The occurrence of toxic and non-toxic cyanobacteria species in water supplies destined for maize meal preparation process: A case study of Vhembe District

Cyanobacteria are common organisms in the phytoplankton of eutrophic rivers, lakes, and freshwater reservoirs, and have become part of human diet for thousands of years. Cyanobacteria can multiply quickly in surface waters and form blooms when favourable conditions prevail, such as high temperature, intense light, high pH, and increased availability of nutrients, especially phosphate and nitrate artificially released by anthropogenic activities. Cyanobacteria produce secondary metabolites called cyanotoxins, which are harmful to human health. Human exposure to cyanotoxins can occur in various ways, however, the oral route is the most important. This is mainly through drinking water or eating contaminated food. Studies on cyanotoxin contamination of food have been conducted on aquatic products (fish, prawns, and crayfish), grains (rice, soybean, and wheat), fresh produce (Lettuce), and dietary supplements. However, no study has been conducted on cyanotoxin contamination of maize meal during maize meal processing. The present study was motivated by the presence of blue-green algae that formed biofilms in 25 L white plastic containers. The process water stored in these containers was used to soften the maize seed and then ground the seed maize into maize meal. The main objective of the present study was to investigate the occurrence of toxic and non-toxic cyanobacteria species in water supplies destined for maize meal processing. To achieve this aim, the present work was subdivided into two specific objectives. In the first objective, the diversity and identities of cyanobacteria in the samples (process water, uncooked maize meal, and cooked maize meal (porridge)) were assessed using Polymerase Chain Reaction (PCR) and Advanced digital flow cytometry (FlowCAM). The molecular techniques, 16S Primers (forward and reverse) tailed with Universal Sequences were used for amplification and sequencing of full-length 16S rRNA genes from cyanobacteria found in all samples. Cyanobacterial species from order Nostocales, Pseudanabaenales, Oscillatoriales, Chroococcales, Synechococcales, and unclassified cyanobacterial order, some of which have the potential to produce cyanotoxins were amplified and identified in process water, raw maize meal and pap porridge samples using PCR. The cyanobacteria species, of the genus Microcystis, Phormidium, and Leptolyngbya were found in process water samples and maize meal samples and none of the cyanobacteria species were found pap porridge using FlowCAM. Maize meal samples were exposed to different thermal temperatures inside the grinding machines during the grinding processes. Temperatures were ranging from 59.8 – 66.0 oC, 21.1 – 25.4 oC, and 28.9 – 29.8 oC in grinding machine 1, grinding machine 2, and grinding machine 3, respectively. Loss of diversity could be expected for the cyanobacteria community when exposed to air with hot temperatures. Another sample that was exposed to extremely high temperatures during its preparation is the porridge sample. An electric stove was used to cook during the preparation of this sample and the temperatures during cooking ranged between 89.5 – 92.7 oC. After cooking and analysis, this sample was found with lowest proportion of cyanobacteria species compared to other samples. Toxic cyanobacteria species die when exposed to these temperatures and they release cyanotoxins. Therefore, for the first time, the present study reveals that cyanotoxins can be transferred from cyanotoxins-contaminated water to food during processing, which could then present another significant route of human exposure to cyanotoxins; and then an analytical method for accurate quantification and identification of these cyanotoxins using LC-MS/MS was developed in the present study. In the second objective, the occurrence of cyanotoxins in water supplies (process water), raw maize meal, and cooked maize (porridge) was investigated; and this was achieved by applying a simple, sensitive, and reliable analytical method developed for the determination of these toxins at ppb (parts per billion) levels. These compounds were extracted using Solid Phase Extraction (SPE) with optimized parameters; thereafter, Liquid Chromatography-Mass Spectrometry (LC-MS/MS) was used for the rapid determination of the analytes selected for the present study. The method developed was applied to samples collected from the meal grinding station and was able to detect and quantify all the target cyanotoxins. MC-LR, MC-YR, and MC-RR were detected at concentrations ranging from 9.2 – 13.3 μg/L, 5.5 – 10.2 μg/L, and 2.3 – 11.2 μg/L, in all the samples, respectively. Toxic cyanobacterial blooms producing cyanotoxins exist where water is collected and may proliferate inside the water containers due to favourable conditions such as light and nutrient availability. However, when environmental conditions are not favourable, cyanobacteria die and release cyanotoxins in process water. Moreover, the effects of grinding machines and their temperatures on the viability of cyanobacteria species was observed in the present study. Proportion of cyanobacteria species detected in maize samples were lower than proportion of cyanobacteria species detected in water samples, implying that different temperatures or extremely warm air within the grinding machines could have killed some cyanobacterial species during the grinding processes. Also, the proportion of cyanobacteria species in maize (used for pap porridge sample) was low compared to pap porridge sample as this sample was subjected to high temperatures during sample preparation (cooking). It was further reported that cyanobacteria species die at high temperatures. Consequently, cyanotoxins were released into maize and porridge during processing as cyanobacteria cells burst and die, which then increased toxin levels. There are various routes through which humans may be exposed to cyanotoxins, but the most important one is the oral, which occurs through the consumption of cyanotoxins-contaminated water or food. Therefore, the present study conducted the assessment of human health risks from exposure to microcystins available in water supplies (tap and groundwater), maize meal, and porridge. For this assessment, the hazard quotient index (HQi) was used to assess the non-carcinogenic risks of MCs to humans. The HQi levels found in the present study ranged between 2.26 – 2.75 for adults, whereas for children the HQi levels ranged between 0.84 – 1.02, representing greater potential risks to human health. These findings show the presence of cyanobacteria species in processed water and maize meal and the absence in cooked maize meal. However, the microcystins (MC-LR, MC-YR, and MC-RR) were found in the process water, maize meal, and in the pap porridge in excess of the WHO guideline of 1 μg/L. Furthermore, it was revealed that cyanotoxins can be transferred from water to food during food processing using cyanotoxins-contaminated water. The presence of cyanobacteria in process water is likely another route of human exposure to cyanotoxins. Moreover, the methods developed in the present study can be used by environmental and health agencies to strengthen the monitoring of cyanotoxins in water and food. Furthermore, the findings of the present study contribute to the understating of cyanotoxin contamination of maize meal during the grinding processes. The basis for the development of a cyanotoxins management framework and assessment of human health risk is provided by the findings of the present study

Author dc:creator

• Mutoti, Mulalo Isaih

Advisors dc:contributor.advisor

• Gumbo, Jabulani R.
• Jideani, Afam I. O.

• Cyanotoxins
• Food contamination
• Liquid chromatography-mass
• Spectrometry
• Microcystins
• Polymerized chain reaction
• Solid phase extraction

Statement dc:rights

• University of Venda

Language dc:language.iso

en

Repository record dc:identifier.uri

http://univendspace.univen.ac.za/handle/123456789/2700

OAI identifier oai:identifier

oai:univendspace.univen.ac.za:123456789/2700