Faculty of Applied Sciences
Permanent URI for this communityhttp://ir-dev.dut.ac.za/handle/10321/5
Browse
2 results
Search Results
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.