Browsing by Author "Tesfay, Samson Zeray."

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Antioxidants composition of moringa (moringa oleifera lam) in different plant organs.
(2015) Mohammed, Fatima Abdelkarim Abdelrahman.; Tesfay, Samson Zeray.
Moringa oleifera Lam. is a versatile plant with various benefits; different parts of the plant have different pharmacological activity such as flavonoid, alkaloids, phenol, and carotenoids. The aim of the seed study was to investigate phytochemicals composition change and their utilization during seed and seedling germination. Seeds were germinated using three different temperature regimes (30/20 °C, 25/15 °C and 20/10 °C). Spectrophotometric determination of proline and phenols was carried out, while sugars were analyzed using HPLC-RID. The data were collected and analyzed using statistical software GenStat 14.1. Results of seed showed significant differences on speed of seed germination at temperature of 30/20°C followed by 25/15°C and 20/10°C respectively. Seed carbohydrates composition changes were observed with germination hours sucrose concentrations peaked within 24h (16 mg/g DW) and the same sugar showed sharp decrease for 96h (6.4 mg/g DW). Glucose and fructose concentrations also increased for 96h (2-6 mg/g DW). Also temperature had significantly influenced the biosynthesis and accumulation of biochemical compounds in the seeds especially 30/20°C. Temperature 30/20°C, increased seed phenols and proline concentration. Phenols and proline started to accumulate at 72h, after seed germination presumed within 48h. Results of leaves showed that Temperature also had significant effect on phenols the proline concentration particularly, 35/18°C, followed by 30/15°C, 25/12°C. The antioxidant levels of post germination phase was investigated, the result showed significant differences in antioxidant concentrations and sugar distribution in various parts of Moringa seedling. The leaf was recorded the highest antioxidant concentration (1.7 mg g-1). Moringa leaf also recorded the highest total phenols. The highest sugar concentration was found in root (258.9 mg g-1), and stem (245.72mg g-1) followed by root and seed. The highest concentration of total crude protein (110.4mg g-1) and vitamin E (28.57 μg g-1) was found in seed. The carotenoids concentration was the highest in the root (29 mg g-1). The result also showed different nutrients at various concentrations on different parts of Moringa tree. High phosphorous accumulated in leaf and seed; Potassium accumulation was found in root, stem, and seed coat. It is concluded that temperature treatments of Moringa seed and leaves resulted in significant differences in the rate of germination and biochemical compounds. Furthermore, the present study showed that Temperature plays an important role in germination seed and development of M. oleifera and antioxidants, phenolic, proline and carbohydrates contents. Further research on the effect of temperature on germination of M. oleifera and biochemical compound is therefore recommended.
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.
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.
The combined effects of daylength and temperature on onion bulb when grown under greenhouse environment.
(2017) Mpanza, Felicia Nobuhle.; Tesfay, Samson Zeray.
Abstract available in PDF file.
A comparative study of antioxidant potentials of some leafy vegetables : emphasis on African leafy vegetable and exotic vegetables.
(2014) Mathe, Sakhile.; Tesfay, Samson Zeray.
Due to malnutrition and food insecurity problem around the globe, mainly in developing countries, cheap nutritional food sources are required. In South Africa, a large proportion of the population is considered “poor” and with limited resources. However, South Africa as a whole is rich in indigenous leafy vegetables which have the capacity to help mitigate the problem of malnutrition and food insecurity. Amaranthus hybridus, an African indigenous leafy vegetable was tested for seed quality and potential essential antioxidants. Exotic (to Africa) leafy vegetables (Brassica oleracea and Brassica oleracea var. capitata f. rubra) were used as references for potential antioxidants. Amaranthus hybridus seed quality was tested using two different coloured seeds, red and white gold. Seed viability and vigor were tested using germination, electrolyte leakage and antioxidant content. Data recorded indicated better seed quality for red seeds than white gold seeds; therefore red coloured seeds were planted along with purchased Brassica oleracea and Brassica oleracea var. capitata f. rubra for quantifying antioxidant content. Selected antioxidant types were measured on weekly harvests of the studied vegetables. From the results it was evident that the indigenous leafy vegetable amaranth with total antioxidants [FRAP(3174.91 mmol Fe2 SO4 100g-1 DW) and DPPH(8.3 mmol trollox 100g-1)], proteins (6.88 mg.g-1 DW), total phenols ( 345 mg 100g-1 DW), flavonoids (79 mg 100g-1 DW), Chlorophyll and carotenoids (2.8 mg 100g-1 DW), ascorbic acid (86 mg 100g-1 DW) and soluble sugars (1.07 Brix %), could be used in conjunction with available commercial leafy vegetables to combat malnutrition and food security problems. Further, these results indicate that in resource limited regions this vegetable can act as a main source of nutrients and a supplement in resource abundant regions of the country and/or continent. Further, analysis of selected enzymatic antioxidants was carried-out on leaf material of the studied vegetable to evaluate the capability of indigenous leafy vegetables to protect themselves against oxidative damage. Indigenous leafy vegetables exhibited high antioxidant activity against lipid peroxidation at early stages of growth and high antioxidant enzyme activity at similar stages thus high capability of mitigating ROS effect. Data obtained from the study indicated that indigenous vegetables are a good source of essential antioxidants which are beneficial to human health; therefore the intensity of their use needs to be increased, especially in areas of high prevalence of malnutrition and diseases.
A comparative study on carbohydrates and antioxidants of indigenous crop black jack (Bidens pilosa L.) and selected commercial vegetable crops.
(2014) Mbokazi, Nelani Simon.; Tesfay, Samson Zeray.
The adequate consumption of African leafy vegetables has been closely associated with a strong reduction of chronically disease such as cancer, diabetes and cardiovascular diseases. The health benefits provided by African leafy vegetables are due to the presence of various primary and secondary metabolites. However, most of the epidemiological studies have indicated that very little is known about the antioxidant activity of African leafy vegetables, which is believed to be responsible for their therapeutic effect. In this present study the physiochemical and antioxidant properties were examined, in relation to other Asteraceae, commercial vegetables (lettuce and chicory). Firstly, the study investigated the physicochemical and antioxidant compounds during seed germination in black jack. Secondly examined the non-enzymatic and enzymatic antioxidants in black jack and compared them with lettuce and chicory. In seed germination test, physicochemical seed quality properties for African leafy vegetable, black jack antioxidants accumulation during seed imbibition were reported. The results revealed that soaking of black jack seeds in water before sowing, induces germination. In this study black jack seeds that were soaked for 15 hours before germinating, showed a highest percentage of germination (72 %) in 5 days. The seeds also showed high considerable total antioxidants capacity of antioxidants (DPPH) and phenols (0.69±0.44 mg/g and 56.45±0.08 mg/g DW). The protein content was also high on the seeds (0.328±0.17 mg/g DW). However, there were high amounts of anti-nutritional factors noticed on the seeds, where the total tannins content was (416.36±1.14 mg/g DW). The results further revealed that African leafy vegetable, black jack contained significant amount of non-enzymatic antioxidants at the early stages of growth than other leafy vegetables. The plant biomass per plant increased with the number of harvests. The plant DPPH antioxidant assay recorded black jack (0.73 ± 0.13mg/g DW - 0.29±0.083mg/g DW), lettuce (0.10±0.64mg/g DW - 0.29±0.03mg/g DW) and chicory (0.35±0.72 - 0.20±0.11mg/g DW). The plant phenolic content recorded black jack (155.46±0.07mg/g DW - 73.11±0.02mg/g DW) for lettuce it was found to be (13.24±0.05mg/g DW - 44.92±0.07mg/g DW) and for chicory (97.09±0.37mg/g DW - 17.88±0.22mg/g DW). However, as black jack all of the secondary metabolites were decreasing drastically when it was reaching maturity, while the phenols were increasing. For carbohydrates, black jack had the lowest concentration of the soluble sugars (glucose, sucrose and fructose). The enzymatic antioxidants of black jack were the lowest for most of enzymes, but SOD activity was higher. Although it decreased as the plant approaches maturity. In conclusion, black jack accumulates different types of antioxidants and their concentration varied over plant developmental stages. The key findings of this study are; the African leafy vegetables have different antioxidant production trends compared to exotic vegetables. Depending on leaf positions and leaf stage, preferably young leaves of the ALVs, there might be sequential harvests, increases the food access for extended period for household consumption. The ALVs also experience higher SOD, CAT, POD activities during early growth stage. These plants have also displayed the highest antioxidant capacity during the early plant development, early stage high accumulation of the studied antioxidants most likely contribute to this antioxidant strength. Furthermore there adaptation to wild environment, exposed to various harsh conditions, their tolerance to survive to this condition probably attributed to plants’ antioxidant production characteristics.
The development of indigenous marula (sclerocarya birrea) fruit leather : effect of drying temperature and sugar concentration on the drying characteristics, physico-chemical and consumer sensory properties of marula fruit leathers.
(2016) Ndlovu, Phindile Faith.; Tesfay, Samson Zeray.; Ngcobo, Mduduzi Elijah Khulekani.
Fruits indigenous to African countries are highly recognised and valued by rural communities for food security purposes. An examples of such fruits include but not limited to marula fruits (Sclerocarya birrea), which is indigenous to many parts of Southern Africa. In some parts of the continent, the role and usefulness of indigenous fruit species still receives little attention in agricultural research. Amongst others, this results from the magnitude postharvest quality losses due to the high moisture content characteristic of these fruits and a lack of access to required postharvest infrastructure by small-scale farmers. The processing of high moisture content commodities offers a convenient way of preserving their quality. The main aim of this research was to develop fruit leathers from the indigenous marula fruits as means of quality preservation. The development of new products from indigenous fruit crops as a means of preserving the fruits quality (nutrients) has a potential of enabling farmers, particularly small-scale farmers, to diversify on their on-farm business and farming activities. It also has the potential of improving the nutrition security and economy of the rural communities. Marula fruit are normally processed and conserved into various product forms (e.g. jams, juice, flavoured water, sweets, essential oils, traditional beer and world exported beverages such as Amarula Cream) which are readily available in the market. The production of such products from the indigenous fruits involves different processing techniques and these techniques ranges from highly sophisticated processes to simple traditional ones. The choice of the processing technique used is dependent on the characteristics of the intended product. Drying is one of the techniques that have not been widely applied in the processing of indigenous fruits. The application of this technique offers the potential to produce healthy, nutritious and flavourful ready to eat snack from the indigenous fruits such as fruit energy bars and fruit rolls which can be accessible and available throughout the year. Very little information have been reported on product development of indigenous marula fruit in previous years. The study conducted independent drying experiments to evaluate the effects of different drying temperature (50, 60 and 70 °C) and different added sugar concentrations (0, 5 and 10% w/w) on the drying kinetics of the marula fruits pulp. Moisture loss from the fruits’ pulp and different drying models in explaining the heat and mass transfer processes and for predicting the drying behaviour of the fruit leathers during drying were assessed. The textural, colour and consumer sensory attributes of the dried fruit leathers were also evaluated. The moisture loss and drying behaviour of the marula fruit leathers were significantly (p ≤ 0.05) affected by the drying temperature and added sugar content. During the evaluation of the colour properties, the drying temperature and the added sugar content increased significantly (p ≤ 0.05) the colour of the fruit leathers. However, the colour properties of fruit leathers with high added sugar concentration for each drying temperature were significantly (p ≤ 0.05) reduced. The texture attributes of the marula fruit leather significantly (p ≤ 0.05) increased with drying temperature (50 and 60 °C) and sugar concentration (0, 5 and 10% w/w), but significantly decreased at 70 °C for 10% w/w treated fruit leathers. The consumer sensory evaluation was also conducted to assess the acceptability of the fruit leathers. In general, all fruit leathers were accepted by panellists, and this demonstrated that marula fruit leather would form an acceptable new product. The sensory analysis showed that the mostly liked and preferred fruit leathers by the panellists were the ones prepared at 50 °C with 10% w/w added sugar.
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.
The effect of daylength and temperature on growth and 'onset of bulbing' in tropical cultivars of onion.
(2005) Tesfay, Samson Zeray.; Greenfield, Peter L.
Onions are widely produced within the tropics, but little scientific research has been done specifically on the Eritrean cultivars, like Hagaz Red 1 and 2 (HR I, and HR 2). Many onion cultivars are limited in their range of adaptation due to the combined effects of photoperiod and temperature. A priority for research on the crop was to elucidate the local crop's growth response to environmental conditions, particularly temperature and daylength. The Eritrean cultivars HR I and 2 and an American (Louisiana) cultivar Red Creole (RC) grown in South Africa were grown in growth rooms under all combinations of three daylengths (11.5h, 12h, 12.5h) and three day/night temperatures (25/12°C, 30/15°C and 35/18°C). Growth responses were determined at 108 days and by using a growing degree day (GDD) base. A broken-stick regression model was used to determine the points of inflection, indicating the initiation of bulbing. Based on leaf area and plant height data, mathematical differentiation equations and coefficient of determination (R2) were applied to determine the base temperature (6.4°C) for these particular cultivars. All three cultivars needed at least 12 h daylength for bulb initiation when assessed by a bulbing ratio >=2.0. A bulbing ratio >=2.0 characterizes the onset of bulbing. Under a 11.5 h daylength, a temperature higher than 25/12°C decreased vegetative growth. Temperature in this region may be a supra-optimal condition for the growth of these cultivars at this daylength. However, the 25/12°C and 30/15°C temperatures were found to be ideal for onion bulb production under 12 hand 12.5 h daylengths. The three cultivars (HR I, HR 2 and RC) showed very similar growth response to the daylength and temperature interactions. The thermal presentation of plant growth indicated that there were relationships between bulb initiation and rate of leaf area growth under inductive conditions (12 hand 12.5 h). Under the 12 h daylength, cultivars needed 343, 482, and 597 GDD units before bulb initiation and 405, 432, and 431 GDD to increase the rate of leaf area development at 25/12°C, 30/15°C, and 35/18°C, respectively. Under a 12.5 h daylength, these cultivars needed 344, 423, and 432.2 GDDs to initiate bulbing and 140, 411, and 579 GDDs to increase leaf growth rates at 25/12°C, 30/15°C, and 35/18°C, respectively. In the 12 h daylength, bulbing was initiated and followed by an increased rate of growth of leaf area. However, the reverse happened for the 12.5 h daylength. Overall, where plant response to temperature can be expressed as the rate of progress towards a morphogenetic change, GDD values can be used to predict a plant developmental stage at a particular temperature. It must be concluded that temperatures induced significant variations in growth components (leaf number, plant height, leaf area), and affected bulbing response. The findings in this study confirmed that the cultivars require only a certain fixed amount of thermal time for their development at a particular temperature, and that, if anything, the slow growth rate at the higher temperature must be due to supra-optimal temperatures. They also require a minimum 12 h photoperiod for bulb formation.
The effect of shadenetting on ‘3-29-5’ avocado production under subtropical conditions.
(2016) Mazhawu, Evidence.; Savage, Michael John.; Blakey, Robert John.; Tesfay, Samson Zeray.
Abstract available in PDF file.
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.
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.
Evaluation of fruit growth and development over a very extended harvesting period of 'Hass', ‘Fuerte’, ‘Gem’ and ‘Ryan’ avocado fruit.
(2017) Mbele, Nosipho Precious.; Bertling, Isa.; Tesfay, Samson Zeray.
Assessing avocado fruit growth and development by measuring fruit diameter during ontogeny may, therefore, offer clues to better understand whole plant behaviour. Plant sampling was carried out over different developmental stages from early to an extended growing season on four cultivars (‘Hass’, ‘Fuerte’, ‘Gem’ and ‘Ryan’). Mesocarp, exocarp and seed fruit tissues were used to determine internal parameters such as sugars, antioxidant, oil content, dry matter, and calcium). The sugars were extracted and analysed by isocratic HPLC. D-Mannoheptulose in mesocarp+exocarp tissues was found in significant amounts (‘Hass’ = 16.47±1.140 mg/g DM, ‘Fuerte’ = 11.92±1.780 mg/g DM, ‘Gem’ = 9.35±1.410 mg/g DM, ‘Ryan’ = 7.52±1.271 mg/g DM), with perseitol also being significant for all cultivar (‘Hass’ = 4.87±0.662 mg/g DM, ‘Fuerte’ = 5.77±0.650 mg/g DM, ‘Gem’ = 5.09±0.577 mg/g DM, ‘Ryan’ = 3.86±0.227 mg/g DM). D-Mannoheptulose was found in high levels in the mesocarp and exocarp compared to the seed. Perseitol was predominantly found in the seed for all cultivars (‘Hass’ = 7.31±0.486 mg/g DM, ‘Fuerte’ = 6.71±0.842 mg/g DM, ‘Gem’ = 6.76±0.224 mg/g DM, ‘Ryan’ = 8.62±0.473 mg/g DM). The C6 common sugars sucrose and glucose were detected in low concentrations in the mesocarp+exocarp fruit tissue, with sucrose being dominantly present in the seed. Calcium was determined by fruit ashing using HCl/HNO3 for digestion and strontium buffer solution for calcium extraction. Calcium concentration was significantly different during the ontogeny of each cultivar (‘Hass’ p = 0.007, ‘Fuerte’ p < .001, ‘Gem’ p < .001, and ‘Ryan’ p < .001). The calcium uptake peak is mostly reached during early fruit set stages of avocado fruit, followed by a decline and constant continuous low concentrations as approaching maturity. When fertilizer is applied during maturity calcium uptake in the avocado fruit tends to increase. Maturity indicators such as oil content, dry matter and fruit are significantly different across all fruit developmental stages. Oil content percentage (p < .001 all cultivars), dry matter (p < .001 all cultivars) and fruit size for both low and high tree fruit load (p < .001 all cultivars, except ‘Hass’ with p = 0.812 for high tree load fruits). During the extended hanging period maturity indices accumulation had a continually increased per cultivar, Oil% (‘Hass’ = 18.1%, ‘Fuerte’ = 12.74%, ‘Gem’ = 13.41%, and ‘Ryan’ = 17.41%), dry matter (‘Hass’ = 40.37 mg/g DM, ‘Fuerte’ = 24.01 mg/g DM, ‘Gem’ = 44.29 mg/g DM, and ‘Ryan’ = 35.39 mg/g DM), and size (‘Hass’ = 69.73mm, ‘Fuerte’ = 68.46mm, ‘Gem’ = 75.34mm, and ‘Ryan’ = 76.75mm), all significantly increased. Overall this study revealed that avocado fruit development does not necessarily end at the commercial harvesting period, but continues on fruits still attached to the tree after the single sigmoidal growth curve. When fruit harvesting is prolonged, the internal parameter for fruit growth, and C7 sugars, content contributes significantly throughout fruit ontogeny but varies in levels between cultivars. Calcium concentration uptake is in higher demands at early fruit set, where peak accumulation is reached almost at similar period with C7 sugars per cultivar. Therefore, C7 sugars and calcium in avocado are correlated during fruit growth and development. By extending fruit harvesting it allows the avocado fruit to mature by accumulating higher concentrations of sugars and, calcium immature harvest which result in negative market outcomes. This is especially true for late maturing cultivars which are less susceptible to poor postharvest quality. Therefore, avocado fruit development does not only follow a single sigmoidal growth curve but a double sigmoidal one.
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.
Maintenance of carbon 7 sugar levels and effect on ripening of 'fuerte' and 'hass' avocado (Persea americana Mill.) fruit.
(2018) Mathe, Sifundo.; Bertling, Isa.; Tesfay, Samson Zeray.
Avocado fruit are susceptible to a large variety of disorders. These disorders may be a result of an inability of the mesocarp tissue to counteract or tolerate postharvest stress. The C7 sugars D-mannoheptulose and perseitol have been reported to form the predominant portion of antioxidants in the mesocarp and their presence has been associated with avocado fruit quality. It was, therefore, investigated, if mesocarp C7 sugar levels, particularly of D-mannoheptulose and perseitol, can be maintained through infusion of these sugars and further, if this C7 sugar level is associated with fruit quality and shelf life. Avocado fruit, harvested from ‘Hass’ and ‘Fuerte’ avocado orchards in the KwaZulu-Natal Midlands in three different season (early, middle, and late harvest) were infused with 1.5 mL water, 1.5 mL solution of (9.5 mM/fruit; 4.75 mM/fruit D-mannoheptulose), a C7 sugar solution (1.5 mL of 9.5 mM/fruit; 4.75 /fruit; 4.75 mM perseitol/fruit). Fruit quality parameters (firmness, CO2 production, soluble sugar concentrations, moisture content, dry matter, and oil content) were determined over the postharvest ripening period. Early-harvested fruit displayed more severe ripening heterogeneity, with high water loss. The infusion of D-mannoheptulose and perseitol prolonged the shelf life of avocado fruit compared to sucrose-infusion and untreated fruit (control) at different harvesting stages. Water infusion had a considerable effect on mid- and late-season fruit, regarding firmness and respiration rate. Infusion of D-mannoheptulose and perseitol improved the fruit quality attributes flesh firmness and fresh mass retention, and resulted in higher mesocarp C7 sugar concentrations than sucrose- and water-infusion. Regarding the concentration of C7 sugars, water-infused fruit contained the third-highest D-mannoheptulose and perseitol concentration. The oil content was not affected by sugar postharvest infusion, but noticeable differences in oil content were observed through the harvest seasons. Maintaining a certain level of these sugars in the avocado mesocarp tissue seems vital in ensuring a good fruit quality. These C7 sugars could be used as postharvest markers and determining their concentration could become a vital tool in the management of avocado postharvest quality.
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.