Theses and dissertations (Applied Sciences)
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Item Development of electrochemical sensors for the detection of mycotoxins in food matrices using functionalised nanocomposites(2024-05) Naidoo, Lyndon; Bisetty, Krishna; Meier, Florian; Uwaya, Gloria EbubeThe analysis of pathogens in foods is of critical importance to ensure consumer safety and quality assurance, as contaminants pose serious risks to public health. Mycotoxins are naturally occurring carcinogenic toxins that arise from specific strains of fungi as they contaminate food. They are found in a wide variety of grains, cereals, and dairy products, causing cancer in both humans and animals. Thus, there is a growing demand for simple, sensitive and inexpensive sensors for mycotoxin detection in lieu of conventionally employed large-scale instrumentation. In this study, the development of electrochemical sensors for the detection of aflatoxin B1 (AFB1), zearalenone (ZEN) and ochratoxin A (OTA) in foods was investigated and presented as three case studies, respectively. In the first case study, an ultrasensitive aptasensor was developed for the indirect detection of AFB1 in the presence of a ferri/ferrocyanide ([Fe(CN)6]3-/4-) redox probe solution. The sensor was constructed by immobilizing an anti-AFB1 aptamer (Apt) to a carboxylated multiwalled carbon nanotube (cMWCNT) and iron oxide (Fe3O4) nanoparticle (NP) composite using a glassy carbon electrode (GCE). This resulted in the development of the GCE/cMWCNTsFe3O4 NP/Apt sensor. An electrochemical response was exhibited from AFB1 applying cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and differential pulse voltammetry (DPV), respectively, utilizing a [Fe(CN)6]3-/4- redox probe prepared in phosphatebuffered saline (PBS) solution with reference to the Ag/AgCl reference electrode under optimized conditions. DPV findings reported very low limits of detection (LOD) and quantification (LOQ) of 0.43 fg mL-1 and 1.44 fg mL-1 respectively in comparison to current literature, over a calibration range of 0.50 fg mL-1 to 5.00 fg mL-1. For real sample analysis, excellent spike recoveries from 95% to 105% were obtained for corn and rice flour. Density functional theory (DFT) was used to propose a reaction scheme by ascertaining the electronic properties of the redox-active functional groups of AFB1. This supported the experimental anodic response findings of DPV. The second case study focused on how PEGylated Fe3O4 NPs and cMWCNTs fabricated on a GCE could be used for the design of an electrochemical sensor for ZEN analysis. The qualitative and quantitative analyses of ZEN were completed using CV, EIS and DPV, respectively, under optimized conditions in a sodium phosphate buffer solution. The developed sensor reported significantly low LODs and LOQs of 0.34 fg mL-1 and 1.12 fg mL-1 respectively, over a calibration range of 1.00 fg mL-1 to 10.00 fg mL-1 by DPV. Excellent spike recoveries ranging from 92% to 106% were obtained for rice and corn flour. The Monte Carlo (MC) adsorption simulation studies predicted the strong interaction of ZEN with the constructed sensor. In the final case study, an OTA electrochemical sensor was designed using a nickel metalorganic framework (Ni-MOF) and carboxylated reduced graphene oxide (cRGO) on a GCE. The detection of OTA was achieved under optimized conditions in PBS solution with the developed GCE/Ni-MOF/cRGO electrode, employing CV, EIS and DPV as electrochemical tools. Applying DPV, the sensor reported very low LODs and LOQs of 3.29 fg mL-1 and 10.97 fg mL-1 respectively, over a calibration range of 10.00 fg mL-1 to 90.00 fg mL-1. Regarding real sample analysis, excellent spike recoveries from 95% to 105% were obtained for corn and rice flour. Molecular dynamics (MD) studies predicted that the Ni-MOF exhibited a strong electrostatic interaction with the OTA analyte, in agreement with the experimental findings. The synthesized nanomaterials (cMWCNTs-Fe3O4 NP, PEG-Fe3O4 NPs/cMWCNTs, and NiMOF/cRGO) utilized in this study were characterized by an array of techniques, including single particle inductively coupled plasma-mass spectrometry (spICP-MS), transmission electron microscopy (TEM), X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS), scanning electron microscopy (SEM), multidetector asymmetrical flow field-flow fractionation (AF4), and Fourier transform infrared spectroscopy (FTIR). Finally, computational modelling studies were undertaken to establish a synergy with the experimental approaches employed in each case study. These methodologies included DFT, docking studies, MC adsorption and MD simulations, which were aimed at predicting and assessing the atomic and molecular interactions between the mycotoxins and their respective electrode systems.Item Non-nutritive sweeteners: consumer awareness, consumption and inclusion in food and beverage products in South Africa(2022-09) Naicker, Shakun; Naicker, Ashika; Singh, EvonneBackground: While there are several advantages that have promoted the consumption of non-nutritive sweeteners (NNSs) like aiding weight loss and supporting diabetes management, there are also concerns about potential negative side effects, such as cancer, insulin resistance, and compensatory appetite that overshadow their use. Globally, NNSs has become a steadfast ingredient in the reformulation of sugar sweetened beverages (SSBs), but more recently there has been a growing inclusion of NNSs in a wide variety of food items making this ingredient widespread across food categories available in South Africa (SA) due to its functional profile. Furthermore, a sugar tax levy was introduced in SA in 2018 as a counter measure to support the strategic health plan to reduce the country’s prevalence of noncommunicable diseases (NCDs) broadening the widespread usage of NNSs in food and beverage industry. Aim: The aim of the study is to investigate consumer awareness and consumption of NNSs in SA. This study further explores the widespread usage of NNSs through a sub-set of food and beverage products in the South African market. Methodology: The study used exploratory and quantitative methods to gather data for the research through a cross-sectional survey. The NNS consumer survey was administered to South African participants aged 18 years and older, to all races, men, and women. Convenience and snowball sampling methods was used to recruit 385 participants. The NNS consumer survey was adapted and developed from a study that assessed the knowledge and perceptions of NNSs in the (United Kingdom) UK population. At the beginning of the survey, the introductory paragraph described the background and the aim of the survey, a letter of information and ethical approval for the study was also provided. Sequentially, the questions were related to the participants general health, knowledge, and awareness of NNSs. The survey flowed into a regulatory section which give further insight into participants level of knowledge, perception, and trust of NNSs and concluded with a list of beverages, sweeteners and snacks products to determine consumer consumption thereof. The last section was the NNSs product consumption part of the survey where participants were presented with a list of products containing NNSs and were asked to indicate if they consumed these products. The questionnaire design and the reliability of the questionnaire was pilot tested prior to the survey administration among consumers that were excluded from the main study (n=10). The survey was disseminated through social networks, LinkedIn™, Facebook™ and WhatsApp™ and was designed on 2 different survey design platforms: Google Forms and Microsoft Forms. A scientific product database was established to determine the number of products that contain NNSs within specific categories which included snack foods, dairy products, sugar-free chewing gum, candy, sugar-sweetened beverages, energy drinks, diabetic products, and baby foods, found in three major South African retail stores: Checkers, Woolworths and Dis-Chem. The scientific product database also identified the type of NNSs used, singularly and different combination in products and health and wellness claims for all products examined. Results: The NNSs consumer survey was completed by 388 South African adults nationally. The survey was opened to all provinces in SA, but high participation came from Gauteng 31.4% (n=122), and KwaZulu-Natal 29.6% (n=122), followed closely by 19.8% (n=77) from Western Cape. Women participants dominated the survey with a weighted 66.5% (n= 258) of the responses, followed by 33.5% (n=130) of the responses received from men. All races participated in the survey with most responses from Black participants (40.2% n=156), followed by Indian/Asian (30.2% n=117), White (18.0% n=70) and Coloured participants (11.6% n=45). Results showed that mainly the younger South African population with 24.2% (n=94) aged 18-24, 27.6% (n= 107) aged 25-34 and 24.7% (n=96) aged between 35-44 took part in the survey. Participants were asked to indicate if they had any NCDs and the prevalence of the common three NCDs noted were high blood pressure 13.1% (n=51), type 2 diabetes 9.3% (n=36), heart disease 5.4% (n=21) and cancer 2.1% (n=8). A large percentage of participants reported no prevalence of NCDs 73.7% (n=286). Participants were then probed to identify from a list of sweeteners that was provided and indicate which sweeteners they heard off. Interestingly, the results indicated that a large proportion of the participants did not hear of NNSs like neotame 94% (n=363), acesulfame-K 92% (n=356), malitol 84% (n=324), stevia 65% (n=253), saccharin 59% (n=227) and sucralose 59% (n=229) however, a significant 61% (n=238) of participants have heard of xylitol, p<.001 and 45% (174) have heard of aspartame. A total of 33.5% (n=130) p<.001 participants indicated that they consumed products labelled “sugar-free” or “diet” either ‘never’, ‘less often than once a week’ or ‘a few times a week’, p<.001. The relevance of this result is that although a significant 33.5% (n=130) p<.001 of participants consumed products labelled ‘sugar-free’ and/or ‘diet’, they may not actually know the ingredient contained in these products that qualifies it is as ‘sugar-free’ and/or ‘diet’ contain. Participants were given a list of products to select from and were requested to state which products they consume that they think may contain NNSs. A significant 68.3% (n=265) (p<.001) of participants indicated that they consumed cool drinks that they think contain NNSs whilst a significant 71.4% (n=277) (p<.001) did not consume cakes and desserts with NNSs, 70.1% (n=272) did not consume tea, coffee and hot beverages with NNSs and 63.7% (n=247) did not consume chewing gum that contain NNSs. Regarding the use of NNSs in everyday routine, a significant 68.3% (n=265) participants reported that they did not knowingly use NNSs in their everyday routine (p<0.001). The results from the survey further indicated that 50.8% (n=197) of participants were aware of health concerns related to the consumption of NNSs which represents just over half of the participants view. The result for these three statements – ‘I think calling them "artificial" makes me sceptical about their safety’(p=0.00), ‘I worry about the effects that non-nutritive sweeteners can have on my body’ (p=0.00), ‘I have concerns about non-nutritive sweeteners and the risk of cancer’ (p=0.00), was significantly agreed with. There was significant agreement on these benefit statements – ‘non-nutritive sweeteners are helpful for someone who wishes to lose weight’ (p=0.00), ‘non-nutritive sweeteners allow for a little indulgence without feelings of guilt’ (p=0.00), ‘non-nutritive sweeteners allow for diet products to be a viable option’ (p=0.00). When participants were probed on trusting information on health and wellness, the results presented that a significant 55.36% (p=0.00) of participants do not trust the information from government health agencies, regulatory bodies and the information coming from the Department of Health (DOH p=0.00). The results also presented that there was a significant agreement (M=3.11) that NNSs are not good for one’s health, (p=.020). Finally, a list of products consisting of beverages, sweeteners and snack products was provided, and participants were requested to indicate which products they consume. The list of products that was presented to participants in the survey were a mix of products where some were most likely to contain NNSs and some were not, like smoothies, chocolate bars and cakes. The data presented that a significant 92% (n=356) (<.001) consume hot beverages (tea, coffee, hot chocolate), 76% (n=294) consume fruit juice and concentrates, 55% (n=213) said yes to milkshake and 54% (n=208) consume diet cool drink. Interestingly, 68.3% (n=265) of participants that said no to knowingly using NNSs in their everyday routine said yes to consuming beverages that may contain NNSs. Of these 68.3% (n=265), 77.2% (n=95) consume fruit juice and concentrates, iced tea, 73.2% (n=90) consume diet cool drinks, 64.2 % (n=79) consume flavoured sparkling water, 55.3% (n=66) consume milkshakes, 53.7% (n=66) consume energy drinks and 40.7% (n=50) consume protein drinks. Participants also indicated their passion for snacking when they were asked to indicate which snacks they consumed. A significant 81% (n=351) consume crisps, 85% (n=330) consume biscuits/rusks, 87% (n=339) consume chocolate bars, 82% consume (n=320) cakes and 82% (n=319) consume ice-creams. A scientific product database consisting of 419 products that contain NNSs was established. These ranged from snack food, dairy, confectionary, SSBs, energy drinks and diabetic products. The data presented that the highest product category containing NNSs were snacks which made up 45% (n=186) and this was followed by the SSBs category with 21% (n=91) that contained NNSs. The snack food category was made up of the following subcategories: desserts 30% (n=55), crisps 26% (n=48), biscuits 23% (n=43), cereal 9.6% (n=18), sauces 6% (n=12), energy bars 4% (n=7), frozen snacks 1% (n=2) and popcorn 0.53% (n=1). From the NNSs and consumer survey, the results demonstrated that snacks were the highest and most popular consumed products with 81% (n=315) consuming just crisps. From the 419 products that were examined, 65% (n=273) products contained a combination of NNSs used to formulate the product and 34% (n=146) products consisted of single NNS. An interesting outcome that was noted here was that sucralose was most common in formulations where it was found in 38% (n=55) products followed by sorbitol in 16% (n=24) and stevia in 16% (n=23) of the products. Data presented that xylitol was not used individually in products examined. Conclusion: The outcome of this research has highlighted key consumer insights, presenting sound data that brings to light the current consumer position on the topic of NNSs and its broad use in products in SA. The data highlighted the education gap confirming the initial assumption that there is a high probability that many South African consumers are consuming NNSs without being aware of it. This research has created so many opportunities to improve consumer knowledge and investigate if there is a need to enforce stricter formulating measures with NNSs based on the evidence obtained through the NNSs survey and the scientific product database. These findings should be used to challenge manufacturers, the governmental guardians within the Department of Health and regulators in SA to guide consumer knowledge, awareness, perception and trust. There is a much bigger responsibility and significant role to play in protecting, sustaining, and investing in consumer health and wellbeing, with a priority to focus on consumer education.Item Nutritional, antioxidant and metagenomic analysis of 'superfoods' produced with sprouted soybeans(2018) Oyedeji, Ajibola Bamikole; Ijabadeniyi, Oluwatosin Ademola; Mellem, John JasonThis research was aimed at developing different ‘superfoods’ from sprouted soybeans and determining their nutritional, antioxidant and microbial characteristics. The specific objectives were to optimize the sprouting conditions (soaking and germination) of soybeans for the production of soymilk using response surface methodology, determine the effect of these optimized sprouting conditions of soybeans on the nutritional and quality attributes of resulting superfoods, determine their antioxidant activities, identify and evaluate the potentials of optimum sprouting conditions in reducing soy allergens and to determine the microbial community of fermented soy-based superfoods using next generation sequencing approach. In all cases, soy-based foods from unsprouted soybeans served as control samples. For sprouted soymilk production, soaking (12-24 h) and germination times (48-96 h) were optimized with response surface methodology, at a constant temperature of 25°C using central composite rotatable design. The optimum sprouting conditions of soybeans obtained were 12 h soaking and 52 h germination using desirability concept. Soymilk made from optimized conditions had 17% increase in total proteins, 50% reduction in phytic acid, 1.7% increase in total phenolics and a colour change of 4.89 compared to the control produced from unsprouted soybeans. There was a significant reduction in trypsin inhibitor activity (0.03 mg/g TI), with increase in total amino acids and similar rheological properties in optimized soymilk to the control. Soy-based foods, including tofu, naturally fermented soymilk and soymilk-kefir, were produced from soymilk obtained at optimized conditions of soybean sprouting and their nutritional and colour attributes were investigated. Total protein contents of sprouted products were higher than their controls and there were no significant differences in the ash contents (p ≤ 0.05). In vitro protein digestibility ranged between (85.70-99.82%) for sprouted and (81.33-99.50%) for unsprouted ones, with fermented products having the highest digestibility. Generally, no significant difference in amino acid contents (p ≤ 0.05) was recorded for all sprouted soy foods and their controls. Total flavonoids were higher in sprouted tofu coagulated with CaCl2 (60.41mg/g) and sprouted fermented soymilk (48 h) (8.93 mg/g) and there was a general reduction in total condensed tannins for all sprouted products. Colour deviation of sprouted products from their controls were minimally perceivable, as the highest ∆E value was 5.30. Soy products obtained from sprouted soybeans at optimized conditions had nutritional advantage over unsprouted ones, with negligible colour deviations. Antioxidant activities of soy-based foods produced at optimized conditions of soybean sprouting were investigated using different assays. Total phenolic content (TPC) was determined using Folin Ciocalteau method and samples (0.5-5 mg/ml), in appropriate buffers were tested for their abilities to scavenge free radicals. Sprouted soy-based food products had significantly higher (p ≤ 0.05) TPC (13.21-14.21 mgGAE/g) when compared to their controls (13.01-14.07 mgGAE/g). Sprouted soy-based foods scavenged free radicals and demonstrated higher diphenyl-1- picrylhydrazyl (DPPH), superoxide and hydroxyl radical scavenging activities. Over 50% increase in metal ion chelation was observed in all sprouted soy-based food products, however, ferric reducing antioxidant power (FRAP) in both sprouted and unsprouted products were not significantly different (p ≤ 0.05). Production and consumption of soy foods from soybeans sprouted at these optimized conditions as functional foods could be a promising means of preventing the excessive production of reactive oxygen species. The allergenic proteins in optimized sprouted soy-based foods and their respective controls were identified and their levels were evaluated. Protein was extracted from each soy-based food and their concentrations were determined using Bradford assay. Aliquots of proteins previously dissolved in appropriate buffers were separated according to their molecular weight and ionic strengths using 2-dimensional electrophoresis. Protein spots were then excised from the gels and made to undergo complete tryptic digestion to produce peptides. Identities of peptides were determined using MALDI-TOF mass spectrometry and the volumes of protein spots in each gel was determined using PDQuest image analyzer. Protein concentration significantly increased in sprouted products (up to 149% in SSK). Eight differentially expressed protein spots were selected and identified by MALDI- TOF/TOF mass spectrometry as glycinin subunit G2, β- conglycinin (α, α' and β subunits), trypsin inhibitor, 34 kDa soy seed protein and sucrose- binding proteins. Higher extent of breakdown of soy storage protein was obtained in sprouted soy products, as shown by higher protein concentration and spot volumes. Lower spot volumes were obtained in all fermented products. This study suggests higher potentials for soybean-storage-protein breakdown and reduced allergen contents in sprouted soy-based foods. The microbial community of fermented soy-based foods from sprouted soy foods and their respective controls was determined using rep-PCR and high throughput amplicon sequencing (HTS). Samples of spontaneously fermented soymilk and soymilk-kefir were collected at 6 h interval from 0-48 h and subjected to analyses. From rep-PCR, identified LAB species include Weissela cibaria, Lactococcus lactis, Leuconostoc lactis, Leuconostoc messenteroides, and Lecleria adecarboxylata while yeast species are Saccharomyces cerevisae, Pichia fermentans and Torulaspora delbrueckii. In addition to the genera revealed in rep-PCR, HTS showed the presence of Bacillaceae and other bacteria involved in spontaneous and kefir fermentation of soymilk. It could be concluded from the findings of this research that sprouting of soybeans at the suggested optimized conditions has potential for extension of use of soybeans in the production of soy-based foods with enhanced nutritional and functional properties.Item Effect of pectin and emulsifiers on quality and stability of wheat composite bread(2018) Ajibade, Betty Olusola; Ijabadeniyi, Oluwatosin AdemolaFortification and supplementation of wheat flour with other flour sources containing essential amino acids such as lysine, for bread production could help overcome the problem of protein- energy malnutrition. Indigenous and largely underutilised crops such as millet and bambara groundnut could be incorporated into staple foods such as bread. In this study, the rheological behaviour and quality characteristics of dough and bread made from wheat-millet-bambara flour (WMB) containing mixtures of emulsifiers and apple pectin were investigated for their suitability in breadmaking. WMB was prepared by substituting wheat flour (WF) with 25% each of millet flour (MF) and bambara flour. Pectin was added (1.0-2.0 g/100 g flour) and emulsifiers namely sodium stearoyl lactylate (SSL) (0.25-0.4 g/100 g flour), polysorbate 80 (PS80) (0.5-0.8 g/100 g flour), and diacetyl tartaric acid ester of monoglycerides (DATEM) (0.1-0.25 g/100 g flour) were mixed and added in different proportions. A Mixolab was used to measure the rheological behaviour of dough. The resulting bread was analysed for physical characteristics, nutritional composition, and organoleptic properties. Bread samples were stored at room temperature (±25℃), refrigeration (4℃) and freezing (-18℃) for 7 days. The bread samples were then investigated for firmness, compression energy, colour, visual observation of mould growth (VO), total aerobic plate count (APC) and fungal counts (FC). From the Mixolab analysis of composite dough, a significant increase (p<0.05) in the dough development time and dough stability were observed. The loaf volume, specific volume and proximate composition of the composite bread increased significantly (p<0.05) relative to the control. The protein content (33%), protein digestibility (85%) and some essential amino acids (lysine: 54.6%; threonine: 36.4%) increased significantly (p<0.05) compared to wheat bread (control) WF. Sensory evaluation revealed above-average acceptability for composite bread. Also, the pectin-treated bread (PTB) was significantly different (p<0.05) in firmness (8.47 N) compared to wheat flour bread (WF) (10.33 N) at -18℃ after 7 days of storage. The WF had the lowest firmness (8.32 N) at room temperature (±25℃) storage lower than the PTB (9.25 N) and emulsifier-treated bread (ETB) (12.37 N) after 3 days storage at room temperature (±25℃). Bread firmness decreased significantly (p<0.05) with an increase in storage time for all samples. The APC for all bread samples ranged from 3.02 log cfu/g to 6.19 log cfu/g and fungal count (FC) ranged from 3.48 log cfu/g to 4.86 log cfu/g. The PTB had the highest APC (6.19 log cfu/g) among bread samples stored at room temperature (±25℃) while it also had the lowest APC (3.02 log cfu/g) at the same storage temperature (±25℃). It was found that all bread samples stored at -18℃ did not show no sign of mould growth. The use of bakery products’ acceptable limits of emulsifiers and pectin for this study significantly improved the dough rheology, physical characteristics, nutritional and sensory acceptability of WMB composite bread. The shelf life studies showed improved firmness, low microbial counts and a slower rate of degradation in cold storage conditions. This study revealed that there is potential for supplementation and fortification of wheat bread with flours from millet and bambara sources.Item Effect of bacteriophage control and artificial neural networks prediction in the inactivation of Listeria monocytogenes on fresh produce(2017) Oladunjoye, Adebola Olubukola; Ijabadeniyi, Oluwatosin Ademola; Singh, SurenThere has been a global increase in fresh produce consumption, due to its attendant nutritional a nd health benefits. On the other hand, increase in the outbreak of diseases, accompanied with health and economic implications, have been traced to this deve lopment. A good number of pathogenic contaminants along the food chain have been identified as causative agent s with Listeria monocytogenes identified as one of such. Among other control strategies, the use of bacteriophage, was recommended as a palliative measure. Furthermore, the a ppli cation of artificial neural networks (ANN) in food safety remains an emerging concept in risk assessment study. Therefore, the aim of this research is to investigate the effect of bacteriophage or phage control and artificial neural network prediction in the inactivation of L. monocytogenes ATCC 7644 on fresh produce. Fresh-cut tomato and carrot were artificially inoculated with L. monocytogenes (108 CFU/ml) and subjected to antimicrobial treatment of Listex P100 bacteriophage (108 PFU/ml), sucrose monolaurate (SML at 100, 250 and 400 ppm), with chlorine (sodium hypochlorite at 200 ppm) used as control. Also, application of ANN to predict the risk effect of antimicrobial treatments of bacteriophage, sucrose monolaurate and chlorine was evaluated on the fresh-cut produce. Mathematical models were developed using a linear regression and sigmoid (hyperbolic and logistic) activation function-(120). Data sets were trained using Back propagation ANN, containing one hidden layer with four hidden neurons. Furthermore, carbon utilization profile of phage-treated L. monocytogenes using phenotypic micro array method was evaluated. In the first phase, susceptibility of L. monocytogenes subjected to certain stress-adapted conditions (acid,-adapted AA, chlorine-adapted CA, heat-adapted HA) and non-adapted-NA to phage treatment inoculated on the fresh-cut produce stored for 10 days at 4, 10 and 25oC was evaluated. The second phase investigated the combination of bacteriophage and sucrose monolaurate (using chlorine at 200 ppm as control) to inhibit the L. monocytogenes growth on the fresh-cut produce stored for 6 days at 4, 10 and 25oC. Physicochemical properties (pH, titratable acid-TTA, total soluble solids-TSS, and colour values-CIE L* a* b*) of the fresh produce after treatment were evaluated. In the third phase, ANN as a predictive tool was used to evaluate the risk involved in the relationship among the initial bacterial load, fresh-produce type, antimicrobial concentration and residual bacteria. In the final phase, 100 µL of phage-treated L. monocytogenes was introduced into a 96-micro well plate impregnated with a tetrazolium dye. The Carbon utilization profile was evaluated at intervals of 4 hours for 48 hours using a biolog micro station. Generally, L. monocytogenes grew on both fresh-cut produce and the storage temperature did not adversely affect the lytic ability of the phage treatment. Antimicrobial treatment of phage and sucrose monolaurate had minimal variations on the physicochemical properties of both fresh-cut samples. All stress-adapted and non-adapted L. monocytogenes were (p ≤ 0.05) susceptible to bacteriophage control. Phage treatment reduced non-adapted, acid adapted, chlorine-adapted, and heat-adapted L. monocytogenes population by 0.57, 0.81, 0.86 and 0.95 log CFU/ml in fresh-cut tomato, and 2.26, 2.41, 2.49 and 2.54 log CFU/ml in fresh cut carrot respectively. Furthermore, the additive effect of SML at 100 and 250 ppm had no significant effect on phage lysis. However, combination of phage with SML at 400 ppm significantly (p ≤ 0.05) resulted in 1 and 3 fold reductions in tomato and carrot respectively. Control treatment with chlorine resulted in 1-2 log reductions on both fresh produce. Algorithm data set trained using ANN gave 100% accuracy. Prediction with logistic activation function showed the highest positive correlation relationship between predicted and observed values with ~ 0.99 R2-value and MSE of 0.0831. Carbon utilization profile showed hexose and pentose sugars-ribose, glucose, fructose and sugars were maximally utilized while oligosaccharide sugars of sucrose, cellobiose and gentiobiose were similarly observed to be utilized. Notably, utilization of glucose-6-phosphate which determines L. monocytogenes pathogenicity was not very pronounced in the carbon profile. Bacteriophage application in the inactivation of L. monocytogenes contamination of fresh produce provides a safe means of control. Its perceived limitation however, can be overcome by combining with other antimicrobials. Similarly, the use of artificial neural networks prediction, remains an improved approach to harness the potential risk that could occur through this method.Item Characterization and application of bambara groundnut starch-lipid complexes(2017) Oyeyinka, Samson Adeoye; Amonsou, Eric Oscar; Singh, SurenBambara groundnut (Vigna subterranea) is an indigenous underutilised leguminous crop to Africa. It is a good source of protein and carbohydrate including starch. Bambara groundnut is a traditional crop grown mainly for subsistence in Southern Africa. Bambara groundnut has the advantage of being drought tolerant and can thrive in hot temperatures and poor soil conditions. Therefore, it has great potential as an alternative crop to soya bean and peanuts for cultivation and utilisation. Bambara groundnut starch can potentially be used for various industrial applications. However, native starches are not suitable for most industrial applications, hence the need for modification. Bambara groundnut starch has been previously modified using physical and chemical modification methods. Natural alternatives such as the use of lipids are being sought to modify starches due to the associated risk with chemically modified starch. In this research, Bambara groundnut starch was modified with lipids to improve functional properties, utilisation and application. Specifically, the physicochemical properties of native Bambara groundnut starch obtained from five Bambara groundnut genotypes and three landraces (maroon, brown and cream) were determined. Bambara groundnut starch was modified with lipids (palmitic acid, stearic acid, oleic acid, linoleic acid and lysophosphatidylcholine) and the physicochemical properties of the modified starch were investigated. Further, the influence of high-pressure homogenization on complexation of Bambara groundnut starch with lipids was assessed in comparison with maize and potato starches. Lastly, an application of modified Bambara groundnut starch in biofilm production was also studied. Bambara groundnut landraces generally showed higher amylose contents (approx. 33%) than the genotypes (approx. 28%). Differences were observed in the crystalline patterns of these starches. Bambara groundnut genotypes exhibited the C-type-crystallinity, while the landraces showed the unusual A-type pattern. In terms of functionality, landrace starches showed better swelling than the genotypes. Subsequent studies on modification used maroon Bambara groundnut starch since the amylose content was higher than other landraces and there was a consistent supply of the grains during the period of the study. Generally, Bambara groundnut starch showed higher complexing ability with all the lipids than maize and potato reference samples. These differences in complexing ability among the starches could be due to the variation in amylose contents (Bambara groundnut starch: 31.5%, maize: 22.5% and potato: 24.6%). Fatty acids complexed better with Bambara groundnut starch than lysophosphatidylcholine, which could be due to the structural differences in comparison with the lysophosphatidylcholine molecule. The number of fatty acid in the glycerol backbone and the additional steric hindrance of the polar phosphatidic acid group in the lysophosphatidylcholine may have reduced its complexing ability. Among the fatty acids, palmitic acid complexed better than stearic and the unsaturated fatty acids, possibly due to its short chain length compared to other fatty acids. Bambara groundnut starch showed reduced peak and setback viscosities in the presence of stearic acid, linoleic acid and lysophosphatidylcholine, suggesting the formation of V-amylose complex. Bambara groundnut starch pasted with lipids displayed reduced gelling ability compared to their unmodified counterparts. XRD studies of freeze-dried paste revealed peaks at 2Ѳ = 7.4, 12.9 and 19.9o confirming the formation V-amylose complexes in Bambara groundnut starch. Modification of Bambara groundnut starch with lipids resulted in reduced digestibility. High-pressure homogenization significantly increased the complexing ability of Bambara groundnut starch with lipids. Homogenized Bambara groundnut starch-lipid complexes generally exhibited higher complex index than their unhomogenized counterparts. The higher complexing ability could be attributed to the effect of high-pressure which may have enhanced greater dispersion of lipids in the starch-water system. X-ray diffraction studies also revealed the formation of higher complexes as shown by high intensities at peaks (2Ѳ= 7.4, 12.9 and 19.9o) corresponding to V-amylose complexes. Bambara groundnut starch-lipid complexes displayed significantly higher melting temperatures (95.74-103.82oC) compared to native uncomplexed starch (77.32oC). Homogenized Bambara groundnut starch complexes were non-gelling while the unhomogenized types produced weak gels, with G′ ˃ G″ in the range of 0.1- 10 Hz. Complexation of Bambara groundnut starch with lipids using high-pressure homogenization may be employed in the production of modified starch with non-gelling properties and higher thermal stability suitable for certain industrial application, such as fat replacers in mayonnaise, frozen foods and desserts for a better mouth feel. The physicochemical and mechanical properties of biofilm prepared from Bambara groundnut starch modified with stearic acid at varying concentrations of 0, 2, 4, 6, 7 or 10% were further studied. By SEM, Bambara groundnut starch films containing stearic acid (˃ 2%) showed a progressively rough surface compared to those with 2% stearic acid and the control. The addition of 2% stearic acid to Bambara groundnut starch film reduced water vapour permeability by approximately 17%. However, mechanical properties of starch films were generally negatively affected by stearic acid. Bambara groundnut starch film may be modified with 2% stearic acid for improved water vapour permeability and thermal stability with minimal effect on tensile strength.Item Application of thermostable a-Amylase from Thermomyces lanuginosus ATCC 58157 to nutritionally enhance starch based food(2006) Padayachee, ThiriloshaniIn Sub-Saharan Africa there is an urgent need to sustain and improve the quality of its food resources. Poverty eradication features high on the agenda of a number of world health organisations, while the number of underweight children in Africa continues to increase (Pellet, 1996). Providing nutritionally enhanced foods to the poor will help towards achieving this objective. Protein-energy malnutrition has been identified as one of the most important problems facing Africa, with maize as the staple diet (Nkama et al., 1995). However, a combination of several factors limits availability and the nutritional quality of maize. During starvation, energy and protein intakes decrease by 20-30%, with most of the children in Africa having an average protein intake of only 20 g per day (Igbedioh, 1996). Energy availability also affects protein utilization because of interrelationships of protein and energy metabolism (Elwyn, 1993). The diets of inhabitants in developing regions depend mainly on cereals (maize) for both protein and dietary energy which lacks indispensable amino acids, minerals, vitamins and carbohydrates. In light of these growing concerns an attempt was made to devise a scientific strategy to combat the nutritional shortfalls of maize meal. A multidisciplinary and concerted approach was followed within this project aimed at designing an improved thermostable amylase and applying the enzyme to nutritionally enhance maize meal. It was envisaged that the manipulation of maize meal, by the application of enzyme technology will improve the nutritional status of this staple food. The consequences is that an alternate solution for the eradication of an ailing, poverty stricken and malnourished African population is achievable. It is possible that the boundaries defining the limits of life will extend to even greater extremes through the application of novel technologies.