.
Postharvest technologies for predicting and reducing susceptibility of ‘Marsh’ grapefruit (Citrus paradisi MacFad.) to rind pitting disorder.
(2019) Shinga, Mawande Hugh.; Mditshwa, Asanda.; Magwaza, Lembe Samukelo.; Tesfay, Samson Zeray.
Citrus fruit is globally one of the most important fruit due to their nutritional value and sensorial attributes, however, they were susceptible to various postharvest disorders, especially during shipping period. Therefore, the aim of this study was to determine the effect of edible coating, carboxymethyl cellulose (CMC) infused with moringa leaf extracts (MLE) on reducing postharvest physiological rind pitting disorder in ‘Marsh’ grapefruit (Citrus paradisi MacFad.). The study also reviewed the literatures on the ability of edible coatings to improve fruit quality and extend shelf life of citrus fruit. Edible coatings recently received attention due to their ability to enhance fruit quality without compromising human health. The first experimental chapter was conducted to evaluate the ability of CMC and MLE as edible coatings to control the disorder in ‘Marsh’ grapefruit. A total of 300 fruit (150 from outside canopy and 150 from inside canopy) were harvested from a commercial orchard at Dole Bolton Citrus Estate in Nkwalini at Showe, KwaZulu Natal, South Africa. Fruit were subjected to different treatments, control (untreated), CMC (0.5%) + MLE (10%), CMC (1%) + MLE (10%), CMC 0.5% and CMC 1%. Treatments were organised in a factorial design. Fruit were stored at 3 ± 0.5 °C and 90-95 % relative humidity (RH), for nine weeks and thereafter taken to room temperature (22 ± 2 °C) for two weeks to simulate shelf life. The physicochemical attributes (total soluble solids. titratable acidity, maturity index, fruit mass loss, fruit colour, rind dry matter) of the fruit were analysed during this period. Rind pitting as well as sensory quality was evaluated at the end of storage period. This study identified that CMC 0.5% + MLE 10% and CMC 1% + MLE 10% reduced postharvest rind pitting disorder incidence compared to CMC 0.5%, CMC 1% and the control treatment. High mass loss contributes largely to rind pitting development, however, edible coatings managed to provide semi-permeable barrier to the fruit. Uncoated fruit had high mass loss which may be due to high water loss from the rind, most probably rind cell collapsed thereby leading to visible pitting in fruit rind. Coated fruit with low rind pitting incidence had low rind dry matter (RDM) compared to uncoated fruit with high rind pitting incidence. This study reported that total soluble solids (TSS) increased with storage time, however, low rate of increase was noticed in coated fruit compared to uncoated fruit. Fruit with higher TSS at the end of storage had high rind pitting incidence compared to fruit with low TSS. Rind colour was expressed as citrus colour index (CCI). Citrus colour index was noticed to increase with storage, however, the rate of increase in coated fruit was lower than that of uncoated fruit. At the end of storage, CCI was therefore higher in uncoated fruit than coated fruit, while higher CCI was correlated with high rind pitting incidence. These physicochemical quality parameters can be used to predict rind pitting occurrence in ‘Marsh’ grapefruit. The second experimental chapter investigated rind phytochemical quality attributes that can be used as pre-symptomatic markers of rind pitting disorder in ‘Marsh’ grapefruit. Treatments used for this chapter were similar to the abovementioned. Treatments were organised in a factorial design. Visible to near infrared spectroscopy (Vis/NIRS) as a non-destructive technique was used to develop models that can assist in rind pitting disorder prediction. Partial least square (PLS) regression models were developed to predict rind phytochemical quality attributes such as ascorbic acid, phenolics, flavonoids, antioxidant capacity and activity, pigments (chlorophyll a and b, β carotene and total carotenoids) and sugars (sucrose, glucose and fructose), and these models were developed to predict rind pitting disorder of ‘Marsh’ grapefruit. Noticeably, CMC when combined with MLE were able to reduce the incidence of rind pitting disorder when compared to their counterparts. This could be due to the fact that moringa is believed to have high content of flavonoids, phenolics and antioxidants, which may be released to fruit and act as free radical scavengers from the cell matrix and protect fruit from external stress. These studies further investigated the effect of canopy position on susceptibility of rind pitting development. It was found that outside canopy (OC) fruit were more susceptible to rind pitting disorder compared to fruit from inside canopy (IC). This may be due to that OC fruit are exposed to different climate during fruit growth and development which could lead to rind quality stress and damage rind cells. Since OC fruit were more prone to disorder development than IC fruit, it would make financial sense to export fruit to the low demanding market with less penalties if fruit develop pitting prior to destination. Alternatively, fruit with higher chances of developing disorders (OC fruit) must be sent to local markets or fruit may be processed to other sellable products such as juices and dried fruits.
The potential of post-harvest potassium silicate dips to mitigate chilling injury on citrus fruit.
(2012) Mditshwa, Asanda.; Bertling, Isa.; Bower, John Patrick.
The South African Citrus Industry is the second largest exporter of citrus, after Spain. The industry is under pressure to supply high quality fruit as well as to expand into new, high paying markets. However, high paying markets such as Japan and the USA require cold sterilised fruit as obligatory quarantine treatments against Mediterranean fruit fly (Ceratitis capitata) in order to reduce any possible spread of the pest. Citrus fruit originated from tropical climates and hence are chilling susceptible. Chilling injury symptoms appear as dark brown spots, pitting and/or decay when fruit are transferred to shelf temperatures; thus reducing the marketability of citrus fruit. Therefore, there is need for methods to mitigate chilling injury. Previous studies have shown silicon to mitigate many forms of stress without any hazardous effect on human health. Thus, the aim of the study was to investigate the potential of post-harvest silicon dips in mitigating chilling symptoms in citrus fruit. Briefly, fruit from two sources (Ukulinga Research Farm and Ithala Farm) were dipped in different silicon concentrations (0, 50, 150, and 250 mg ℓ-1) for 30 minutes and thereafter stored at -0.5 or 2⁰C for up to 28 days with weekly evaluation for chilling injury symptoms. Total antioxidants were determined using FRAP, ABTS, and DPPH assays under spectrophotometer. In addition, sugars, ascorbic acid, phenolics and flavonoids were analysed using High Performance Liquid Chromatography (HPLC). Fruit from Ukulinga Research Farm showed significantly higher total antioxidants (ascorbic acid total phenolics and specific flavonoids hesperidin and naringin) and sugars relative to fruit from Ithala Farm. Low concentrations of silicon dips significantly reduced the appearance of chilling injury symptoms by inducing an enzymatic conversion of glucose to ascorbic acid, thereby increasing the antioxidant capacity of chilling susceptible fruit. Moreover, silicon increased the concentration of total antioxidants, total phenolics and total flavonoids. High silicon concentrations had a negative effect on post-harvest quality of lemons by increasing fruit weight loss and electrolyte leakage, resulting in appearance of chilling symptoms. In conclusion, the study showed that silicon had potential to reduce chilling injury. However, high silicon concentrations raised concern, in particularly, on fruit appearance.
Response of potato genotypes to production sites and water deficit imposed at different growth stages.
(2020) Mthembu, Sizwe Goodman.; Odindo, Alfred Oduor.; Magwaza, Lembe Samukelo.; Mditshwa, Asanda.
In South Africa, potato is an important food security crop widely cultivated by smallholder farmers due to its extensive adaptation characteristics. However, drought adaptive responses of potato genotypes vary under different environmental conditions. Potato is generally categorized as the most sensitive crop to water deficit than other root and tuber crops. However, there is insufficient evidence regarding adaptive responses of potato genotypes to water deficit imposed at different growth stages. Therefore, this study sought to identify growth stage-specific drought adaptation of selected potato genotypes for recommendation and cultivation in targeted production sites in South Africa. The specific objectives of this study were: (1) to determine morpho-physiological traits related to water use efficiency among selected potato genotypes subjected to water deficit at the different growth stages; (2) to determine the effect of water deficit imposed at different growth stages on yield performance and tuber quality of selected potato genotypes; and (3) to investigate the effect of different production sites/regions on growth, physiological and yield responses of potato genotypes. For objective 1, a glasshouse study was conducted using a 8×4×2 factorial experiment involving the following factors: potato genotypes - 8 levels (Bikini, Challenger, Electra, Mondial, Panamera, Sababa, Sifra, and Tyson); growth stages - 4 level (vegetative stage, tuber initiation, tuber bulking and maturity) and watering regimes - 2 levels (Well-watered [Ww] and Water deficit [Wd] conditions). The treatments were replicated three times to give a total of 192 experimental units. Water deficit was imposed by withholding irrigation at the beginning to the end of each growth stage. A highly significant (p < 0.001) interaction among genotypes, water condition and growth stages was observed for morphological traits and physiological responses including number of leaves and total above-ground biomass, and photosynthetic rate (A), instantaneous water use efficiency (IWUE), transpiration rate (Tr), chlorophyll content index (CCI), and relative water content (RWC). Potato genotypes Bikini, Challenger and Mondial with growth-stage specific drought adaptation were identified and recommended for water-limited environments. The second study (objective 2) determined the effect of water deficit imposed at different growth stages on yield performance and tuber quality of selected potato genotypes. The study was conducted as 8×4×2 factorial experiment (See objective 1) replicated three times and data was collected on tuber yield (TY), number of tubers (NT), tuber size distribution (TSD) and dry matter content (DMC). Results revealed a highly significant (p < 0.001) genotype x water condition x growth stages interaction for tuber yield and dry matter content. Imposing water deficit at the tuber initiation and tuber bulking stages resulted in significantly lower yields, whereas drought stress at maturity stage resulted in high number of small tubers. ‘Bikini’, ‘Challenger’, ‘Mondial’ and ‘Tyson’ were identified as tolerance genotypes to water deficit at vegetative stage, tuber initiation and maturity stage due to high yield potential and DMC. This finding suggests that these genotypes could be suitable for processing industry (chipping) and baking. For objective 3, eight potato genotypes were grown across two environments namely: Ukulinga research farm (URF) in Pietermaritzburg which characterised with semi-arid environment and eChibini area (CB) in Bamshela with seasonal rainfall and high humidity. The experiments were laid out using a randomised complete block design (RCBD) replicated three times. Data was collected on morphological and physiological traits. Significant (p < 0.05) genotype x environment interaction effect was observed for studied traits at URF and CB. Potato genotypes planted at CB had a significant (p < 0.05) lower gs and Tr resulting to low A, than at URF. The CCI at CB compared to URF was significant (p < 0.05) higher at the beginning and gradually decreased towards maturity while at URF was constant. Moderately to poorly drained soils at eChibini resulted in low yields and low dry matter content. Various genotypes with better yield and high quality were obtained at URF. This suggested that genotypes were suitable for production in cool temperate regions with humid climate areas like URF. The study showed that different production regions can significantly affect the potato yield performance, suggesting URF sites as suitable environment. Overall, the study identified potato genotypes with growth stage-specific drought tolerance and environment specific adaptation for high yield and good quality.
The effect of biocontrol agents and plant extracts on postharvest quality of ‘kent’ mangoes.
(2023) Radebe, Siphokazi Anele.; Mbili, Nokwazi Carol.; Mditshwa, Asanda.
Mango is a tropical fruit grown in all parts of the world, hence is economically important. This fruit is beneficial as it has medicinal properties helpful to human health. Mango fruit is climacteric with a high respiration rate, leading to rapid ripening, and limiting the shelf life. This also limits the import and export, whilst the fruit is under duress, there are also fungal pathogens that infect this fruit both pre and postharvest. Anthracnose is one of the diseases affecting mangoes which is caused by the fungal pathogen Colletotrichum gloeosporioides (Penz.) Penz. & Sacc. The susceptibility of mango fruit to fungal diseases affects the total yield and profits of the producers. Synthetic fungicides have been used to control the infection caused by fungal pathogens. However, excessive use of fungicides has a negative impact on human health and is hazardous to the environment. Notably, fungal pathogens develop resistance to fungicides over time. The chemicals such as prochloraz have also been used as a treatment in cold storage to prolong the shelf life of mangoes, and the risk of consumers ingesting these chemicals is reported. Contrary to fungicides, this study evaluated the efficacy of biocontrol agents and plant extracts against C. gloeosporioides and in prolonging the shelf life of mangoes. During the in vitro studies, 150 yeast and 150 Bacillus strains were isolated from different plant leaf materials and screened against C. gloeosporioides. A dual assay was conducted, and potato dextrose agar (PDA) was inoculated with the fungal pathogen and biocontrol agents and then stored at 28˚C for 7 days. The best two Bacillus isolates (SL and Sl) and 1 yeast isolate (Ba) that inhibited the pathogen by more than 65% and were selected from a dual culture assay in secondary screening and identified using BLAST. These isolates were further used as potential biocontrol agents against the pathogen in vivo on ‘Kent’ mango fruits. The BLAST results identified isolate Ba as Meyerozyma guilliermondii, isolates SL and Ss as Burkholderia contaminans. These isolates were overall the best treatments with mycelial growth inhibition of 67.91%, 70.00%, and 74.04%, respectively. M. guilliermondii and two B. contaminans inhibited anthracnose disease incidence on ‘Kent’ mango fruit by 50% compared to the control treatment (0%) after 7 days at 25˚C. The scanning electron microscopy (SEM) images showed breakage and shrinkage of C. gloeosporioides mycelia in vitro, and there was little damage to mycelia and no spore germination on mango fruit. The different plant extracts, Aloe vera, Tetradenia riparia, Pelargonium sidoides, and Moringa oleifera were prepared and screened against C. gloeosporioides. PDA was amended with different concentrations of the plant extracts (1%, 1.5%, 2%, 2.5%, and 3%) then inoculated with the pathogen, and stored at 28˚C for 7 days. P. sidoides was selected as the best-performing plant extract at 2.5% and 3% concentrations with 100% mycelial growth inhibition in vitro. Anthracnose disease incidence was significantly reduced by P. sidoides at 3% and 2.5% concentrations (≤50% and ≤75%, respectively) compared to the control fruit with 100% infection. The SEM interaction of 2.5% and 3% of P. sidoides with C. gloeosporioides in vitro; and mango fruit treated with 2.5% and 3% of P. sidoides and the pathogen had a limited number of spores and thin mycelia in comparison to the control. Furthermore, this study evaluated the individual and combined effect of B. contaminans, P. sidoides, and carboxymethyl cellulose (CMC) edible coating on mango fruits at 10˚C for 21 days, followed by 7 days at 25°C. Untreated fruit had the highest mass loss (18.53%) compared to all treatments (CMC, BCA, BCA+PE and PE) which had 15.3%, 14.64%, 14.18% and 14.04%, respectively. Mango fruit coated with PE had DPPH scavenging activity at 51.11 μM TE/g DM, whereas CMC treated fruit had 29.66 μM TE/g DM, even lower than untreated fruit which had 36.52 μM TE/g DM. Phenolic content was recorded at 116.4 μg GEA/g DM on PE treated fruit compared to 95.1 μg GEA/g DM for the control fruit. The concentration of AA was 51.95 mg/g on PE treated mango compared to 24.61 mg/g on the control fruit. This study showed that B. contaminans, P. sidoides, and CMC edible coating can be exploited as postharvest treatments to extend the shelf life of mango fruit.
The effect of edible coatings and ZnO nanoparticles based on Moringa extracts on the postharvest quality of avocado (persea americana mill.) fruit.
(2024) Ngubane, Sibonelo.; Tesfay, Samson Zeray.; Mditshwa, Asanda. ; Magwaza, Lembe Samukelo.
Abstract available in PDF.