Doctoral Degrees (Food Science)

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Browsing Doctoral Degrees (Food Science) by browse.metadata.advisor "Fawole, Olaniyi Amos"

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    Bruise damage susceptibility of pomegranates and impacts on fruit quality
    (Stellenbosch : Stellenbosch University, 2019-03) Hussein, Zaharan; Opara, Umezuruike Linus; Fawole, Olaniyi Amos; Sigge, G. O.; Stellenbosch University. Faculty of AgriSciences. Dept. of Food Science.
    ENGLISH ABSTRACT: The consumption of pomegranate (Punica granatum, L) fruit is attributed to its health and nutritional benefits, which are linked with reported high antioxidant capacity, antimutagenic, anti-inflammatory, anti-atherosclerotic and anti-hypertension activities. Postharvest handling of pomegranate fruit takes a couple of weeks (5 – 8) and includes a series of operations from harvest to export (i.e. harvesting, sorting, packing/repacking and transportation). In the course of these operations, there are various situations where pomegranate fruit are subjected to multiple modest drop impacts that predispose the fruit to varying levels of excessive external forces resulting in bruise damage. Impacts may occur as the result of sudden fall of fruit onto other fruit, parts of the tree, harvesting bucket and bin, or any other uncushioned surfaces in the course of loading and offloading. The presence of a bruise on pomegranate fruit causes produce quality deterioration that contributes to downgrading, rejection of produce and ultimately, to postharvest losses. It is therefore important to understand the mechanism of bruising and how to minimise it. The overall aim of this research was to investigate the bruise damage susceptibility of selected pomegranate fruit cultivars, to ascertain the effects of bruising and storage duration on fruit quality attributes and finally, to explore the feasibility of non-destructive measurements to detect and characterise bruise damage. The studies reported in Chapter 4 investigated the susceptibility of three pomegranate fruit cultivars (‘Acco’, ‘Herskawitz’ and ‘Wonderful’) to impact bruising. The impact threshold required to bruise pomegranate fruit was investigated for each cultivar with a view to identify the cultivar that is most susceptible to bruising. The probability of bruise occurrence (PBO) was determined from the population of selected fruit impacted at minimal drop heights (0.10, 0.15, 0.20 m). At the drop impact of 0.10 m, results showed that ‘Wonderful’ had the lowest impact threshold, with a PBO value of 0.44 and an impact energy of 371.87 mJ, whereas neither ‘Acco’ nor ‘Herskawitz’ showed any signs of bruising. At the drop impact height of 0.15 m the highest bruise occurrence was seen in ‘Wonderful’ (PBO = 1; 692.98 mJ), followed by ‘Acco’ (PBO = 0.75; 406.26 mJ) and ‘Herskawitz’ (PBO = 0.5; 511.57 mJ). These results showed that ‘Wonderful’ fruit had a higher susceptibility to bruising compared to the other investigated cultivars, and therefore needs to be handled with extra care during harvest and postharvest handling. Furthermore, the study investigated the effect of cold (5 ºC) and ambient (20 ºC) storage temperatures on bruise damage susceptibility. Fruit were dropped at higher drop impact levels (0.2, 0.4 and 0.6 m), stored for a period of 10 d at either 5 ºC or 20 ºC, during which the physiological responses including weight loss and respiration rate were evaluated. Bruise size were determined in terms of bruise volume (BV) and bruise area (BA), while bruise susceptibility was calculated as the BV per unit of impact energy. The results revealed that bruise size and bruise susceptibility at higher drop heights (0.2, 0.4 and 0.6 m) were cultivar dependent and in the order of ‘Wonderful’ > ‘Herskawitz’ > ‘Acco’. The bruise size of cold (5 ºC) conditioned pomegranate fruit was significantly higher than that of fruit conditioned at an ambient (20 ºC) temperature. Further results showed that drop impact bruising had a larger effect on the fruit physiological response (respiration rate and weight loss) for bruised fruit in comparison to non-bruised fruit. Fruit impacted at higher drop impact levels (0.4 or 0.6 m) exhibited two to three-fold higher respiration rate than fruit bruised at a lower impact level (0.2 m) or nonbruised fruit. Respiration rate and weight loss increased with prolonged storage duration and at an ambient temperature, both in bruised and non-bruised fruit. Further study to evaluate the feasibility of X-ray micro-computed tomography (X-ray µCT) in detection and characterization of bruise damage on pomegranate fruit is reported in Chapter 5. Pomegranate fruit bruised by dropping at 0.6 m was scanned with X-ray µCT. The results showed that two-dimensional CT images of fruit scanned at 0 h (immediately after drop impact), 48 h, 3 d and 5 d after impact bruising showed no evidence of bruise damage. Changes in bruise-damaged tissue as characterised by a darker appearance were observed in pomegranate fruit scanned after 7 d of impact bruising. Furthermore, visual assessment of two-dimensional X-ray µCT images were buttressed by the results of quantitative µCT data analysis. The latter demonstrated that bruised pomegranate fruit can be visualised and differentiated from 7 d after impact bruising with lower grey values (18000 - 30000) compared with non-bruised fruit (26000 - 34000). The image analysis and quantitative µCT data obtained in this study confirmed that X-ray µCT is not a suitable non-destructive method to detect and characterise fresh bruises (immediately bruised) on pomegranate fruit. Studies to explore alternative non-invasive techniques, such as a hyperspectral imaging system for early detection of fresh bruises on pomegranate fruit, are warranted. Chapter 6 focused on evaluating the physical, biochemical and microstructural changes of impact-bruise damaged pomegranate fruit. The results showed that there were significant changes in colour (browning), peel electrolyte leakage (PEL), polyphenol oxidase (PPO) enzyme activity and accumulation of reaction oxygen species (ROS) measured in pomegranate fruit peel with increasing drop impact bruising. The combination of time and temperature (in which fruit was incubated) significantly (p < 0.05) contributed to changes in PEL, PPO enzyme activity and fruit browning. Cellular microstructural differences between control and bruised fruit tissues were visible in scanning electron microscope images after 4 and 48 h of drop impact. These findings provided evidence that the loss of membrane integrity of pomegranate fruit skin cells are caused by impact bruising. Chapter 7 covered the study on bruise damage of pomegranate during long-term cold storage, focusing on susceptibility to bruising and changes in textural properties of fruit. Fruit from cold (5 ºC) storage were impact bruised from different drop heights (0.2, 0.4 and 0.6 m). The bruise volume and bruise area of pomegranate fruit increased with increasing drop impact heights and storage duration for the first two months of storage, and then decreased in the last month of storage. Similarly, the results of textural properties showed that increase both in puncture resistance, cutting and compression strength were dependent on impact bruising and storage duration. These results have demonstrated that bruise damage would result in significant changes in fruit textural attributes with concomitant low consumer appeal. Studies in Chapter 8 investigated the effects of bruising and long-term cold (5 ºC) storage on the physiological response, physico-chemical quality attributes, textural properties and antioxidant content of pomegranate fruit. Respiration rate and weight loss of whole fruit were both influenced by increasing drop impact bruising and storage duration. Furthermore, there were increases in chemical quality attributes (total soluble solids, titratable acidity, Brix-to-acid ratio and BrimA), and antioxidant content of bruised pomegranate fruit during long-term storage. This was partly attributed to the concentration effect due to an increased moisture loss from bruise damaged fruit. Results on changes in aril colour and texture were dependent on both bruising and storage duration (p < 0.05). Overall, this research represents a pilot study aimed at providing scientific insights to broaden the understanding of pomegranate fruit susceptibility to bruising during postharvest handling and its impacts on fruit quality. The findings in this dissertation have established that bruise susceptibility of pomegranate fruit is dependent on the level of drop impact, cultivar, storage temperature and duration. Furthermore, this study showed that bruising, storage conditions and duration play a crucial role on physiological responses (i.e. respiration rate and weight loss), textural properties and chemical quality attributes of the fruit. From a practical point of view, the study has revealed that, bruise damage affects the sensory appeal of pomegranate fruit during storage, which could result in downgrading of fruit market value or complete fruit loss.
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    Non-destructive measurement of pomegranate fruit quality
    (Stellenbosch : Stellenbosch University, 2017-12) Arendse, Ebrahiema; Opara, Umezuruike Linus; Fawole, Olaniyi Amos; Magwaza, Lembe Samukelo; Stellenbosch University. Faculty of AgriSciences. Dept. of Food Science.
    ENGLISH ABSTRACT: Pomegranate (Punica granatum L.) is an emerging fruit within the South African horticultural industry, which has experienced dramatic growth in annual production from 350 tonnes in the 2009 season to over 8000 tonnes in 2017. Literature shows that the fruit consists of considerable amount of sugars, organic acids, vitamins, mineral elements and possess potent pharmacological activities due to an array of phytochemical compounds found in the fruit. However, the fruit is highly susceptible to pest and disease infestation, including the development of physiological rind disorders during storage and shipping. The increased growth of the pomegranate industry has coincided with consumer demand for consistent supply of safe, nutritious and traceable fruit and processed products. Hence, non-destructive assessment of fruit quality and its processed products can contribute to the implementation of suitable management strategies to predict and control desired quality attributes. This will ensure delivery of high quality fruit and its derived products without the presence of defects in international and local markets. Therefore, the overall aim of this study was to develop non-destructive methods to predict external and internal quality attributes of pomegranate fruit. Section I of the thesis focuses on a critical review of non-destructive techniques for assessing the external and internal quality of fruit with thick rind. Thick rind fruits, such as pomegranate, have been reported to interfere with accurate measurement of internal quality using near-infrared spectroscopy. Hence, this review provides an overview of the issues related to quality measurement using non-destructive methods, including a concise summary of the current research and potential commercial applications. In section II (chapter 3), the feasibility of X-ray micro-computed tomography (μCT) as a non-destructive technique to characterise and quantify the internal structure of pomegranate fruit was investigated. μCT in combination with image analysis successfully characterised and quantified the volumes of the internal fruit components (arils, peel, kernel, juice content, air space). The calculated volume for total arils, peel, and air space were 162.45 ±16.21, 163.87 ±21.42 and 10.89 ±2.57 mL, respectively, which accounted for 48.04, 48.46 and 3.22% of the total fruit volume (338.19 ±22.4 mL). The calculated volume of juice content and kernels were 146.07 ±16.28 and 16.38 ±1.81 mL per fruit which were equivalent to an average of 89.92 and 10.08% of the total aril volume. Destructive validation results showed no significant difference with those obtained from the μCT-based non-invasive method. This study has demonstrated the potential use of μCT and associated image analysis as a promising tool for non-destructive characterization of the internal and external structure of pomegranate fruit. In chapter 4, the prospects of Fourier-transform near-infrared (FT-NIR) spectroscopy (FT-NIRS) and associated chemometric analysis were evaluated for the prediction of external and internal quality parameters of intact pomegranate fruit. Two diffuse reflectance spectral acquisition modes were assessed, namely, direct contact between the sample with an integrating sphere (IS) using the Multi-Purpose Analyser (MPA) and a contact-less measurement (distance 17 cm) using an optic fibre coupled emission head (EH) of the MATRIXTM-F analyser. Partial least squares (PLS) regression was used to construct calibration models over a spectral region of 800-2500 nm, and the results showed that optimal model performance was obtained using first derivative and second derivative spectral pre-processing methods. It was found that models obtained from the EH spectral data predicted fruit firmness, colour components (a* and C*), total soluble solids, titratable acidity, BrimA, total phenolics and vitamin C with high accuracy (RPD values ranging from 2.06 to 3.34), while the IS showed good prediction ability for h° colour component (RPD = 2.50), TSS:TA (RPD = 2.72) and total anthocyanin (RPD = 1.64). The results suggest that the contactless option of the MATRIX-F could be used to evaluate quality attributes of intact pomegranate fruit. In chapter 5, the development of calibration models by FT-NIRS for the evaluation of pomegranate aril quality was investigated using two different FT-NIR acquisition methods (IS and EH) over 800-2500 nm spectral region. Model development was based on pre-processing methods that yielded higher values of coefficient of determination (R2) and residual predictive deviation (RPD), lower root mean square error estimation (RMSEE) and root mean square error of prediction (RMSEP). The results showed that models based on the EH provided good prediction of TSS, pH, TA, BrimA, aril hue, total phenolic, total anthocyanin and vitamin C concentration, while those based on IS provided the best results for TSS:TA, firmness, arils redness (a*) and colour intensity (chroma). Furthermore, a follow-up study was conducted to compare near and mid infrared (MIR) spectrometers for predicting organoleptic and phytochemical quality attributes of pomegranate juice (chapter 6 (section II)). Three Fourier transform infrared (FT-IR) spectrometers (representing three different spectral acquisition modes) were assessed; namely, MPA FT-NIR spectrometer, Alpha-P FT-MIR spectrometer and WineScan FT-NIR/MIR spectrometer. Results obtained showed that spectral acquisition mode affected model ability to accurately predict various pomegranate quality attributes, with the WineScan in the NIR/MIR region outperforming the Alpha-P and MPA instruments. However, statistical comparison using Bland and Altman and Passing-Bablok analytical algorithms showed no statistical differences among the three spectrometers for the prediction of selected aril quality parameters. Section III of the thesis investigated the prospects for non-destructive detection and classification of pomegranate fruit affected by internal defects and postharvest rind scald. In chapter 7, the feasibility of μCT with a calibration function to differentiate between fruit fractions (albedo and arils) and detect the presence of false codling moth and blackheart disease in pomegranate fruit was assessed. A calibration function was implemented using different homogenous polymeric materials with a density ranging from 910 to 2150 kg m−3. The estimation of fruit density was successfully accomplished within the calibration range. The density of whole fruit (1070 ±20 kg m−3), arils (1120 ±40 kg m−3) and albedo 1040 ±30 kg m−3) were significantly higher compared to the larva of codling moth (940 ±40 kg m−3) inside the fruit. Furthermore, healthy fruit had significantly higher density (1070 ±20 kg m−3) compared to those with blackheart (870–1000 ±50 kg m−3). An increase in the severity of blackheart infestation was characterised by a decrease in density of affected fruit. The results of this study suggested that the use of X-ray μCT, in combination with a calibration function of polymers and image analysis, could be applied to non-destructively identify and differentiate between fruit fractions, and detect the presence of larva of false codling moth and blackheart in pomegranate fruit. The research reported in chapter 8 (section III) evaluated several biochemical markers associated with the development of husk scald (peel browning) and based on these markers, assess the feasibility of non-destructive discrimination of healthy and scalded affected fruit using Fourier transform near-infrared (FT-NIR) spectroscopy. The results suggest that enzymatic browning was the main cause of husk scald, phenolic compounds such as tannins acting as substrates for polyphenol oxidase and peroxidase activity. The severity of browning index increased with storage temperature and duration. FT-NIR reflectance spectroscopy spectral data and reference data were subjected to orthogonal partial least squares discriminant analysis (OPLS-DA) to discriminate between healthy and scalded fruit. Resulting in high classification accuracy (100%, 93% and 92.6% for healthy, severe and moderately scalded fruit, respectively). Therefore, this study has successfully demonstrated that biochemical markers associated with the development of husk scald could potentially be used to non-destructively discriminate between healthy and scalded fruit.
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    Value addition of pomegranate seed oil: Effect of seed pretreatment methods on yield, quality attributes and functional properties
    (Stellenbosch : Stellenbosch University, 2021-04) Kaseke, Tafadzwa; Opara, Umezuruike Linus; Fawole, Olaniyi Amos; Sigge, G. O.; Stellenbosch University. Faculty of AgriSciences. Dept. of Food Science.
    ENGLISH ABSTRACT: Efficient and cost-effective processing protocols which enhance oil recovery and quality are required by processors in the seed oil industries. Currently, there is no established pomegranate seed oil processing procedure in South Africa, which could be one of the reasons hindering the development of pomegranate seed oil industry, despite the readily available fruit raw material. Furthermore, cold pressing, which is the current and most preferred pomegranate seed oil extraction technique by oil processors and consumers is associated with low recovery of oil. Physical or chemical pretreatment of seeds has been demonstrated to improve oil recovery and quality in other fruit seeds and field crops; however, the application of these pretreatments to enhance pomegranate seed oil extraction efficiency and quality is limited. Therefore, the overall aim of this study was to establish a suitable pomegranate seed pretreatment method for high oil yield, quality, and functional properties. In Theme B, the effect of seed pretreatment on three common pomegranate cultivars in South Africa was examined. To evaluate if blanching as a pretreatment technique for oil extraction adds value to pomegranate seed oil (PSO), seeds of ‘Wonderful’ pomegranate fruit were blanched at 80, 90, and 100 °C for 3 and 5 min. Blanching pomegranate seeds at 90± 2 °C for 3 to 5 min significantly improved oil yield, stigmasterol, punicic acid, total phenolic content (TPC) and 2.2-diphenyl-1-picryl hydrazyl (DPPH) radical scavenging capacity. Given the significance of cultivar on seed pretreatment efficacy and oil quality, blanching (95± 2 °C for 3), microwave heating (261 W for 102 s) and enzyme pretreatment (1.7 %, 40 °C, pH=4.5 and 5 h) were investigated on the seeds of three different pomegranate cultivars (‘Wonderful’, ‘Herskawitz’, and ‘Acco’). Blanching and microwave heating of ‘Wonderful’ and ‘Acco’ seeds improved the oil yield and colour, whilst they enhanced the antioxidant capacity of oil extracted from ‘Herskawitz’ seeds. However, oil extracted from ‘Acco’ after seed enzyme pretreatment exhibited higher oil yield, total carotenoids content (TCC) and, DPPH radical scavenging capacity relative to ‘Wonderful’ and ‘Herskawitz’. The results showed that the quality of PSO from pretreated seeds is cultivar dependent. The study reported in Theme C investigated the influence of blanching (95± 2 °C/3 min) and microwave heating (261 W for 102 s) pomegranate seeds on the quality of oil extracted by cold pressing, the most preferred seed oil extraction technique by oil processors and consumers but with low oil yield. Both blanching and microwave pretreatment of seeds prior to pressing enhanced oil yield, TCC, TPC, DPPH and 2.2-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) radical scavenging capacity. Although the levels of oil oxidation indices were significantly higher in microwaved than blanched seeds, they remained within the limits of Codex Alimentarius Commission (CODEX STAN 19-1981) standard on cold pressed vegetable oils. The oil palmitic acid, oleic acid, and linoleic acid significantly increased after microwave heating of seeds, whilst punicic acid decreased, which could be attributed to increased heat penetration and oxidation of the fatty acid. Conversely, the fatty acid composition of PSO was not significantly altered by seed blanching, indicating that the nutritional quality of the oil was not affected. Blanching of seeds is, therefore, a valuable step that could be incorporated into the PSO production process. The studies in Theme D, focused on blanched seed storability, oxidative stability, shelf-life and functionality of PSO from blanched seed and blended oils. Blanching pomegranate seed did not cause significant deterioration of the oil quality after seed storage. More so, storing pomegranate seed at 25 and 35 °C for 6 months did not result in a considerable reduction in oil quality, with respect to peroxide value, anisidine value and total oxidation value. In paper 9, the lipid oxidation kinetics, thermodynamics parameters, and shelf-life were estimated, given the improved extractability of bioactive compounds and enhanced antioxidant capacity of PSO from pretreated seeds. The Arrhenius model and activated complex theory were applied to calculate the activation energy (Ea), enthalpy (ΔH‡), entropy (ΔS‡) and Gibbs free energy (ΔG‡), which ranged from 6.2 to 8.59 kJ mol⁻¹, 3.69 to 6.38 kJ mol⁻¹, -146.62 to -155.06 J K⁻¹ mol⁻¹ and 48.13 to 64.74 kJ mol⁻¹, respectively. These thermodynamic parameters showed that the lipid oxidation reactions in all PSO extracts were non-spontaneous, endothermic, and endergonic. Moreover, the developed Arrhenius models established that blanching seeds may increase the PSO shelf-life at 25 °C from 21 to 24 days. In contrast, microwave heating may not change the shelf-life. The higher initial level of peroxide value and increased polyunsaturated fatty acids could explain the insignificant effect of seed microwaving heating on the oil shelf-life. The study provided valuable insights useful in the design of PSO packaging, the establishment of storage conditions and application of novel technologies to preserve the storage life. In paper 10 (Theme D) the functionality and oxidative stability of PSO from unblanched and blanched seeds (95± 2 °C/ 3 min) were investigated by blending with semi-refined sunflower oil (SO) considering the detrimental health effects of synthetic antioxidants. The study showed that blended oils (85: 15 w/w) had better oxidative stability, a lower rate of antiradical activity depletion and concentration of volatile oxidation compounds than SO, although this did not significantly (p > 0.05) vary between the blended oils. Despite this, the formulation of PSO blends is a novel and desirable development for the food industry, which is currently interested in specialty oils and functional foods formulations to improve human nutrition and health. Overall, this study has established that the improvement of PSO quality through seed pretreatment is a function of cultivar. This could be ascribed to the genetic variation of the pomegranate cultivars investigated. The study has also demonstrated that seed pretreatment is essential to improve the performance of safe and green but low oil yielding technologies such as cold pressing. Blanching of pomegranate seed may enhance the oxidative stability and shelf- life of PSO. Furthermore, the study provides scientifically based information that can be used to develop strategies to improve the storability of PSO from pretreated seeds and retain the health promoting properties.