Browsing by Author "Magwaza, Lembe Samukelo."

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Agronomic characterization and evaluation of pigeon pea landraces in KwaZulu-Natal Province of South Africa.
(2015) Hluyako, Lindah London.; Magwaza, Lembe Samukelo.; Odindo, Alfred Oduor.
Abstract available in PDF file.
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.
Biocontrol agents in combination with moringa oleifera leaf extract for integrated control of botrytis cinerea of tomato.
(2022) Malevu, Nonkanyiso.; Mbili, Nokwazi Carol.; Magwaza, Lembe Samukelo.
Tomatoes and tomato-based foods provide essential nutrients beneficial to human health. Despite these benefits from tomatoes, postharvest losses result in unprofitable tomato production in some parts of the world. During ripening and harvesting, tomato becomes susceptible to diseases resulting in shorter shelf life. Susceptibility of tomato plants to Botrytis cinerea which causes grey mould infection can occur at any growth stage and the most susceptible growth stage is during ripening and senescing. Factors such as mechanical injuries, inadequate storage conditions, inappropriate handling, and transport affect tomato quality. The use of chemicals not only negatively affects farmers' yield by further enhancing pesticide resistance to crop pathogens but also influences other sectors of communities through contamination of drinking water sources which is an environmental hazard. There is a need to emphasise and encourage sustainable agricultural strategies such as biological control and plant extracts as alternative strategies which are eco-friendly and economically sustainable. Therefore, the main aim of this research was to examine the effect of biocontrol agents and Moringa oleifera leaf extract, individually and in combination, to control B. cinerea on tomatoes in vitro and in vivo. A total of 48 biocontrol agents were isolated from different parts of tomato leaves, citrus leaves, mushrooms and erect prickly pear. The isolates were screened against B. cinerea for the inhibitory effect and as potential control of the pathogen on potato dextrose agar (PDA) and tomato fruits. Serratia marcescens, Bacillus pumilus and Bacillus safensis inhibited B. cinerea by more than 50% in vitro. During in vivo screening, Serratia and Bacillus isolates inhibited grey mould incidence on ‘Jam’ tomatoes by more than 70%. The scanning electron microscopy images of the pathogen samples treated with biocontrol agents showed swollen and lysed mycelia. Moringa leaf extracts (MLE) were prepared into four concentrations MLE 1%, MLE 2%, MLE 3% and MLE 4%. The MLE concentrations were tested for their antifungal activity on the pathogen growth during in vitro studies. High concentrations were found to have some inhibitory effect on the mycelial growth of B. cinerea. There was no significant difference observed in the control, MLE 1% and MLE 2% since no mycelial inhibition was observed after 7 days at 25°C. For in vivo studies, all the concentrations had some inhibitory effect against grey mould on ‘Jam’ tomatoes. This was evidenced by lower disease incidence observed on the fruits treated with the moringa leaf extract compared to the control treatment. Scanning electron micrographs showed morphological changes in the hyphae on the samples treated with concentrations of MLE and there was also a breakage on the pathogen hyphae. Furthermore, this study evaluated the integrated control of B. cinerea using S. marcescens, B. safensis and B. pumilus integrated with MLE 2% and MLE 3% in vitro and in vivo. S. marcescens, B. safensis and B. pumilus integrated with MLE 2% and MLE 3% successfully suppressed mycelial growth of B. cinerea in vitro. Treating tomato fruits with S. marcescens, B. safensis and B. pumilus integrated with MLE 2% and MLE 3% reduced the disease incidence of grey mould compared to the control. The SEM images of the mycelial growth of B. cinerea showed shrinkage, and breakage of pathogen mycelia and the spores were damaged showing breakage and immature spores both in vitro and in vivo. Integrating moringa leaf extract, Serratia spp. and Bacillus spp. have the potential to be an alternative to synthetic fungicides to control postharvest pathogens.
Characterisation of ganoderma species using morphological, molecular and biochemical markers and evaluation of substrate enhancement influence on their development and biochemical profile.
(2024) Sihlangu, Sydwell Mcebo.; Magwaza, Lembe Samukelo.; Mditshwa, Asanda.; Tesfay, Samson Zeray.; Ramachela, Khosi.; Mbili, Nokwazi Carol
Ganoderma, also known as Reishi mushroom, is used for its potential health benefits in several countries. The current study characterised Ganoderma species using molecular and biochemical markers and evaluated the substrate enhancement influence on its development and biochemical profile. The overall research study consisted of four objectives. The first objective focused on the isolation and characterisation of fifteen fungal specimens collected from the three provinces of South Africa, namely, Mpumalanga, KwaZulu-Natal, and North- West. Five fungal specimens were collected in each province and growth media potato dextrose agar (PDA), malt extract agar (MEA), and sabouraud dextrose agar (SDA) were used to grow sample isolates. After 8 days of incubation, MEA recorded the highest mycelial diameter followed by PDA and SDA. Samples were identified using comparative morphology traits and supported by internal transcribed spacer region (ITS) and phylogenetic analyses. Based on the ITS of ribosomal DNA, fungal samples KG3SY219 and MG1SY119 were found to be closely related to Ganoderma resinaceum and Ganoderma austroafricanum, respectively. The species were further characterised by biochemical compounds, including antioxidants, proteins, essential elements, and heavy metals. The antioxidant capacity exhibited a higher radical scavenging activity in G. austroafricanum compared to G. resinaceum. The concentrations of total phenolics, flavonoids, proteins, essential elements and heavy metals were more abundant in G. austroafricanum compared to G. resinaceum. This study also evaluated the effect of different growth conditions on mycelial growth and development of Ganoderma austroafricanum and Ganoderma resinaceum. The experimental treatments included three levels of pH (4, 6 & 8), temperature (20, 25 & 30 °C), and different types of plant residues namely; beech sawdust (BS), sugarcane bagasse (SB), and buffalo grass (BG). Three independent in vitro experiments were conducted, PDA and MEA were used as standard growth media to grow each fungal species. Mycelial growth and development were measured over 9 days where they reached maximum growth. The culture media pH results demonstrated that the maximum growth for mycelia was reached on day 9 for both species. Typically, G. resinaceum showed the highest mycelial growth for both cultures except for days 6 and 9 where the mycelial growth of the species was decreased by low levels (pH 4) and high levels (pH 8), respectively. The addition of BG to the growth media delayed the mycelial growth of G. resinaceum for both growth media (PD+MEA). Experiment three investigated the effect of different substrates on the development, total biomass, and biochemical profile of Ganoderma species. The experiment involved growing G. austroafricanum (GA) and G. resinaceum (GR) on different substrates; beech sawdust (BS), sugarcane bagasse (SB), and buffalo grass (BG), and suspension of all substrates (BSSBBG). The growth parameters such as pileus size, weight, total biomass, and biological efficiency were measured. Additionally, each substrate was analysed for biochemical composition. The biochemical composition of the harvested samples was also analysed to determine the levels of biochemical compounds such as minerals, antioxidants, and protein. The substrate pH levels demonstrated that all substrates were within the optimal growth pH range (5-6). SB exhibited greater levels in the majority of essential elements such as Zn and K, also, heavy metals Pb and Hg. The results on the development and total biomass production of Ganoderma species revealed significant variations across different substrates. In terms of development, GRBS was faster to reach the 100% rate of all production parameters in 40-52 days after inoculation. However, GASB exhibited higher quantities in total yield and biological efficiency. In addition, pileus from GASB demonstrated higher concentrations of all evaluated biochemical compounds. GASB also yielded higher levels of DPPH, phenolic compounds, flavonoids, and protein. Experiment four examined the impact of substrate fortified with essential elements on the development, total biomass, and biochemical compounds of Ganoderma species. The experiment involved growing G. austroafricanum (GA) and G. resinaceum (GR) on beech enhanced with elements; no element (Control), Zn(NO3)2.6H2O (Zn), Fe2SO4 7H2O (Fe), Na2SeO3 (Se), and suspension of all essential elements (ZnFeSe). The growth parameters such as the pileus size, weight, total biomass, and biological efficiency were measured. In addition, the biochemical profile of Ganoderma spp. was analysed to evaluate the concentration of compounds. The development and total biomass production findings for the substrate fortified with essential elements exhibited significant differences. GRZn developed expeditious, reaching 100% of all production parameters in 52 days after inoculation. In comparison to all treatments, GAFe showed larger quantities in total yield and biological efficiency. The substrate enhancement with Zn had a significant increase in the majority of minerals. GAZn exhibited higher concentrations of essential elements such as Zn, K, and Mg. Higher levels of heavy metals such as Cd, Pb, and As were recorded from GAControl. GASe produced higher levels of DPPH, phenolic compounds, flavonoids, and protein reading. These findings demonstrate the variability of morphological characteristics, biochemical compounds, and growth conditions requirements between Ganoderma species. These findings provide valuable insights into the diversity, taxonomy, and potential therapeutic applications of Ganoderma species in South Africa. Further investigation is required to identify Ganoderma species and its pharmaceutical properties.
Conservation agriculture and its impact on soil quality and maize yield: A South African perspective.
(2018) Sithole, Nkanyiso Justice.; Magwaza, Lembe Samukelo.
The countries in sub-Saharan Africa (SSA) are faced with the problem of soil degradation resulting from unsustainable soil management practices such as conventional tillage (CT) and the removal of soil biomass from crop land. Conventional tillage leads to deterioration of important soil physical properties, the decline in soil organic carbon (SOC) and increase the risk of soil erosion. The reduction of SOC further affects soil macrofauna which has important key roles in soil processes such as soil structural formation, decomposition of soil organic matter (SOM) and recycling of soil important nutrients. This combined with water scarcity, low inherent soil fertility, increasing population and the predicted negative impacts of climate change poses threat to the regions ability to self-supply enough food for current and future generations. In response to this conservation agriculture (CA) has been endorsed because of its powerful mechanism to adapt by increasing resilience to land degradation, drought and increasing water use efficiency. Soils under no-till CA have been recognised widely that they generally contain higher SOC, the key principal indicator of soil quality, than CT system. These responses, however, are site-specific and depends on soil type, cropping systems, climate, fertilizer application and other management practices. Moreover, most of the published literature on the effect of CA on soil quality parameters comes from cooler temperate regions. As a result, the effect of CA on soil quality parameters in sub-tropical semi-arid environments remains unknown or controversial. Therefore, the primary objective of the study was to assess the effect of no-till (NT), rotational tillage (RT), CT and nitrogen fertilizer application rates on selected physical, chemical and biological properties of the soil and, their influence on maize yield. The secondary objective of the study was to explore the use of visible to near infrared spectroscopy (VIS-NIRS) as a possible cheap alternative for SOC quantification. The study was conducted at Bergville in KwaZulu-Natal Province of South Africa. The trial was established in 2003/04 growing season. This area forms the most important part of rainfed maize production in KwaZulu-Natal Province. The trial was arranged as a split plot with randomized tillage strips forming the whole plot and rate of application forming the sub-plots which are randomized within the whole plots. The experiment included three tillage treatments: 1) no-till (NT) with permanent residue cover, 2) annual conventional tillage (CT) and 3) rotational tillage (RT) every after four years. Nitrogen was applied at three rates, namely; 0 kg/ha, 100 kg/ha and 200 kg/ha. Lime ammonium nitrate (LAN) was used as a source of nitrogen. Unsuitable soil management in agriculture is known to results in deterioration of soil health and the decline in biodiversity. The objective of the study in soil biological properties was to assess the effect of no-till CA on the abundance and order diversity of soil macrofauna in continuous maize monocropping system. Soil macrofauna was sampled at the end of the 2015/2016 growing season using 25 × 25 × 25 cm steel monoliths. The mean density of individual orders was significantly higher (p < 0.001) under NT (46%) and RT (38%) compared with CT (16%). However, the Shannon-Weaver index (H, E index) revealed that the diversity and evenness of orders were similar, H= 2.6 and E~ 1, for all treatments. Macrofauna patterns revealed that NT and RT contained a significantly (p < 0.001) higher population of orders Isoptera and Diplopoda. Order Isoptera was 51% and 17% higher in NT than CT and RT, respectively while in Diplopoda, NT was 39% and 2% higher than CT and RT, respectively. It was concluded that NT and RT mulch-based system favoured the development of macrofauna communities in the studied maize continuous monoculture cropping system but did not favour order diversity of macrofauna. This suggests the importance of crop rotation for the development of the more diverse macrofaunal population. Soil degradation associated with the loss of soil organic carbon (SOC) has been a major concern in sub-Saharan Africa because of the subsequent yield reduction. The objective of the study in soil physical properties was to investigate the effect of NT, RT, CT and N fertilizer applications rate on soil aggregate stability, infiltration, SOC and its size fractions at 0-10, 10-20 and 20-30 cm depth. Soil samples were taken at the end of 2015/16 growing season using soil auger. On average, total SOC did not vary (p > 0.05) across the tillage treatments, 27.1 t/ha (NT) vs 26.0 t/ha (RT) and 26.6 t/ha (CT), but varied with depth where it was stratified in the 0-10 cm depth in NT and RT. Particulate organic C, however, varied significantly (p < 0.05) across the treatments where it decreased with increase in tillage intensity but only in the 0-10 cm depth. Mean weight diameter (MWD) was high under NT and RT and this was correlated to higher infiltration observed in these treatments. The results of this study showed that reduced soil disturbance improves physical protection of SOC, soil structure and infiltration. Soil management practice may change soil chemical properties and thus fertility. The magnitude of change varies depending on soil type, cropping systems, climate, fertilizer application and management practices. The objective of this study on soil chemical characteristics was to assess the effects of tillage systems, residue retention and fertilizer application rates on the amount and distribution of soil major nutrients in the 0-10, 10-20 and 20-30 cm depth. The soil samples were taken at the end of 2015/2016 growing season using soil auger and transported to the University laboratory for chemical analysis. The concentration of total Nitrogen (N) followed the same trend as that observed in soil physical properties. SOC and N were found to be concentrated on the soil surface (0-10 cm depth). Phosphorus was significantly higher (p < 0.001) under NT (0.0213 t/ha) than in RT (0.0127 t/ha) and CT (0.00704 t/ha). A large amount of P was in the 0-10 cm depth in NT and it was distributed more uniformly under RT and CT. Potassium was also higher (p < 0.05) under NT (9.73 t/ha) than in CT (8.00 t/ha) and RT (9.52 t/ha). It was found to be uniformly distributed across the soil depths in all tillage treatments. The soils from NT and RT had lower pH values than CT at 0-10 cm depth while increased significantly in the lower depths. Cation exchange (CEC) capacity followed the same trend. The results indicated that NT treatment increased nutrient availability in the studied soil which was more linked to the distribution of SOC and variability of pH along the soil profile, thus this indicating the potential of implementing NT in the semi-arid environment. Resilient and sustainable soil management systems are needed to overcome soil degradation, arrest soil fertility decline and to offset the predicted negative impact of climate change. This study investigated the long-term (13 years) impact of soil quality parameters (soil physical, chemical and biological properties), N fertilizer application rate and rainfall on maize grain yield. On average (across the years) maize yields were higher in NT (12.3 t/ha) and RT (12.4 t/ha) under higher rate on N fertilizer application (200 kg/ha) than CT (11.8 t/ha). However, yields decreased in NT with the reduction of N fertilizer application rate in medium N rate (100 kg/ha) and low rate (0 t/ha). The yields decreased by 1.7 t/ha, 1.4 t/ha and 0.4 t/ha from high N application rate (200 t/ha) to medium N application rate (100 t/ha) in NT, RT and CT, respectively. Under low rainfall of < 400 mm/year and high N application rate (200 kg/ha), the yield was 9.13 t/ha, 7.96 t/ha and 7.00 t/ha in NT, RT and CT, respectively across the years. However, when the average rainfall was above 600 mm/year, yields averaged at 13.3 t/ha, 13.7 t/ha and 13.5 t/ha in NT, RT and CT under high N fertilizer application rate across the years. Principal component analysis (PCA) was performed to VI assess some biological, physical and chemical properties of the soil that contributed to maize yield. The results showed no parameter that seemed to be related to maize yield. This was attributed to the complex interaction of bio-physio-chemical parameters with the environment. The results of this study found that yields improve over time under CA and this was more pronounced during the drought period. Yields improvements under CA require the application of the higher rate of N fertilizer in correct amount. Therefore, it is recommended that CA is implemented in semi-arid subtropical areas to improve soil conditions, water conservation and to achieve optimum yields. Application of spectroscopy for assessment of soil nutrition in the field may be affected by the depth at which the radiation spreads to, the analysed nutrient, and management practices such as tillage systems. The visible to near infrared spectroscopy (VIS-NIRS) was explored as a technique to predict soil organic carbon (SOC) and soil organic nitrogen (SON) in soils differing in soil tillage management practices. Partial least square regression (PLSR) models were developed using the leave-one-out cross validation method. The models were then tested on independent samples (54) randomly selected from the total 324 samples. The best prediction model was observed for SOC with the coefficient of determination (R2) = 0.993, root mean square error of prediction (RMSEP) = 0.157% and residual predictive deviation (RPD) = 2.55 compared with R2= 0.661, RMSEP= 0.019%, RPD= 2.11 for SON. Considering the predictive statistics and accuracy created by the model in the prediction of SOC, VIS-NIRS can be recommended as a fast, accurate technique for SOC determination in the studied soil. This will significantly reduce the cost associated with SOC and SON analysis for researchers and farmers. UKUFINYEZWA KWENDABA YONKE JIKELELE Amazwe asezansi ne Afrikha abhekene nengwadla enkulu yokudicileka phansi nokuphelelwa umsoco komhlabathi. Lokuphelelwa umsoco komhlabathi kubangelwa izindlela zokutshala ezingalungile ezingahlali isikhathi eside njengokutshala lapho oqale ulime umhlabathi khona bese usebenzisa igeja ususe nokhula. Lokhukulima ngegeja bese ususa ukhula kubangela ukuthi umhlabathi unganothi ngoba usuke ususe amacembe namagatsha agayekile (noma ayimvuthuluka) abaluleke kakhulu ekwakheni inqalasizinda sokuthi umhlabathi ubumbane ubeyimbumba futhi ukwazi ukuthi unikeze izitshalo umsoco wokuthi zikhule kahle. Lezizimvuthuluka zezitshalo um
Effect of canopy position and non-detructive determination of rind biochemical properties of citrus fruit during postharvest non-chilling cold storage.
(2017) Olarewaju, Olaoluwa Omoniyi.; Magwaza, Lembe Samukelo.; Tesfay, Samson Zeray.; Fawole, Olaniyi Amos.; Opara, Umezuruike L.
No abstract provided.
Effect of maturity and postharvest handling of prunus persica ‘landrace’ produced in KwaZulu-Natal: case study of physicochemical properties, tunnel solar drying and quality of processed products.
(2017) Mkhathini, Khangelani Maxwell.; Workneh, Tilahun Seyoum.; Mwithiga, Gikuru.; Magwaza, Lembe Samukelo.
Farmers in KwaZulu-Natal produce peach fruit. However, they are faced with overwhelming losses of the fruit due to lack of proper handling techniques, skills and facility during postharvest. In addition, these farmers have limited formal markets where they could sell fresh fruit immediately after harvesting. Thus, they are forced to consume the least they can and leave the rest of the fruit hanging on the tree. As a result, they lose close to 45% of their fruit. The literature review congruently pointed out such challenges of food losses in less developed countries and South Africa is not an exception. With a limited understanding of peach properties, it becomes increasingly difficult for farmers to handle the fruit. The cost of storage and processing facilities (such as sophisticated refrigeration) is very high and a decision table was used to determine which affordable method can be employed to process the peach fruit. The study is significantly important for the reduction of massive losses of fresh produce in the small-scale household farming sector as whole in South Africa. This study had three main aims to address. Firstly, it aimed to understand the physiological maturity and ripening of the peach fruit by determining physicochemical properties such as days to maturity, mass, volume, shape, moisture, pH, total soluble solids, colour (CIELab) and firmness. Secondly, the study aimed to install and test a tunnel solar dryer according to a decision table criteria that used to decide on a fruit processing method. Thirdly, the study aimed to process the fruit into dried peach slice with pre-treatments of lemon juice (LJ), ascorbic acid (AA) and a control, using a tunnel solar dryer. In addition, the study also aimed to process the peach into dried peach leather also using a tunnel solar dryer. This study included both objective and subjective methods to test the quality of the peach slice and leather products processed. Fruits reached maturity 129 days after full bloom (DAFB) and this coincided with fruit mass, volume and moisture content at respective averages of 80.00 g, 66.10 cm3, and 83%. Fruit firmness decreased significantly from 79.00 N to 24.70 N with increasing ripeness. Total soluble solids increased significantly from 13.50 to 19.00 °Brix during ripening. The pH value significantly increased from 3.40 to 4.00 indicating that acidity decreased with ripening. The TSS: TA ratio increased from 21.11 to 35.84. Moreover, it has been statistically verified that due the colour, yellow peach fruit produced the best products (as seen by the receipt of the highest sensory evaluation overall acceptability scores and based on the texture profile analysis results provided by Texture Analyser instrument). The utilisation of treatment such as AA or LJ did not have a significant effect in the overall drying between the yellow and white landraces. Ascorbic acid had a tendency to perform better than LJ which was also better than the untreated slices (control) in terms of the taste and overall acceptabilty. The experiment revealed that white leather moisture was approximately 7% and received the lowest overall acceptability scores from panellists. Less quality results were also received according to the texture profile analysis, in contrast to the yellow peach leather, which had 13% of moisture content. Yellow leather received the highest overall acceptability scores by both texture profile analysis and sensory evaluation tests. Thus, this study suggests that drying is possible in the KwaZulu-Natal Midlands. Overall, the results developed from the current study demonstrate that the fruit produced in small-scale farming sector is of good quality regardless of low yields because fertilizers and pesticides are not used. More importantly, this study reveals the significant potential of solar drying to be used by small-scale farmers to develop on-farm interventions aiming to add value to their produce and thus be able to preserve, use and sell later. It was concluded that DAFB, firmness, mass, TSS, volume, TTS: TA ratio are potential parameters to be used for maturity indexing of white peach ‘landrace’. Regardless of the misty conditions that prevail during the period of harvesting fruits, it was concluded by a statistical significant difference that the tunnel solar drying is a possibility in the KwaZulu-Natal Midlands. Days after full bloom, firmness, TSS, pH and mass have a critical role to play since they significantly differ between different ripeness degrees. These can be used to monitor peach growth stages and estimate yield for the small-scale peach grower in the area. The DAFB are a good tool that farmers can stick to without the use of advance technologies other than monitoring the number of days. Firmness is also a very important parameter for farmers in the area as the fruit hardly changes colour but can be soft showing signs of ripeness. The study has also devised a step-by-step process, which can be followed by small-scale processors in order to reduce losses using solar dryer to process fruit into leather and slice.
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.
Effect of water stress imposed at tillering, flowering and grain filling in irrigated wheat (Triticum Aestivum L.) genotypes.
(2017) Liwani, Unathi.; Magwaza, Lembe Samukelo.; Odindo, Adeyemi Oladado.
Wheat is one of the most important crops grown in South Africa. However, its production is threatened by the current drought periods the country has been experiencing. This includes a decline in the production of irrigated wheat which boosted the country’s wheat production. In South Africa information which could guide irrigated wheat farmers in using less water at water stress tolerant growth stages is still in its infancy. In order to assist these farmers, the International Maize and Wheat Improvement Centre (CIMMYT) bred genotypes reported to withstand very hot and dry conditions. In contribution, this study was undertaken with the following objectives: 1) to select water stress tolerant irrigated genotypes through evaluating the response of their physiological traits after water stress at tillering, flowering and grain filling 2) to determine the growth stage at which limited water supply would have minimal effect on the growth, development and yield of eight newly developed wheat genotypes. An 8 (genotypes) × 2 (water treatments (stress and no stress (control)) × 3 (growth stages (tillering, flowering and grain filling)) factorial experiment was conducted in a randomized complete block design and replicated three times. Results for the first objective indicated that the rate of photosynthesis was only affected (p < 0.05) for genotype LM98 after water stress at tillering and LM43 after water stress at flowering. The rest of the genotypes showed tolerance (p > 0.05) in these growth stages and at grain filling. Water stress in the three growth stages did not affect (p > 0.05) the transpiration rate and stomatal conductance. Only the instantaneous water use efficiency of genotype LM43 and LM35 was not affected (p > 0.05) by water stress at tillering but affected (p < 0.05) for the same genotypes at flowering. Whereas, water stress at grain filling affected (p < 0.05) the instantaneous water use efficiency of genotype LM35, LM79, LM57 and LM98. Water stress imposed at grain filling had no effect (p > 0.05) on the relative water content. It, however, had an impact (p < 0.05) on the relative water content of LM43 and LM35 when it was imposed at tillering. The genotypes also showed susceptibility (p < 0.05) to water stress at the flowering stage with genotype LM98, LM79, LM83 and LM57 affected. It was then recommended that genotype LM35, LM79, LM57 and LM98 maintained a higher water use efficiency after water stress at grain filling. While the instantaneous water use efficiency of LM43 and LM35 was higher after water stress at tillering but reduced by water stress at flowering stage. From the results of the second objective it was discovered that the plant height of the studied genotypes was not affected (p > 0.05) by water stress at tillering and grain filling. The number of fertile tillers was reduced (p < 0.05) by water stress at tillering in susceptible genotypes while at flowering and grain filling the number of fertile tillers for all the genotypes was not affected (p > 0.05). The spike length was affected (p < 0.05) by water stress at all growth stages while the harvest index was not affected (p > 0.05). Aboveground biomass was only affected (p < 0.05) at tillering stage. Grain yield production which was the primary concern declined only after water stress at tillering. Grain yield production was more linked to the number of fertile tillers after water stress at each growth stage. Based on overall findings this study was able to recommend that the studied genotypes can be subjected to water stress at grain filling and flowering. At tillering, genotype LM83 is better at tolerating water stress while genotype LM47, LM79 and LM66 are susceptible.
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 seed quality and performance of low and high phytic acid maize (Zea mays L.) under varying phosphorus rates and water regimes in dryland conditions.
Bakhite, Mohammed Abdalla Elgorashi.; Odindo, Alfred Oduor.; Magwaza, Lembe Samukelo.
Maize (Zea mays) being the staple crop for many communities in Sub-Saharan Africa and also used for animal feeding, a considerable effort has been made to improve quality and yield. In recent times plant breeders have focused on reducing phytic acid (PA) on maize seeds to improve grain nutritional quality. Although studies of low phytic acid genes have been reported in temperate maize, the current research was based on the tropical genetic background which was screened for low phytic acid. This is the first report for applied breeding of the trait in the tropical maize. Little is known on the agronomy and responses of tropical maize specifically to water stress and its response to phosphorus application. No studies provided on the seed quality performance and response of low phytic acid maize to water stress and phosphorus application. Reducing Phytic acid of tropical maize could have negative effects on seed quality and yield. The primary objective of this study was to compare the performance of low phytic acid (LPA) maize seeds of tropical origin with three other varieties i.e. high phytic acid (HPA) of tropical origin, SC701 and LS8520 based on seed quality and water stress. The study consisted of two maize synthetic populations differing in phytic acid (PA) content (from the African Center of Crop Improvement (ACCI)); namely, LPA and HPA synthetic populations. Both the LPA and HPA synthetic populations were derived from a tropical second generation (F2) population and were selected based on their phytic acid (PA) content. They were produced at the Ukulinga Research Farm, University of KwaZulu-Natal (29°40'05.7"S 30°24'20.9"E), in Pietermaritzburg, South Africa. These two maize synthetic populations were compared with two commercial maize varieties (from McDonald Seeds), white maize (SC701) and yellow maize LS 8520 R (484) which in this study was coded LS8520. All seeds used in this study were produced under identical production conditions and in the same growing season, thereby ensuring that the seeds were of the same physiological age. The first experiment investigated the characterisation of LPA maize varieties for seed germination and vigour. Seed quality was evaluated using the standard germination test and accelerate aging test together with electric conductivity test (EC). The second experiment was conducted as a pot trial to investigate the effect of exogenous phosphorus application on seed quality and yield of low phytic acid maize varieties. In third experiment, a field study over two seasons (2015/2016 and 2016/2017) was conducted at Ukulinga Research Farm in Pietermaritzburg, under dryland conditions. The objective of the experiment was to evaluate the newly produced ACCI’s two genetically synthetic maize populations of LPA and HPA under dryland field condition and compare them with the commercial white and yellow tropical maize varieties their germination, growth, yield and yield components. Lastly, an experiment under controlled conditions on photosynthetic efficiency and yield responses of LPA and HPA maize tropical lines to deficit irrigation. The study was carried out under controlled environment conditions. The objective was to evaluate the photosynthetic efficiency of low phytic acid (LPA) and high phytic acid (HPA) tropical maize varieties grown under water-stressed conditions. The results of the first experiment indicated that the performance of LPA varieties was comparable to those of commercially produced varieties. This study suggests that the combination of LPA lines of tropical origin used in this study was satisfactory to meet the minimum seed quality parameters particularly seed germination and vigour. The results for phosphorus application showed that the application of phosphorus improved the growth, flowering and yield of LPA and other varieties as well. The mean germination time (MGT), germination vigour index (GVI), electrical conductivity (EC) (μS g-1), root length, shoot length and the root-shoot ratio of the harvested seeds after phosphorus application were also improved. When the LPA and HPA tropical maize exposed to dryland environments the results revealed that the SC701 variety outperformed the other three varietiess in growth and yield. It was concluded that the LPA maize performed lower under field conditions. In the water stress trial, results showed that LPA maize varieties recorded higher values of stomatal conductance (gs) and transpiration rate (T) compared to HPA and SC701 for both normal and water stress conditions. HPA showed a significantly (P< 0.001) higher value of photosynthetic rate (A) than LPA and SC701 for all the water stress treatments. HPA and SC701 were comparable in most of chlorophyll fluorescence parameters. With regard to yield, HPA showed increased performance in terms of overall yield and seed weight, and this suggests that HPA varieties are less sensitive to water stress than LPA maize varieties. The results from this study have proven that LPA maize varieties are sensitive to limited conditions and further research under a wide range of environmental conditions is required. Overall, the results indicated that the seed germination of LPA was comparable to other varieties but the yield remains low. There is a need to conduct more experiments to demonstrate the performance of LPA under field conditions in response to phosphorus application and water stress. These differences between the traits could help breed programs. The selection for LPA and HPA tropical maize should be based on their physiological performance to be planted in temperate zones to grant higher yield performance.
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.
Evaluating water use efficiency of maize in different intercropping systems with legumes.
(2016) Bambalele, Nonjabulo Lynne.; Mafongoya, Paramu L.; Magwaza, Lembe Samukelo.
Abstract available in PDF file.
Evaluation of a low-cost energy-free evaporative cooling system for postharvest storage of perishable horticultural products produced by smallholder farmers of Umsinga in KwaZulu-Natal.
(2017) Nkolisa, Ntombizandile Sylvia.; Magwaza, Lembe Samukelo.; Workneh, Tilahun Seyoum.; Chimphango, A.
In this study, a low-cost energy-free evaporative cooling system for postharvest storage of perishable horticultural was investigated. The evaporative cooler is a cost effective, energy free and easy to maintain way of cooling fruit and vegetables. It is basically what smallholder farmers can use as a postharvest storage condition to maintain their fruits and vegetables. However, before the evaporative cooling system was selected, the area of Umsinga where the cooler was installed was studied. The first chapter is a general introductory chapter, which clearly explains problem statement, has justification, hypothesis and outlines the aims and objectives. The second chapter is a review of literature which gives a broad idea of cooling technologies used to preserve quality and reduce postharvest losses on horticultural products. Consequently, it also gives an overview of the causes of postharvest losses. The third chapter of the study assesses vegetable postharvest loss challenges of smallholder farmers in the rural area of Umsinga in KwaZulu-Natal. The assessment was carried out as survey questionnaires. The fourth chapter of the study was evaluating the evaporative cooling system as an energy-free method for postharvest storage of tomatoes for smallholder farmers. The fifth chapter is evaluating the effect of different storage conditions on biochemical quality of tomatoes. The last chapter of the study is chapter six which has the general discussion, conclusion and recommendations.
Evaluation of maturity parameters of 'Fuerte' and 'Hass' avocado fruit.
(2014) Olarewaju, Olaoluwa Omoniyi.; Bertling, Isa.; Magwaza, Lembe Samukelo.
Avocado fruit is one of the most important horticultural crops produced in South Africa. The fruit does not give obvious indication of maturity as it does not ripen as long as it remains attached to a tree. Harvesting avocado fruit at full physiological maturity, a stage at which it will continue normal development, plays a vital role in the postharvest physiological processes and the successful postharvest management of the fruit. Common maturity parameters used in various avocado fruit industries include mesocarp oil content, moisture content (MC) and dry matter (DM). However, the difficulty of measurement (oil content) and unreliability (MC and DM), can result in immature fruit reaching the consumer. To ensure that avocado fruit of good quality are delivered to the market and for growers to maximise profits, possible factors indicating optimal harvest maturity were investigated during the South African 2013 and 2014 avocado growing season. Additionally, the growth pattern of fruit, beyond what is currently regarded as physiological maturity, was examined for the possibility of the fruit exhibiting a double sigmoidal growth pattern, typical of nut crops. Fruit were harvested from two commercial orchards in the cool subtropical area of KwaZulu-Natal, South Africa. Fruit were harvested bi-weekly from February to March and then monthly from April to October, 2014. The MC decreased over the harvesting period, (p < 0.001), while oil content increased (p < 0.001). The study of the pattern of avocado fruit growth and development over the eight months observation period revealed that the fruit exhibits a single sigmoidal growth pattern. It could also be deduced from the experimental results that MC is a better indicator of maturity compared with oil content. In a quest to find an alternative maturity indicator that could provide a more reliable measure of avocado harvest maturity, total soluble solids (TSS) was evaluated for the possibility of providing an objective maturity index. Seven carbon (C7) sugars, D-mannoheptulose and perseitol, are dominant sugars in avocado fruit and have been suggested as likely indicators of avocado fruit maturity. D-mannoheptulose, a major component of mesocarp TSS, has been suspected to be responsible for the continued growth of the fruit. 'Fuerte‟ and „Hass‟ avocado fruit were harvested during the early, mid and late harvesting period in 2013 from Bounty Farm and during the 2014 season (February to August) from Bounty Farm and Everdon Estate. Sample ws taken along the equatorial region of each fruit and analysed for TSS, measured by squeezing juice out of the mesocarp using a garlic press and determining its °Brix using a digital refractometer. A high level of significant difference was observed between TSS and harvesting period for „Fuerte‟ during both seasons (p < 0.001) and a significant difference was found between the two production locations during the 2014 growing period (p < 0.001). There was no significant difference (p = 0.344) between production sites for „Hass‟ fruit harvested during the 2014 season. The results of the study reveal that TSS cannot be used as an indicator of avocado fruit maturity. In an attempt to non-destructively predict maturity parameters of avocado fruit, a total of 150 intact avocado fruit were scanned in reflectance mode of near-infrared spectroscopy (NIRS) during the 2013 and 2014 growing seasons. Reference maturity parameters, including MC, DM and oil content were measured using conventional destructive methods. Calibration models developed during 2013 season were used to predict the dataset acquired during 2014. NIRS prediction results showed that MC and DM were predicted with significant accuracy compared with oil content, prediction of which was not accurate. The prediction statistics for NIRS predicted MC and DM content demonstrated the potential of this system for non-destructive evaluation of avocado fruit maturity parameters (MC and DM). The high prediction accuracy recorded when models developed in 2013 were used to predict maturity of fruit harvested during the 2014 season demonstrated robustness of partial least square (PLS) models. Where speed and accuracy are required for assessing the maturity status of individual, intact avocado fruit, the method developed in this study is recommended.
Investigating the effect of thermal processing on biochemical composition and kernel shelf-life of macadamia (macadamia integrifolia).
(2018) Buthelezi, Nana Millicent Duduzile.; Magwaza, Lembe Samukelo.; Tesfay, Samson Zeray.
Rancidity is a major limiting factor affecting the postharvest quality and consequently, the storability and market value of macadamia nuts. Initial high moisture content accelerates the primary stages of rancidity where hydroperoxides accumulate as main oxidation products, eventually breaking down to form low molecular weight oxygenated constituents such as alcohols, aldehydes, ketones and free fatty acids, eventually resulting in the development of off-odours and off-flavours. Hydroperoxides can also react with amino acid residues in the Maillard reaction, thereby initiating excessive browning. Kernel browning may be evident as surface discolouration or internal as ‘concealed damage’ of nuts. Internal browning may be accompanied by off-odours and off-flavours and is impossible to detect during processing, often with no visible signs. Such kernels are unacceptable to both the export and local market. The aim of this chapter was to review the potential of thermal processing on delaying the onset of rancidity and therefore, improving kernel shelf life and nutritional quality of macadamia nuts; and to review the reliability of visible to near infrared spectroscopy (Vis/NIRS) to non-invasively predict kernel rancidity. Keywords: Rancidity, browning, free fatty acids, near infrared spectroscopy
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.